Interspecific hybridization between urdbean (Vigna mungo (L.) Hepper) and adzukibean (Vigna angularis (Willd.) Ohwi and Ohashi)

Summary To introduce resistance to fungal and viral diseases into urdbean (Vigna mungo), it was crossed with adzukibean (Vigna angularis) to achieve an interspecific hybrid between the two species by using different non-conventional breeding methods. Partial success was obtained with the use of UV irradiated pollen, intraspecific hybrids as parents and spray of immuno-suppressants on the female parent under glass house conditions and to the extent of callusing in aseptic culture.     

Quantitative resistance to Cercospora leaf spot disease caused by Pseudocercospora cruenta in cowpea

Six populations (Parent 1, Parent 2, F1, F2, BC1 and BC2) generated from each of four crosses involving four resistant and two susceptible varieties of cowpea (Vigna unguiculata L. Walp) were evaluated for resistance to Cercospora leaf spot (CLS) disease caused by Pseudocercospora cruenta under induced epiphytotic conditions, in four separate field experiments. Climatic conditions determined the onset of CLS disease in the susceptible cultivar and varied in the four experiments from 35 to 48 days after planting (DAP). Genetic analysis revealed that the mode of inheritance of resistance to P. cruenta can be oligogenic or polygenic depending upon the cross. This is the first report of polygenic inheritance of CLS resistance. Number of nodes infected fitted a simple additive dominance model with predominance of additive effects based on generation mean analysis. Oligogenic resistance was observed for the other three crosses, with the most plausible models being: a single gene model with incomplete dominance in CB27 × IT87D-939-1; a single gene model with complete dominance in CB27 × VRB-10; and a triger model in Los Banos Bush Sitao × IT86D-792, based on segregation analysis of symptomatic : non-symptomatic plants. The role of minor genes was also indicated in the above crosses. Suggested approaches to breeding for resistance to CLS are discussed.     

ISSR and SCAR markers linked to the mungbean yellow mosaic virus (MYMV) resistance gene in blackgram [Vigna mungo (L.) Hepper]

A recombinant inbred line (RIL) mapping population (F₈) was generated by crossing Vigna mungo (cv. TU 94‐2) with Vigna mungo var. silvestris and screened for mungbean yellow mosaic virus (MYMV) resistance. The inter simple sequence repeat (ISSR) marker technique was employed to identify markers linked to the MYMV resistance gene. Of the 100 primers screened, 54 showed amplification of which 36 exhibited polymorphism between the parents TU 94‐2 (resistant) and V. mungo var. silvestris (susceptible). Individual plants from 53 RIL populations were analysed and one marker (ISSR811₁₃₅₇) was identified as tightly linked to the MYMV resistant gene at 6.8 cM. Both the phenotype as well as the ISSR811₁₃₅₇ marker segregated in a 1 : 1 ratio. The ISSR811₁₃₅₇ marker was sequenced and sequence characterized amplified region (SCAR) primers were designed (YMV1‐F and YMV1‐R) to amplify the marker. Screening for the SCAR marker in the RIL population distinguished the MYMV resistant and susceptible plants, agreeing well with the phenotypic data. The ISSR811₁₃₅₇ marker was validated using diverse blackgram genotypes differing in their MYMV reaction. The marker will be useful for the development of MYMV‐resistant genotypes in blackgram.     

Genetics of resistance to ascochyta blight in chickpea (Cicer arietinum L.)

Summary Six chickpea lines resistant to Ascochyta rabiei (Pass.) Lab. were crossed to four susceptible cultivars. The hybrids were resistant in all the crosses except the crosses where resistant line BRG 8 was involved. Segregation pattern for diseases reaction in F₂, BCP₁, BCP₂ and F₃ generations in field and glasshouse conditions revealed that resistance to Ascochyta blight is under the control of a single dominant gene in EC 26446, PG 82-1, P 919, P 1252-1 and NEC 2451 while a recessive gene is responsible in BRG 8. Allelic tests indicated the presence of three independently segregating genes for resistance; one dominant gene in P 1215-1 and one in EC 26446 and PG 82-1, and a recessive one in BRG 8.Research paper No. 3600     

Inheritance of seed resistance to bruchids in cultivated mungbean (Vigna radiata, L. Wilczek)

Bruchid beetles or seed weevils are the most devastating stored pests of grain legumes causing considerable loss to mungbean (Vigna radiata (L.) Wilczek). Breeding for bruchid resistance is a major goal in mungbean improvement. Few sources of resistance in cultivated genepool were identified and characterized, however, there has been no study on the genetic control of the resistance. In this study, we investigated the inheritance of seed resistance to Callosobruchus chinensis (L.) and C. maculatus (F.) in two landrace mungbean accessions, V2709BG and V2802BG. The F₁, F₂ and BC generations were developed from crosses between the resistant and susceptible accessions and evaluated for resistance to the insects. It was found that resistance to bruchids in seeds is controlled by maternal plant genotype. All F₁ plants derived from both direct and reciprocal crosses exhibited resistance to the bruchids. Segregation pattern of reaction to the beetles in the F₂ and backcross populations showed that the resistance is controlled by a major gene, with resistance is dominant at varying degrees of expressivity. Although the presence of modifiers was also observed. The gene is likely the same locus in both V2709BG and V2802BG. The resistant gene is considered very useful in breeding for seed resistance to bruchids in mungbean.     

