Inheritance of temperature sensitivity of the photoperiod response in common bean (Phaseolus vulgaris L.)

Summary Photoperiod response of flowering in common bean (Phaseolus vulgaris L.) is thought to be controlled by the genes Ppd and Hr. However, cultivars also vary in the degree that cooler temperatures reduces their sensitivity to photoperiod. To examine the inheritance of this temperature sensitivity, crosses of cvs. Gordo x de Celaya and Flor de Mayo × Rojo 70 were evaluated at two sites differing in mean temperature and using 12.5-h natural photoperiod or 18-h artificially extended photoperiod. Under 18-h photoperiod at the warmer site, Palmira, no plants of the parents or of the F₂ populations flowered, confirming that the parents were sensitive to photoperiod. Under 12.5-h photoperiod at the cooler site, Popayan, the parents for each cross flowered at similar dates and no segregation for days to flower was observed. However, under 18-h photoperiod, de Celaya and Rojo 70 and the F₁ populations did not flower within 100 days after planting, while the F₂ and F₃ populations showed segregation that was consistent with single gene inheritance, late flowering being dominant. Late flowering at Popayan under 18-h photoperiod indicates a lack of temperature sensitivity, so temperature insensitivity of the photoperiod response was dominant to sensitivity. The name Tip, for temperature insensitivity of photoperiod response, is proposed for this gene, with the recessive form of this gene conditioning earlier flowering at cooler temperatures with long daylengths. It is recognized that the observed segregation patterns could represent the effect of multiple alleles at the Ppd or Hr loci, and studies are proposed to test this possibility with molecular markers and recombinant inbred lines.     

Slow-growth conservation of potato microplants: efficacy of ancymidol for long-term storage in vitro

Ancymidol was investigated as an alternative mediumsupplement to mannitol for slow-growth conservation ofpotato microplants in vitro. Differentconcentrations of ancymidol (0, 5, 10, 15, 20, 25, 30,35 and 40 M) were tested in slow-growthmedia based on MS medium supplemented with either 30or 60 gl^-1 sucrose. The cultures were conservedunder a 16-h photoperiod at two temperature regimesi.e. 24 ± 1 ^°C and 6 ± 1 ^°C. Therewere significant interactions between ancymidol andother factors such as sucrose, temperature andgenotype for microplant survival, microshoot heightand overall microplant growth. Ancymidol did have abeneficial effect on culture viability after prolongedmaintenance in vitro. The growth-inhibitingeffect of ancymidol persisted through a 16-monthculture period. Combined effect of ancymidol, sucroseand temperature showed that optimum culture viabilityand desirable microplant growth were obtained when thecultures were grown in MS medium supplemented with 10M ancymidol plus 60 gl^-1 sucrose at6 ± 1 ^°C. Vitrification and flaccidity, whichare very frequently observed in potato microplantcultures during prolonged maintenance in vitrounder osmotic stress (mannitol), were not observedwhen the microplants were conserved in ancymidolmedia. Genetic stability of potato microplantsconserved in ancymidol media was evaluated usingrandomly amplified polymorphic DNA (RAPD)fingerprints. Ancymidol did not induce any detectablegenetic variation in genomic DNA as visualized by theabsence of either any additional RAPD fragment oralterations in RAPD fragment patterns.     

Inheritance of time to flowering in cowpea (<Emphasis Type="Italic">Vigna unguiculata</Emphasis> (L.) Walp.)

