Estimates Of General Combining Ability Effects Research Articles

Combining ability and heritability of soybean resistance to groundnut leaf miner

Groundnut leaf miner (GLM) (Aproaerema modicella) (Deventer) is one of the most destructive pests of soybean and groundnuts. In this study, the mode of inheritance, general combining ability (GCA), specific combining ability (SCA) effects, maternal effects of resistance to GLM and grain yield ha−1 were determined. Thirteen soybean parental genotypes and 81 F2 populations were evaluated for resistance to GLM in a 5 × 19 alpha lattice diallel design with two replications under natural GLM infestation in northern (Arua) and eastern (Iki-iki) Uganda during September to December 2016 rainy season. Highly significant differences were observed among parental genotypes and F2 populations for GLM incidence, severity, and grain yield. The estimates of GCA effects were significant for GLM incidence and severity scores but not for the number of larvae per plant and grain yield ha−1. SCA effects were non-significant for all the studied traits, suggesting that GCA effects were the major component responsible for soybean resistance to GLM with additive gene effects being more important for these traits. Baker’s ratio ranged from 0.44-1.0 for most of resistant traits except number of larvae per plant and grain yield ha−1. The results indicated also that cultivars Maksoy1 N, PI615437, PI578457A and NIIGC4.1-2 were good combiners against GLM incidence and severity. Parent PI615437 was a good combiner for grain yield and Maksoy1 N × PI615437 was a superior cross for grain yield and against GLM incidence. There were no maternal effects for the inheritance of resistance to GLM. The study provides a basis for understanding patterns of inheritance of soybean resistance to groundnut leaf miner for an efficient breeding program.

Diallel analysis for aflatoxin accumulation and fall armyworm leaf-feeding damage in maize

ABSTRACTTwo major impediments to profitable maize, Zea mays L., production in the southern United States are from feeding by fall armyworm, Spodoptera frugiperda (J.E. Smith), and losses from the production and accumulation of aflatoxin in maize grain. A diallel cross was produced by making all possible crosses among five germplasm lines developed as sources of resistance to fall armyworm leaf feeding and five lines developed as sources of resistance to aflatoxin accumulation. For resistance to both leaf feeding and aflatoxin accumulation, general combining ability (GCA) was a significant source of variation. Specific combining ability (SCA) was significant for fall armyworm feeding only. Estimates of GCA effects for reduced aflatoxin accumulation were significant for Mp715 and Mp719, two lines selected for resistance to aflatoxin accumulation. The GCA effects for reduced fall armyworm damage were significant for all five lines selected for fall armyworm resistance: Mp707, Mp708, Mp713, Mp714, and Mp716.

Combining Ability Analysis for Yield and its Related Traits in Pearl Millet

A 10 × 10 half diallel excluding reciprocals was evaluated in 3 environments to study the combing ability and gene action involved in respect of yield and its attributers in pearl millet. The environment wise combining ability analysis revealed significant differences for GCA (general combining ability) and SCA (specific combining ability) variances for characters viz. days to 50% flowering, days to maturity, productive tillers/plant, plant height, panicle length, panicle girth, biological yield/plant, dry fodder yield/plant, grain yield/plant, harvest index, test weight and protein content in all the three environments, except GCA for productive tillers per plant in E2 and panicle girth in E3 and SCA for panicle girth in E3, indicating the importance of both additive and non-additive gene effects for the genetic control of all the characters studied. The estimates of GCA effects indicated that the parents 71–75 and 76–80 emerged as good general combiners for grain yield and its components in the entire environment. Out of 45 crosses combinations only seven combinations such as 26–30 x 71–75, 26–30 × RIB-135-144, 31–40 × 76–80, 31–40 × RIB-135-144, 31–40 × 101–105, 41–50 × RIB-20 and RIB-20 × 71–75 showed significant and positive SCA effects in all the three environment for grain yield and other yield attributing characters. These parents and crosses have immense potential for pearl millet improvement and may be utilized in multiple crossing programme.

