HORTSCIENCE 30(1):65–68. 1995. ey betale-gea-

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Role of Excess Water in Tomato FruitCrackingM.M. Peet1 and D.H. Willits2

North Carolina State University, Raleigh, NC 27695

Additional index words. Lycopersicon esculentum, splitting, fruit quality, physiologicaldisorders, growth cracks, russetting

Abstract. Excess irrigation water was provided to spring crops of bag-grown greenhoustomatoes (Lycopersicon esculentum Mill.) to test the effect on radial fruit cracking. Variednumbers of emitters were placed in bags filled with soilless medium to provide differenamounts of irrigation water. In 1990, all emitters provided water containing nutrientsolution, but in 1992, the extra water added in one treatment did not contain nutrientsolution. In both years, the percentage of cracked fruit was 20 percentage points higher the treatments receiving more water. The increase in cracking was similar whether or nonutrient solution was added to the extra water. There also were some effects of the extwater on yield. Fruit count per plant was slightly higher (9.5%) when extra water wasprovided without nutrient solution, but was the same when nutrient solution was added tothe extra water. Fruit weights per plant were 18.6% higher in 1990 when watering wasincreased. In 1992, fruit weights were similar, except for the treatment where the extrawater provided did not contain nutrient solution. Fruit weight in this treatment was 19.7%higher than in the other treatments. In both crops, the percentage of cracking increaseas linear and quadratic functions of cluster positions, i.e., there was more cracking in thupper clusters. In greenhouse situations, growers should consider water reduction wheexperiencing high levels of fruit cracking and as a precautionary measure when harvestinfrom the upper clusters. Providing excess water to greenhouse-grown tomatoes may beviable technique for screening cultivars or for conducting research on practices to reduccracking.

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Fruit cracking in tomatoes can cause seous economic losses in the field. Cracks dcrease the attractiveness of the fruit and oan entry point for insects and decay organismAlthough this can cause significant incomloss in the fresh market and processing tomindustries (Calbo, 1990; Cotner et al., 196Walter, 1967), cracking occurs only sporadcally for most commercial tomato growebecause they use crack-resistant cultivarsaddition, fruit grown commercially for freshmarket is normally harvested at the matugreen or breaker stage when cracking is llikely. Home gardeners, greenhouse groweand growers for local or specialty markets amuch more vulnerable to fruit cracking lossbecause their cultivars lack crack resistanand because fruit is harvested at the pink stor later.

HORTSCIENCE, VOL. 30(1), FEBRUARY 1995

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Received for publication 23 Mar. 1994. Acceptefor publication 10 Sept. 1994. The research reportin this publication was funded by the North CarolinAgricultural Research Service (NCARS). Researcmaterials were provided without cost by DeRuiteSeeds (Columbus, Ohio) and Premier Brands (NeRochelle, N.Y.). Use of trade names in this publiction does not imply endorsement by the NCARS products named nor criticism of similar ones nomentioned. The assistance of W. Hall, R. Scott, athe staff of the North Carolina State Univ. Horticulture Field Laboratory is gratefully acknowledgedThe cost of publishing this paper was defrayed part by the payment of page charges. Under posregulations, this paper therefore must be heremarked advertisement solely to indicate this fact.1Professor, Dept. of Horticultural Science, Box 7602Professor, Dept. of Biology and Agricultural Engineering, Box 7625.

The environmental and physiologiccauses of cracking of soft fruit, apples, acitrus are not well understood. The literatuon radial fruit cracking in tomatoes was rcently reviewed (Peet, 1992). Tomato frcracking is most likely to occur when thmovement of water and solutes into the tomfruit is rapid or protracted. Fruit are particlarly susceptible if physiological changes the tomato skin during ripening or under ctain soil moisture conditions reduce the strenand the ability of the tomato skin to stretch. Ffield-grown tomatoes, this most likely occuwhen low soil-moisture levels are suddenrelieved by rain. Rain has several effecKamimura et al. (1972) reported that a suddincrease in soil moisture reduced the tenstrength of the skin and increased root prsure. They also noted rainwater could berectly absorbed into the fruit through auncallused minute cracks in the skin athrough the corky tissue around the stem s

Little is known, however, about the causof fruit cracking in greenhouse-grown tomtoes, where it is a serious problem (Koskeal., 1980). The above explanation for craing—a rapid increase in soil moisture of water-stressed plants—would explain few eamples of fruit cracking. In greenhouses, plaare watered about the same amount everyand seldom water-stressed. In our studies,in normal greenhouse practice, plants are tered several times daily and watering fquency or quantity increased at the first sign ofwilting. Abbott et al. (1986) increased thfrequency of daily watering of greenhoutomatoes from 1 to 4, keeping the total amo

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of water and fertilizer added the same. Threported that variations in watering shouldminimized, but when the same amount of towater was provided, effects of irrigation frquency on cracking were not particularly laror consistent between cultivars, years, or wtering regimes and media.

