Mechanism of resistance of selected cowpea (Vigna unguiculata (L.)) varieties to the beanfly (Ophiomyia phasboli) Tryon.
1988
Abdirahman Ali Guled
Resistant Acc. No.3 (II81D-1069) was significantly less preferred for feeding than the other resistant Acc. No.1 (TVX 3671-14C), moderately resistant Acc. No.4 (II82D-906) and No.7 (II82D-789) or the susceptible check Acc. No.11 (ASV). Based on egg count, the check was significantly more preferred for oviposition than the other four accessions. No significant variations in plant height, internode length and trichome length or density were observed among test plants to allow their correlation with host preference. Significant variations were observed in leaf area but this characteristic did not show significant influence on host preference. The observed antibiotic effects of Acc. No. 1, 3 and 4 were higher insect mortality and shortened adult life. The first two accessions also had an adverse effect on body length. The lowest percentage of dry weight loss at high beanfly population was observed in the moderately resistant Acc. No. 4. As a whole the results showed that the mechanisms of resistance of the resistant Acc. No. 1 and 3 were antibiosis and antixenosis. The former had higher level of antixenosis but the latter had higher level of antibiosis while Acc. No. 7 had low level of antibiosis. There were indications that all the four accessions also had tolerance to beanfly damage with Acc. No. 4 having the highest level. Great variability in resistance level was observed among test plants of the same accession suggesting the need to use adequate number of plant samples in varietal screening for beanfly resistance and the possibility to select individual resistant plants for generally susceptible populations.
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