Genetics of Resistance to Aphid in Cowpea
- R. S. Pathak
Aphid (Aphis craccivora Koch) is a major insect pest of cowpea [Vigna unguiculata (L.) Walp.] particularly in Africa and Asia, causing direct damage by removal of plant sap and indirect damage by transmitting mosaic viruses. The objectives of this study were to determine the inheritance of resistance to aphid in four resistant cultivars of cowpea and to determine if the genes for resistance were independent. The parental, F1, F2, and BC1 populations involving resistant × susceptible and resistant × resistant cultivars were evaluated in the screenhouse. Three-day-old seedlings were each infested with 10 apterous adult aphids and injury reactions were recorded 8 to 10 d after infestation by counting dead (susceptible) and surviving (resistant) seedlings in each population. The reactions of F1, F2, and BC1 populations arising from the crosses of four resistant cultivars, ‘ICV10’, ‘ICV12’, and ‘Tvu 310’ with susceptible cultivar ‘ICV1’, revealed that resistance in each of these cultivars was governed by a single dominant gene. Tests for allelism in the F1 and F2 populations from crosses between resistant cultivars indicated that the resistance of ICV10 and Tvu 310 is controlled by a common locus as are those of ICV11 and ICV12. The locus of the resistance gene in ICV10 and Tvu 310 is not linked to the locus of the resistance gene in ICV11 and ICV12. Thus, the resistance gene common to ICV10 and Tvu 310 was nonalletic to, and independent of the resistance gene of cultivars ICV11 and ICV12. The gene symbols Rac1 and Rac2 (resistance to A. craccivora were assigned for the nonallelic and independent loci controlling this trait.
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