Host genotype effects and biological control potential of bacterial endophytes in cotton (Gossypium hirsutum L.)

The capacity of bacterial endophytes to colonize both external and internal plant parts has prompted favorable interest in their use as potential alternative biological control agents. However, little is known concerning their interaction between host genotypes for colonization or their ability to control multiple soil-borne plant pathogens, particularly in cotton. This crop is affected by numerous soil-borne pathogens that attack during early seedling development. Consequently, chemical inputs for disease control are high, and, for some pathogens, little to no control is available. Therefore, the purpose of this study was to determine the spectrum of colonization of bacterial endophytes across cotton host genotypes and their potential for disease control against a number of soil-borne pathogens.; Results indicated that whether originating from seed or predominantly from soil, endophytes in cotton seedlings reach a population threshold after seed germination. Host genotype significantly affected total population density and population densities of indigenous functional groups of endophytic bacteria four to five days after germination.; Establishment of introduced bacterial endophytes was also affected by cotton genotype. Differences in initial seed populations, 24 hrs. after treatment among cotton cultivars, may have consequently contributed to cultivar differences observed for total and internal populations of the selected strains and indigenous bacteria. Morphological and physiological changes in roots of the host genotype, as well as changes in population composition between indigenous bacteria and the introduced bacterial strain, may also have contributed to these population differences among cotton cultivars.; Of the selected endophyte strains, 89B-61 was consistent in anti-fungal activity against all fungal pathogens tested. This strain, and nearly three-fourths of the remaining endophytic strains used in this study, produced siderophores in vitro. Five of the strains were also active for protease production in vitro.; Greenhouse and growth chamber experiments showed that introduced bacterial endophytes some control a number of fungal pathogens, and this control was strain specific. All fourteen bacterial endophytes were effective in controlling root-knot nematodes. Due to adverse weather conditions, the effect of these strains on control of Fusarium wilt under field conditions could not be observed. However, vigor stands indicated that bacterial endophytes were capable of increasing plant growth 21 days after planting when compared to the non-treated paired plot.