Effect of host genotype on indigenous bacterial endophytes of cotton (Gossypium hirsutum L.)

The purpose of this study was to determine if populations of indigenous bacterial endophytes in seed, stem and root tissue of cotton seedlings are influenced by host genotype. Growth chamber and field experiments were conducted to test the hypothesis that host genotype has an effect on endophytic bacterial populations in seed tissues and the developing cotton seedling. Initially, population densities of bacteria within seed of nine cotton cultivars were very low (i.e., <log(10) 2.0 colony forming units seed(-1)). However, after 4 days growth on water agar, population densities within developing radicles increased significantly (log(10) 2-5 colony forming units) and significant cultivar differences were found. Significant cultivar differences occurred for populations of endophytic bacteria and the composition of bacterial functional groups differed among cultivars in field-grown seedlings at 5, 8, and 15 days after planting. Differences in the ranking of cultivars occurred for endophytic populations recovered from seed and aseptically and field-grown radicle and seedling tissues. These results suggest that whether originating from seed or from soil, cotton plants are capable of immediately establishing a carrying capacity for communities of endophytic bacteria following seed germination. During germination and development of the seedling, there are genetic and possible morphological/physiological effects that contribute to significant differences in colonization of bacterial endophytes among cotton cultivars.