In the following experiments, we test thhypothesis that cracking can be reduced ingreenhouse by decreasing the amount of wapplied. This hypothesis is based on the ithat high root pressure caused by excess wwould increase turgor pressure in the fruPreliminary data to support this hypothewas obtained as part of a Fall 1989 experimon the effect of nighttime cooling (Willits anPeet, 1992). As part of that experiment, effects of irrigation with one, two, or threemitters on yield and cracking were compafor fruit at clusters 1 to 8. There was a cletrend for plants receiving the least water (single-emitter treatment) to have less crackbut generally similar yields compared to trements receiving more irrigation. Fruit havested from the lower clusters were less likto be cracked than those harvested fromupper clusters.

We report here the effect on yield and frcracking of providing varying amounts of watand nutrient solution to two spring crops bag-grown greenhouse tomatoes and discthe implications. We also report on diffeences in fruit cracking between early and ladeveloping clusters on the plant. On a practbasis, fruit cracking is difficult to study because, to our knowledge, no experimental ptocols are known that reliably induce crackiin attached fruit. Screening for cracking-resistant cultivars must be done either in enronments where high levels of cracking habeen observed in the past or in the laborawhere vacuum infiltration (e.g., Kamimur1977) is used to artificially pull water intdetached fruit. Our study assesses the feasity of using excess watering in greenhousestudy cracking or to screen cultivars for craing.

Materials and Methods

Varying amounts of nutrient solutio(Spring 1990). ‘Caruso’ tomato was seededDec. 1989. On 12 Feb. 1990, seedlings wtransplanted into individual upright black polethylene grow-bags (Hydro-Gardens, Corado Springs, Colo.) containing 19 liters medium. Bag medium consisted of a mixtuof 50% (by volume) of Pro-Mix-BX (PremieBrands, New Rochelle, N.Y.) and 50% agpine bark. Plastic sheeting was placed unthe bags to prevent root penetration throubag bottoms. Bags were placed in a 5.2 × 6.1-m freestanding, gutter-connected-style expmental greenhouse. A detailed descriptionthe experimental greenhouses is given in Wiand Peet (1989).

Day/night heating setpoints were 21C/16Setpoints for low-vent, high-vent, and evaprative pad cooling were 25, 27, and 28respectively. The date on which each invidual flower opened fully was considered

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Fig. 1. Effect of emitter treatment on percentage of cracked fruit on the basis of total number and total weightin Spring 1990 and 1992. For treatments of one and two emitters, both emitters delivered nutrientsolution. One of the emitters in the 1 + 1 treatment delivered nutrient solution and the other deliveredwater. Within the same series (year and weight or year and number), columns with the same letter on topwere not significantly different (for number: P ≤ 0.10, n = 12 for 1990; P ≤ 0.05, n = 28 for 1992; forweight: P ≤ 0.05, n = 12 for 1990, n = 28 for 1992).

be the date of anthesis and was recordeallow comparison of days to maturity for fruthat eventually cracked and those that did n

A modified Hoagland’s solution was injected into the watering lines each time tplants were irrigated. Solution concentratiwas modified as follows during crop develoment. After transplanting, initial fertilizer levels were (mg•liter–1) 90 N, 45 P, 195 K, 155 Caand 44 Mg. On 28 Mar., these levels weraised to 125 N and 310 K (Stage II), with othnutrient concentrations maintained. On 6 JuN levels were raised to 165 (Stage III). Plawere irrigated daily at 0900, 1200, 1500, a1800 HR, with the number of minutes pewatering depending on crop water usage. the two emitter treatments, this averaged tween 1.6 and 2.0 liters/plant per day. ensure uniformity of water delivery, turbulent-flow emitters and pressure regulators wincorporated in the irrigation system. The nuber of emitters was the same in all lines andlength of the line was <5 m to reduce wadelivery differences from the first to last emter in the line. Amount of water delivered at tend of each line was measured by taping emitters to an empty bucket at about the saheight as the emitters providing water to tplant. The amount of water in the bucket wregularly measured to ensure irrigation schuled by the computers actually took place athat there were no significant differencesamount of water delivered between lineNutrient solution pH and soluble salts wealso monitored regularly. Soluble salts levin representative bags in each greenhouse wmeasured at the end of the experiment.

