Assessing performance of simplified bioassays for soil-borne pathogens in smallholder systems of western Kenya

The soil bioassays, which involved counting galls on lettuce roots and lesions on soybean were well correlated with the abundance of gall forming (<i>Meloidogyne</i>) and root lesion nematodes (e.g., <i>Pratylenchus</i>) recovered in standard laboratory-based extractions. Effectiveness of a <i>Fusarium</i> bioassay, involving the counting of lesions on buried bean stems, was verified via sequencing and a pathogenicity test of cultured <i>Fusarium</i> strains. Finally, a <i>Pythium</i> soil bioassay using selective media clearly distinguished pathogen infestation of soils and infected seeds. When examining management impact on nematode communities, soils amended with manure had fewer plant parasites and considerably more bacterivore and fungivore nematodes compared to soils amended with synthetic N and P. Similarly, <i>Pythium</i> presence was 35% lower in soils amended with manure, while the <i>Fusarium</i> assays indicated 23% higher <i>Fusarium</i> infection in plots with amended manure. Our findings suggest that relatively simple bioassays can be used to help farmers assess soil-borne pathogens in a timely manner, with minimal costs, thus enabling them to make informed decisions on soil health and pathogen management.