fruit quality and production of cactus pear (opuntiaspp.) fruit clones selected for increased frost...

Fruit quality and production of cactus pear (Opuntiaspp.) fruit clones selected for increased frost

hardiness

John Parish & Peter Felker

Center for Semi-Arid Forest Resources, Caesar Kleberg Wildlife Institute,Texas A&M University, Campus Box 218, Kingsville, TX 78363,

U.S.A.

(Received 2 December 1996, accepted 1 February 1997)

The principal limitation to cultivation of cactus for fruit in the south-westernUnited States is lack of hardiness to freezing weather. This field trialcompared 22 Opuntia clones selected for increased cold hardiness, fruit yield,and fruit quality, i.e. pH, sugar content and seed content. Mexican accessions1380, 1277, 1281 and 1300 had the highest yields averaging between 2·5 and5·2 kg m–2 while the Chilean clones had lower yields, yet greater sugarcontent and generally lower seed contents. As there is considerable aversionby first time consumers of cactus pears to seed size and number, we evaluatedseed number, seed weight per fruit and weight per seed. Our trial found aconsiderable range in seed weight from 2·19 to 6·37 g fruit –1. While theChilean varieties had among the lowest seed weight per fruit (2·2 g fruit–1)and were similar in seed weight to the recently reported BS1 parthenocarpicclones in Israel, a few Mexican varieties were comparable. In summary,Chilean varieties were most promising for high sugar content and low seedweight per fruit. Mexican varieties with high yields did not contain highsugar.

©1997 Academic Press Limited

Keywords: arid; desertification; fruit; cactus pear; Latin America; Opuntia

Introduction

Cactus pear (Opuntia spp.) is in the Cactaceae family and is native to arid and semi-arid regions of the western hemisphere (Benson, 1982). The success of Opuntia inthese areas has been attributed to its CAM metabolism (Kluge & Ting, 1978) whichpromotes high drought resistance and high water-use efficiency. Such efficientconservation of water in times of drought has caused it to be widely used as anemergency livestock feed (Griffiths, 1905). Also its tender young pads, known as‘nopalitos’, are used in Mexico and south Texas as a green vegetable (Russell & Felker,1987). Many Opuntia species, known as ‘tuna’ in Mexico, produce sweet edible fruit(Griffiths & Hare, 1907).

While the cultivation of Opuntia for fruit production in Mexico is widespread

Journal of Arid Environments (1997) 37: 123–143

0140–1963/97/010123 + 21 $25.00/0/ae970261 © 1997 Academic Press Limited

(Mondragon & Perez, 1994; Pimienta 1994), the exploitation of this resource for fruitproduction in Texas is non-existent. The major limitation to cultivation of cactus inthe south-western United States, excluding California (Curtis, 1977), is hardiness tofreezing weather (Griffiths, 1915; Uphof, 1916). As of yet there is no commercialfruiting variety of Opuntia that can withstand the seasonally intermittent freezes thatoccur in south Texas (Gregory et al., 1993).

When temperatures in a Texas field trial dropped to –12°C in 1989, the native spinyO. lindheimeri Engelm. and the spineless O. ellisiana Griffiths were not damaged(Gregory et al., 1993). However, all clones from Mexico, Chile, Brazil, South Africaand Algeria froze to ground level. Since then additional collections have been made toimprove the genetic diversity of coldhardy fruit-producing Opuntia clones in our fieldsite (Barrientos et al., 1992). We were fortunate enough to obtain selections from theUniversidad Autonoma Agraria Antonio Narro (UAAAN) Germplasm at Saltillowhere scientists have been conducting research on cold hardy Opuntia fruit since the1960s (Martinez, 1968; Borrego-Escalante et al., 1990; Barrientos et al., 1992). Someof the selections originated from breeding materials that had survived a freeze of –16°Cin 1962 in Saltillo without damage (Barrientos et al., 1992). Other collections weremade from the Sierra Madras at 2300 m elevation near Saltillo where villagers statedtemperatures often reached –12°C.

Along with the need to increase cold hardiness is the importance to select for fruitquality. Principal factors affecting fruit quality in cactus pear include sugar content,peel color, fresh weight, pulp weight, and seed content (Cantwell, 1991). Manypopular cultivars in Mexico vary greatly in color, exceed 120 g fruit–1 and averagebetween 12 and 17% sugar (Pimienta, 1994). This differs considerably from the Texasnative O. lindheimeri which produces small purple seedy fruits averaging about 40 gwith only 8% sugar (Russell & Felker, 1987). Collections in this trial included fruitfrom O. ficus-indica (L.) Mill., O. megacantha Salm-Dyck, O. hyptiacantha Weber, O.streptacantha Lem., O. inermis DC., and O. crassa Haw.

As there is considerable aversion by first time consumers of cactus pears to seed sizeand number, reducing seediness is a major objective for the enhancement of itscommercialization (Caplan, 1995). Studies by Pimienta & Engleman (1985) havereported that the principal pulp parts in cactus pear develop from the dorsal epidermisof the funicular envelope, thus a reduced seed number may in turn reduce pulp weight.However, Pimienta & Engelman (1985) suggested that seediness might be reducedthrough the production of aborted seeds.

With five growing seasons since the establishment of newer cold hardy material fromSaltillo, the clones in this trial have approached commercial production levels. Thus,the objective of this study was to compare fruit quality and production, at commercialproduction levels, of the newer cold hardy material to more standard clones fromChile, Brazil, and central Mexico.

Materials and methods

Experimental design

For fruit analysis, ten 5-year-old plants in Kingsville, Texas ranging from 3 to 5 m inheight were used. The ten plants were located in two, five plant row-plots with a 1 minter-row and a 4 m between-row spacing. For the purposes of fruit characterization,individual fruits were considered as replicates. Twelve to 18 fruits were collected fromthe two, five plant row-plots with no less than five fruits harvested from a row-plot.While there were 70 accessions in this trial, only 22 accessions from Brazil, Chile andMexico produced sufficient fruit in both row-plots for analysis. The accessions were

J. PARISH & P. FELKER 124

evaluated for fruit yield, mean sugar content, mean fresh weight, mean pulp weight,mean seed number, mean seed weight per fruit and mean weight per seed.

For yield estimations, the entire row-plot was considered as a replicate and thusthere were only two replications for the yield estimates. The row-plots were arrangedin a randomized complete block design. As these plants did not have guard rows, theproduction per m2 estimates are greater than could be expected in commercialproduction. Nevertheless these yields can be used to compare the accessions andprovide an estimate of general productivity.

