L. C. Prasad

Combining ability analysis for grain filling duration and yield traits in spring wheat (Triticum aestivum L. em. Thell.)

A diallel analysis of wheat (Triticum aestivum L. em. Thell) parents (n = 11) and their F1 (n = 55) and F2 (n = 55) offspring was carried out for the following four traits: grain filling duration (GFD), GFD for growing degree days (GDD), 1000 seed weight and seed yield per plant. Analysis of variance for general combining ability (GCA) and specific combining ability (SCA) displayed significant F1 and F2 general and specific combining ability effects for the four traits studied. For all the traits the GCA effects were relatively more important than the SCA effects, indicating that additive genetic effects were predominant. Crosses displaying high SCA effects for grain filling duration, seed weight and yield were observed to be derived from parents having various types of GCA effects (high x high, high x low, low x low and medium x low). The single seed descent method can be applied to exploit additive gene effects whereas dominance gene effects could be valuable in hybrid wheat breeding programs. Among the parents, genotypes from the International Maize and Wheat Improvement Center (Centro Internacional de Mejoramiento de Maiz y Trigo, CIMMYT) as well as South Asia were found to be superior general combiners for grain filling duration. Likewise, crosses involving diverse parents from CIMMYT and South Asia showed significant SCA effects for grain filling duration and other traits.

Inheritance and identification of molecular markers associated with spot blotch (Cochliobolus sativus L.) resistance through microsatellites analysis in barley

Spot blotch resistant (IBON 18) and susceptible (RD 2508) lines were crossed to investigate inheritance of resistance and to identify simple sequence repeats (SSRs) associated with resistance. F1 resistance was intermediate and suggested additive nature of inheritance. Three additive genes was noted in the distribution of F3, F4 and F5 generations. In F6 and F6-7, the quantitative and qualitative approaches also suggested the control of three resistance genes. The parents and the RILs (F6/F6-7) were grown in four environments and spot blotch severity recorded. Forty five SSR primers, specific for chromosomes 1 (7H) and 5 (1H), were applied. Of these, 12 were polymorphic between the parents, and between the resistant and susceptible bulks. Three markers BMS 32, BMS 90 and HVCMA showed association with resistance, which was further confirmed through selective genotyping. The co-segregation data on the molecular markers (BMS 32, BMS 90 and HVCMA) and spot blotch severity on 173 RILs was analyzed by single marker linear regression approach. Significant regression suggested linkage among BMS 32, BMS 90 and HVCMA and the three resistant genes (designated as Rcs-qtl-5H-1, Rcs-qtl-5H-2 and Rcs-qtl-1H-1.) respectively. These markers explained 28%, 19% and 12% of variation respectively, for spot blotch resistance among the RILs.

Diversity in Indian barley (Hordeum vulgare) cultivars and identification of genotype-specific fingerprints using microsatellite markers

1Department of Genetics and Plant Breeding, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi 221 005, India 2Directorate of Wheat Research (DWR), Karnal 132 001, India 3Present address: Department of Biology, Massachussetts Institute of Technology, 77 Massachusetts Avenue 68–659, Cambridge 02139, USA 4Present address: CIMMYT-South Asia, Post Box 5186, Singha Durbar Marg, Kathmandu, Nepal

Study of inheritance and allelic relation of resistance to spot blotch (Bipolaris sorokiniana) of wheat

Six varieties viz., Chirya-1, Chirya-3, Chirya-7, Yangmai-6, Ning-8201 and Ning-8319 known for their resistance to spot blotch were crossed with the most susceptible parent i.e., Sonalika for studying inheritance pattern and establishing allelic relationship among different resistance sources. Disease severity of F1 ’s were intermediate to slightly tilted towards resistant parents and thus indicated either no dominance or partial dominance. Progeny rows of these crosses were evaluated in the F3 and F4 generations. Disease severity for each progeny rows was measured at three different growth stages viz., late anthesis (69), late milk (77) and early dough (83) stages. Based on disease severity, the F3, F4 and F5 progenies were grouped into three classes: homozygous dominant, segregating and homozygous susceptible. Based on this ratio, number of effective genes was estimated following χ2 analysis and quantitative approaches. Chirya-1, Chirya-3, Chirya-7, Yangmai-6 and Ning-8201 showed involvement of two genes in resistance while, Ning-8319 showed the presence of three resistance genes to spot blotch. Resistant × resistant crosses were made to establish the allelic relationship of resistance genes. The F3 progeny of all the crosses did not show susceptible plants. This proved that at least one gene was common among parents for resistance. However, the appearance of transgressive segregants was an indication of the non-allelic relationship. The present study also indicated the possibility of achieving enhanced resistance through gene pyramiding.

Genetic diversity in the isolates of spot blotch of wheat caused by Bipolaris sorokiniana using RAPD markers

Genetic variation among 20 random iso-lates of Bipolaris sorokinian belonging to five mor-pho-pathological groups was analyzed by DNA finger printing based on RAPD analysis. Twenty random primers of different origin were used. Diag-nostic RAPD bands were generated from fungal DNA. UPGMA cluster analysis clustered the 20 isolates into two distinct groups. Of the 20 isolates, 19 were in the first group, while only one was in the other. An average genetic similarity between both the clusters was only 0.05 (5%). Isolate be-longing to different groups of morpho-pathological traits, were dispersed across several sub-clusters. In general, the classification based on morpho-pathological traits showed about 60% conformity with the grouping based on molecular markers. Re-sults illustrated the potential value of RAPDs for detecting polymorphism among isolates.