irri - upland rice ecosystem

Upland rice ecosystem 55

Research programsUpland rice ecosystem

GERMPLASM IMPROVEMENT 56A new upland rice variety for the Philippines (PBGB) 56On-farm characterization of upland rice varieties in Thailand (APPA, PBGB) 56Genotype × environment interaction (PBGB, APPA) 58Allelopathy in rice germplasm 61

Root growth of allelopathic cultivars (APPA) 61Toward a perennial rice 61

Screening wild rice species for perenniality (PBGB) 62Building a population segregating for perenniality (PBGB) 62Study of nematode resistance in O. longistaminata (PBGB) 64

PROGRESS OF UNREPORTED PROJECTS 64Rehabilitation and sustainability of upland rice-based farming systems 64Upland Rice Research Consortium 65

PROGRAM OUTLOOK 65

56 IRRI program report for 1997

Upland rice ecosystem

Upland rice is grown on more than 17 million haworldwide with annual production about 20 million t.The total area supporting upland rice-based croppingis considerably larger than 17 million ha because ofrotations with fallow and other crops. The crop growsin a wide range of climate, topography, and soil type,often as a subsistence crop receiving few purchasedinputs. Upland farmers are among the poorest inmany parts of Asia, Africa, and Latin America.

The major objectives of the upland rice programare to develop knowledge and technology to maximizeproductivity and sustainability of upland rice where itis grown, to help maximize returns for farmer effort,and to reduce the area needed to satisfy demands forupland rice.

Research on germplasm improvement of uplandrice seeks to overcome major abiotic (drought,nutrient availability, acidity, erosion) and biotic(weeds, blast, nematodes) yield constraints by usingnew technology to identify, characterize, and incorpo-rate desired genes. Projects are aimed at develop-ment of perennial rice for the uplands and investiga-tion of allelopathy in rice to assist with sustainableweed management. The perennial rice and allelopathyprojects provide valuable information on geneticcharacterization of rice and its wild relatives and thegenetics and physiology of tolerance for such yieldconstraints as drought and nematodes.

Research on abiotic constraints focuses onunderstanding of nutrient availability in upland soils.The work on biotic constraints investigates the biologyand management of weeds, nematodes, and blast.Socioeconomic research aims to characterize andunderstand the dynamics of the upland croppingsystems and the impact of new technologies andpolicies on upland farmers.

The program is implemented in close collaborationwith national agricultural research systems (NARS)through the Upland Rice Research Consortium(URRC), which includes Brazil, India, Indonesia, Lao

PDR, Philippines, Thailand, and Vietnam. Bangladesh,China, and Myanmar are URRC associates. Theconsortium, in operation since 1991 with supportfrom the Asian Development Bank, the GermanAgency for Technical Cooperation (GTZ), and Japan,provides a framework for NARS-IRRI collaboration.

Germplasm improvement

Improving upland rice productivity provides an en-try point to alleviating the interrelated problems ofproductivity, sustainability, and poverty in the up-lands. Improved germplasm can contribute to thisobjective at a relatively low cost to farmers. Varie-ties are being developed with good and stable yieldsthrough improved tolerance for drought, good inter-ference with weeds through combined competitive-ness and allelopathy, resistance to blast and nema-todes, and adaptation to acid soils with low phos-phorus availability.

A new upland variety for the Philippines

PSBRc5 (or Arayat) is one of two upland rice vari-eties released in 1997 by the Philippine Seed Board.It is derived from a 1983 cross IRAT104 (improvedvariety from Africa)/Palawan (traditional varietyfrom the Philippines). PSBRc5 is a tropical japonicaadapted to acid soils and is for cropping systemswith low to moderate level of inputs.

On-farm characterization of upland ricevarieties in Thailand

An on-farm diagnostic survey on the extent andcauses of the variability of upland rice yields wasdone during 1993-96 in Mae Haeng, a highlandLahu village of Chiang Mai Province, Thailand.


Data were obtained over four wet seasons from423 squares (1 m-2) in 63 farmers’ fields represent-ing an extensive range of upland rice cropping con-ditions in a predominantly swidden cultivation sys-tem. The plots were monitored every 2 wk to quan-tify key physiological and agronomic parameters.An isozyme analysis assessed the genetic variabil-ity of the farmers’ varieties.

All upland rice cultivars were found to belong togroup 6 (tropical japonicas) of Glaszmann’s classi-fication. Heterogeneity was sometimes detected be-tween samples of the same variety coming from dif-ferent farmers. The rare allele 3 at locus Amp-1,typical of the varieties from Himalayan foothills,was observed in some of the cultivars. Only twolate-maturing varieties were found to be glutinous.