Comparison of sources of resistance to leaf aphids in lettuce (Lactuca sativa L.)

Summary Three lines of lettuce with resistance to Nasonovia ribisnigri, based on the dominant Nr-gene, and four lines selected for partial resistance to Myzus persicae were tested against three species of leaf aphid: N. ribisnigri, M. persicae and Macrosiphum euphorbiae. The effect of the Nr-gene was also studied in a segregating F2 population.In the material tested, resistance to N. ribisnigri was exclusively based on the Nr-gene, lines selected only for resistance to M. persicae showed no resistance to N. ribisnigri. The Nr-gene also induces partial resistance to M. persicae, but the level of this resistance is influenced by other genes, because the lines with Nr-gene differed significantly from each other for reproduction of M. persicae. The Nr-gene had no effect on the resistance of lettuce to M. euphorbiae.In lines with the Nr-gene, levels of resistance to M. persicae and to M. euphorbiae were correlated, suggesting that the resistance may be determined by the same genes. The Nr-line with highest resistance to M. persicae was comparable for this characteristic to the lines selected for resistance to M. persicae.The cultivars Taiwan and Ravel possess a resistance factor to M. euphorbiae that has no effect on M. persicae or N. ribisnigri. Lines selected for resistance to M. persicae also showed partial resistance to M. euphorbiae. Based on the present results no conclusions can be drawn whether this resistance is based on the same genes that provide resistance to M. persicae, or on a resistance factor comparable to that found in Taiwan and Ravel.     

Inheritance of ‘domestication’ traits in bambara groundnut (Vigna subterranea (L.) Verdc.)

Controlled crosses in bambara groundnut were attempted between a range of thirty-six bambara groundnut landraces (thirty domesticated (V. subterranea var. subterranea) and six wild (V. subterranea var. spontanea)). Ten F₁ seed were produced. Of these, eight germinated producing F₂ populations. On seed set, four populations could be unambiguously confirmed as true crosses by F₃ seed coat colour. A single F₂ population, derived from a domesticated landrace from Botswana (DipC; female parent) crossed with a wild accession collected in Cameroon (VSSP11; male parent) was used to study a range of agronomic and domestication traits. These included; days to emergence, days to flowering, internode (fourth) length at harvest, number of stems per plant, leaf area, Specific Leaf Area (SLA), Carbon Isotope Discrimination (CID), 100 seed weight, testa colour and eye pattern around the hilum. On the basis of variation for internode length and stems per plant, 14 small F₃ families were selected and grown under field conditions to further investigate the genetic basis of the ‘spreading’ versus ‘bunched’ plant character, a major difference between wild and cultivated bambara groundnut. Results presented suggest that traits including leaf area, SLA, CID and 100 seed weight are controlled by several genes. In contrast, the variation for traits such as internode length, stems per plant, days to emergence and seed eye pattern around the hilum are likely to be under largely monogenic control. The results of this work are discussed in relation to the domestication of bambara groundnut.     

Inheritance of photoperiod response in mungbean (Vigna radiata [L.] Wilczek)

Summary A dominant or partially dominant gene for sensitivity to photoperiod in mungbean strain PI 180311 was identified and labeled Ps. The gene was expressed when strain P1180311, or crosses involving PI 180311 were grown in 16- or 14-hour photoperiods but was not expressed when the populations were grown in a 12-hour photoperiod or in the field at Columbia, Missouri. Dominance × dominance epistatic effects were indicated as governing days to flower in absence of the obvious effect of the Ps gene. A gene A for purple hypocotyl was independent of the gene Ps.Contribution No. 7894 from the Missouri Agriculture Experiment Station.     

Inheritance of resistance to angular leaf spot (Isariopsis griseola Sacc.) in french bean (Phaseolus vulgaris L.)

Summary Angular leaf spot (Isariopsis griseola Sacc.) is a serious disease of French bean in the hills of India and 40 to 70 per cent of the green pods are damaged and rendered unmarketable. Crosses were made between PLB 257, (Phaseolus coccineus L.), a red flowering pole tope, resistant to angular leaf spot, and Contender (Phaseolus vulgaris L.), a highly susceptible commercial cultivar. Studies of the F₁, F₂, and F₃ progenies indicated that PLB 257, carries a recessive gene imparting resistance to angular leaf spot.     