We also tested for significant (p < 0·10) general linear and quadratic relationshipsbetween easily measurable fruit morphological characteristics and sugar content todetermine which morphological measurements would be most useful in predictingfruit maturity. Quadratic relationships were considered to be significant (p < 0·10)only if the coefficient of the quadratic term was significant (p < 0·10). Themorphological variables used for these general linear regression analyses were fruit scardepth, fruit scar diameter, fresh weight, pulp weight, peel weight and pH.

Fruit collection and analysis

After measuring the picked fruit height, the color of each fruit was graded according tothe Royal Horticultural Society Colour Chart. Fruits were stored and refrigerated inpaper bags for no more than 24 h before analysis. Each fruit was measured for length,width, scar depth, scar diameter, fresh weight and pulp weight. Each fruit pulp wasblended in a kitchen blender and subjected to vacuum filtration (Fisherbrand P8) toextract juice for sugar content and pH analysis. Sugar content was measured with aReichert-Jung temperature compensated hand refractometer (model 10430) calibratedusing an 8–15% glucose solution. Peel weights were determined by subtracting pulpweights from fresh weights. Four blended pulps for each accession (two pulps fromeach block) were strained through a fine mesh screen to capture seeds, which werethen air-dried, counted, and weighed. Weight per seed was determined by dividing thetotal weight of seeds for the four pulps by the total number of seeds.

Fruit yield

Fruit yield for each accession was determined by counting all fruits on the five plantsin each of the two replicates at the end of each month. The number of fruits per fiveplants in the highest yielding month was multiplied by the estimated mean fresh weightper fruit at harvest in July or August 1995, and 2500 plant ha–1 population density toobtain estimated fruit yield in kg m–2 ( = 0·1 (ton ha–1)).

Soils

Two soil series, Hidalgo and Palobia, occurred in these plots (USDA, 1975). Hidalgois most extensively distributed. This series is taxonomically identified as a member offine loamy mixed hyperthermic family of Typic Calcuistolls (USDA, 1978). Thesesoils lack a fluctuating ground-water table in their deep layers. They are well-drained,have slow runoff, and are moderately permeable. They have high inherent fertility andhigh production potentials. Mean values for five soil samples were organic matter0·5%, pH 6·5 and nitrate N 3 mg kg–1. A total of 100 kg N ha–1, 100 kg P ha–1 and100 kg K ha–1 was applied to the soil surface within 0·5 m of the plants in the winterof 1994–95.

OPUNTIA FRUIT FROST HARDINESS 125

Table 1. Mean yield and frost scores, color, and presence of thorns for cactus pearsharvested in the summer of 1995 in Kingsville, Texas

Species, Yield, Royal HorticulturalAcc.#, origin and kg m–2† Society Color Frost Thorns¶UAAAN code* (mean±S.D.) Chart Code‡ score§ (+/–)

O. megacantha 5·2±2·6 Y-O grp. 22A na –1380 MexicoAN-V5O. ficus-indica 4·1±0·41 Y grp. 22A 80±13 –1277 Mexico Y grp. 26A

Y grp. 6BO. streptacantha 3·0±0·56 R grp. 50B 47±0 –1281 Mexico R grp. 46C

R grp. 47CO. ficus-indica 2·5±3·4 R-P grp. 59A 52±16 –1300 Mexico V grp. 86AO. ficus-indica 2·1±0·19 Y-Gn grp. 152D 57±23 –1320 Chile Y-O grp. 22A

Y-O grp. 20AO. ficus-indica 1·8±2·1 Y grp. 11A na –1278 Mexico Y grp. 5BO. inermis 1·6±0·71 Y grp. 153 D 38±18 –1270 Brazil O grp. 26BOpuntia sp. 1·4±1·6 Y-Gn grp. 151A na +1393 Mexico Y-Gn grp. 154AO. megacantha 1·3±0·38 Y-Gn grp. 145C na +1383 Mexico Y grp. 4CAN-T3 Y-Gn grp. 154CO. hyptiacantha 1·2±0·24 Y grp. 11A 26±6 +1287 Mexico O grp. 26AO. megacantha 1·0±0·91 Y-Gn grp. 150C na +1297 Mexico Y-Gn grp. 154CO. ficus-indica 1·0±0·72 O grp. 26B na –1294 Mexico Y-O grp. 26BO. ficus-indica 0·87±0·25 Gn-Y grp. 1B na +1376 Mexico Y-Gn grp. 153DAN-V1O. megacantha 0·74±0·26 Y-Gn grp. 154C na –1390 Mexico Y-Gn grp. 150CAN-TV6O. ficus-indica 0·70±0·30 Y-Gn grp. 153C 28±14 –1319 ChileOpuntia sp. 0·65±0·070 Gy-R grp. 179A na –1392 Mexico R grp. 40CO. ficus-indica 0·56±0·18 V grp. 86A na –1279 MexicoO. ficus-indica 0·44±0·32 P-V grp. 80A na –1282 Mexico R-P grp. 60BO. ficus-indica 0·43±0·42 R grp. 50C 56±19 –1301 Mexico Gy-R grp. 34A


Table 1. (continued)

Species, Yield, Royal HorticulturalAcc.#, origin and kg m–2† Society Color Frost Thorns¶UAAAN code* (mean±S.D.) Chart Code‡ score§ (+/–)

O. crassa 0·22±0·21 Gy-R grp. 179B na –1379 Mexico R grp. 42AAN-V4 R grp. 47AOpuntia sp. 0·20±0·097 Y-Gn grp. 151B na +1398 Mexico Y-O grp. 17DO. ficus-indica 0·15±0·087 Gy-O grp. 163C 88±11 –1321 Chile Y-Gn grp. 144B

*Designation of clone by Universidad Autonoma Agraria Antonio Narro.†Standard deviation, N=2.‡Y=yellow; Gn=green; O=orange; R=red; P=purple; V=violet; Gy=greyed; grp.=group.§Frost score is estimate of % above-ground height remaining after freeze of 1990 (Gregory et al., 1993);

na=frost score unknown.¶+=thorns present; –=thorns absent.

Climate

The climate of Kingsville is semi-arid and subtropical. Mean maximum temperaturesexceeded 30°C from May through October for 1961–1990. Mean monthly minimumtemperatures dropped below 10°C from December through February for 1961–1990.Mean minimum temperatures were 8°C for December, 7°C for January and 9°C forFebruary (National Oceanic and Atmospheric Association (NOAA), 1992). Frostscores reported here were taken from Gregory et al. (1993). As a severe freeze has notoccurred since 1991, after which many new clones were obtained, frost scores were notavailable for many new accessions. Mean annual precipitation in Kingsville from 1961to 1990 was 690 mm (NOAA, 1992). Rainfall in 1995 however was higher than usualat 864 mm with a peak in August of 198 mm (Kingsville Record and Bishop News,1996).

