Cowpea aphid-borne mosaic virus (CAB-MV) is a major virus disease in Uganda that causes substantial loss of the cowpea crop especially in growth and yield. The mode of gene action conferring resistance to the virus is not well understood. The objective of the study was to determine the genetic inheritance of resistance in cowpea crosses. Three susceptible (S) cowpea landraces that are commonly grown by farmers were crossed with five introduced resistant cowpea varieties in accordance with a North Carolina mating design II scheme. The F 1 , F 2 and BC 1 F 1 progenies generated were evaluated in the field together with their parents. They were then infected with two infection methods namely: by spreader-rows of S cultivar (Ebelat) and artificial inoculation of virus extracts. The results obtained showed that general combining ability (GCA) and specific combining ability (SCA) effects were significant, indicating that both additive and non-additive gene effects controlled virus infection. The results further demonstrated that the GCA effects (59.8 %) were more important than SCA effects (40.2 %) in determining virus resistance in the cowpea varieties. Utilisation of good general combiners of the varieties MU-93, IT82D-516-2, SECOW-2W and IT85F-2841 in hybridisation to improve virus resistance in cowpea crosses would be recommended. The result of this study provided an indication that CABMV resistance was conditioned by more than one recessive gene in eight populations, but also revealed resistance to be conditioned by a single recessive gene in the other seven populations. Observation of continuous distribution of progenies for severity data in the F 2 populations also confirmed significance of quantitative inheritance for CABMV resistance. Therefore, the significance of GCA effects suggests that recurrent selection could be applied to accumulate the additive genes for resistance in F 2 populations.
Cowpea viruses are economically important diseases of cowpea in the major growing areas of Uganda and have inflicted negatively on food security, nutrition and income for many households. The objective of the study was to determine the prevalence and identity of viruses infecting cowpea in the growing districts of Uganda. Surveys were conducted in the field of grown cowpea, and virus symptoms were recorded on the basis of virus incidence and severity in the districts of Apac, Lira, Pader and Kumi. Symptomatic virus leaf samples were also collected from the same fields surveyed for serological test for detection of virus types using antibodies to cowpea aphid-borne mosaic virus (CABMV), cowpea mild mottle virus (CPMMV), cowpea severe mosaic virus (CPSMV), cowpea mosaic virus (CPMV), cowpea chlorotic mottle virus (CPCMV), cucumber mosaic virus (CMV) and cowpea chlorotic mosaic virus (CCMV) in double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA). Results showed that there was the highest percentage of incidence and severity in Kumi (85.4% and 13.8%, respectively) with the lowest percentage of incidence and severity observed in Apac (55.9% and 4.7%, respectively). Serological test revealed the presence of CABMV, CPMMV, CPSMV and CMV in the leaf samples as the major virus types in the surveyed districts. However, CPCMV, CPMV and CCMV were not detected in the leaf samples surveyed in the cowpea growing districts. Serological test also revealed that among the virus types detected, single and multiple virus types occurred in the plant samples. The highest single virus type occurring in the plant samples was CPMMV (11.6%) and the lowest was CABMV (1.8%). The virus types namely CMV, CABMV, CPMMV and CPSMV occurred in combinations with proportion of 7.1% in the infected plant samples. Therefore, this information obtained on the virus types provides an opportunity for breeders to develop cowpea variety with multiple resistance genes to control several virus types infecting cowpea.
Fusarium related root rots have been associated with reduced cowpea productivity in Uganda. Sources of genetic resistance to Fusarium redolens which was found to be the most virulent have been identified but the mode of inheritance of the genes conferring the resistance is unknown. This study aims to investigate how the genes for resistance to F. redolens are inherited in cowpea. Four F. redolens root rot resistant cowpea genotypes were crossed with four intermediately resistant and 2 susceptible cowpea genotypes using North Carolina mating design II. The F 1 and the parents were evaluated and data were collected on resistance to seed rot, leaf chlorophyll amount, produced lateral roots, response to plant mortality and root rot severity. Results revealed that additive gene effects were significant for all evaluated traits and non-additive genetic effects were significant in resistance to seed rot and chlorophyll amount. General combining ability (GCA) effects showed that the Asontem genotype was a good combiner for increased lateral roots production and resistance to root rot. Degree of dominance estimates revealed that response to plant mortality, root rots and increased lateral root production traits were recessively inherited while seed rot and amount of leaf chlorophyll were dominantly inherited.
Cowpea [Vigna unguiculata L. (Walp.)], is an important legume crop widely grown in the tropics. Biotic and abiotic stresses cause significant yield reduction in cowpea. In this chapter, we provide a synthesis of information on the damage/economic importance of soilborne diseases of cowpea and present options that can be used to manage these diseases. The aim is to demonstrate that a wide array of control options are available for potential use within an integrated disease management (IDM) framework. Reviewed literature indicated presence of several sources of resistance to fusarium wilt (FW) and charcoal rot but few sources for stem rots, collar rot and damping-off. Major resistant genes and quantitative trait loci (QTL) were identified for FW and charcoal rot and these may be exploited in marker assisted selection (MAS). Cultural practices such as crop rotation and compositing were found to be effective against soilborne diseases, however, there is lack of knowledge regarding their adoption. Similarly, several botanicals were found to be effective against several soilborne fungal diseases but these studies were limited to controlled environments necessitating the need for large scale field trials. Several effective microbial control agents (MBCAs) and fungicides exist and can be incorporated in IDM.
Populations with high genetic variability are targeted by breeders as they create opportunity for selection and genetic improvement. To achieve this, multiple populations are created, but resources are often scarce. This calls for identification of populations with the desired traits at early generation. The study was carried out at MUARIK in seasons 2017A and 2017B on 135 F2 and 40 F3 cowpea populations respectively together with 25 parental lines aimed at: Determining best performing populations for yield, resistance to scab, virus and flower thrip based on usefulness criterion and selection index methods. Usefulness criterion computed for yield identified NE 36 x 2392 as the best population. Usefulness criterion computed for yield and its components identified NE 5 x Sanzi as the best population. WC 48A x 2392 was identified as the best population using selection index values that included resistance to virus, thrips, scab, yield and its component and when only yield and its components were fitted in the model. Variability and high yield performance was maintained in the forty best populations identified and therefore amendable for future improvement. No differences were shown among the methods used for selection hence can be adapted for breeding in cowpea.
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