Two main types of cultivars, early (95–115 d)and late (138–177 d) maturing, were distinguished(Table 1). Late-maturing varieties constitutedclearly the most important type in terms of produc-

tion volume, whereas early-maturing varieties wereplanted to improve food security before the mainharvesting period. When expressed in degree days,the crop duration cycle was evenly split between thevegetative and reproductive phases for earlycultivars while in the case of late-maturing cultivarsthe reproductive phase was longer.

Maximum grain yields for the two dominant va-rieties, Chaloina and Chaae (Table 2) were mea-sured in fields where no purchased inputs were ap-plied but where environmental constraints wereminimal. Yields of 3.1 t ha-1 for Chaloina and 4.4 tha-1 for Chaae are considered yield potentials basedon subsequent analyses of yield buildup processesand agronomic diagnosis of limiting factors. Maxi-mum values of yield components characterizing theclassic four successive phases of the yield buildupprocesses are shown in Table 2.

The maximum number of panicles per unit areawere similar for both cultivars but were reached dif-

Table 1. Physiological and genetic characteristics of local upland rice cultivars in Mae Haeng Village, Chiang MaiProvince, Thailand, 1993-96.

Early-maturing cultivars Late-maturing cultivars

Variety Chaloina Kochokai Chaloioe Kochole Chaae Chanoko Chafuma Chazu Komu ChanonaImportance Dominant Common Rare Rare Dominant Common Common Common Rare RareVarietal groupa Tropical japonica Tropical japonicaPhotoperiodism Weakly sensitive Strongly sensitiveGrain type Nonglutinous Nonglu- Gluti- Nonglu- Nonglu- Nonglu- Gluti-

tinous nous tinous tinous tinous nousDDb to PI 650 800 670 590 1060 1060 1000 1230 1150 860DDb to harvest 1340 1400 1350 1270 1900 1910 1860 2120 1960 1790

aBased on isozyme analysis. bDD=degree days (13 0C threshold temperature), PI=panicle initiation.

Table 2. Agronomic characteristics of the most common upland rice cultivars in MaeHaeng Village, Chiang Mai Province, Thailand, 1993-96.

Cultivar Chaloina ChaaeMaturity type Early Late

Observations (no.) 75 234Maximum grain yield (g m-2 at 0% H2O) 308 438Maximum thousand grain weight (g at 0% H2O) 23.2 25.0Threshold valuea for filled spikelets m-2 13,300 17,500Maximum value for filled spikelets m-2 16,200 20,600Maximum percentage grain filling 81 98Threshold value for spikelets m-2 20,100 21,500Maximum value for spikelets m-2 22,000 26,700Maximum spikelets panicle-1 144 183Threshold value for panicles m-2 155 146Maximum panicles m-2 228 237Maximum panicles plant-1 2.8 3.6

Threshold value for plants m-2 81 66

aThreshold value: value required to achieve the maximum value for the yield component that follows.


ferently. Because of its lower maximum number ofpanicles plant–1, Chaloina required a higher thresh-old value for plants m-2 to achieve the same numberof panicles m-2 as that of Chaae.

The difference between Chaloina and Chaaestarted at spikelet formation and continued in a cu-mulative way during following phases. Chaae hada higher maximum number of spikelets per panicleas well as a better rate of grain filling (possibly duemore to favorable climate than to genetic differ-ences) and a higher maximum grain weight.

These maxima and associated threshold valuesfor yield components can be used to construct anempirical model of upland rice yield buildup pro-cesses. Such a model can be used for agronomic di-agnoses of limiting factors of the yield and for de-signing and evaluating improved sequences of cul-tivation practices.

Genotype × environment interaction

Genotype × environment (G×E) interactions com-plicate breeding work and varietal evaluation. G×Einteractions are reported to be stronger in uplandecosystems than in environments such as the irri-gated ecosystem. This was discussed during thefirst International Upland Rice Breeder Workshopin 1993 and a collaborative multiyear, multisite ex-periment was established with the following objec-tives:

● Quantify G×E interactions by partitioning theyield variability of a set of core varieties

Table 3. Upland rice varieties included in the GxE interaction experiment initiated at 13 sites insix countries. 1994.