Time to flowering and maturity is an important adaptive feature in annual crops, including cowpeas (Vigna unguiculata (L.) Walp.). In West and Central Africa, photoperiod is the most important environmental variable affecting time to flowering in cowpea. The inheritance of time from sowing to flowering (f) in cowpeas was studied by crossing a photoperiod-sensitive genotype Kanannnado to a photoperiod-insensitive variety IT97D-941-1. Sufficient seed of F₁, F₂, F₃ and backcross populations were generated. The parental, F₁, F₂, F₃ and the backcross populations were screened for f under long natural days (mean daylength 13.4 h per day) in the field and the parents, F₁, F₂ and backcross populations under short day (10 h per day) conditions. The result of the screening showed that photoperiod in the field was long enough to delay flowering of photoperiod-sensitive genotypes. Photoperiod-sensitivity was found to be partially dominant to insensitivity. Frequency distribution of the trait in the various populations indicated quantitative inheritance. Additive (d) and additive × dominance (j) interactions were the most important gene actions conditioning time to flowering. A narrow sense heritability of 86% was estimated for this trait. This will result in 26 days gain in time to flowering with 5% selection intensity from the F₂ to F₃ generation. At least seven major gene pairs, with an average delay of 6 days each, were estimated to control time to flowering in this cross.     

Bolting resistant breeding of Chinese cabbage. 1. Flower induction of late bolting variety without chilling treatment

Summary When a local slow bolting variety Osaka Shirona Bansei (Brassica rapa L. ssp. pekinensis, syn. B. campestris L. ssp. pekinensis) was grown in a phytotron (25°C, 16 hours day length without chilling treatment), one third of the plants bolted and flowered. In order to clarify the different flowering responses in the variety, a progeny line (FNC) of the flowering plants was chilled for 4 different periods (0, 22, 36 and 53 days) in a chamber of 2 7°C, then transplanted to three different conditions, i.e. PHY: 25–20°C day and night temperatures, 16 hours day length, GHL: 10 25°C, 16 hours day length with supplementary light and GHN: 10 25°C, natural day length (10 15 hours). In PHY, FNC bolted and flowered with almost the same leaf numbers in all 4 different chilling treatments. This means that FNC has very low sensitivity and no requirement to low temperature for its reproductive growth. In GHN (short day length), FNC bolted very slowly. Then the bolting and flowering of FNC were promoted by both long day length and high temperature. The newly found bolting characteristics of Osaka Shirona Bansei could be applied to breed unique slow bolting Chinese cabbage (B. rapa L. ssp. pekinensis) which might be non-sensitive to low temperature and its bolting and flowering would be induced with the combination of long day length and high temperature. Using the unique variety, it might be also possible to establish a new cropping type of Chinese cabbage (late autumn sowing, spring harvest).Abbreviations PHY Phytotron, long day and high temperature condition - GHL Greenhouse, long day and medium temperature condition - GHN Greenhouse, natural (short) day and medium temperature condition - FNC A progeny line of Osaka Shirona Bansei which flowered with no chilling treatment - FC A progeny line of Osaka Shirona Bansei which flowered with chilling treatment     

Genetic analysis of inbred lines and their crosses for resistance to head blight (Fusarium culmorum,F. graminearum) in winter rye

Summary For genetic analysis of head blight in winter rye (Secale cereale) caused by Fusarium culmorum, six homozygous inbred lines from the Petkus gene pool were crossed in all combinations to obtain 15 diallel F₁ crosses and the corresponding 15 F₂ crosses. These materials and 10 additional inbreds were artificially inoculated in a 2-year field experiment. The inbreds were also tested with F. graminearum in a separate sub-experiment.Single disease rating, average disease rating, and yield components (grain-weight per spike, 1000-grain weight, kernel number per spike) relative to the non-inoculated treatment were significantly affected by Fusarium head blight in all material groups. The relative grain weight per spike ranged from 26% to 88%. Significant genotypic and genotype x year interaction variances were found throughout. Heritabilities were highest for homogeneous inbreds (h²=0.6–0.8) and lowest for heterogeneous F₂ crosses (h²=0.4–0.6). Disease rating and relative grain-weight per spike were highly correlated for the inbreds and F₂ crosses (r0.7, P0.01), but lower for the F₁ crosses (r0.6, P0.05). Inter-annual correlation coefficients for disease ratings and relative grain-weight per spike ranged from r0.7 (inbreds) to r0.5 (F₂ crosses). The diallel analysis showed significant GCA effects only for relative 1000-grain weight in 1990, but significant SCA and SCAx year interaction variances for most traits. The resistances of 16 inbreds to F. culmorum and F. graminearum were tightly associated for all traits (r=0.96–0.97, P0.01).In conclusion, only slow progress can be expected from selecting for Fusarium head blight resistance in rye due to the limited amount of additive genetic variance and the great improtance of environmental factors.     