Results

Fruit production

Mexican varieties were among the greatest fruit producers with yellow-fruitedaccession 1380 (AN-V5) ranking highest with a mean yield of 5·2 kg m–2 (Table 1).Accession 1277 from Milpa Alta, Mexico was second with a mean yield of 4·1 kg m–2

and second highest in frost score at 80% (Gregory et al., 1993). Although third rankingaccession 1281 from Chapingo, Mexico, with a mean yield of 3·0 kg m–2 had a muchlower frost score of 47% (Gregory et al., 1993), its red fruit was unique among the highfruit yielding clones in our study. The fourth ranking accession 1300, from Chapingo,Mexico had a mean yield of 2·5 kg m–2. Overall, fruit yields were very variableaveraging between 0·15 and 5·2 kg m–2. Yields for Chilean clones averaged between0·15 and 2·1 kg m–2. Accession 1270, the only Brazilian clone, ranked seventh in yieldwith a mean of 1·6 kg m–2 The top seven fruit yielding cacti were spineless. Eight ofthe top ten fruit yielding varieties were yellow as graded by the Royal HorticulturalSociety colour chart. Chilean variety 1320 was the highest yielding of the Brazilian andChilean clones in mean fruit production, ranking fifth with 2·1 kg m–2. While Chilean


accession 1321 ranked highest in frost score at 88% (Gregory et al., 1993), it had thelowest mean yield of 0·15 kg m–2.

Sugar content

The Chilean varieties 1319 and 1321 had the greatest mean sugar content at 14·6%and 13·8%, respectively (Table 2). Accession 1383 (AN-T3) had the greatest meansugar content of the Mexican clones and ranked third overall at 13·4%. Sugar contentfor fruits in this study averaged between 10·7 and 14·6%. Half of the top rankingMexican varieties for mean sugar content were collected from Chapingo. Accession1320 was the lowest ranking Chilean variety in mean sugar content at 12·3% and washigher than the only Brazilian clone, 1270, at 11·9% sugar. Accession 1376 (AN-V1)from Mexico ranked lowest in mean sugar content at 10·7%.

Fresh weight

The largest fruits in the trial were from Mexican accession 1287 and Chilean accession1320 averaging 160 and 151 g, respectively (Table 2). The thorny yellow-fruitedMexican accession 1398 from Los Llanos ranked third in mean fresh weight at 148 g.Out of the 22 accessions in this trial, 17 produced individual fruits averaging between120 and 160 g. Fresh weights overall averaged between 113 and 160 g. Fresh weightsfor Chilean accessions averaged between 120 and 151 g. Brazilian clone 1270 hadrelatively low mean fresh weight of 121 g. Chilean clone 1321 was the lowest rankedvariety among Chilean and Brazilian accessions in mean fresh weight at 120 g. Overall,accession 1376 (AN-V1) was the lowest ranked variety in mean fresh weight at 113g.

pH

Mexican varieties 1398 and 1383 (AN-T3) ranked the lowest in fruit pH at 5·6 and5·8, respectively (Table 2). Chilean accession 1320 had the lowest pH of Chilean andBrazilian varieties at 5·9. The only Brazilian clone 1270 ranked fourth in lowest pH at6·0. The pH of fruit in the trial ranged between 5·6 and 6·5. The pH for Chileanvarieties ranged between 5·9 and 6·3. Yellow-fruited thornless variety 1278 fromChapingo ranked the highest in pH at 6·5.

Pulp and peel weight

The Chilean varieties varied greatly in mean pulp weight, with accession 1320 rankinghighest at 81 g, and 1319 ranking next to last at 48 g (Table 2). Accession 1297 fromChapingo was the highest ranking Mexican variety in mean pulp weight at 79 g. Themean pulp weight of the only Brazilian clone 1270 ranked ninth at 69 g. Thornlesspurple-fruited Mexican variety 1282 from Chapingo ranked last in mean pulp weightat 47·5 g.

Mexican varieties 1398 and 1287 ranked the highest in mean peel weight at 88 and84 g, respectively (Table 2). Mexican accessions 1278 from Chapingo and 1390 fromSaltillo had the lowest mean peel weight in the study at 41 and 44 g, respectively.Brazilian clone 1270 ranked third in lowest mean peel weight at 53 g. While peelweights overall averaged between 41 and 88 g, Chilean peel weights were roughlysimilar, averaging between 67 and 76 g.


Fruit seed measurements

Mexican and Chilean varieties shared the top four rankings in lowest mean seed weightper fruit, with accession 1282 and 1279 from Mexico being first and third at 2·19 gfruit–1 and 2·27 g fruit–1, and accessions 1319 and 1321 from Chile being second andfourth at 2·21 and 2·30 g fruit–1, respectively (Table 3). However, the other Chileanvariety 1320 was ranked near last in lowest mean seed weight per fruit at 4·63 g.Brazilian clone 1270 was ranked fourteenth in lowest mean seed weight per fruit at3·54 g. Seed weight per fruit averaged between 2·19 and 6·37 g. Accession 1393 fromSaltillo ranked last in lowest mean seed weight per fruit at 6·37 g.

Chilean accession 1319 and Mexican accessions 1282 and 1380 had the lowestmean weight per seed at 10, 11 and 11 mg, respectively (Table 3). Two accessionsfrom Chapingo, Mexico, 1278 and 1300, and one from UAAAN, accession 1390(AN-TV6), ranked next in lowest mean weight per seed at 12 mg. Chilean variety1321, Mexican variety 1277 and the only Brazilian clone, 1270, ranked next in lowestmean weight per seed at 13 mg. The weight per seed in this trial averaged between 10and 21 mg. The weight per seed for Chilean fruit averaged between 10 and 14 mg.Mexican accessions 1376 (AN-V1) and 1393 ranked last in lowest mean weight perseed at 21 mg.

Mexican accession 1279 from Chapingo had the lowest mean seed number at 144seed fruit–1 (Table 3). Of the four clones producing fruit averaging less than 200 seedsfruit–1, accession 1321 from Chile ranked second at 174 seeds fruit–1. Other clonesaveraging less than 200 seeds fruit–1 were Mexican accessions 1392 and 1287 at 186and 191, respectively. Brazilian clone 1270 was among the most seedy, averaging 279seeds fruit–1. Chilean clone 1320 was the most seedy averaging 342 seeds fruit–1.