Within the greenhouse, irrigation treaments of one vs. two emitters were imposed12 blocks of two adjacent plants arrangedtwo double rows of six plants for a total of 2plants in the greenhouse (12 replicationInitially, two emitters were placed in each baWithin each two-plant block, irrigation treaments of one vs. two emitters were assignrandomly to the grow-bags. Irrigation treaments were imposed on 21 Mar., by removone emitter. The 5-week delay in imposiirrigation treatments was to ensure that plain all treatments had equivalent vegetatcover and fruit set at the start of ripening, tperiod in which fruit are most sensitive cracking. Bright, sunny weather in mid-Aprwilted plants in the one-emitter bags. At tsame time, excess solution was draining outhe two-emitter bags. To reduce the differenbetween the treatments in amount of waprovided, an additional emitter was addedeach bag on 18 Apr. 1990. From this time only 50% rather than 100% more water wprovided to the high soil moisture treatmen

Normal cultural practices for greenhoutomatoes were employed, including removiall suckers and training one main stemplastic twine attached to an overhead wThe growing tip of the plant was removed 16 Apr. after six clusters had formed. Fruwere harvested at the “turning to red” statwo to three times weekly, beginning 16 ApWeight and number of cracked fruit werecorded separately. Any fruit with crackin

66

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detectable to the naked eye was counte“cracked.” The cluster from which fruit weharvested also was recorded.

Tensiometers to monitor soil water potetial were installed in two bags in each trement on 19 Sept. and connected to a datalogTensiometers were removed for repairs seral times, but recorded soil water potentialmost of the season. Because of the limnumber of tensiometers installed, tensiomdata were analyzed by paired t tests rather thaSAS analysis of variance as was done withother data (SAS Institute, Cary, N.C). Regrsion equations were plotted with JMP statical software (SAS Institute).

Varying amounts of nutrient solution aamounts of water independently (Spring 199Procedures followed in Spring 1992 differfrom Spring 1990 as follows. Seeding atransplanting took place on 20 Dec. 1991 18 Feb. 1992, respectively. We used lar(6.7 × 12.2 m) freestanding, gutter-connecgreenhouses. Both greenhouses were divinto beds raised 0.3 m above ground level wdimensions 2.4 × 1.2 m. Each watering treament was imposed on two beds in each hoeach bed containing 12 plants. This resultea total of four replications, two in each hou

From the time plants were placed in beds to the first harvest, each bag recenutrient solution through two emitters. On Mar., the following three irrigation treatmenwere imposed on two beds in each greenhofor a total of six experimental beds per grehouse: 1) two emitters per bag, both delivernutrient solution (2EN); 2) one emitter pbag, delivering nutrient solution (1EN); 3) tw

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emitters per bag, one delivering nutrient sotion and one delivering water (1EN + 1EWThe line providing only water was set to irrgate 20 min after the end of irrigation winutrient solution. Irrigation treatments weassigned to beds randomly in the two grehouses. The design was completely randoized, with two replications in each house awith the two greenhouses providing additionreplication. Nutrient solution concentratiowas raised to Stage II on 17 Mar. and to StIII on 11 May. Plants were topped on 15 Apleaving seven clusters on each plant. Fwere harvested beginning 13 Apr.

Spring 1992 was cool and humid compared to 1990, and it was possible to avwilting in the one-emitter plants, without providing so much water that excess drained frthe two-emitter plants. Excess watering wdetected by placing catch pans under selecplants in the 2EN bags. When there was arunoff within 5 min after the end of the firswatering in the morning, the amount of irrigtion was decreased by shortening or deletthe next scheduled irrigation. Wilting in th1EN plants signaled the need for resumprevious irrigation levels.