Variety Country Varietal group Varietal type Av yield (t ha-1)

Azucena Philippines Japonica Traditional 1.2B6144 Indonesia Indica Improved 2.0Brown Gora India Aus Traditional 1.2Caiapo Brazil Japonica Improved 1.3Guarani Brazil Japonica Improved 1.5IR60800-46A Philippines Japonica Improved 1.4IRAT146 Côte d’Ivoire Japonica Improved 1.2IRAT216 Côte d’Ivoire Japonica Improved 1.1Oryzica Llanos 5 Colombia Indica Improved 1.2Oryzica Sabana 6 Colombia Japonica Improved 1.5UPLRi-5 Philippines Indica Improved 1.6Vandana India Indica Improved 1.5WAB181-18 Côte d’Ivoire Japonica Improved 1.4WAB56-125 Côte d’Ivoire Japonica Improved 1.5WAB56-50 Côte d’Ivoire Japonica Improved 1.5WAB96-1-1 Côte d’Ivoire Japonica Improved 1.3

between genotype, environment, and G×Einteractions.

● Identify the key environmental factors(weather, soil, cultural practices) responsiblefor a large part of G×E interactions.

● Evaluate the extrapolation domain of IRRIupland breeding materials by identifyingsimilarities among sites.

Sixteen varieties, mostly breeders’ checks, wereused as the core sample. Their characteristics arepresented in Table 3. They represent a broad diver-sity of genotypes in terms of isozyme groups, andgeographic and genetic origins.

Standard soil analyses were performed to charac-terize the environment, and weather data were col-lected. Cultural practices were the standard ones forthe sites (Table 4). The basic experiment used arandomized complete block design with three tofour replications. All trials were rainfed except W2and W3, which received a complement of sprinklerirrigation.

The yield of a subsample of 3–5 rows per plot at14% moisture content was analyzed. The yield sumof squares was partitioned into genotype, environ-ment, G×E, and error sum of squares using analysisof variance (ANOVA). The G×E sum of squareswas further partitioned using an additive main ef-fects and multiplicative interaction (AMMI) model.Correlation between the environmental factors andthe interaction principal component axis scores(IPCA) were computed. Hierarchical cluster analy-sis was performed on the residuals from the additive


model in order to cluster varieties and environmentswith respect to interaction effects.

The average yield per variety across sites (Table3) was similar for all varieties except for B6144,which yielded 2 t ha-1. It was in the experiment from1995 onward.

The ANOVA table for the additive modelshowed that 27% of the total sum of squares can beaccounted for by the G×E interaction, 69% by vari-ations in environments, and slightly more than 4%by variations in genotypes (Table 5). The G×E in-teraction is not the major component of the variabil-

Table 4. Sites for the upland rice G×E experiment, 1994-96.

Country Site Codea Latitude Longitude Elevation (m)

Philippines Maligaya, Luzon P1 15°45' N 120°56' E 50P2

Philippines Cavinti, Luzon C1 14°17' N 121°30' E 305C2C3

Philippines Ubay, Bohol B1 10°03' N 124°25' E 50B2B3

Philippines Arakan Valley, U1 8°00' N 124°00' E 500Mindanao U2

India Hazaribagh, Bihar H2 23°56' N 85°21' E 600H3

Thailand Samoeng, Chiang Mai T2 18°17' N 98°36' E 820T3

Indonesia Sitiung, Sumatra S1 1°02' S 101°31' E 130S2S3

Côte d’Ivoire M’be W1 7°44' N 5°04' W 380W2W3

Côte d’Ivoire Man M1 7°23' N 7°31' W 340M2M3

Colombia Carimagua R1 4°30' N 71°20' W 150Colombia Estacion La Libertad E1 4°03' N 73°29' W 400

E2Colombia Altillanura Colombiana (nativa) N1 4°03' N 73°29' W 190

N2Colombia Altillanura Colombiana (soya) Y1 4°03' N 73°29' W 190

Y2

aNumbers in site code are 1=1994, 2=1995, 3=1996.

Table 5. Yield decomposition analysis of variance and AMMI modelfor an upland rice GxE interaction experiment, 1994-96.

Source df Sum of Mean Totalsquares square sum of

squares (%)

Genotype 15 15.82 1.055 4.6Environment 29 235.09 8.107 68.8G×E 363 90.74 0.250 26.6

IPCA1 43 25.53 0.594 28.1IPCA2 41 19.54 0.477 21.5IPCA3 39 11.42 0.293 12.6IPCA4 37 9.81 0.265 10.8Residuals 203 24.43 26.9

Total 407 100.0


ity but it is still high at 27%—almost seven timesthe size of the genotype effect. This decompositionconfirms the rationale of a decentralized breedingstrategy. However, in the results using first-yeardata, G×E interaction was not higher than one ob-served in a similar type of trial in an irrigated riceecosystem.