Transfer of resistance to race 2 of Plasmodiophora Brassicae from Brassica napus to cabbage (B. oleracea var. Capitata). I. Interspecific hybridization between B. napus and B. oleracea var. Capitata

Summary Interspecific hybridization between Brassica napus L. (2n=38, a₁a₁c₁c₁) and B. oleracea var. capitata L. (2x- and 4x-cabbage; 2n=2x=18, cc and 2n=4x=36, cccc) was carried out for the purpose of transferring clubroot disease resistance from the amphidiploid species to cabbage. Nineteen hybrids with three different chromosome levels (2n=28, a₁c₁c; 2n=37, a₁c₁cc and 2n=55, a₁c₁cccc) were obtained. The F₁ plants were mostly intermediate between the two parents but as the number of c genomes in the hybrids increased, the more closely the hybrids resembled the cabbage parent. All F₁ hybrids were resistant when tested against race 2 of Plasmodiophora brassicae wor. The complete dominance of resistance over susceptibility suggested that the gene(s) controlling resistance to this particular race of the clubroot pathogen is probably located on a chromosome of the a genome in Brassica.Contribution No. J654.     

Inheritance of duration from sowing to first flowering in pigeonpea

Duration from sowing to flowering is the most important trait influencing adaptation in pigeon pea (Cajanus cajan), but the inheritance of this trait has not been elucidated clearly. Crosses were made between two early (60 to 70d) and one late (160 to 170d) flowering pigeonpea genotype and F₁, F₂ and BC₁ populations produced. These populations, comprising 60 to 100 parents, 30 F₁, 400F₂ and 40 to 50 BC₁ plants, were grown under natural (mean13.4 hd^-1) and artificially extended (to 15 hd^-1) daylength and duration from sowing to first flowering recorded. Genetic analysis of the segregation ratios, supported by Chi-square tests, indicated that the duration from sowing to flowering in each of the crosses was controlled by two genes assorting independently and with predominantly additive quantitative effects. The segregation patterns were most clearly defined in the 15 hd^-1 daylength. This revised version was published online in July 2006 with corrections to the Cover Date.     

Physiological responses of six bread wheat and durum wheat genotypes to water stress

Summary The responses of six wheat genotypes to water stress were analysed. Soil moisture (H), leaf water potential (_w), photosynthesis (P_N), stomatal resistance (r_s) and transpiration (T) were measured during a water stress. The genotypes investigated differed in their stress avoidance (_w-H relationship) and their stress tolerance (P_N-_w and r_s-_w relationships). The most important differences observed concern the mechanisms of tolerance at low leaf water potential: two varieties, Haurani 27 and Baalback, can then maintain a high photosynthetic activity. These observations are in agreement with the drought resistance characteristics already known for these genotypes. Possible applications to wheat breeding are considered     

Genetic variance of six agronomic characters in three lentil (Lens culinaris Medic) crosses