Results and Discussion

Numbers of emitters and cracking. In bothyears, the percentage of cracked fruit increasignificantly when irrigation water was increased (Fig. 1). In 1990, fruit cracking wsignificantly higher on the basis of proportioof fruit cracked (40% vs. 60%) and on the baof weight of fruit cracked (43% vs. 65%) whe

HORTSCIENCE, VOL. 30(1), FEBRUARY 1995

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Fig. 2. Percentage of cracked fruit on the basis of total number at each cluster for greenhouse-grown tomatoesin (A) Spring 1990 and (B) Spring 1992. Vertical lines show standard error of the mean. Cluster 1 isnearest the base of the plant.

we used two rather than one emitter. In 19the percentage of cracked fruit grown in 2Eand 1EN + 1EW treatments was significanhigher on the basis of number (13.0% v26.5%) and on the basis of weight (14.5% 28.4%) compared to those from the 1EN trement. For some of the early harvests in 19differences between treatments were alm5-fold. On 5 May 1992, for example, only 6%of the total number of fruit was cracked wi1EN, while 25% was cracked with 2EN an29% with 1EN + 1EW.

In 1992, significantly more cracked fruwere harvested from one house than the otHowever, the interaction of house and irrigtion treatment was not significant for numbor weight of cracked fruit and the houses dnot differ in yield. The only difference in thpercentage cracking data between the thouses was that in the house with more craing, the 2EN treatment had a higher perceage of cracking than the 1EN + 1EW treatme(39% vs. 34% by number and 39% vs. 35%weight), while in the house with less crackinoverall, the 2EN and the 1EN + 1EW treaments did not differ significantly. For morconvenient comparison with 1990, data frothe two houses were therefore combinedFig. 1. For the combined data from both houin 1992, there were no significant differencbetween the 2EN and the 1EN + 1EW trements in percentage of cracked fruit.

The 1992 experiment allowed us to seprate the effects of providing extra water frothose of providing extra nutrients, effects thwere confounded in the 1990 experiment. Whtreatments receive differing amounts of fertizer as well as different amounts of water (as1990), plants receiving more fertilizer mahave grown faster. This more rapid growmight, in and of itself, result in greater cracing. There is, indeed, evidence that rapid frgrowth from any of a number of causes icreases fruit cracking. Dutch investigators ported increased incidence of russettingdisorder related to cracking where minucracks appear all over the skin) when frwere developing more rapidly (Bakker anJanse, 1988; Schilstra-van Veelen and Bakk1985). Our 1990 data also provide partsupport for the hypothesis that rapid frugrowth increases cracking (Peet, 1992). Frthat were cracked at harvest had matured nificantly (P ≤ 0.05) more rapidly thanuncracked fruit (58.4 days vs. 61.8 dayHowever, once cracking occurred, fruit mahave ripened more rapidly and so were hvested sooner.

Based on our 1992 data, however, we sgest that extra water alone can cause crackeven if no extra fertilizer is provided, and thincrease in cracking is not a secondary resof more rapid plant growth. Plants receivinthe most water had the most cracking, regaless of the amount of fertilizer provided. Planin the 1EN treatment received half as muwater as those in the other two treatments had only half as much cracking. Plants in t1EN treatment received the same amounfertilizer as 1EN + 1EW plants, but still hamuch less cracking.

HORTSCIENCE, VOL. 30(1), FEBRUARY 1995

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Our data have practical application fogreenhouse production of tomatoes. Whefruit cracking is a problem, irrigation shoulbe reduced. Overirrigating is particulartempting late in the season in the spring cras the plants become older and days becolonger and hotter. By the end of the seashowever, few fruit remain on the plant, anleaf area is either the same or may be leslower leaves have been removed, a normcultural practice. The remaining leaves aolder, leathery, and may transpire less. Thit would probably be safer in terms of prevening fruit cracking to reduce irrigation at thend of the crop than to automatically raiseThis concept has several implications for atomatic greenhouse watering. If the concepcorrect, models that predict watering requirments on the basis of evapotranspiration aleaf area would overpredict water usage uless they take into account changes in pltranspiration. Lysimeter-based control sytems, which add water only as it is actuaused by the plant, may lead to reduced craing if properly set.

A Japanese study on the effect of smoisture content on cracking in field-growtomatoes offers a partial explanation for icreased cracking in the treatments receivmore water. Kamimura et al. (1972) found thfruit of tomato plants grown under high somoisture differed anatomically from thosgrown under low-moisture conditions. Und

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high soil-moisture growing conditions, fruenlarged rapidly and minute cuts occurrfrequently on the surface. These minute ccould later act as focal points for stresses tfurther tear the cuticle (Brown and Considin1982). The cuticle was also thinner and tepidermal and subepidermal cells flatter amore markedly stretched compared to thosefruit grown under low soil moisture. Fruit oplants grown under low soil moisture wesmaller and had higher tensile strength wfew minute cuts.