The AMMI model with four IPCAs (AMMI4)accounted for 73% of the G×E sum of squares withthe two first axes accounting for 50%. There was adrop in G×E contribution between the second andthe third IPCAs but one-fourth of the variation con-tained in the G×E term could still be explained byIPCA3 and IPCA4.

Correlation analysis was performed for availablesite characteristics (weather, soil characteristics,amount of fertilizer) and scores of the four IPCAsin order to determine which environmental factorsplayed important roles in G×E interaction in thisdata set. IPCA1 was negatively correlated withmaximum temperature during wk 7 to 12. IPCA2was positively correlated with latitude and longi-tude, exchangeable Ca, exchangeable Mg, cationexchange capacity, and minimum temperature dur-ing wk 1 to 10,and negatively with soil fertility (or-ganic C, C/N, total N). IPCA3, which correspondedmostly to an acidity syndrome, was negatively cor-related with pH and with exchangeable bases (K,Ca, and Mg) and positively with exchangeable Al.IPCA4 represented a fertilization axis with negativecorrelation with basal N and organic C but positivewith topdressed N. It was striking that none of theaxes was correlated with rainfall at a significant pe-riod, although rainfall is one of the main determi-nants in upland yield variation and huge variationsin rainfall from year to year were observed. Thiscould be partly explained by the fact that the varie-ties tested represented a relatively wide range ofduration. Thorough analysis of long-term weatherdata is necessary to clarify weather patterns and dif-ferentiate target environments on this basis.

The interaction biplot with sites and varieties su-perimposed (Fig. 1) can be used to determine thestability of the varieties and their adaptation to agiven set of sites. Genotypes situated close to thecenter can be regarded as stable across a gradient ofsoil acidity and soil fertility because of their consist-ent yield performance across sites. On the otherhand, genotypes far from the center can be regardedas sensitive to the environmental factors differing

1.2

0.5

–0.2

–0.9–1.40 –0.88 –0.36 0.16 0.68 1.20

IPCA1

7

5

1

2

4

2

6

11

1625

39

N2Y2

M3

C3

M1M2

B2 W2N1

Y1

E2R1

10W3

E1

C2C124

S1T3

C2

H3U2U1

P1

P2

W1

S3B3

B1

22

23

8IPCA2 Model fit: 49.7% of G×E SS

1. Interaction biplot for the AMMI2 model based on yieldof 16 varieties tested at 13 sites (1994-96). Codes:Philrice main station (P) and Cavinti (C); IRRI uplandbreeding site at Bohol, Visayas (B) and Arakan, Minda-nao (U); Sitiung, Indonesia (S); Samoeng, Thailand (T);Hazaribagh, India (H); Carimagua, Colombia (R); twosites at Altillanura, Colombia, one following fallow (N)and one following soybean (Y); M’be, Côte d’Ivoire (W)and Man, Côte d’Ivoire (M). The number added to eachletter represents years 1994 (1), 1995 (2), and 1996 (3).IRRI, 1997.

over sites because their performance varies acrosssites. This is the case for UPLRi-5 (7), Vandana (8),WAB 56-50 (11) and, to a lesser degree, for BrownGora (2) and Oryzica Llanos 5 (2). The dendrogramof varieties structured by interaction pattern (Fig. 2)shows some degree of agreement with the biplots.The first split separates B6144 from the other varie-ties. Vandana, Oryzica Llanos 5, and UPLRi-5 arepooled together. All these varieties are indica types.The cluster dendrogram for genotypes appears to bewell related with the clustering based on isozymicgroups.

By projecting the varieties on the site vectors inFigure 2, it is possible to evaluate their specific in-teraction. Varieties used as checks for a site gener-ally have positive interaction at that site. This is thecase, for example, for the four WAB varieties (9,10, 11, and 12) which have positive projections onthe W1, W2, and W3 vectors, the station where theywere bred, or for Brown Gora in Hazaribagh.


The sites can also be subdivided using clusteranalysis on interactions. The pattern of clusteringoften grouped two different years of the same sitebut never three. The Asian sites tended to group andto separate from the African and Latin Americanones.

Allelopathy in rice germplasm

A laboratory screening procedure for allelopathicpotential in rice was established at IRRI in 1995(IRRI program report for 1995) and used to ensurethat field observations resulted from allelopathy andnot from competition. Laboratory screenings incombination with field experiments during 1995-96consistently showed that 19 rice cultivars (among111 tested) suppressed growth of Echinochloa crus-galli by more than 40%. Seven of the cultivars re-duced E. crus-galli dry weight by more than 50%.Two field experiments with the same 111 cultivarsand Trianthema portulacastrum as the target weedidentified two rice cultivars strongly allelopathic forboth E. crus-galli and T. portulacastrum. This veri-fies a pattern found by researchers in Arkansas,USA, and Egypt, indicating more than one chemi-cal is responsible for the allelopathic effect.Taichung Native 1 has shown allelopathic effectagainst E. crus-galli, T. portulacastrum, Heteran-thera limosa, and Ammannia coccinea. Cultivarswith promising allelopathic effects in IRRI trial

were tested in Korea with results comparable withthose obtained at IRRI.