Ear rot, aflatoxin accumulation, and fungal biomass in maize after inoculation with Aspergillus flavus

Aflatoxin, a toxin produced by the fungus Aspergillus flavus Link: Fries, occurs naturally in maize (Z ea mays L.). Aflatoxin is a potent human carcinogen and is also toxic to livestock, pets, and wildlife. When contaminated with aflatoxin, the value of maize grain is markedly reduced. This investigation was conducted to compare ear rot, aflatoxin accumulation, and fungal biomass in maize single crosses with varying degrees of resistance to aflatoxin accumulation and to determine the relative importance of general combining ability (GCA) and specific combining ability (SCA) in the inheritance of resistance to ear rot, aflatoxin accumulation, and fungal biomass. Eight germplasm lines with different levels of resistance to aflatoxin accumulation were used as parents of a diallel cross. The cross was evaluated for visible ear rot, aflatoxin accumulation, and A. flavus infection in the grain. A. flavus infection was determined by quantitative real-time polymerase chain reaction (qRT-PCR) assays. Both GCA and SCA were significant sources of variation in the inheritance of the three traits although GCA accounted for a greater portion of the variation among single crosses. The interactions of GCA and SCA with years were highly significant for aflatoxin accumulation, but not significant for A. flavus infection. Estimates of GCA effects were highly significant for both reduced A. flavus infection and reduced aflatoxin accumulation for Mp313E, Mp715, and Mp717. Conversely, GCA effects associated with GA209 were significant for reduced levels of A. flavus infection and ear rot, but high levels of aflatoxin accumulation. Mp313E, Mp715, and Mp717 should be useful in breeding programs targeting both reduced levels of fungal infection and aflatoxin accumulation.

Combining ability under drought stress relative to SSR diversity in common wheat

Eight-parental diallel cross and SSR molecular markers were used to determine the combining ability of common wheat lines grown under well-watered (WW) and water-stress (WS) conditions. Analysis of variance of yield indicated highly significant differences among the progenies. General combining ability (GCA) determined most of the differences among the crosses. Specific combing ability (SCA) was also significant but less important. The estimates of GCA effects indicated that one line was the best general combiner for grain yield under drought. Nei’s genetic distance, measured using SSR markers, differed from 0.20 to 0.48 among the eight genotypes. The correlation of Nei’s genetic distance with SCA for grain yield and heterosis ranged from 0.4 to 0.5. These results indicate that the level of SCA and heterosis depends on the level of genetic diversity between the wheat genotypes examined. Microsatellite markers were effective in predicting the mean and the variance of SCA in various cultivars combinations. However, selection of crosses solely on microsatellite data would miss superior combinations.

Reaction of a diallel cross of maize to Meloidogyne incognita under field conditions

Meloidogyne incognita (Kofoid and White) Chitwood is an important pathogen of maize ( Zea mays L.), cotton ( Gossypium hirsutum L.) and soybean ( Glycine max (L.) Merr.) in the southeastern USA. Maize has been used, but not always successfully, in rotation with the other two crops to reduce nematode populations. The use of hybrids that support only low rates of M. Incognita reproduction should not only limit damage to the maize crop, but also to the other crops. Unfortunately, maize hybrids with resistance to M. incognita are not commercially available. A diallel cross of inbred lines with varying levels of resistance to M. incognita reproduction was previously evaluated in the greenhouse. The current investigation was undertaken to evaluate F 1 hybrids of the diallel cross for nematode reproduction in field naturally infested with M. incognita in 1989 and 1990. Egg counts were analyzed using Griffing's Method 4, Model I. General combining ability was a significant source of variation in egg production, but specific combining ability was not. Estimates of general combining-ability effects for Mp307 were significantly and negative, indicating that hybrids with this inbred line as a parent tended to be most resistant. The results of the field evaluations were consistent with the earlier evaluation of M. incognita reproduction on these F 1 hybrids. The results further suggest that maize hybrids with resistance to M. incognita reproduction can be developed.