Generally, fruits with the lowest mean seed weight per fruit also had a lower meanweight per seed and/or a lower mean seed number per fruit (Table 3). This was truefor Chilean accession 1321 which ranked fourth in lowest mean seed weight per fruitat 2·3 g, seventh in lowest mean weight per seed at 13 mg, and second in lowest meanseed number at 174 seeds fruit–1. Another Chilean variety, 1319, ranked second inlowest mean seed weight per fruit at 2·21 g, first in lowest mean weight per seed at 10mg, and yet ranked only eleventh in lowest mean seed number at 226 seeds fruit–1.Some Mexican varieties also showed this trend with accession 1282 ranking first inlowest mean seed weight per fruit at 2·19 g and second in lowest mean weight per seedat 11 mg, and sixth in lowest mean seed number at 204 seeds fruit–1. Mexicanaccession 1279, which ranked fourth in lowest mean seed weight per fruit at 2·27 g,ranked only fifteenth in lowest mean weight per seed at 16 mg, and yet ranked first inlowest mean seed number at 144 seeds fruit–1.

There also appeared to be a relationship between high peel/pulp ratio and low meanseed weight per fruit. Five of the top six accessions in lowest mean seed weight per fruitpossessed peel/pulp ratios greater than one, as was the case for Mexican varieties 1282,1279, and 1287 and Chilean varieties 1319 and 1321. Chilean variety 1319 had thehighest peel/pulp ratio of 1·57 while Mexican variety 1278 had the lowest of 0·56. Nineof the 22 varieties in the trial possessed peel/pulp ratios greater than one. Purple-fruited thornless variety 1300, from Chapingo, produced fruits with peel/pulp ratiosclosest to one at 0·97. Accession 1300 was also the only variety to rank within the topthree in both lowest mean peel and lowest mean pulp weight at 79 g and 77 g,respectively.

Morphological characters

Chilean and Mexican accessions 1320 and 1300 shared top rankings in highest meanfruit width at 6·0 cm (Table 3). While accession 1287 was third in highest mean fruit


Table 2. Mean sugar content, fresh weight, pulp weight, peel weight and medianpH for cactus pears harvested in the summer of 1995 in Kingsville, Texas

SpeciesAcc. #, Fruit

Origin and number Sugar Fresh Pulp PeelUAAAN code* (N) (%)† weight (g)† weight (g)† weight (g)† pH†

O. ficus-indica 12 14·6±0·7 124·2±18·7 48·3±10·1 75·9±9·7 6·3±0·21319 ChileO. ficus-indica 13 13·8±0·7 120·0±16·6 53·2±7·2 66·8±12·4 6·3±0·01321 ChileO. megacantha 14 13·4±0·4 132·1±11·4 71·6±9·3 60·1±4·5 5·8±0·01383 MexicoAN-T3O. ficus-idica 13 13·1±0·7 125·9±21·1 67·8±11·8 58·2±9·8 6·2±0·01294 MexicoO. ficus-indica 18 12·9±0·4 114·4±12·7 73·4±7·4 41·0±5·9 6·5±0·01278 MexicoO. megacantha 14 12·8±0·4 117·4±14·3 73·6±10·4 43·9±4·1 6·3±0·01390 MexicoAN-TV6O. ficus-indica 13 12·8±0·7 134·4±21·1 57·8±10·5 76·5±11·8 6·3±0·01279 MexicoO. megacantha 14 12·7±0·4 140·1±15·1 79·2±10·2 60·9±8·2 6·0±0·21297 MexicoO. hypticantha 13 12·6±0·7 160·3±22·4 76·0±13·1 84·2±11·5 6·3±0·01287 MexicoO. streptacantha 14 12·5±0·4 135·3±9·9 70·7±6·5 64·6±5·2 6·2±0·01281 MexicoO. ficus-indica 14 12·3±0·6 151·5±12·1 81·1±7·3 70·3±6·5 5·9±0·01320 ChileO. inermis 13 11·9±0·7 121·2±10·5 68·7±7·2 52·5±5·0 6·0±0·01270 BrazilOpuntia sp. 13 11·8±0·7 127·8±10·5 65·2±7·0 62·6±4·6 6·2±0·01392 MexicoO. ficus-indica 12 11·6±0·4 121·2±17·2 47·5±8·8 73·7±9·9 6·2±0·01282 MexicoOpuntia sp. 12 11·5±0·7 114·3±18·9 60·3±10·8 54·1±9·2 6·2±0·21393 MexicoO. ficus-indica 16 11·5±1·1 139·3±13·0 76·4±12·1 62·8±6·6 6·2±0·01277 MexicoO. ficus-indica 14 11·4±0·4 148·4±21·6 78·9±21·2 76·6±11·0 6·2±0·21300 MexicoO. ficus-indica 12 11·3±0·4 116·1±14·7 56·2±9·5 59·4±6·2 6·3±0·01301 MexicoO. megacantha 14 11·1±0·9 131·5±10·6 78·1±13·2 60·7±4·8 6·3±0·01380 MexicoAN-V5O. crassa 12 11·0±0·4 129·5±11·4 60·3±5·7 69·2±9·2 6·3±0·01379 MexicoAN-V4


Table 2. (continued)

SpeciesAcc. #, Fruit

Origin and number Sugar Fresh Pulp PeelUAAAN code* (N) (%)† weight (g)† weight (g)† weight (g)† pH†

Opuntia sp. 15 10·9±0·6 148·7±29·2 61·2±11·6 87·5±19·3 5·6±0·21398 MexicoO. ficus-indica 13 10·7±1·1 112·9±19·6 53·2±11·1 64·3±13·1 6·0±0·21376 MexicoAN-V1

*Designation of clone by Universidad Autonoma Agraria Antonio Narro.†95% confidence interval.

width at 5·9 cm, it was first in highest mean fruit length at 11·1 cm and also had thehighest mean fresh weight at 160 g. The second highest mean fruit length was forMexican accession 1398 at 10·1 cm. Chilean accession 1320 had the highest meanfruit length of all the Chilean and Brazilian varieties at 9·3 cm. The only Brazilianclone, 1270, had a relatively low mean fruit length at 8·1 cm. Mexican accessions 1376(AN-V1) and 1393 had the lowest mean fruit lengths at 7·3 cm. Mexican accessions1278 and 1390 (AN-TV6) had the lowest mean fruit widths at 5·2 and 5·3 cm,respectively.

