Associations of bacterial endophyte populations from red clover and potato crops with potential for beneficial allelopathy

Clover and potatoes, in a crop rotation, were found to share specific associations of bacterial endophytes. Twenty-five bacterial species from 18 genera were common to both clover and potatoes and represented 73% of all the bacteria recovered from clover root tissues and 73% of all the bacteria recovered from potato tubers. Endophytic bacteria tested in potato plant bioassays were predominantly plant growth neutral (56%). The remainder were either plant growth promoting (21%) or plant growth inhibiting (24%)(P < 0.05). Of the plant growth promoting bacteria, 63% increased shoot height, 66% increased shoot wet weight, and 55% increased root wet weight. The effects of plant growth inhibiting bacteria were restricted to reductions in plant height (86%) and shoot wet weight (36%); root weight was not affected. Of the bacteria tested, 74% showed some degree of in vitro antibiosis to the clover and potato pathogen Rhizoctonia solani. Such endophytic intercrop bacterial associations appear to be complementary in nature and support the view that there are microbial benefits to be gained from clover in crop sequences with potatoes, beyond those of the residual nitrogen left in the soil and the organic matter added.