Genetic Diversity and resistance of African nightshade Solanum nigrum L Complex to Bacterial wilt Ralstonia solanacearum in Western Kenya

Abstract

African nightshade, Solanum nigrum L .is one of the most significant leafy vegetable rich in nutritional and medicinal value, and can be used to feed people with human immune deficiency virus, HIV/AIDS in Kenya. There is limited information available of this species that hinders its sustainable conservation and development. Limited information on the crop pests and diseases also present major challenges that limit production of the African nightshade species since farmers are still using farm saved seed which is a danger of inadvertently spreading quarantine pest and diseases like Ralstonia solanacearum. The utilization of genetic diversity in breeding programs can be employed to enhance the development of African nightshade accessions that exhibit better yield potential for both leaf and fruit production, while also displaying resistance to various biotic and abiotic challenges. The objective of this study was to assess the presence of genetic diversity among African nightshade accessions by conducting morphological and genotypic characterisation. Additionally, the study aimed to determine the inherent resistance to bacterial wilt caused by Ralstonia solanacearum by field and greenhouse screening experiments. A total of 30 samples from three counties Bungoma, Kakamega and Trans Nzoia were evaluated. For morphological characterization the African nightshade accessions were planted at Kibabii University farm and scored for several agro morphological characters based on National Bureau of Plant Genetic Resource NBPGR descriptors on following qualitative traits; Leaf surface as Glaborous or pubscent, Colour of ripe fruit as Orange or Dark purple or Black, Stem ridge as Smooth ridges or Dented, Leaf shape as Lanceolate or Ovate or rhomboid, Leaf margin as Sinuate dented or Entire and Inflorescence orientation as Simple or Forked the plant type was scored as Semi erect or erect. Cluster analysis of morphological data was done using PASW Version 20 Statistical software. Results showed that there was phenotypic variation amongst accessions of African nightshade collected from the three counties since they were grouped into two major clusters A and B meaning that there is rich diversity both within and among African nightshade accessions which can be used for the crop breeding work. Molecular characterization was done using SSR markers on 30 African nightshade accessions. Each of the 6 SSR primers utilized produced a single polymorphic band. The mean polymorphic information content was 0.5881, with values ranging from 0.4215 to 0.8212. He=0.9111 is the mean heterozygosity for SSR markers utilized. The dendrogram indicated that the accessions were categorized into three primary clusters, each characterized by a high degree of diversity. Furthermore, it disclosed that the coefficient distance separating the majority of the accessions was below 79.56. These results indicate that cross-breeding was a possibility among the accessions; genetic variation between regions was not apparent. Screening of the 30 African nightshade accessions, to Ralstonia solanacearum was done in the screen house at Masinde Muliro University of science and Technology. Seedlings were inoculated at four to six leaf stages with 30 ml of 108cfu/ml per seedling in the pot and disease incidence was recorded. The different accessions of Solanum nigrumL, Solanum villosum L from Trans Nzoia, Bungoma and Kakamega counties were identified as susceptible. However, improved accessions of Solanum scabrum L sampled from the African nightshade growing areas in Western Kenya were resistant to bacterial wilt, the accessions that were found to be susceptible, symptoms appeared 4 days after inoculation, while the accessions that were found to be resistant/ tolerant no symptoms were observed even after 14 days after inoculation. The resistant accession of improved variety of Solanum scabrum L can be used in production and also breeding programmes for developing new varieties of the African nightshade crops.