ROOT GROWTH OF ALLELOPATHIC CULTIVARS

A 1996 experiment at IRRI measured early growthcharacteristics in allelopathic and nonallelopathiccultivars. Allelopathic cultivars were Taichung Na-tive 1, Woo Co Chin Yu, IR64, and AC1423. Aus196 and IR38 were the nonallelopathic cultivars.The cultivars were grown in hydroponics in a green-house using a randomized complete block designwith three blocks. No significant difference be-tween allelopathic and nonallelopathic cultivars wasobserved during the early growth stages. Shoot androot dry weight showed similar trends with the ex-ponential growth starting 20–30 d after transplant-ing (DT). The other growth parameters such as leafarea and tiller number also had the same tendency.This suggests that allelopathic cultivars have thesame growth patterns as nonallelopathic cultivarsand indicates that allelopathic cultivars do not useextra energy to obtain allelopathic ability.

Toward a perennial rice

Erosion and consequent loss of the crop productionbase (soil, nutrients, organic matter) is an importantproblem in the uplands of Southeast Asia. The tra-ditional shifting cultivation system in which annualcrops are grown is sustainable with long fallow pe-riods but now contributes to soil degradation inmany areas because population pressure has de-creased land availability, and leads to shorter fallowperiods.

National policies in Lao PDR, Vietnam, Thai-land, and China are increasingly prohibiting shift-ing cultivation and encouraging reforestation or soilconservation measures. In many areas, however,upland rice cultivation is the only way for farmersto produce rice, their staple food. Even in more di-versified and cash-oriented cropping systems, suchas those of northern Thailand, farmers still use up-land fields to grow rice for home consumption.

The advantages of a perennial upland rice wouldbe a product that addresses the immediate needs forfood as well as erosion control, does not require amajor change in farming practices, and minimizescapital, labor, and resource investments.

2. Cluster dendrogram for genotypes based on the yieldof 13 sites (1994-96). Numbers on the left are genotypecodes; labels in the dendrogram are cluster numbers.IRRI, 1997.

2524

12231011

936

161

24857

31

2226

28

27

2320

18

21

19

2417

2529

30

–0.4 1.3 3.0 4.7 6.4 8.1

Fusion level


SCREENING WILD RICE SPECIES FOR PERENNIALITY

Perennial wild rices are generally found in areasflooded most of the year. However, in areas with along dry season, the African wild species Oryzalongistaminata has been observed to persist becauseits rhizomes produce new shoots at the beginning ofthe following rainy season.

A set of 10 O. rufipogon and 22 O. longistami-nata accessions from different origins were testedfor perenniality and survival of drought. Testingwas in greenhouse concrete tanks filled with acidupland soil. Two O. sativa cultivars, IRAT216 (up-land) and C4-137 (irrigated, good ratooning ability)were used as control. During Nov 1995-Dec 1997,moderately dry periods (1 Apr-30 Jun 1996 and 10Mar-30 Jun 1997) were induced. Intermittent water-ing reproduced natural conditions providing theplants with 90 mm water, twice in 1996 and threetimes in 1997. The percentage of survival was re-corded after one and two dry periods and after ma-turity. Surviving plants were counted for O.rufipogon and percentage of plot area covered withplants estimated for O. longistaminata, which hasrhizomes that allowed plants to spread and cover thewhole plot surface.

Because both perennial species are photoperiod-sensitive, most of the accessions flowered after thefirst drought, and panicle initiation took place withdecreasing daylength. Only one O. rufipogon acces-sion, 106647 from Thailand, behaved like an annualcrop, showing no photoperiod sensitivity.

All the tested accessions of O. longistaminatasurvived the dry periods and almost no differencewas observed in percentage of plot area covered,showing the ability of the species as a whole to sur-vive drought. Strong differences appeared in per-centage of surviving O. rufipogon individuals(Table 6). The best accessions were 106114 and106138 from India and 106352 from Myanmar.However, variability within populations was highfor vigor and ratooning ability, even in accessionswith a low survival rate. On the basis of survival,vigor, and ratooning ability after cutting, 15 indi-viduals out of 7 accessions were selected as donorsof perenniality in crosses with O. sativa uplandcultivars.

