Seed borne Phaeoisariopsis Griseola assessment and it's influence on angular leaf spot of Phaseolus Vulgaris cv Rosecoco-glp-2.

Abstract

Angular leaf spot (ALS) disease caused by Phaeoisariopsis griseola has been reported in all areas where Phaseolus vulgaris cultivars are grown. However the relative importance of the disease in terms of seed infection is lacking. Therefore, cv Rosecoco GLP-2 seeds were sampled from small scale farmers' from Embu, Machakos and Kiambu districts and assessed for seedborne infection/contamination levels by P. griseola using agar plate, blotter and grow-on tests as recommended by International Seed Testing Association. The results revealed higher levels ofP. griseola infections on cv Rosecoco GLP-2 seed samples obtained from low compared to high altitude bean growing zones. The grow-on test revealed higher seed infection levels as compared to the Agar and blotter tests. Therefore higher levels ofP. griseola become seed transmitted when P. vulgaris are grown in low as compared to high altitude. Though the fungus P. griseola is seedborne, it's tolerance levels under Kenyan conditions have not been worked out. Therefore cv Rosecoco GLP-2 seeds having five varying levels of P. griseola infections were planted in the field and assessed for disease progress and the resulting yield. The results revealed that the seed infection levels directly I enhanced ALS levels and also equally negatively influenced yield and yield components that were recorded. The disease progressed more rapidly at Katumani (low altitude) as compared to Kabete (high altitude). From these experimental results, it can be concluded that any cv Rosecoco GLP-2 seed sample having above 15% p, griseola incidence level in the grow-on test (value for pathogen free seeds), when planted in the field will ultimately influence disease progress and the resultant yield. - xvi - Angular leaf spot is thought to attack P. vulgaris plant late during growth season. To verify the importance of age of plant at time of infection, pathogen free seeds were planted and inoculated with P. griseola at different ages in the field. From the results no significant relationship could be deduced between age of plant at inoculation time and disease development. There were no significant differences on yield levels obtained among the inoculated plots, but higher yield reduction levels and seed infection levels of harvested seed were obtained from plots inoculated at 2 compared to those inoculated at 5 weeks after germination. This study has found that the age of cv Rosecoco GLP-2 plants at time of P. griseola infection does not significantly influence ALS disease development nor the resultant yield.