Samuel Kimaru Linguya

African nightshade (ANS) is known for high micronutrient content, medicinal properties and fast growth with low production costs. The challenges facing its production include low quality seed, low leaf/seed yields per hectare, pests and diseases, poor harvesting and processing methods. The objectives of this study were to evaluate the quality status of African nightshade seed, detect seed borne pathogens, identify the most prevalent viral pathogens and determine a suitable seed processing method for clean ANS seed production. A household survey was conducted in 240 farms in Nyanza and Western Kenya where ANS is grown in abundance and seed samples were collected from farms and local markets. Certified seed samples were purchased for comparison. Quality and purity tests were done following International Standard Testing Association rules (ISTA). Purity was determined by separating seed samples into pure, discoloured, weed, other crop seeds and other foreign matter. Germination percentage was obtained by planting lots of 100 seeds on paper towel where number of germinated seeds, normal seedlings and infected seedlings were counted. Seedling vigour index was assessed by measuring seedling length and seedling dry weight. Fungal and bacterial pathogens were isolated and identified using appropriate methods to species level. Serology and molecular techniques were used to identify viruses and the major viruses were sequenced using next generation sequencing. Certified seeds were used as a standard check.  The seed processing methods used by farmers were evaluated. Data was analyzed and treatment means compared using the fisher’s protected LSD test at 5% probability level.

Seed quality tests showed that farm saved seed was of poor quality compared to seed obtained from the local market and certified seed. Farm saved and local market seed had low seed purity of 68.6% and 74%, respectively compared to certified seed at 94.4%. In addition, only certified seeds met the recommended moisture and germination percentage as per ISTA rules. There was a significant (p≤ 0.05) correlation between seed quality and germination parameters. For example seed purity had significant positive correlation (r=0.76**) with germination percentage. The following major pathogens were detected in African nightshade: Aspergillus flavus (42.4%), Aspergillus niger (32.5%), Xanthomonas campestris pv. vesicatoria (31%), Potato virus Y (26%), Penicillium chrysogenum (23.5%), Cucumber mosaic virus (21%) and Pseudomonas syringae pv. tomato (17%). Three major viruses namely Potato virus Y (PVY), Cucumber mosaic virus (CMV) and Tobacco mosaic virus (TMV) were confirmed by next generation sequencing revealing genomic homology of more than 90% with 22 isolates from all over the world. Three strains of Potato virus Y were identified as PVYNTN, PVYO and PVYN:O. Evaluation of seed processing methods revealed that wet seed fermentation method, produced seeds with the highest purity of 96.3% and yielded more (913.8 kg/ha) compared to other processing methods. The high level of ANS seed infection, contributes to poor seed quality leading to poor plant growth and low yields. There is need to train farmers on appropriate processing methods for clean seed production to increase ANS productivity. The current study recommends routine inspection of seeds by seed producers to ensure that the seed is of acceptable quality and within the tolerable levels of infection.