BUILDING A POPULATION SEGREGATING FOR

PERENNIALITY

Breeding for perenniality is a long-term goal. Twocomplementary dominant lethal genes present in O.sativa and O. longistaminata cause embryo abortionwhen the two species are directly crossed. Conse-quently the transfer of the rhizome trait from O.longistaminata to O. sativa is done through a com-plex scheme of interspecific crosses (Fig. 3) and theuse of molecular markers would greatly help in se-lecting for perenniality in the progenies.

To identify markers linked with genes responsi-ble for the presence of rhizomes and for their ex-pression, an interspecific population segregating forthat trait was created. A F1 O. sativa/O. longistami-nata (BS125/WL 02) hybrid created at L' Institutfrançais de recherche scientifique pour ledéveloppement en coopération (ORSTOM) wasbackcrossed on two different O. longistaminata in-dividuals (WL 02-2 and SL 313-13) used as maleparents. The BC1F1 progeny (65 individuals)showed 100% plants with rhizomes and was thenselfed to produce a BC1F2 population segregatingfor rhizome expression. Because of restoration ofself-incompatibility from O. longistaminata andlow pollen fertility, seed setting was low in BC1F1plants and hand-pollination was used to improve it.Special techniques used included in vitro seed andembryo culture to overcome the low germinationrate and poor vigor of BC1F2 seeds, and hydroponicgrowth to improve seedling vigor and increase thenumber of plants obtained. A total of 227 F2 plants

Table 6. Survival in O. rufipogon accessions after drought.IRRI, 1995-97.

Accession Source Surviving Survival Selectedno. plants (%) plants

(no.) (no.)

105832 Thailand 5 28 3106114 India 16 89 2106133 India 8 44 1106138 India 17 94 3106144 India 7 39 2106145 Laos 7 39 0106340 Myanmar 4 22 2106352 Myanmar 13 72 0106417 Vietnam 8 44 2


(150 with WL 02-2 as parent and 77 with SL 313-13) showing a wide range of rhizome expressionwere derived from 30 BC1F1 plants. That populationis being mapped using restriction fragment lengthpolymorphism, sequence-tagged site, andmicrosatellite markers. Phenotyping for traits asso-ciated with rhizome expression and root develop-

ment is under way. Furthermore, to broaden therange of genetic recombination, the BC1F1 individu-als are being intercrossed to produce an intercrosspopulation (currently with 120 individuals). Thispopulation will be used as an adjunct for mappingif the BC1F2 population shows significant segrega-tion distortion.

3. Breeding scheme for transferring the rhizome trait from O. longistaminata to O. sativa to build a populationsegregating for perenniality. IRRI, 1997.

×

×

O. sativa O. longistaminata

O. longistaminata

× O. sativa× BCLF2 with rhizomes

and acceptable pollen fertility

BC1SF1 (no rhizomes)

× O. sativaupland cultivars

selfing

BC2SF1 BC1SF2

BC1LF1 (100% rhizomes)

selfing

B1CLF2 mapping population(segregating for rhizomes)

Complex hybrids (F1)segregating for rhizomes

F1 complex hybridswith rhizomes

selection

F1 hybrid

BS125 WL02

selfing intercrossing

F2 complex/complex complex/BCSwith rhizomes segregating for rhizomes

complex/complex//BCSsegregating for rhizomes

selection

× BC1SF1

× BC1SF1

F1 hybrids with rhizomes

× BC2SF1

complex/complex//BC1S///BC2Sand complex/BC1S//BC2Ssegregating for rhizomes


STUDY OF NEMATODE RESISTANCE IN

O. LONGISTAMINATA

Two greenhouse experiments were conducted todetermine the degree of resistance of O. longistami-nata to the rice root-knot nematode Meloidogynegraminicola, the most damaging species of nema-tode in the uplands of Southeast Asia, and to under-stand the genetics of the resistance. The materialtested included four O. longistaminata individuals(DL 01-1, WL 02-2, WL 02-15, and SL 313-13), theF1 hybrid BS125/WL 02-15, the O. sativa parentBS125, 10 BC1F1 hybrids from backcrosses on SL313-13, and 17 BC1F1 hybrids from backcrosses onWL 02-2. The O. sativa upland cultivar UPLRi-5was the susceptible control.

