Spatial distribution of virus diseases on okra (Abelmoschus esculentus L. Moench) plants and resistance to Cucumber mosaic virus disease in Minna, Nigeria

Abstract

Okra is an important vegetable crop in the diet of millions of peoples in the tropical and subtropical regions of the world. Unfortunately, its yield is seriously threatened by several virus diseases, including Cucumber mosaic virus (CMV) and Okra mosaic virus (OkMV). To date, adoption of resistant cultivars is by far the most effective and sustainable management measure against plant pathogenic viruses. This study was conducted to determine the: (1) occurrence and distribution of CMV and OkMV diseases in selected Local Government Areas (LGAs) of Niger State, and (2) growth and yield responses of four genotypes of okra virus under CMV infection. A survey was carried out in six LGAs (Borgu, Bosso, Gbako, Mashegu, Mokwa and Paikoro) of Niger State in 2019 cropping season. Four communities were surveyed and five symptomatic leaf samples of crops were collected from each community amounting to 20 leaf samples from each Local Government Areas. A total of 120 symptomatic leaf samples were indexed for all the local government areas surveyed. The samples were subjected to Double Antibody Sandwich Enzyme-Linked Immunosaobent Assay (DAS-ELISA). The polyclonal antibodies (PAbs) used were Cucumber mosaic virus (CMV) and Okra mosaic virus(OkMV).The screenhouse evaluation of four okra genotypes was laid out in completely randomised design with three replicates. Okra seedlings were inoculated with CMV at 10 days after sowing (DAS) by sap transmission. Each genotype was evaluated as CMV-infected and control. Data on disease incidence and severity, growth and yield variables were subjected to analysis of variance (ANOVA) and means separated using the Least Significant Difference (LSD) at p=0.05 probability level. Cucumber mosaic virus and OkMV were detected during the survey, with the former being more prevalent. A total of 11 samples (9.2 %) reacted positively with CMV PAb. Incidence of CMV disease was highest in Borgu (3.3 %) and Mokwa LGAs (3.3 %), followed by Paikoro LGA (1.7 %) while an incidence of 0.8 % was found in Gbako LGA. On the other hand, none of the samples from Bosso and Mashegu reacted positively with CMV PAb. In Borgu LGA, CMV disease was found at Dogongari, Gadaoli, Fakun and Malele. In Gbako LGA, the virus was detected only at Emisomma community. In Mokwa LGA, the disease occurred at Government Teachers College, Waabi, Wuya- Kede and Rail Station. The two CMV-positive samples in Paikoro LGA came from Jankpan and Jyipe communities. On the other hand, only 2 samples (1.7 %) tested positive for OkMV disease. These were found at Gidan-Mugoro and Edokota, in Bosso and Gbako 2 LGA, respectively. Overall, “OKR_19_01” genotype exhibited the highest fruit length (5.3cm), fruit weight (4.3 g/plant) and fruit diameter (2.5 cm) under CMV infection. Therefore, cultivation of “OKR_19_01” okra genotype is recommended in CMV-endemic areas. Although100 % incidence of CMV disease was found on “OKR_19_01” plants as early as 1 WAI, it eventually gave the greatest yield performed among the okra genotypes evaluated. It is therefore, recommended to farmers in CMV-endemic locations for better productivity. However, further extensive survey is needed so as to reveal virus diversity in okra farmlands. In the meantime, the okra genotypes “OKR_19_01” could be adopted in CMV-endemic areas. Plant breeders could also cross this genotype with CMV-resistant genotype for improved resistance and yield.