Fertility Improvement in Autotetraploids of Pea — Selection for Seed-Set and Disjunction Index

Four seed-set groups of plants, viz. unselected ‘general’ and selected ‘high’, ‘medium’ and ‘low’ were constituted in C₁ generation from randomly selected autotetraploids of two pea cultivars, T 163 and 5064-S. In C₂ generation, ten plants were selected at random in each of the four groups. Two seeds each from selected autotetraploids were drawn and bulked to make 20 seeds in each of the four groups to raise C₃ generation. Selection resulted in a gradual shift in seed-set, though the magnitude and nature varied with the group and generation. Improvement in the seed-set from C₁ to C₃ generation was associated with the increase in bivalents per cell, disjunction index and total chiasmata. Increase in total chiasmata was mostly due to an increase in proximal ones. Increase in seed-set was reflected in improvement of grain yield per plant.     

Vernalization of immature embryos of winter wheat genotypes

Summary The effect of direct vernalization of immature embryos on flowering was studied in six winter wheat genotypes. Fourteen-, 17-, and 20-day-old embryos were excised and vernalized for 0–6 weeks on synthetic medium during a conditioning period. Percent germination of embryos was high (overall 96.1%), and free from genotypic effects. Genotypes differed for flowering in response to cold treatment of excised embryos. Embryo vernalization was as effective as or more than conventional vernalization (control, seedling vernalization for 6 weeks). Seventeen-day-old embryos were the most responsive to vernalization. With a 5-week vernalization of 17-day-old embryos, the percentage of plants anthesed was higher than those from 14-and 20-day-old embryos. For 17-day-old embryos vernalized for 5 weeks, the mean number of days from culture to anthesis was less than that of 6 week vernalization, less than that of 14- and 20-day-old embryos, and less than controls.Purdue Univ., Agronomy Dept., W. Lafayette, IN 47907, USA.     

Wheat grain yield and stability assessed through regional trials in the Eastern Gangetic Plains of South Asia

Improving the level and stability of grain yield is the primary objective of wheat breeding programs in the Eastern Gangetic Plains (EGP) of South Asia. A regional wheat trial, the Eastern Gangetic Plains Yield Trial (EGPYT), was initiated by CIMMYT in collaboration with national wheat research programs in Bangladesh, Nepal, and India in 1999–2000 to identify wheat genotypes with high and stable grain yield, disease resistance, and superior agronomic traits for the EGP region. A set of 21 wheat experimental genotypes selected from a regional wheat screening nursery in South Asia, three improved widely grown cultivars (Kanchan, PBW343 and Bhrikuti), and one long-term cultivar (Sonalika) were tested at 9–11 sites in six wheat growing seasons (2000–2005) in the EGP. The 21 experimental genotypes were different in each year, whereas the four check cultivars were common. In each year, one or more of the experimental genotypes showed high and stable grain yield and acceptable maturity, plant height, and disease resistance compared to the check cultivars. Three improved cultivars have already been commercially released in the region through EGPYT and many germplasm lines have been used in the breeding programs as parents. Identification of wheat genotypes with high-grain yield in individual sites and high and stable yield across the EGP region underlines their value for regional wheat breeding programs attempting to improve grain yield and agronomic performance.     

Genotypic effects of sorghum accessions on fecundity of sorghum head bug,Calocoris angustatus Lethiery

Summary Sorghum head bug (Calocoris angustatus Leth.) (Hemiptera: Miridae) is an important pest of grain sorghum in India. We studied the fecundity of head bug females reared for one to three generations on head bug-resistant and head bug-susceptible genotypes during the 1988 and 1989 rainy and 1988–89 post-rainy seasons. Head bug population increase was lower for the first, second and/or third generation when the bugs were reared on IS 2761, IS 19955, IS 14334, IS 23748, IS 16357, IS 17610, and IS 21444 compared with the susceptible controls CSH 1, CSH 5, and CSH 9. These genotypes also suffered a low grain damage (damage rating (DR) 5) (except IS 2761) compared with the susceptible controls (DR>6). A marginal decrease in fecundity was observed when the bugs were reared on IS 2761, IS 14334, IS 16357, IS 20740 and IS 17610 and then transferred to the susceptible control, CSH 1. Sorghum genotypes having lower increase in bug population across generations, suffering low grain damage, and showing adverse effects on fecundity can be used in breeding for resistance to head bugs.     