Presumably because of these anatomidifferences, Kamimura et al. (1972) found thmost severe cracking under high, comparedlow, soil-moisture conditions. This explanation fits our tensiometer data from 1990, cracking was significantly higher and somoisture tensions were significantly lowe(–3.45 kPa compared to –16.21 kPa) in ttreatment given more water over the coursethe study. The –12.2 kPa difference in smoisture tension was significant at P < 0.0001using paired t tests (SE = 1.99 kPa).

Position of the cluster and cracking. Inboth years, the upper clusters were more prto cracking, regardless of irrigation treatmeFor both seasons, linear regressions of craing percentage (on the basis of number) cluster were significant (P ≤ 0.01 with r2 = 0.90for Spring 1990 and r2 = 0.98 for Spring 1992).Linear regression of cracking percentage cluster position resulted in the following pre

67

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Table 1. Total number and weight (grams) of fruit per plant (Spring 1990 and Spring 1992) irrigated withdifferent amounts of water.

FruitCount Wt

Treatmentz 1990y 1992x 1990y 1992x

1EN 37.3 a 26.2 b 8129 b 4209 b2EN 38.4 a 26.4 b 9639 a 4647 b1EN + 1EW 28.8 a 5302 az1EN = one emitter per bag providing nutrient solution; 2EN = two emitters per bag providing nutrientsolution; 1EN + 1EW = two emitters per bag, one of which provided only nutrient solution and one of whichprovided only water.yOne-way analysis of variance indicated no treatment effects (P = 0.66, n = 12) for fruit count, effectssignificant for fruit weight (P = 0.003, n = 12).xMean separation within columns by Duncan’s multiple range test, P < 0.1, n = 12.

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dicted parameters: intercepts were 2.2 a–4.7 and slopes were 13.1 and 7.5 for 19901992, respectively.

There was evidence of nonlinearity in Spri1990, when the percentage of cracked fwas fairly stable from the first to third clusterthen doubled for the fourth through sixth cluters (Fig. 2A). However, regression of cracing percentage vs. cluster count did not sport a quadratic relationship in that the sond-order term was not significantly differefrom zero (P that “c” = 0 > 0.2). The increasalso appeared to be linear in 1992, when percentage of cracked fruit increased from in the first cluster to 38%, 41%, and 45%clusters 5 , 6, and 7, respectively (Fig. 2B)

Several factors, including temperature airradiance, may contribute to greater crackin the upper clusters. Upper fruit were moexposed to the sun than those on the loclusters, especially once plants were toppVerner (1935) found that apples (Malusdomestica Borkh.) grown on the outside of thtree and exposed to the sun were most likelcrack. Because of their greater exposure tosun, fruit on upper clusters could also expected to heat up more during the day tfruit on lower clusters. Frazier (1947) founthat higher temperatures in general, and sden high temperatures in mid-afternoon particular, caused ripe tomato fruit to crackthe greenhouse, probably because of expsion of the fruit pulp as temperatures increaLang and Düring (1990) reported that raisithe temperature of grape berries dramaticincreased the pressure exerted by the pulpthe skin while simultaneously decreasing stiffness and strength of the skin.

An additional component of cracking upper clusters may be the reduced fruit loadfruit is progressively harvested up the mastem. Low fruit load has been associated wincreased cracking in greenhouse tomat(Bakker and Janse, 1988; Schilstra-van Veeand Bakker, 1985).

Number of emitters and fruit productioEffects of the various irrigation treatments total fruit number were not significant in Sprin1990 (Table 1). In Spring 1992 (Table 1), t1EN and 2EN treatments did not differ signicantly in fruit count, but count was signifcantly higher (P < 0.10) in the 1EN + 1EWtreatment compared to the other two trements. Although the differences were not la(9.8%), they suggest that plants in the 1EN1EW treatment may have benefited from tdaily flushing with water a few minutes aftreceiving nutrient solution. Further studineed to be done to confirm this hypothessince the number of samples of the meditaken at the end of the experiment was insficient to determine if salt levels differed significantly between treatments. All were in thnormal range, however.

