Applications of area under disease progress curves in assessing resistance to Cowpea aphid-borne mosaic virus infection in groundnut.

Abstract

Three methods of processing Area Under Disease Progress Curve (AUDPC) estimates were compared for consistency and reliability. Twenty groundnut cultivars were mechanically inoculated with Cowpea aphid-borne mosaic virus (CABMV) in a field trial during the 2015 cropping season in Minna, Southern Guinea Savanna agro-ecology of Nigeria. The trial was laid out in Randomised Complete Block Design (RCBD) with three replications. Seedlings were inoculated at 10 days after sowing. Disease severity was rated on 1 – 5 point scale based on percentage of leaf surface covered with symptoms. Symptom severity scores were subjected to AUDPC and further used for resistance class determination. There was no complete agreement among the three methods in allocating cultivars into resistance classes. Considering instances of general consensus, two (ICG – 01276 and ICG – 5195) cultivars were unanimously rated as resistant. Based on the principles employed in Methods 1 and 2, three (FDR7 – 67, ICGV – 91317 and ICGV – IS – 76855) cultivars were susceptible, six (ICG – 02189, ICG – 6654, ICG – IS – 13003, ICG – IS – 13986, SAMNUT 24 and SAMNUT 25) were moderately susceptible, and two (ICG – 01276 and ICG – 5195) were resistant. With Methods 2 and 3, one (FDR7 – 61) cultivar was unanimously placed in highly susceptible class, whereas two (ICG – 94169 and SAMNUT 14) were rated as highly resistant. Based on Methods 1 and 2, the probability of placing a highly susceptible genotype in either moderately susceptible or susceptible group is relatively low. If the purpose of the investigation is to identify only two classes of response (resistant and susceptible), all the methods are suitable in that there was 100 % agreement with respect to the cultivars found in each category.