Summary Three lentil (Lens culinaris Medic) crosses (cross 1 = Chilean × PI 297784; cross 2 = Tekoa × PI 212611; cross 3 = Precoz × PI 212611) were advanced in a hierarchal design from the F₂ generation to the F₅ generation and tested in replicated field experiments. The purpose was to estimate the genotypic variances and covariances for several characters and to partition these into components due to additive, dominance, and additive × additive variances.Additive genetic variance was the major component of variance in cross 2 for all characters, except plant height and seed weight. Unexpectedly, estimates of dominance variance appeared to be high in crosses 1 and 3. Estimates of the additive × additive component seemed very small in all three populations. The dominance variance component estimates were consistently high for plant height in the three crosses and for seed weight in crosses 2 and 3. Where parental means were close, additive variance estimates were often low and in many cases negative. The unexpected high ratio of dominance variance to additive variance indicated that dominance variance was important in the crosses we studied.Cooperative investigations of Agricultural Research Service, US Department of Agriculture and the College of Agriculture, Washington State University, Pullman, Washington 99164, Work sponsored by Fellowship from Univ. of Jordan, Amman, Jordan. Scientific paper no. 5825.Formerly: Department of Agronomy and Soils, Washington State University, Pullman, WA., USA. Presently: Department of Plant Production and Plant Protection, University of Jordan, Amman, Jordan.Statistical Services, Washington State University, Pullman, WA 99164, USA.US Department of Agriculture, Agricultural Research Service, Washington State University, Pullman WA 99164, USA.     

Effect of ploidy on stomatal and other quantitative traits in plantain and banana hybrids

Summary Ploidy polymorphism occurs in the hybrid offspring derived from interspecific crosses between triploid plantains (Musa spp. AAB group) and diploid bananas (M. acuminata). Therefore,Musa breeders are interested in the determination of ploidy and its effects on phenotypic expression of quantitative traits. The aim of this research was to examine the reliability of stomatal and other phenotypic traits to determine ploidy in segregating plantainbanana hybrid families. Stomatal density and size were significantly correlated (P<0.01) with ploidy, although the correlation coefficients were not high (r=–0.49 and r=0.47, for stomatal density and size, respectively). High density of small stomata was correlated with low ploidy level, and vice versa. However, stomatal size and density were also influenced by a significant genotype effect (P<0.001) within the same ploidy level. Ploidy had an important effect on fruit traits and plant height in the hybrids of Obino l'Ewai×Calcutta 4, but this was not so clear in Bobby Tannap×Calcutta 4 hybrids. Obino l'Ewai derived tetraploids have medium to tall plants with large bunches and big fruits. Most of the tetraploids derived from Bobby Tannap have short stature due to the gene action of the dwarf,dw, allele. Also, a few selected diploids derived from Bobby Tannap outyielded their non-selected tetraploid full-sibs. In conclusion, chromosoem counting remains the only accurate proof of ploidy levels inMusa germplasm.     

Effect of Zinnia angustifolia HBK genotype on morphology and flowering of Z. angustifolia × Z. elegans Jacq. hybrids

Summary Interspecific hybrids were generated from crosses between 4 Zinnia angustifolia clones (maternal parents) and an inbred line of Z. elegans Orange King (paternal parent) to investigate the influence of Z. angustifolia genotype on morphology and flowering of hybrids. Leaf length, leaf width, flower diameter, number of ray petals, and days to flowering of interspecific hybrids were significantly influenced by Z. angustifolia clonal genotype. Genetic analysis of hybrid morphology and development was performed using 2 parental Z. angustifolia clones and 18 F₁ (9 seedlings from each of 2 populations generated from reciprocal crosses between parental clones) as maternal parents in crosses with Z. elegans Orange King. Genotype of Z. angustifolia significantly affected plant height, fresh weight, number of nodes, and days to flowering of interspecific hybrids. Control of these traits was through the Z. angustifolia nuclear genome. Improvement in interspecific hybrid morphology or development, i.e., shorter stature, earlier flowering, or larger flowers, may be possible by selection of superior-performing Z. angustifolia clones as parents.     