Seeds of O. sativa were germinated on moist pa-per in petri dishes. Five-day-old seedlings of O.sativa and 1-wk-old cuttings of the rest of the mate-rial were transplanted in 20-cm-diameter × 35-cm-high polyvinyl pots containing 6 kg of sterile soil.Three M. graminicola inoculations were made witha total of 1000 second-stage juveniles (J2) kg-1 soil.The first inoculation was 1 wk after transplanting.After 60 d, root systems were chopped into 0.5-1 cmpieces and M. graminicola (J2) were extracted from3 g subsamples by placing them for 5 d in amistifier.

In the first experiment, WL 02-2 and WL 02-15were found resistant, while DL 01-1 and the F1 hy-brid were susceptible (Table 7), suggesting that theresistance of WL 02 could be due to a recessivegene. Because BS125 plants did not grow well,slowing down the multiplication of the nematodepopulation, the number of J2 extracted per 3 g rootswas relatively low and BS125 was rated as moder-ately susceptible.

The second experiment confirmed the resistanceof WL 02-2 and susceptibility of the F1 hybrid andBS125 (Table 8). The accession SL 313-13 showeda moderately susceptible reaction, while all theBC1F1 from backcross on SL 313-13 were suscepti-ble, except for one individual which did not growwell. Among the 17 BC1F1 hybrids from a back-cross on WL 02-2, eight individuals were resistantand nine were susceptible. That proportion corre-sponds to a 1:1 resistant vs susceptible ratio ex-pected in the backcross progeny on the resistant par-ent when the resistance is due to a recessive gene.

The BC1F1 hybrids evaluated in this experimentwere used to develop the population segregating forrhizome expression that is being mapped.Phenotyping of the population for nematode resist-ance is under way. Molecular markers linked withthe gene of resistance to M. graminicola should beidentified soon.

Progress of unreported projects

Rehabilitation and sustainability of uplandrice-based farming systems

● Socioeconomic characterization of upland ricesystems in two sites in northern Vietnam andone site in eastern India was completed.Characteristics of upland rice systems can beexplained partially by a population vs marketaccess model.

Table 8. Number of second-stage juveniles (J2) in roots ingreenhouse tests of O. sativa, O. longistaminata, andBC1F1 on WL 02-2. IRRI, 1997.

Entry Species or hybrid J2 3 g-1 Ratinga

roots (no.)

UPLRi-5 O.sativa 106,440 SBS125 O. sativa 12,476 SBS125/ O. sativa/O. longis- WL 02-15 taminata 12,721 SSL 313-13 O. longistaminata 3,742 MSWL 02-2 O. longistaminata 521 RBC1F1 O.sativa/O.longistami-

nata//O.longistaminata 339 RBC1F1 O.sativa/O.longistami-

nata//O.longistaminata 9,024 S

aR = resistant, MS = moderately susceptible, S = susceptible.

Table 7. Number of second-stage juveniles (J2) in roots ingreenhouse tests of O. sativa, O. longistaminata, and theirF1. IRRI, 1997.

J2 3 g-1

Entry Species or hybrid roots Ratingb

(no.)a

WL 02-2 O. longistaminata 87a RWL 02-15 O. longistaminata 297a RBS125 O. sativa 2,591b MSDL 01-1 O. longistaminata 28,900c SF1 BS125/ O. sativa/ 32,060c SWL 02-15 O. longistaminataUPLRi-5 O. sativa 57,120c S(control)

aMean of five replications. bR = resistant, MS = moderately suscep-tible, S = susceptible.


● Economic analysis of contour hedgerowsystems for soil erosion control in the Philip-pines was completed. Econometric analysisquantified the extent of adoption, the effect onproductivity, factors encouraging adoption,patterns of hedgerow species shifts, andfactors determining economic viability.

● Data sets to characterize the variability andlimiting factors of upland rice production innorthern Thailand were assembled and initialanalyses performed.

● Analyses of soil erosion risks associated withdiversified cropping systems in northernThailand were partially completed.

● Achievable grain yields of 3-5 t ha-1 for uplandrice in rainfall favorable upland weredemonstrated when nutrient supply wasadequate.

● Progress was made in institutionalizing thelong-term P experiment (LTPE) presentlyongoing in Indonesia, India, Philippines, andThailand. A long-term soil sample archive wasestablished at IRRI and the construction of theLTPE long-term database is at an early stage.

● Phosphorus addition along with split applica-tions of N was found to stimulate deeperrooting by upland rice in a highly weatheredacid upland soil. Moderate N applicationsenhanced water uptake under mild stress butnot under severe and prolonged stress.

● Use of controlled-release N fertilizersachieved the same N recovery and N use effi-ciency as split applications of ordinary urea.

● An alternative methodology for field assess-ment of weed suppression by rice wasinitiated.