The lowest mean fruit scar diameters were for Mexican accessions 1278 and 1390(AN-TV6) at 18·4 and 19·5 mm, respectively (Table 3). Chilean accessions hadrelatively high fruit scar diameters, averaging between 24·5 and 28·2 mm. However,the highest mean fruit scar diameter belonged to Mexican variety 1297 at 28·5 mm.

While 1297 had the highest mean fruit scar diameter, it also had the lowest meanfruit scar depth at 0·8 mm (Table 3). Accessions from UAAAN, 1376 (AN-V1) and1383 (AN-T3) ranked second and third in lowest mean fruit scar depth at 2·1 mm and2·5 mm, respectively. The four clones with the lowest mean fruit scar depths werespiny and produced yellow–green fruit. While overall fruit scar depth in the trialaveraged between 0·8 and 8·5 mm, scar depth for South American clones averagedbetween 4·4 and 6·6 mm. UAAAN accession 1390 (AN-TV6) had the highest meanfruit scar depth at 8·5 mm.

Relationships between fruit length, width and floral scar measurements and fruit sugar

In an effort to develop quantitative maturity indices, we examined relationshipsbetween easily measurable fruit morphological characters and sugar content. Cantwell(1991) suggested that fruit maturity was associated with the filling in of the fruit scar(receptacle) to form a nearly flat surface. Thus, we included fruit scar depth and widthmeasurements. To examine which external morphological measurements would bemost useful in predicting fruit maturity, as judged by sugar content, we report p-valuesfor significant (p < 0·10) linear regression relationships and significant (p < 0·10)quadratic coefficients (Table 4).

Twelve of the 22 varieties in the trial had some significant (p < 0·10) morphologicalrelationship with sugar content. As only one accession had a significant (p < 0·10)quadratic coefficient for scar depth and sugar content as compared to six accessionswhich had significant (p < 0·10) quadratic coefficients for scar diameter, scar depth isa less useful morphological character in predicting fruit maturity than scar diameter.

Of the six accessions, 1282, 1287, 1297, 1301, 1319 and 1380 (AN-V5), that had


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±1·

6215

206±

785·

6±0·

47·

8±0·

923

·0±

1·3

6·0±

1·3

1294

Mex

ico

Opu

ntia

sp.

3·12

±1·

4317

186±

725·

8±0·

28·

1±0·

223

·8±

1·1

5·0±

0·9

1392

Mex

ico

O. m

egac

anth

a3·

18±

0·57

1227

4±56

5·3±

0·2

9·2±

0·6

19·5

±0·

98·

5±0·

613

90 M

exic

oA

N-T

V6

O. fi

cus-

indi

ca3·

23±

0·22

1227

6±81

5·2±

0·2

9·2±

0·2

18·4

±1·

17·

1±0·

612

78 M

exic

oO

. ficu

s-in

dica

3·27

±1·

0212

276±

946·

0±0·

29·

3±0·

424

·4±

2·2

4·6±

1·1

1300

Mex

ico

O. s

trep

taca

ntha

3·29

±1·

7216

201±

755·

6±0·

28·

8±0·

621

·9±

1·9

6·5±

0·9

1281

Mex

ico


Tab

le 3

.(c

ontin

ued)

Spe

cies

See

dA

cc. #

,w

eigh

t pe

rW

eigh

t pe

rS

eed

no. p

erF

ruit

Fru

itS

car

Sca

rO

rigi

n an

dfr

uit†

‡se

edfr

uit†

‡w

idth

†le

ngth

†di

am.†

dept

h†U

AA

AN

cod

e*(g

)(m

g)(g

)(c

m)

(cm

)(m

m)

(mm

)

O. fi

cus-

indi

ca3·

33±

2·10

1621

3±11

15·

7±0·

27·

5±0·

425

·4±

1·8

3·0±

1·3

1301

Mex

ico

O. i

nerm

is3·

54±

0·64

1327

9±47

5·7±

0·2

8·1±

0·4

23·5

±1·

56·

1±0·

912

70 B

razi

lO

. cra

ssa

3·64

±1·

6017

212±

695·

9±0·

27·

7±0·

425

·7±

1·3

3·4±

0·7

1379

Mex

ico

AN

-V4

O. m

egac

anth

a3·

68±

0·80

1425

7±78

5·6±

0·2

8·9±

0·4

28·1

±1·

12·

1±0·

613

83 M

exic

oA

N-T

3O

punt

ia s

p.3·

68±

2·22

1721

1±13

65·

8±0·

410

·1±

0·6

25·2

±3·

06·

9±1·

113

98 M

exic

oO

. ficu

s-in

dica

3·92

±1·

1413

296±

695·

7±0·

28·

8±0·

621

·9±

1·3

5·6±

1·1

1277

Mex

ico

O. m

egac

anth

a4·

31±

1·18

1430

4±56

5·7±

0·2

9·2±

0·6

28·5

±1·

30·

8±0·

612

97 M

exic

oO

. ficu

s-in

dica

4·63

±1·

2114

342±

726·

0±0·

29·

3±0·

224

·5±

1·1

6·6±

0·9

1320

Chi

leO

. ficu

s-in

dica

5·59

±3·

4721

268±

136

5·6±

0·4

7·3±

0·4

25·8

±2·

02·

5±1·

113

76 M

exic

oA

N-V

1O

punt

ia s

pp.

6·37

±4·

2621

310±

180

5·7±

0·4

7·3±

0·4

27·3

±1·

82·

7±0·

913

93 M

exic

o

*Des

igna

tion

of c

lone

by

Uni

vers

idad

Aut

onom

a A

grar

ia A

nton

io N

arro

.†N

=4.

‡95%

con

fiden

ce in

terv

al.


Tab

le 4

.p-

valu

es fo

r sig

nific

ant (

p<

0·10

) lin

ear

(L)

and

quad

ratic

(Q

) re

gres

sion

rela

tions

hips

bet

wee

n su

gar

cont

ent a

nd fr

uit l

engt

h,fr

uit w

idth

, sca

r di

amet

er a

nd s

car

dept

h fo

r ca

ctus

pea

rs h

arve

sted

in th

e su

mm

er o

f 199

5 in

Kin

gsvi

lle, T

exas

Spe

cies

Acc

. #,

Sca

rS

car

Sca

rS

car

Fru

itF

ruit

Fru

itF

ruit

Ori

gin

and

dept

hde

pth

diam

.di

am.

leng

thle

ngth

wid

thw

idth

UA

AA

N c

ode*

N(L

)(Q

)(L

)(Q

)(L

)(Q

)(L

)(Q

)

