Development of delivery systems for introducing endophytic bacteria into cotton

Experiments were designed to evaluate the effectiveness of several methods for delivering 15 endophytic bacteria into cotton stern and root tissues. The delivery, methods included stab-inoculation of bacteria into stems, soaking seeds in bacterial suspensions, methyl cellulose seed coating, foliar spray, bacteria-impregnated granules applied in-furrow vacuum infiltration and pruned-root dip. The success of delivery was gaged by recovery of the bacteria from internal plant tissues 2 weeks after the plants had been grown in a glasshouse potting mix. Following stab-inoculation into sterns or radicles, 10 of the bacterial endophytes which previously exhibited biological control against fusarium wilt of cotton were successfully re-isolated from > 50% of the plants inoculated; however, this method was labor-intensive, involved wounding the plant and sometimes reduced plant growth. Four of the other methods established,from six to eight of the 15 strains, and, with some strains, all methods effectively established endophytic bacteria, based on re-isolation of strains from internal tissues 2 weeks after inoculation. A method was developed which allowed more convenient isolation of endophytes from a large number of plants. The results suggest that introduction of beneficial endophytic strains into cotton plants could be accomplished by practical methods chosen specifically for each strain.