Variance components and heritabilities of yield and agronomic traits among cowpea genotypes

The phenotypic expression and heritability of quantitative traits vary due to genotypic differences, environmental influences and genotype by environment interactions. The objective of this study was to determine variance components and heritabilities of seed yield and its components in cowpea. Field experiments were conducted at three locations, three planting dates using ten diverse cowpea genotypes during 2004/2005. The experiments were laid out in the randomized complete block design with three replications. Results indicated significant interactions (P ≤ 0.01) among genotypes, locations and planting dates. The genotypic variance contributed ≥50% of the total phenotypic variance for the numbers of days to 50% flowering, seeds per pod, productive branches per plant and seed yield. The heritabilities of the numbers of days to 50% flowering were estimated at 50%, pods per plant (23%), days to maturity (66%), productive branches per plant (53%), 100 seed weight (11%) and seed yield (55%). The presence of considerable degree of genotypic variance among tested genotypes under various environments suggests that success in cowpea breeding could possibly be achieved through direct phenotypic selection.     

Genetic control of acquired high temperature tolerance in winter wheat

Summary The development of high temperature-tolerant wheat (Triticum aestivum L.) germplasm is necessary to improve plant productivity under high-temperature stress environments. The quantification of high temperature tolerance and the characterization of its genetic control are necessary for germplasm enhancement efforts. This study was conducted to determine the genetic control of acquired high temperature tolerance in common bread wheat cultivars. Reduction of 2,3,5-triphenyltetrazolium chloride (TTC) by heat-stressed seedling leaves was used as a quantitative measure to characterize acquired high temperature tolerance. Eleven-day-old seedlings of 20 F₁ progeny produced through a complete 5×5 (Payne, Siouxland, Sturdy, TAM W-101, and TAM 108) diallel mating design were acclimated at 37° C for 24 hours, followed by a 2-hour incubation at 50° C. Under these test conditions, acquired high temperature tolerance ranged from a high of 75.7% for the genotype TAM W-101 × TAM 108, to a low of 37.3% for the genotype Payne × Siouxland. Partitioning of genotypic variance revealed that only the general combining ability component effect was statistically highly significant, accounting for 67% of the total genotypic variation. These results suggest that enhancing the level of high temperature tolerance in wheat germplasm is feasible utilizing existing levels of genetic variability and exploiting additive genetic effects associated with high temperature tolerance.Contribution of the Texas Tech College of Agric. Sci. Journal no T-4-386. This work was supported by USDA specific agreement No. 58-7MNI-6-114 from the Plant Stress and Water Conservation Laboratory, USDA-ARS, Lubbock, Texas, USA     

Low temperature storage of pistachio pollen

Summary Pollen from four male pistachio (Pistacia vera L.) clones was stored at –196°C and –20°C for up to 12 months and tested for ability to germinate in vitro following a period of hydration at high humidity. Germination of fresh pollen was high (>80%) for each clone. At –196°C, pollen of cv. Peters survived freezing, storage and thawing with no loss of germinability; pollen of the other three clones had sharp declines in germination possibly attributable to cellular lesions incurred during freezing or thawing. When the relative humidity of the –20°C storage environment was maintained at or near 33%, Peters pollen had high rate of germination through 12 months storage. Without control of relative humidity, Peters pollen germination was high at 4 months, but declined at 12 months. Germination requirements became more exacting for pollen stored at –20°C for 12 months at suboptimal humidity conditions. Pollen of the other three clones did not tolerate storage at –20°C as well as Peters pollen regardless of the storage humidity environment.     

Plant regeneration from in vitro cultures of cotyledon explants and anthers of Sinapis alba and its implications on breeding of crucifers