O. i

nerm

is13

1270

Bra

zil

O. fi

cus-

indi

ca16

1277

Mex

ico

O. fi

cus-

indi

ca18

0·04

512

78 M

exic

oO

. ficu

s-in

dica

130·

060

0·04

712

79 M

exic

oO

. str

epta

cant

ha14

0·09

80·

001

1281

Mex

ico

O. fi

cus-

indi

ca12

0·04

00·

013

0·00

612

82 M

exic

oO

. hyp

tiaca

ntha

130·

005

1287

Mex

ico

O. fi

cus-

indi

ca13

1294

Mex

ico

O. m

egac

anth

a14

0·02

112

97 M

exic

oO

. ficu

s-in

dica

1413

00 M

exic

oO

. ficu

s-in

dica

120·

090

0·09

013

01 M

exic

oO

. ficu

s-in

dica

120·

068

0·09

60·

056

0·04

313

19 C

hile

O. fi

cus-

indi

ca14

0·05

113

20 C

hile


Tab

le 4

.(c

ontin

ued)

Spe

cies

Acc

. #,

Sca

rS

car

Sca

rS

car

Fru

itF

ruit

Fru

itF

ruit

Ori

gin

and

dept

hde

pth

diam

.di

am.

leng

thle

ngth

wid

thw

idth

UA

AA

N c

ode*

N(L

)(Q

)(L

)(Q

)(L

)(Q

)(L

)(Q

)

O. fi

cus-

indi

ca13

1321

Chi

leO

. ficu

s-in

dica

1313

76 M

exic

oA

N-V

1O

. cra

ssa

1213

79 M

exic

oA

N-V

4O

. meg

acan

tha

140·

013

0·00

313

80 M

exic

oA

N-V

5O

. meg

acan

tha

1413

83 M

exic

oA

N-T

3O

. meg

acan

tha

1413

90 M

exic

oA

N-T

V6

Opu

ntia

sp.

130·

073

1392

Mex

ico

Opu

ntia

sp.

120·

094

0·09

713

93 M

exic

oO

punt

ia s

p.15

1398

Mex

ico

*Des

igna

tion

of c

lone

by

Uni

vers

idad

Aut

onom

a A

grar

ia A

nton

io N

arro

.


significant (p < 0·10) quadratic coefficients for sugar content and fruit scar diameter,Mexican accessions 1287 (p = 0·005) and 1380 (p = 0·003) had the lowest p-values.Chilean accession 1319 had the most number of significant (p < 0·10) relationships(4) between morphological features and sugar content.

Relationships between fruit weight, peel weight, pH and fruit sugar

Relationships between fruit pH and sugar content were the most frequent compared toall the variables tested in the trial and were significant (p < 0·10) for nine of the 22accessions (1270, 1278, 1279, 1294, 1300, 1376, 1383, 1392 and 1398) and thus maybe the most useful characteristic in predicting fruit maturity as judged by sugar content(Table 5). Only one accession (1383) had a significant (p = 0·042) quadraticcoefficient for fruit pH and sugar content with no significant (p = 0·153) linearregression relationship. Pulp weight and sugar content had a significant (p < 0·10)linear regression relationships with seven accessions (1277, 1278, 1281, 1282, 1301,1321, and 1393). Only Mexican accessions 1278 and 1279, both from Chapingo, hadsome significant (p < 0·10) linear regression relationship or quadratic coefficient for allfour variables (fresh weight, pulp weight, peel weight and pH). Fresh weight, pulpweight and pH had more significant (p < 0·10) linear regression relationships withfruit sugar content than significant (p < 0·10) quadratic coefficients. Brazilianaccession 1270 had the strongest (p = 0·0001) linear regression relationship betweenpH and sugar content. Accession 1383 (AN-T3) was the only variety to have asignificant (p = 0·042) quadratic coefficient between sugar content and pH. Accession1379 (AN-V4) was the only accession not to have a significant (p < 0·10) relationshipwith any of the measured variables in our trial. Accession 1287 (p = 0·042) and 1297(p = 0·027) had significant (p < 0·10) linear regression relationships between sugarcontent and picked fruit height. Accession 1390 (AN-TV6) was the only variety tohave a significant (p = 0·013) quadratic coefficient for sugar content and picked fruitheight.

Discussion

The two fruit clones with the highest mean sugar content (13·8 and 14·6%) were bothof Chilean origin. All Chilean fruit clones (3) in this trial also had a higher mean sugarcontent than the previously reported 12% sugar for a Chilean fruit clone grown in aTexas greenhouse (Russell & Felker, 1987). While only a few fruits of top rankingvariety 1321 were measured in a previous trial at 13·7% sugar (Gregory et al., 1993),we found the fruits of accession 1321 to be very similar at 13·8% sugar. Thus, with theexception of the Chilean varieties and Mexican clones 1383 and 1294, our values weresimilar to that reported by Gregory et al. (1993), where sugar for Opuntia fruit averagedbetween 11 and 14%. Likewise, sugar measurements in our trial were also comparableto reports in Israel where the sugar content averaged 11·8% in winter and 12·8% in thesummer (Nerd et al., 1991). Some sugar contents were lower than reported valuesfrom Mexico where sugar contents for 18 selected varieties averaged between 12 and17% (Pimienta, 1994). Mondragon & Perez (1994) reported that the leading cactuspear cultivar in Central Mexico (Reyna) had 14·8% sugar. While this sugar content iscomparable to Chilean accession 1319, Reyna had greater seed content and greateryield potential.

Though we experienced great variability in fruit yields between blocks, themagnitude of our fruit production was similar to reports in Italy at 13–33 ton ha–1

(1·3–3·3 kg m–2) (Inglese et al., 1995a,b). The Mexican varieties whose estimatedyields averaged between 0·2 and 5·2 kg m–2 (2 to 52 ton ha–1) had the greatest range


in productivity. However, as mentioned in the materials and methods, our yields arean overestimate of what would be obtained in commercial production as they werebased on unbuffered row-plots of five plants. Pimienta (1994) reported fruitproduction for typical plantations in Mexico to be a very low 2–8 tons ha–1, due toinsufficient fertilization, pruning, and weed control. California fruit yields reported byD’Arrigo Bros., which ranged between 7 and 14 tons ha–1, were similar to nine of the22 accessions in our trial and slightly higher than in Mexico (Curtis, 1977).