Increasing the amount of water providincreased total fruit weight per plant by 18.6(Table 1) in 1990. In 1992, there were differences in weight of fruit per plant between the 1EN and 2EN treatments, butwith fruit count, fruit weight per plant wasignificantly (19.7%) higher in the 1EW

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We have demonstrated in two crops greenhouse tomatoes that increasing amount of water applied increases crackiThis result suggests that in greenhouse sitions where cracking is severe, a reductionwatering should be considered. These resalso may apply to field crops (Kamimura et a1972; Nassar et al., 1971; Nitzsche and Storunpublished data). Caution should be usedwatering reduction, however, because low rpressures will make the plants more susctible to blossom-end rot. The number of fruwith blossom-end rot was lower than the nuber of cracked fruit in all crops studied but winversely proportional to cracking. That iwhen the amount of water was increascracking increased, but blossom-end rot creased. Good Ca nutrition is important preventing blossom-end rot and has also bimplicated in controlling fruit cracking (Pee1992). The best strategy to protect the younclusters if cracking appears in the older cluters would be to reduce watering graduawatching for the appearance of blossom-erot, severe wilting, or reduced fruit size. At thappearance of any of these signs, watershould be stabilized and gradually increasagain avoiding sudden increases, which wof themselves, trigger cracking. Where posible, water provided should be tied to wausage, as through the use of lysimeter-bairrigation systems.

Our data suggest that by deliberateoverwatering the plants, cracking resistanof cultivars or the efficacy of treatments prevent cracking could be compared.

We cannot draw any conclusions on tmechanism by which overwatering increascracking, but we demonstrated in Spring 19that soil water potential was less negativethe treatments receiving more water. This likeincreased root pressure and seems the mlikely explanation for increased fruit crackinUsing the Spring 1992 data, we demonstrathat the effect water supply has on fruit cracing was independent of the effect of providimore nutrient solution.

Literature Cited

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etmaaltemperatuur geeft meer kans zwelscheuren bij tomaat. Weekblad Groenen Fruit. 26 Feb. 1988. p. 30–31.

Brown, H.D. and C.V. Price. 1934. Effect of irrigation, degree of maturity, and shading upon yield and degree of cracking of tomatoes. PrAmer. Soc. Hort. Sci. 32:524–528.

Brown, K. and J. Considine. 1982. Physical aspeof fruit growth. Stress distribution around lenticels. Plant Physiol. 69:585–590.

Calbo, A.G. 1990. Physiology of vacuum inductomato fruit cracking. Revista Brasileira dFisiologia Vegetal 2:55–61.

Cotner, S.D., E.E. Burns, and P.W. Leeper. 19Pericarp anatomy of crack-resistant and susctible tomato fruits. J. Amer. Soc. Hort. Sc94:136–137.

Frazier, W.A. 1947. A final report on studies tomato fruit cracking in Maryland. Proc. AmeSoc. Hort. Sci. 49:241–255.

Kamimura, S. 1977. A method of testing craresistance in tomatoes. Jpn. Agr. Res. Qu11:111–114.

Kamimura, S., H. Yoshikawa, and K. Ito. 197Studies on fruit cracking in tomatoes. Bul. HoRes. Sta. Ministry of Agr. & For. Series (Morioka) #7.

Koske, T.J., J.E. Pallas, and J.B. Jones, Jr. 1Influence of ground bed heating and cultivar tomato fruit cracking. HortScience 15:760–76.

Lang, A. and H. Düring. 1990. Grape berry splittiand some mechanical properties of the skVitis 29:61–70.

Nassar, Z.L., A. Kamal, and R. Khalidy. 197Cracking behaviour of tomato varieties unddifferent moisture and nitrogen levels. Pamph40. Fac. Agr. Sci., Amer. Univ. of Beirut.

Peet, M.M. 1992. Radial fruit cracking in tomatHortTechnology 2:216–223.

SAS Institute. 1985. SAS/STAT guide for personcomputers, version 6 ed. SAS Inst., Cary, N

Schilstra-van Veelen, I.M. and J.C. Bakker. 198Cracking of tomato fruits. 1985 Annu. RpGlasshouse Crops Res. & Expt. Sta. NaaldwThe Netherlands.

Verner, L. 1935. A physiological study of crackinin ‘Stayman’ Winesap apples. J. Agr. Re51:191–222.

Walter. 1967. Hereditary resistance to diseasetomato. Annu. Rev. Phytopathol. 5:131–162

Willits, D.H. and M.M. Peet. 1989. Predicting yieresponses to different greenhouse CO2 enrich-ment schemes: Cucumbers and tomatoes. A& For. Meteorol. 44:275–293.

Willits, D.H. and M.M. Peet. 1992. Nighttime cooing using heat pumps in warm-weather greehouse tomato production. Amer. Soc. Agr. EnIntl. Summer Mtg., 21–24 June 1992, CharlotN.C. Paper 92-4005. Amer. Soc. Agr. Eng., Joseph, Mich.

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