Summary Protocols for plant regeneration from cotyledon explant and anther cultures of Sinapis alba have been developed for creating doubled-haploids and somaclonal variation. Among the several cultivars tested in this study, only Arda responded well to in vitro plant regeneration both from anther-as well as cotyledoncultures. Multiple shoot formation in cotyledon explants, which always followed a brief callusing phase, was found to be the best on MS medium with ZEA (1.0mg/l) and NAA (0.1mg/l). Regeneration frequency declined sharply in the absence of auxin or presence of other cytokinins and/or auxin. The frequency of shoot regeneration also declined with reduction in the photoperiod to 16h. On MS + BAP (1.0mg/l) + NAA (1.0mg/l) medium, cotyledonary explants showed profuse callusing, which could regenerate shoots on high ZEA + low NAA/IAA medium. However, it declined with progressing time in culture. Anthers, excised from fresh as well as cold pretreated buds, cultured on 10% sucrose containing MS media with different hormonal constitution, developed calli and/or embryos. Initial culture temperature was important with embryogenesis occurring only in anthers cultured at 30°C for 3 weeks. A high temperature (35°C) treatment was lethal for both callus as well as embryo formation. While BAP + NAA and ZEA + NAA/IAA supported embryogenesis, further plant regeneration from anther-or embryo-callus could be achieved in ZEA + NAA/IAA media. Some of the regenerants flowered already in vitro and had small and sterile flowers. Cytological examination of some of the root differentiating calli indicated the presence of haploid as well as diploid cells. Shoots were rooted during prolonged incubation on the same medium or on transfer to MS (reduced)/ B5 + ZEA + NAA media.     

Inheritance of N2 fixation efficiency in cowpea

Summary Host plant genetics of N₂ fixation in the cowpea (Vigna unguiculata (L.) Walp.) — Rhizobium symbiosis was investigated in the field with a mixed strain inoculum and in the greenhouse with a single strain inoculum. Five cowpea genotypes, including H-Brown Crowder and L-Bush Purple Hull, were used to generate populations for genetic studies. Diallel analysis for general combining ability (GCA), specific combining ability (SCA) and reciprocal effects was carried out for the N₂ fixation variables nitrogenase activity, nodule number, nodule weight, and top dry weight, in the field study. Generation mean analysis and heritability estimates were performed on the greenhouse population which included P₁ (H-Brown Crowder), P₂ (L-Bush Purple Hull), F₁, F₁. F₂, BC₁, and BC₂. Positive and significant correlations were observed between nitrogenase activity and both nodule weight and nodule number. Correlation coefficients between top dry weight and the other 3 variables were not significant. Estimates of SCA were highly significant for all variables except top dry weight, while those of GCA were significant only for nodule weight. Generation mean analysis revealed that additive gene action was more prominent than dominance and interallelic gene action for nodule number and nitrogenase activity, while the opposite was true for nodule weight and top dry weight. Narrow sense heritability estimates were moderately high for nodule number (0.55) and nitrogenase activity (0.62), and low for nodule weight (0.39) and top dry weight (0.17).Texas Agricultural Experiment Station Technical Article 20385. Research supported in part by a grant under USAID PASA AG/TAB 610-9-76 (USDA-CSRS-701-15-59).     

Genetic relationship between some cytoplasmic male sterility systems in sorghum

Summary Genetic analysis of cytoplasmic male sterility systems in sorghum was undertaken by evaluating a set of 25 A×B crosses and another set of 171 A×R crosses. Male steriles included diverse sources reported from U.S.A. and India. Fertility restoration in crosses was assessed by studying pollen sterility under microscope and seed setting under selfed earheads. Male fertility restorers are identified for diverse cytoplasms. Accordingly the diverse cytoplasms are grouped and listed in the increasing order of their sterility as A₁ & CK 60A A₂ A₄ M31-2A & M35-1A (A₄ tentative) A₃ & VZM2A G₁A (A₅ tentative) and consequently fertility restoration also becomes difficult in the same order for utilization in the breeding programmes. Among the non-milo cytoplasms, A₂ among exotics and maldandi (M31-2A and M35-1A) among Indian sources, can be utilised for practical exploitation in breeding programmes.     

