Seed health tests of traditional leafy vegetables and pathogenicity in plants

Abstract

Traditional leafy vegetables play a significant role in the daily diets of many people in Zimbabwe. They are produced by smallholder farmers with limited knowledge on the agronomic value of high-quality seed, on seed storage, and on plant-and seed-borne pathogens. The quality of the seed is rarely tested for seed-borne pathogens posing risks of pathogen build-up. This study was conducted in order to determine the seed-borne pathogens associated with traditional leafy vegetable seeds. Seeds were collected from five different farmers in three provinces of Zimbabwe and tested for the presence of pathogens in the plant pathology laboratory of the University of Zimbabwe. A total of 154 fungal and 233 bacterial infections were recorded on 450 seeds for each type of pathogen. Significantly high percentages of the isolates (Xanthomonas campestris, Curvularia spp., Alternaria alternata, Fusarium oxysporum and Pseudomonas syringae) were obtained from the three different species of traditional leafy vegetables (Amaranthus hybridus, Bidens pilosa and Cleome gynandra). F. oxysporum, A. alternata, X. campestris and Bacillus spp. isolates were pathogenic to traditional leafy vegetable plant species as confirmed by pathogenicity tests, hence may have significant effects on traditional leafy vegetables production. The results indicate that seed sourced from farmers 1, 2, 3 and 4 resulted in seed-borne pathogens on both the seed and plants, clearly showing that seed quality was poor. Although most pathogens observed have a broad host spectrum, pathogenicity and virulence tests confirmed that some pathogens were likely to be closely associated with these traditional leafy vegetable seed species.Key words: Seed-borne pathogens, disease occurrence, pathogenicity, bacteria, fungi, seed quality. INTRODUCTIONTraditional leafy vegetables (TLVs) of Africa refer to plant species, which originated on the continent and have a long history of cultivation, domestication and use in African conditions (Ambrose-Oji, 2009). Amaranthus spp. combine both social and socio-economic importance in Kenya and Tanzania as a multi-purpose vegetable with environmental adaptability, nutritional, medicinal and income generation properties (Weinberger and Msuya, 2004;Abukutsa-Onyango, 2007), and have gained popularity also in Zimbabwe. Mukwereza (2002) Across Africa, TLVs are produced and marketed by smallholder farmers (Ngugi et al., 2007) with limited access to advanced agro-technology including limited knowledge of the agronomic value of high-quality seed (Biemond et al., 2012), lack of information on seed storage (Cernansky, 2015), on appropriate use of chemicals like pesticides and fertilizers (Schippers, 2000), plants and seed-borne pathogens. These smallholder farmers obtain most of their seeds from their neighbours or informal seed markets (Ngwerume and Mvere, 2003;Adebooye et al., 2005;Guei et al., 2011).This seed is most likely to be of poor quality. Seed is rarely tested for germination and seed-borne pathogens, increasing risks of seed degeneratio...