SURVEY OF INDIGENOUS BACTERIAL ENDOPHYTES FROM COTTON AND SWEET CORN

The genotypic diversity of indigenous bacterial endophytes within stem s and roots of sweet corn (Zea mays L.) and cotton (Gossypium hirsutum L.) was determined in field trials throughout one growing season. Str ains were isolated from surface-disinfested tissues and identified by fatty acid analysis. Gram-negative bacteria comprised 70.5% of the end ophytic bacteria and 27 of the 36 genera identified. The most frequent ly isolated groups from sweet corn roots, were Burkholderia pickettii and Enterobacter spp.; from sweet corn stems, Bacillus megaterium. Bac terial genera present in sweet corn roots were also generally present in sweet corn stems. However, Burkholderia gladioli, Burkholderia sola nacearum and Enterobacter cloacae were isolated much more frequently f rom sweet corn roots than stems, whereas Methylobacterium spp. were fo und more frequently in sweet corn stems than roots. Agrobacterium radi obacter, Serratia spp. and Burkholderia solanacearum, were the most fr equently isolated groups from cotton roots; and Bacillus megaterium an d Bacillus pumilus from cotton stems. Acinetobacter baumannii and Arth robacter spp. were present in cotton stems but not in cotton roots. Th ere were 14 taxonomic groups present in cotton roots that were not in cotton stems; all but one were Gram-negative. These included, Agrobact erium radiobacter, Bacillus megaterium, Bacillus pumilus, Enterobacter asburiae, Pseudomonas chlororaphis, Serratia spp. and Staphylococcus spp. Rhizobium japonicum and Variovorax paradoxus were isolated, almos t exclusively, from the roots of both crops. Bacterial taxa present in both sweet corn and cotton early in the season were generally present late in the season. The diversity of bacteria was greater in roots th an stems for each crop.