Problems in breeding the legume Indigofera spicata for tropical pastures

A survey of I. spicata introductions showed the majority to be tetraploid perennials and similar to each other with red stems, strongly stoloniferous habit, and poor seeding ability. The rest were green stemmed annuals or biennials which were either diploid or tetraploid and which were free seeding and almost non-stoloniferous.Crosses were attempted using several green stemmed introductions as the female parents with a representative red stemmed one as the male. The ploidy of a diploid parent was raised with colchicine treatment before crossing. F₁ seed was obtained in all crosses except in that involving the induced tetraploid. The F₁ generations were sterile except for one cross from which a small quantity of F₂ seed was obtained. A high degree of sterility was maintained in the F₂ and F₃ generations but fertile F₃ selections produced mostly fertile progeny. The sterility could be followed by the percentage stained pollen and appeared to be controlled by genetic factors.Normal types of distribution of the phenotypic classes for yield and stoloniferous development were obtained for the F₃ population which contained 26.3 per cent perennial plants. Two F₃ lines were obtained which combined the desirable characters of the two parents.The effect of temperature and photoperiod on all introductions used as parents and the two promising lines was investigated in a phytotron. All types flowered at both the 8 hour and 16 hour photoperiods and temperatures 27°/22°C and 30°/25°C favoured flowering. The better flowering of the green stemmed parent had apparently been transferred to the selected F₃ lines. The highest plant dry weights occurred at 30°/25°C and the effect of photoperiod on yield was reversed as the temperature increased.     

Effects of photoperiod and temperature on flowering in mungbean (Vigna radiata (L.) Wilczek)

Summary Forty strains of mungbeans, including all of the entries in the 1st and 2nd International Mungbean Nurseries (IMN), were grown in plant growth chambers in photoperiods of 12, 13, 14, 15, and 16 hours and mean temperatures of 18, 23, and 28°C. Results show that (1) mungbean strains differ in their flowering response to photoperiod and to mean temperature; (2) increasing the photoperiod of reducing the mean temperature delayed flowering, the amount of delay varied with the strain: (3) variations in mean temperature may alter the effect of the photoperiod on flowering in particular strains. Twenty-five strains which flowered in all photoperiod-temperature treatments could be divided into four groups, each group being successively later in flowering. The remaining 15 strains could be divided into four groups, according to their failure to flower within 105 days in specific photoperiod-temperature treatments. Flowering response in the growth chamber is useful in explaining flowering response in the 2nd IMN at three locations varying from 14°N to 49°N latitude.Contribution No 7516 from the Missouri Agricultural Experiment Station.     

Resistance of cowpea and cereals to the parasitic angiospermStriga

Summary Striga species are parasitic angiosperms that attack many crops grown by subsistence farmers in sub-Saharan Africa and India. Control of the parasite is difficult and genetically resistant crops are the most feasible and appropriate solution. In cowpea, complete resistance toStriga gesnerioides has been identified. Breeding for resistance in sorghum has identified varieties with good resistance toS. asiatica in Africa and India. One variety was also resistant toS. hermonthica in W. Africa. No such resistance toStriga has been found in maize or millets.Resistant varieties have usually been sought by screening germplasm in fields naturally infested withStriga. However, laboratory techniques have also been developed, including anin vitro growth system used to screen cowpeas for resistance toS. gesnerioides. Two new sources of resistance in cowpea have been identified using the system. The technique has also been used to investigate the mechanisms of resistance in this crop. Two mechanisms have been characterised, both were expressed after penetration of cowpea roots by the parasite.The resistance of some sorghum varieties toStriga is controlled by recessive genes. In cowpea, resistance toStriga is controlled by single dominant genes. The genes for resistance are currently being transferred to cowpea varieties which are high yielding or adapted to local agronomic conditions. OneStriga resistant cowpea variety, Suvita-2, is already being grown widely by farmers in Mali. Reports of breakdown of resistance in cowpea toStriga have not yet been confirmed, but a wider genetic base to the resistance is essential to ensure durability ofStriga resistance.Abbreviations ICRISAT International Crops Research Institute for the Semi-Arid Tropics - IITA International Institute of Tropical Agriculture - LARS Long Ashton Research Station - SAFGRAD Semi-Arid Food Grain Research and Development