Varietal Response of Cowpea (Vigna unguiculata (L.) Walp.) to Striga gesnerioides (Willd.) Vatke Race SG5 Infestation
AbstractThe parasitic plant Striga gesnerioides (Willd) Vatke is becoming a serious threat to cowpea production in Sub-Saharan Africa. At least 7 races of S. gesnerioides exhibiting specific virulence have been identified. The objectives of this study were to identify sources of resistance to S. gesnerioides race SG5 spreads in northern Cameroon and to study the inheritance of the resistance. Twelve accessions of cowpea, IT98K-205-8, IT98K-503-1, IT98K-1092-1, IT99K-216-1-1, IT98K-494-6, IT99K-529-4, IT99K-573-1-1, IT99K-573-2-1, IT00K-1207, IT03K-378-4, IT04K-227-4 and VYA were assessed in field trials for resistance to S. gesnerioides race SG5 in Maroua, northern Cameroon and the genetics of the resistance from two sources was elucidated in artificially infested pots. Data on resistant and susceptible cowpea plants were analyzed using the chi-square test to ascertain the goodness of fit to different genetic ratios. Tests of resistance using field screening techniques showed that among these varieties, four were susceptible, four tolerant, two partially resistant while IT99K-573-1-1 and IT98K-205-8 appeared completely resistant to Striga race SG5. On susceptible varieties, the mean number of emerged S. gesnerioides plants 9 weeks after sowing was 1.8 to 2.4 per cowpea plant, while completely resistant lines carried none. The cowpea genotypes showed significant differences for percentage of infected plants, the decimation rates and Striga height. On susceptible genotypes, the seeds yield losses due to Striga infestation varied from 28.4 to 36.6% while for the fodder yield these losses ranged between 23.63 to 41.03%. The analysis of F1 and F2 populations resulting from crossings between resistant varieties and the susceptible tester VYA demonstrated that resistance is was controlled by two factor inheritance with duplicate dominant genes (Rsg5a and Rsg5b) for IT99K-573-1-1 and a single dominant gene (Rsg5) for IT98K-205-8. These two varieties provide newly additional sources of resistance to S. gesnerioides and can be used in programmes of genetic improvement of this legume.
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