A unique introgression from Moricandia arvensis confers male fertility upon two different cytoplasmic male-sterile lines of Brassica juncea

A Brassica juncea line carrying an introgression from Moricandia arvensis restored male fertility to two cytoplasmic male‐sterile (CMS) B. juncea lines carrying either M. arvensis or Diplotaxis catholica cytoplasm. Genetics of fertility restoration was studied in the F₁, F₂, F₃ and backcross generations of the cross between CMS and fertility‐restorer lines. No male‐sterile plants were found in F1‐F₃ generations of the cross between CMS [M. arvensis] B. juncea and the restorer. However, a 1: 1 segregation for male sterility and fertility was observed when the F1 was pollinated with non‐restorer pollen from a euplasmic line. These results clearly show that restoration is mono‐genic and gametophytic. In CMS lines carrying D. catholica cytoplasm, the restorer conferred male fertility to the F1 and showed 3: 1 and 1: 1 segregations for male fertility and sterility in F₂ and BC1 generations, respectively, indicating a monogenic, sporophytic mode of fertility restoration. The results were also supported by pollen stainability in the F1 which was about 65% in M. arvensis‐based CMS and >90% in D. catholica‐based CMS. The above results are discussed in the light of previous molecular studies which showed association between CMS and atpA in both systems.     

High yielding spring bread wheat germplasm for global irrigated and rainfed production systems

Global wheat (Triticum aestivum L.) production must increase 2% annually until 2020 to meet future demands. Breeding wheat cultivars with increased grain yield potential, enhanced water-use efficiency, heat tolerance, end-use quality, and durable resistance to important diseases and pests can contribute to meet at least half of the desired production increases. The remaining half must come through better agronomic and soil management practices and incentive policies. Analyses of the recent International Yield Trials indicate that grain yields of the best new entries were usually 10% higher than the local checks globally, as well as within a country across sites. Variation in yield across sites within a country/region underline the role of genotype × environment (GE) interaction and provides opportunities to select for stable genotypes, which is not often done. The lack of proper analysis undermines proper utilization of germplasm with high yield potential and stability in the national wheat breeding programs. Some of the best performers in irrigated areas were amongst the best in semiarid environments, reinforcing the fact that high yield potential and drought tolerance can be improved simultaneously. The best performing lines often had genotypic base of widely adapted genotypes Kauz, Attila, Baviacora, and Pastor, with genetic contributions from other parents including synthetic wheat. We recommend within country multilocation analysis of trial performance for a crop season to identify lines suiting particular or different locations within a country. The immediate feedback on GE interaction will also help in breeding lines for countries having substantial variation across locations and years.     

Environmental factors influence the expression of resistance to sorghum midge, Stenodiplosis sorghicola

Host plant resistance is an effective means of controlling sorghum midge (Stenodiplosis sorghicola). We studied the influence of environmental factors on expression of resistance to sorghum midge in three midge-resistant and two midge-susceptible genotypes. Midge-resistant lines AF 28, ICSV 197, and TAM 2566 suffered 8.8 to 17.3% damage across seven so wings compared to 25.6%damage in ICSV 112, and 69.4% damage in CSH 5. Susceptibility of the midge-resistant lines (AF 28, ICSV 197, and TAM 2566) decreased with an increase in open pan evaporation, maximum and minimum temperatures, and solar radiation; while the midge-susceptible lines (ICSV 112 and CSH 5) showed a poor interaction with these factors. Midge damage in ICSV 197 showed a negative correlation with minimum temperature and relative humidity and positive correlation with sunshine hours,while the reverse was true for CSH 5. Grain growth rate between 0 and 3 days after anthesis was lower in crops sown on 1st October, when AF 28 and ICSV 197 suffered maximum midge damage. Maximum and minimum temperatures and maximum relative humidity influenced the moisture content of the grain, grain growth rate, and sorghum midge damage. There was considerable variation in genotype × environment interaction for expression of resistance to sorghum midge,and the implications of these results have been discussed in relation to development of sorghum cultivars with resistance to this insect. This revised version was published online in August 2006 with corrections to the Cover Date.     

Initial screening of chili and sweet pepper germplasm for resistance to chili thrips, Scirtothrips dorsalis Hood

Summary A preliminary evaluation for resistance to chili thrips, Scirtothrips dorsalis Hood of 41 and 194 pepper (Capsicum annuum L.) germplasms during 1987 and 1988, respectively, indicated chili accessions may be a promising source of resistance. In contrast, all sweet pepper accessions tested were highly susceptible. A number of chili accessions produced a moderate yield, in spite of a high thrips infestation indicating tolerance to S. dorsalis. Rating for thrips damage was more reliable and efficient than estimating thrips numbers in screening pepper accessions for resistance to thrips. Highly significant, positive correlation between ratings at the seedling stage and final rating for thrips damage indicated the feasibility of screening pepper accessions at the seedling stage. Comparing the similarities in rating among accessions resulted in 40 distinct groups. The variance-covariance matrix of the data from these 40 groups was subjected to principal component analysis. This accounted for 56 and 18 per cent of the variation across the two principal axes, respectively. Projection of chili and sweet pepper accessions along these two axes revealed three distinct clusters. About 80 per cent of chili accessions formed the first cluster, 58 per cent of the sweet pepper accessions formed the second cluster and a third cluster exhibited intermediate ratings for thrips damage. The significance of these findings in relation to geographical divergence and resistance to thrips among pepper accessions is discussed.