Mesophilic microorganisms and endotoxin levels on developing cotton plants.

Healthy cotton leaf, bract, fiber and soil were collected twice each week during growing season. These samples were studied to determine the epiphytic total and gram-negative bacterial (GNB) populations and endotoxin levels from seedling development to harvest. Since bract is a significant trash component of raw cotton, a study of the epiphytic bract fungi was performed also. Bract and soil had the highest total bacterial count (TBC) until senescence, when the bract count increased significantly over that of the soil. Leaf TBC was usually third while fiber had the least TBC. Leaf senescence did not result in an increase in TBC as with bract. GNB counts paralleled, but were approximately 10-fold lower than that of the TBC. Enterobacter agglomerans was the most predominant bacterium on leaf and bract. Gram-positive rods were the most common bacteria on fiber with E. agglomerans second. Gram-positive rods were by far the predominant species in soil. Senescence affected the population levels of the various genera on leaf and bract. Endotoxin varied greatly for all sample types. Soil usually gave the highest amounts, followed by bract, fiber leaf surface. Statistical analysis showed some minor correlations between the presence of certain bacteria with other bacteria. No correlations were found between weather data and bacterial types present or endotoxin levels. The epiphytic fungal population on bract was studied through the growing season. Though different genera appeared, the predominant genus throughout the study was Cladosporium.