Adaptation and competition in mixtures of cowpea (Vigna unguiculata (L.) Walp.)

Summary Six pure lines and four mixtures were grown in six environments throughout lowland Papua New Guinea. There were no significant transgressive increases in the grain yield of mixtures above their pure line components, and mixture yields were adequately predicted by the mean of components. In yield stability it was found that the individual buffering of pure lines was of more importance than population buffering, and that the magnitude of population buffering varied with the particular combination of components. Competitive effects in all the mixtures were of the compensating type. Dramatic changes in mixture composition resulting from natural selection precluded their use in local agriculture. The outcome of competition in mixtures was strongly influenced by the growing environment, such that selective index was correlated to general fertility.     

Genetics of resistance to early blight (Alternaria solani Sorauer) in tomato (Lycopersicon esculentum L.)

The genetic nature of early blight resistance in tomato was studied in three crosses at seedling and adult plant stages. A six generation mean analysis of the cross Arka Saurabh (susceptible) × IHR1939 (resistance) and its reciprocal cross revealed that the resistance to early blight was conferred by recessive polygenes at both seedling and adult plant stages. This polygenic early blight resistance revealed the importance of additive and additive × additive gene effects at seedling stage and higher magnitude of dominance and dominance× dominance gene effects at adult plant stage. Evaluation of parents, F₁, F₂ and backcross generations of IHR1816 (resistance) × IHR1939 (resistance) revealed that the early blight resistance genes in IHR1816 (Lycopersicon esculentum NCEBR-1) and IHR1939 (Lycopersicon pimpinellifolium L4394) are independent. This revised version was published online in July 2006 with corrections to the Cover Date.     

Breeding for resistance to coffee berry disease caused by Colletrotrichum coffeanumNoack (Sensu Hindorf) in Coffea arabica L. I. Methods of preselection for resistance

Summary Two methods of preselection for resistance to coffee berry disease, by artificial inoculation of young coffee seedlings, have been developed recently at the Coffee Research Station in Kenya. The efficiency of these methods has been investigated in a series of experiments by comparing the results of the preselection tests with mature plant resistance, as indicated by visual field scores and artificial inoculation of berries and bud leaves of mature trees and including a large number of varieties and cultivars of Coffea arabica. The preselection test, by which the hypocotyl stems of 6-week old seedlings are inoculated with a spore suspension of the pathogen, proved to be more reliable than the second preselection test with shoot-tips of 10-month old plants. Correlation coefficients between the preselection test and mature plant resistance were resp. r=0.73–0.80 for the first test against r=0.60 for the latter.     

Genetic diversity of the black gram [Vigna mungo (L.) Hepper] gene pool as revealed by SSR markers

In this study, 520 cultivated and 14 wild accessions of black gram (Vigna mungo (L.) Hepper) were assessed for diversity using 22 SSR markers. Totally, 199 alleles were detected with a mean of 9.05 alleles per locus. Wild black gram showed higher gene diversity than cultivated black gram. Gene diversity of cultivated accessions among regions was comparable, while allelic richness of South Asia was higher than that of other regions. 78.67% of the wild gene diversity presented in cultivated accessions, indicating that the domestication bottleneck effect in black gram is relatively low. Genetic distance analysis revealed that cultivated black gram was more closely related to wild black gram from South Asia than that from Southeast Asia. STRUCTURE, principal coordinate and neighbor-joining analyses consistently revealed that 534 black gram accessions were grouped into three major subpopulations. The analyses also revealed that cultivated black gram from South Asia was genetically distinct from that from West Asia. Comparison by SSR analysis with other closely related Vigna species, including mungbean, azuki bean, and rice bean, revealed that level of gene diversity of black gram is comparable to that of mungbean and rice bean but lower than that of azuki bean.     

Andean beans (Phaseolus vulgaris L.) with resistance to the angular leaf spot pathogen (Phaeoisariopsis griseola) in southern and eastern Africa

Common beans (Phaseolus vulgaris) are separated into two distinct groups: Andean and Middle American. We identified CAL 143 as the first Andean bean with resistance to angular leaf spot disease caused by Phaeoisariopsis griseola. Angular leaf spot is the most widespread and economically important bean disease in southern and eastern Africa, and it is especially severe on the extensively grown Andean beans. Cal 143 was resistant in Malawi, South Africa, Tanzania, and Zambia, but it was susceptible in Uganda. This was attributed to the presence of races of P. griseola in Uganda not present in the other countries. We identified two additional Andean bean lines, AND 277 and AND 279, with resistance to angular leaf spot in Malawi. We also characterized the virulence diversity of 15 isolates of P. griseola from southern and eastern Africa into nine different races. Five of six isolates from Malawi and two of seven from Uganda, obtained from large-seeded Andean beans, were characterized into four different races considered Andean. These were compatible only or mostly with large-seeded Andean cultivars. The other eight isolates from Uganda, Malawi, and the Democratic Republic of Congo, obtained from a small- or medium-seeded Middle American beans, were characterized into five different Middle American races. These were compatible with Middle American and Andean cultivars. CAL 143 was resistant or intermediate under greenhouse conditions to all but one of the same 15 isolates from southern and eastern Africa, but it was susceptible to an isolate from Uganda obtained from a medium-seeded Middle American bean. This revised version was published online in July 2006 with corrections to the Cover Date.     