Since seediness is a major obstacle to commercialization in cactus pear (Caplan,1995), low seed weights and low seed number are crucial for its success in the worldmarket. Seed weight per fruit in our trial, which averaged between 2 and 6 g, wasslightly lower than previously reported Mexican values averaging between 3 and 8 g(Pimienta, 1994). Twenty of the 22 accessions in our trial had mean seed weightslower than that for the most widely used cultivar in Central Mexico, which was 5·2 gfruit–1 (Mondragon & Perez, 1994). The lowest mean seed weight per fruit valuesobserved in this trial compare very favorably to the ‘parthenocarpic’ BS1 clonereported by Weiss et al. (1993). The mean seed weight per fruit we measured forChilean clones (2·2 g fruit–1 for 1319 and 2·3 g fruit–1 for 1321) and for Mexicanclones (2·2 g fruit–1 for 1282 and 2·3 g fruit–1 for 1279) compare favorably to BS1 seedweights of 2·0 g fruit–1 measured in the autumn. In the spring the BS1 clone had lowerseed weights (0·9 g fruit–1) but had smaller mean fruit weights (100 g) as well. The peelto pulp ratio of clone BS1 of 2·4 in the spring was much greater (less desirable) thanvalues of 1·6 for clone 1319 and 1·3 for clone 1321. Thus, when combined withoutstanding sugar contents and low seed weight per fruit values, the Chilean clonesappear exceptional.

There have been many conflicting reports on the existence of vegetative partheno-carpy in cactus pear. Gil et al. (1977) reported that fertilization is needed for fruit setwhile Pimienta (1990) suggested that vegetative parthenocarpy cannot exist in cactuspear because the pulp develops from the seed. Nonetheless, research in Chile hasrevealed that gibberellic acid sprayed on intact and emasculated flowers yieldedparthenocarpic fruits of normal size containing false seeds consisting only of ovuleinteguments (Diaz & Gil, 1978; Gil & Espinoza, 1980). Since fruits would need to betreated individually, the induction of parthenocarpy in this manner may not be a viablealternative for commercial production.

Studies in Israel have revealed a suspected parthenocarpic clone (BS1) thatproduced 100% aborted seeds without growth hormones (Weiss et al., 1993). In BS1,flowers are produced with incomplete pollen tubes penetrating only to the micropyle,and thereby need no fertilization for fruit set and development. Ovules of BS1 werenotably larger than other seeded clones, suggesting that a thicker nucellus may be thephysical barrier that prevents the male gametes from fertilizing the embryo within theovules. This would be consistent with Tisserat et al. (1979) who stated that there aremany wild and ornamental varieties of Opuntia that set fruit without pollination bymeans of nucellar embryogenesis. In this state, a degenerating embryo is replaced byan enlarged nucellus that divides to form a proembryo.

An enlarged nucellus is apparently not the only barrier to successful sexualreproduction in Opuntia. Its ovules possess a circinotropic shape, with an extendedfunicular stalk causing the ovule to wrap around on itself (Fahn, 1967), covering theentrance to the embryo through the micropyle. Also, different levels of ploidy (2 3 ,3 3 , 4 3 , 5 3 , 6 3 , 8 3 , 10 3 , 11 3 , 12 3 , 13 3 , 19 3 and 20 3 ) in cactus pears(Pimienta & Munoz, 1995) may result in aneuploidy, an uneven matching ofchromosomes during metaphase, which may in turn cause seeds to abort (Srb et al.,1965). Perhaps the low mean number of seeds for Mexican accession 1279 (144) andChilean variety 1321 (174) may be a result of aborted seeds from aneuploidy.

In Mexico during the 1500s, the native American Indians were known to trekhundreds of miles to reach isolated clusters of particularly sweet cactus pears (Ciesla,


Tab

le 5

.p-

valu

es fo

r sig

nific

ant (

p<

0·10

) lin

ear

(L)

and

quad

ratic

(Q

) re

gres

sion

rela

tions

hips

bet

wee

n su

gar

cont

ent a

nd fr

esh

wei

ght,

pulp

wei

ght,

peel

wei

ght a

nd fr

uit p

H fo

r ca

ctus

pea

rs h

arve

sted

in th

e su

mm

er o

f 199

5 in

Kin

gsvi

lle, T

exas

Spe

cies

Acc

. #,

Fre

shF

resh

Pul

pP

ulp

Pee

lP

eel

Ori

gin

and

wt.

wt.

wt.

wt.

wt.

wt.

pHpH

UA

AA

N c

ode*

N(L

)(Q

)(L

)(Q

)(L

)(Q

)(L

)(Q

)

O. i

nerm

is13

0·00

112

70 B

razi

lO

. ficu

s-in

dica

160·

062

0·01

60·

065

1277

Mex

ico

O. fi

cus-

indi

ca18

0·01

20·

008

0·03

40·

042

0·00

612

78 M

exic

oO

. ficu

s-in

dica

130·

001

0·02

90·

001

0·01

912

79 M

exic

oO

. str

epta

cant

ha14

0·09

20·

005

1281

Mex

ico

O. fi

cus-

indi

ca12

0·01

30·

020

0·03

512

82 M

exic

oO

. hyp

tiaca

ntha

130·

033

1287

Mex

ico

O. fi

cus-

indi

ca13

0·01

212

94 M

exic

oO

. meg

acan

tha

1412

97 M

exic

oO

. ficu

s-in

dica

140·

096

0·02

70·

016

1300

Mex

ico

O. fi

cus-

indi

ca12

0·06

60·

045

1301

Mex

ico

O. fi

cus-

indi

ca12

1319

Chi

leO

. ficu

s-in

dica

1413

20 C

hile


Tab

le 5

.(c

ontin

ued)

Spe

cies

Acc

. #,

Fre

shF

resh

Pul

pP

ulp

Pee

lP

eel

Ori

gin

and

wt.

wt.

wt.

wt.

wt.

wt.

pHpH

UA

AA

N c

ode*

N(L

)(Q

)(L

)(Q

)(L

)(Q

)(L

)(Q

)

O. fi

cus-

indi

ca13

0·01

813

21 C

hile

O. fi

cus-

indi

ca13

0·03

013

76 M

exic

oA

N-V

1O

. cra

ssa

1213

79 M

exic

oA

N-V

4O

. meg

acan

tha

140·

052

1380

Mex

ico

AN

-V5

O. m

egac

anth

a14

0·04

213

83 M

exic

oA

N-T

3O

. meg

acan

tha

1413

90 M

exic

oA

N-T

V6

Opu

ntia

sp.

130·

037

0·05

213

92 M

exic

oO

punt

iasp

.12

0·09

40·

031

1393

Mex

ico

Opu

ntia

sp.

150·

055

1398

Mex

ico

*Des

igna

tion

of c

lone

by

Uni

vers

idad

Aut

onom

a A

grar

ia A

nton

io N

arro

.


