ISSN: 0041-3216 (Online), 0041-3216 (Print)
Volume 65 Number 1
Leaf rust epidemics of certain promising cowpea varieties compared by using logistic and Gompertz models
Rates of development of Uromyces phaseoli vignae (Barl.) Arth. on nine cowpea varieties, C-152, S-488, RC-19, RC-48, Guj-2, V-16, V-70, V-105 and V-118, were monitored to identify their rate-limiting resistance. Varieties RC-19 and Guj-2 showed a highly resistant response, while V-105 supported few late infections. The remaining varieties showed varying degrees of compatibility which facilitated calculation of apparent infection rates. Varieties V-16, V-70 and V-118 had low infection rates (Gompertz model) of 0.02 units or less day-1, indicating a slow rusting behaviour. Weekly observation of rust severity recorded as uredia cm-2 was subjected to either Gompertz or logistic transformations before computing apparent infection rates. Although both models effectively linearized disease proportions, Gompertz was more suitable, with lower variation in infection rate, lower standard errors of estimate and higher correlation coefficients.
Keywords: Leaf rust; Cowpea; Logistic model; Gompertz model