New sources of resistance to anthracnose and angular leaf spot of beans (Phaseolus vulgaris L.)

Summary over 13000 CIAT bean accessions were evaluated for their reactions to the anthracnose (Colletotrichum lindemuthianum) and angular leaf spot (Isariopsis griseola) pathogens over a 3 yr period. Among these accessions, 156 were resistant to all races of the anthracnose pathogen collected from Popayán, Colombia. Thirty were resistant to numerous races obtained from other parts of the world, including Europe. Although many of these new resistant sources originated in Mexico and Central America, they are quite diverse for geographic origin, plant type, seed color and seed size. In addition, more than 50 of the 156 lines were also resistant to isolates of I. griseola with diverse sources of origin throughout Colombia.     

Multifactor inheritance of seedcoat colour in greengram (Vigna Radiata (L.) Wilczek.)

Summary Seedcoat colour in greengram (Vigna radiata (L.) Wilczek.) is a useful marker for genetic studies and varietal identification. Its mode of inheritance was examined in five crosses among nine parents which differed for seedcoat colour. Four of the parents had sap green seedcoat colour while the others had raw sienna, brownish green, densely black spotted, black and greenish yellow seedcoat colour, respectively. At the F₂ generation, no more than 20 different colour classes were observed. The segregation in F₃ and backcross generations indicated that at least five major genes were involved in seedcoat colour inheritance. Sap green seemed to be dominant over raw sienna. The segregation ratios further indicated the role of non-allelic gene interactions (epistasis) in inheritance of seedcoat colour. Gene symbols were assigned to each colour and genotypes to each parent.     

Inheritance of seed size in cowpea (Vigna unguiculata (L.) Walp.)

Summary The inheritance of seed weight in cowpea was examined in a field planting of the parents, reciprocal F₁s, F₂s and backcrosses to both parents of a cross between TVu 1977-OD (small seeded) and ACC 70002 (large).Seed weight was inherited quantitatively and small seed was partially domiminant to large seed size. Gene action was predominantly additive but dominance and additive × additive epistatic effects were also significant.Broad and narrow sense heritabilities were 85.1±5.3% and 75.4±18.6% respectively. The minimum number of loci involved in the inheritance of seed size was eight, and each gene pair contributed up to 1.02 g increase to seed weight. The estimate of genetic advance from F₂ to F₃ generations with 5% selection intensity was 3.58 g.International Institute of Tropical Agriculture, Semi-Arid Food Grain Research and Development Project/National Cowpea Improvement Program, B.P. 1783, Ouagadougou, Upper Volta.Department of Primary Industries, Hermitage Research Station, Warwick 4370, Queensland, Australia.International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), ICRISAT Center, Patancheru, P.O. 502 324, A.P., India.     

Validity of a leaf inoculation test to assess the resistance to Phytophthora megakarya in a cocoa (Theobroma cacao L.) diallel mating design

Cocoa pod rot, caused by different Phytophthora species, is rife in all production zones. Phytophthora spp. control is therefore a major challenge for world cocoa cultivation, and selection of resistant material is a priority research theme for many producing countries. Various genetic trials have been set up over many years in zones affected by the disease. In Cameroon, a 6x6 diallel mating design was set up to study heritability of the resistance trait. Field observations led to the classification of parents according to their ability to transmit resistance to their progenies. These field measurements were long and laborious, so a resistance test based on artificial leaf inoculations was developed. This article studies the correspondence between results obtained with the test and observations of rot rates in the field. There was a significant genetic correlation between pod rot rate in the field and leaf test data, so using this resistance test could shorten cocoa tree selection cycles. This revised version was published online in July 2006 with corrections to the Cover Date.     

Resistance of lettuce (Lactuca) to the leaf aphid Nasonovia ribis nigri. 2. Inheritance of the resistance

Summary The inheritance of resistance to Nasonovia ribis nigri in L. sativa was investigated. Parents and F₁ and F₂ populations from crosses between the susceptible cultivar Ravel and two resistant breeding lines were tested. In both breeding lines one dominant gene appeared responsible for resistance.     

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.