Responses of Bean to Root Colonization WithPseudomonas putidain a Hydroponic System

Abstract

Colonization of bean roots by Pseudomonas putida was maintained at 0.6-1.8 .times. 105 colony-forming units per gram of root tissue during growth for 18 days under hydroponic culture involving complete as well as iron- and boron-deficient media. Leaves from 18-day-old transplants colonized by P. putida had reduced iron contents compared with uninoculated seedlings, and roots had 17-93% higher lignin contents than did uninoculated seedlings. Plants with roots colonized by P. putida gained more weight after inoculation with Fusarium solani f. sp. phaseoli compared with plants grown without P. putida. In plants inoculated with both P. putida and Fusarium, foliar wilting and onset of lesion formation were delayed by 2-3 days. Colonization by P. putida decreased the amount of lignin normally generated at the lesioned root-shoot interface in plants infected by Fusarium. These data suggest that P. putida may afford some protection against F. solani in the early stage of disease development. Protection may involve alteration of the plant''s defense potential through an increase in lignin in the root tissues.