Analysis of a combined F1/F2 diallel cross in wheat

Analysis of a conventional diallel cross offers only perfect-fit estimates of the genetic components of variation, but no test for the goodness of fit of the model based on these estimates. When F2 progenies are available, however, combining F1 and F2 diallels in a single experiment overcomes these problems. Least-square estimates of these components can be calculated, errors attached to them and the goodness of fit of the resultant model tested. This analysis was applied to data on the severity of yellow rust (caused by Puccinia striiformis) infection in an F1/F2 half-diallel cross among eight bread wheat lines adapted to the East African highlands. After removing two interacting arrays, genetic analysis indicated that an additive/dominance model of gene action satisfactorily explained the variation observed among the remaining six parents and their progenies, in both the individual F1 and F2 diallels and the combined F1/F2 diallel. Resistance to yellow rust was dominant to susceptibility and genes for increased resistance were more frequent

Cross prediction in bread wheat germplasm using single seed descent lines

Populations of F6 recombinant inbred lines, generated by single seed descent from a half diallel among eight bread wheat lines adapted to the East African highlands, were used to identify those crosses that were more likely to produce cultivars which combined resistance to yellow rust with improved yield. Crosses having the most resistant line as one parent offered the best prospect of success, particularly those which produced F1hybrids exhibiting better parent heterosis. For plot grain yield there was a highly significant correlation between the observed and predicted rankings of the recombinant inbred line populations for the proportion of individual lines equalling or surpassing the target value. For yellow rust severity, however, this correlation was non-significant when a target value of zero was used. Adopting a slightly less stringent target of 0.25, coupled with the omission of two aberrant populations, increased this correlation significantly. The plant breeding implications of these results are discussed

Implications of Market Access on Soil and Water Conservation Investment in the Highlands of Eastern Uganda

Market access is one of the motivating mechanisms for farmers to invest in soil and water conservation (SWC). Areas of relatively high agricultural potential but remote from major markets face numerous challenges in marketing their outputs. The objective of this study was to explore the market access determinants of farmer investment in SWC technologies in the highlands of eastern Uganda. A multi-stage sampling technique involving purposive sampling was used to determine the areas where the problem of market access is predominant. A Semi-structured questionnaire was administered to 192 randomly selected household heads. Data was analysed with soft ware packages for social scientist (SPSS). Binary logistic model was fitted to determine the influence of market access to investment in soil and water conservation. The probability distribution of the final chi-square ratio, in respect to market access, was 0.042 (<5%) implying the significant influence of market access to investment in SWC. Linking farmers to better markets for their agricultural commodities would create a positive contribution in raising high economic return and investment in SWC.L\u2019acc\ue8s au march est l\u2019un des m\ue9canismes de motivation des fermiers pour investor dans la conservation des eaux et de sol (SWC). Les milieux constituant un potentiel agricole relativement \ue9lev\ue9 mais \ue9loign\ue9s de grands march\ue9s font face \ue0 d\u2019importantes contraintes en rapport avec l\u2019\ue9coulement de leurs produits. L\u2019objectif de cette \ue9tude \ue9tait d\u2019explorer les d\ue9terminants de l\u2019acc\ue8s au mach\ue9 des investissement des fermiers dans des technologies de SWC dans les hautes terres de l\u2019Est de l\u2019Uganda. Une technique d\u2019\ue9chantillonnage \ue0 \ue9tapes multiples impliquant un \ue9chantillonnage cibl\ue9 \ue9tait utilis\ue9e pour d\ue9terminer les milieux o\uf9 le probl\ue8me d\u2019acc\ue8s au march\ue9 est predominant. Un questionnaire semi-structur\ue9 \ue9tait administer \ue0 192 chefs de m\ue9nages s\ue9lectionn\ue9s al\ue9atoirement. Les donn\ue9es \ue9taient analys\ue9es avec le logiciel SPSS. Le mod\ue8le logistique binaire \ue9tait utilis\ue9 pour d\ue9terminer l\u2019influence de l\u2019acc\ue8s au march\ue9 sur l\u2019investissement dans la conservation du sol et des eaux. Connecter le fermiers sur les meilleurs march\ue9s pour \ue9couler leurs produits agricoles pourrait \ueatre d\u2019une contribution positive en terme de l\u2019accroissement du revenue \ue9conomique et l\u2019investissement dans le SWC

Heritability of and correlations among genotype-by-environment stability statistics for grain yield in bread wheat

Several genotype-by-environment stability measures are in use, but little information exists about their inheritance or genetic interrelationships. Among those measures in common use are the linear regression coefficient (b), deviations from regression (sb), coefficient of determination (R2), coefficient of phenotypic variation (CPV) and, more recently, interaction principal components (IPCA) of the additive main effect and multiplication interaction (AMMI) model. Because of the factorial structure of the data, the diallel cross is well suited to study these parameters and their relationship to quantitative traits. For this study a complete diallel cross, derived by mating eight lines (Buri, Kenya Chiruku, Edsa\Lira, Vee "S", Atilla, CY8801, F6603147 and Car853) from a broad based bread wheat breeding population, was grown for several growing seasons at two Ugandan locations (Kalengyere and Buginyanya), one of which was prone to yellow rust [Puccinia striiformis]. Stability parameters and grain yield were measured for each cross. CPV had the highest narrow-sense heritability (h2=0.522) followed by IPCA1 of the AMMI (h2=0.461). Lowest narrow-sense heritabilities were calculated for b and R2 (h2=0.150 and 0.100 respectively). There were high additive genetic correlations (rA) between grain yield and CPV (rA=-0.933), grain yield and IPCA1 (rA=0.707), and grain yield and IPCA2 (rA=0.751). The genetic association between CPV and IPCA1 was also high and negative (rA=-0.934). These results suggest that it may be possible to select simultaneously for high and stable grain yield in this broad-based bread wheat breeding pool by selecting outyielders that exhibit a low CPV

Additive main effect and multiplicative interaction model for a diallel-cross analysis

Diallel mating designs have proved informative in determining the inheritance of quantitative traits of interest to plant breeders. Apart from the well established analyses of a complete diallel, the two-way factorial data structure of this design lends itself to analysis by the additive main effects and multiplicative interaction (AMMI) model. This research article describes the joint application of the AMMI model and Griffing's method 1, model I, to gain insight into the breeding value of inbred lines in a self pollinated crop such as disomic, hexaploid bread wheat. Data from a multienvironment trial of a complete diallel cross between eight lines adapted to the East African highlands were analysed to provide an example of this joint analysis. This combined approach identified not only the direction of a cross, i.e. which parent should be male or female, but also which crosses produce offspring showing F1 heterosis