● Weed infestation especially in early cropgrowth and, to a lesser extent, brown spot andleaf blast were identified as pest managementpriorities for upland rice in Lao PDR.

Upland Rice Research Consortium

The URRC has been supported by ADB, GTZ, andJapan since 1991 and provides for IRRI-NARS col-laboration on strategic issues in upland rice re-search. Collaboration focuses on strong upland riceresearch and development groups around Asia.URRC has provided many NARS scientists with anopportunity to develop a more strategic focus in

their research and to interact internationally.Phase 3 of URRC was initiated in 1997 with sup-

port from BMZ-GTZ. New URRC partners in Viet-nam, Lao PDR, and Brazil were introduced at theannual technical and planning meeting at IRRI. Re-search results for 1996 were reviewed, and planswere developed for collaborative 1997 research.

Collaborative research has continued to focus ongermplasm improvement and better resource man-agement. Some 50 experiments are conducted annu-ally within URRC.

Program outlook

In the germplasm improvement project, new statis-tical procedures (AMMI for G×E analysis, patternanalysis) and new geographical information sys-tems (GIS) techniques will be used to furtheranalyze the agroecological diversity of the uplandsubecosystems and refine understanding of targetenvironments. The ecosystem is extremely hetero-geneous and G×E interaction in germplasm per-formance is strong across environments. Decentrali-zation of conventional breeding activities to NARSpartners who have a mandate and an obvious com-parative advantage in developing and releasing va-rieties for regional environments will continue.

IRRI’s program will focus more strongly on im-proving germplasm through use of new technolo-gies in prebreeding to provide better genetic mate-rial and more genetic understanding to support thebreeding programs of the NARS. Priorities are

● marker-aided selection to target and use genesassociated with tolerance for drought (deepand thick root system and osmotic adjust-ment), resistance to blast, and allelopathy;

● physiology investigations to understand keytraits associated with tolerance for drought;

● recurrent selection to improve traits with poly-genic control such as partial resistance to blast;

● interspecific hybridization for better utiliza-tion of the genetic diversity present in the wildspecies of Oryza bearing the A genome; and

● participatory plant breeding to test whetherfarmer participation in the breeding andselection programs improves adoption.

Resource management research will focus on de-veloping more basic understanding of upland pro-cesses, including nutrient cycling, soil acidity, biol-ogy of pests, and erosion. Such understanding can


underpin the development of more productive, sus-tainable rice-based cropping systems. It can also berelevant for the management of emerging uplandsystems, which have a diversity of rice and othercrops. It can also provide spillover benefits intoother ecosystems.

Research will focus on the following:● Production potential of upland rice. Costs of

inputs and technology may seem unaffordablefor farmers based on present income levels.However, limiting input treatments to suit thepresent income of farmers does not provide anunderstanding of the wide range of yieldresponses that are possible. The IRRI strategyis to explore the potential of sustainable highproductivity and generate a range of optionsfor farmers to achieve desired production.

● Long-term strategic studies on nutrients.Short-term seasonal studies cannot adequatelyaddress the dynamics of nutrients and produc-tivity of the land. An understanding of pro-cesses that control nutrient supply, producti-vity, and sustainability require long-term stra-tegic studies that are now a feature of IRRI’supland resource research.

● Nutrient-water interactions. There has beenemphasis in the past to alleviate drought byimproving plant traits through breeding. Butresearch has shown that drought effects areexacerbated in the absence of proper plantnutrition. IRRI’s focus in this area is tounderstand nutrient-water interactions and toimprove plant nutrition by better formulationand placement of fertilizers.

● Weeds. Weeds, a major constraint in uplandrice production, are difficult to managebecause, in contrast to irrigated systems,weeds and the crop emerge together and flood-ing is not an option for weed suppression.Weed research will continue to focus on cropcompetitiveness, allelopathy, and weed bio-logy to provide options for better weed controland reduce the burden of hand weeding.

Economic and policy analysis research will con-tinue to investigate technological, policy, and insti-tutional interventions that enhance food security ofupland farmers and sustainability of upland sys-tems. Through research based on economic andpolicy analysis, answers will be sought to questionssuch as

● Will rapid change toward systems based oncash crops expose farmers to income fluctua-tions and jeopardize their food security?

● What institutional arrangements are needed toenhance food security in commercializingsystems?

● How do farmers cope with increasing popula-tion pressure and environmental degradation?

● What institutional and policy interventions areneeded to encourage adoption of sustainableland use practices?

The URRC will continue to provide a strongframework to facilitate collaborative NARS-IRRIresearch and institution building in Asia and,through Brazil, into Latin America.

irri - upland rice ecosystem

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