1988). Some of these clusters, known as ‘backyard’ varieties, are of higher quality thanwild strains (Pimienta, 1994). This would suggest that cross pollination andfertilization in the wild was still taking place as recent as the age of man. Perhaps theexpansion of drier areas into some previously more mesic environments (Axelrod,1958) eliminated a key pollinator that was once instrumental in sexual reproduction inOpuntia. Such an event would not be wholly disastrous for Opuntia since fragmenta-tion allows it to vegetatively reproduce. Perhaps the success of asexually reproducing(Mondragon & Pimienta, 1995) has eliminated the evolutionary pressure to maintainthe necessary forms and functions required for sexual reproduction. Since Opuntiadoes produce flowers and has great genetic diversity in Mexico (Pimienta, 1994), it ispossible that at some time in the relatively recent past this genus relied more heavily onsexual reproduction as a means of propagation.

Using Italian standards, where cactus pears have been cultivated for nearly half amillennia, first class fresh fruit weighs between 120 and 160 g. Based on this grading,17 of the 22 accessions in our trial produced first class fruits while only five accessionsproduced second class fruits (Inglese et al., 1995b). Fruit weight in our trial could havebeen increased by thinning the number of fruits per cladode to less than six assuggested by Inglese et al. (1995a). Mean fresh weights for five accessions in our trialwere similar or higher than that for Reyna, the leading cactus pear cultivar in centralMexico, at 141 g (Mondragon & Perez, 1994). The largest fruits (160 g) in our studywere produced by spiny orange–yellow accession 1287. In Mexico however, varietiessuch as Cristalina and Burrona weigh 240 and 205 g, respectively (Pimienta, 1994).

In this summer fruit trial, 15 of the 18 Mexican accessions and all of the Chilean andBrazilian accessions produced fruits with a higher mean fresh weight than Israel’ssummer fruit crop (116 g). Yet all the accessions in our trial produced less than Israel’swinter crop (178 g) (Nerd et al., 1991). The mean pulp weights in our study averagedbetween 47 and 81 g and were generally lower than the reported values for Mexicanvarieties (Pimienta, 1994). Pulp weights in our trial (59–152 g) were similar toreported values from Israel where summer pulp weight was 62 g (Nerd et al., 1991).Peel weights averaged between 41 and 87 g and were similar to fruits produced inMexico where peel weights averaged from 52 to 79 g (Pimienta, 1994) and in Israelwhere summer crop peel weight was 57 g (Nerd et al., 1991).

The mean pH values ranged from 5·6 to 6·5 and were generally lower than reportedin Mexico where 18 selected fruits ranged from 6·4 to 7·1. When compared withreports from Gregory et al. (1993) where pH ranged from 4·1 to 6·1, our trial overallyielded fruits that were less acidic. Gregory et al. (1993) also noticed that varieties withlower pH (less than 5) generally had lower sugar contents and cited a significant(p < 0·10) relationship between sugar content and pH in Opuntia fruit (p = 0·002).The significant (p < 0·10) relationship between sugar content and pH as observed byGregory et al. (1993) is probably related to maturity, i.e. as the fruit becomes moremature, the pH increases with sugar content. This is supported by nine accessions inour trial that showed significant (p < 0·10) linear regression relationships betweensugar content and pH. However, there were two accessions (1383 and 1320) that hada lower pH value of 5·9 with higher sugar contents. One of us (J.P.) feels that 1383 hasa more pleasing taste than the other varieties due to a high sugar content/lower pHcombination.

Summary

While Chilean clones had the highest fruit sugar, Mexican clones were the highestproducers of fruit. Perhaps cultural practices can be identified that will permit eitherChilean varieties to have higher yields or Mexican varieties to have greater sugarcontent. In Israel applications of N fertilizer (0, 30, 60, 120 kg ha–1 at the end of the


summer has increased bud initiation in the autumn and the number of buds in thefollowing spring (Nerd et al., 1993). Studies by Karim et al. (1996) have found positivecorrelations between cladode Mg concentration and fruit sugar content.

While some researchers have suggested that fruit maturity in Opuntia might bedetermined through morphological characters, this trial has shown a great variabilitybetween accessions in morphologic/maturity relationships as determined throughsugar content. Morphological characters such as scar depth may not be as helpful asscar diameter in determining fruit maturity in cactus pear.

Since economic returns for cattle-based forage systems in semi-arid regions onlyrange from $2–3 ha–1 year–1 (Gregory et al., 1993), developing high value droughtresistant crops for these areas is essential. Since a single clone that possesses all thedesirable traits has not yet been identified, selecting the most desirable traits in variousclones for use in a breeding program is necessary. Unfortunately little is known aboutbreeding techniques, such as emasculation and seed germination in Opuntia.

Of the six UAAAN varieties developed by Borrego-Escalente et al. (1990) thatproduced fruit in this trial, accession 1380 (AN-V5) is most promising as it had thegreatest yields, but unfortunately had an unacceptable sugar content of only 11·1%.Accession 1383 (AN-T3), with a much lower estimated yield, had an acceptable sugarcontent (13·4%) and lower pH (5·9), resulting in a good acidity/sugar tastecombination. In spite of the thorns on this variety, accession 1383 (AN-T3) possesseda good balance of agronomic and fruit quality characteristics.

While accessions 1279, 1281, 1282, and 1300 from the research station atChapingo, Mexico are all thornless, produce red or purple fruit, and rank high in eitheryield, pulp weight, fruit length, fruit width, low seed weight, and low seed number,they unfortunately had low frost scores. For example, in the mild freeze of 1991 (–7°C)many accessions from this region had 50% of their above-ground height killed(Gregory et al., 1993). Thornless accession 1277 deserves further attention as it wasthe only accession from central Mexico (Milpa Alta) that had both high yield and highfrost resistance.

While Mexico contains the greatest source of genetic diversity in Opuntia, theChilean clones possessed exceptional fruit characteristics, i.e. sugar content, and lowseed weight that rivaled the Mexican varieties. Chilean clone 1321 also had thegreatest cold resistance of the varieties examined thus far. These Chilean clones alsocompared favorably in seed weight per fruit and peel/pulp ratio with parthenocarpicclones (BS1) grown in Israel. While no single Chilean clone has high sugar, low seednumber, high freeze hardiness and high productivity, these varieties still representgood genetic stock for further hybridization and research. However, in the south Texasenvironment, Mexican clones still dominate in fruit production.

The financial assistance of the International Arid Lands Consortium Cooperative Agreement28-G3-694 and the USDA CSRS Agreement No. 95 34312-1309 is gratefully acknowledged.Publication number 97–117 of the Caesar Kleberg Wildlife Research Institute.

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