Phenotypic and Molecular Screening of Okra (Abelmoschus esculentus L. Moench) Genotypes against Okra Leaf Curl Disease

Abstract

Okra leaf curl disease (OLCD) is a major constraint on okra (Abelmoschus esculentus L. Moench) production in West Africa. The most effective way of managing this disease is through breeding and planting of resistant varieties. In order to identify sources of resistance and or tolerance, 21 okra genotypes were screened against OLCD in field trials which were conducted from May to October, 2015 (rainy season) and November 2015 to March 2016 (dry season). Field resistance was assessed at 2, 6 and 10 weeks after sowing (WAS) based on disease symptoms, and then confirmed by PCR amplification of viral coat protein gene. Populations of whitefly (Bemisia tabaci), the vector of begomoviruses associated with OLCD, as well as fruit yields were also assessed. Both PCR and field trials showed that all the okra genotypes were susceptible to the viral infection. The genotypes varied significantly (P<0.05) among them in terms of severity of OLCD, whitefly infestation, mean fruit yield (t ha-1), and the average fruit weight per plant. Higher cumulative average population of whitefly and mean fruit yield (t ha-1) were recorded in the dry season than in the rainy season. Genotypes GH5332 and GH6105 consistently showed mild symptoms of OLCD and also had very high fruit yields of 11.88 t ha-1 and  9.34 t ha-1 respectively in the rainy season, and 6.108 t ha-1and 4.05 t ha-1 respectively in the dry season, far above the overall mean yields for all the okra genotypes. Both genotypes GH5332 and GH6105 should be evaluated multi-locationally at farmers’ fields prior to their release as varieties or they should be incorporated into breeding lines.