VARIATION IN ROOT LEACHATE AND RHIZOSPHERE-RHIZOPLANE MICROFLORA AMONG CULTIVARS REPRESENTING DIFFERENT LEVELS OF MULTI-ADVERSITY RESISTANCE IN COTTON

Twenty-three multi-adversity resistant (MAR) cotton strains and two commercial cultivars were used to study the associations between root leachate components, rhizosphere-rhizoplane microflora, yield, earliness, and resistance to three soil-borne diseases.;Concentrations of carbohydrates, potassium, calcium, and sodium were the same for 18- and 30-day-old plants, but were significantly lower for 55-day-old plants. Magnesium ion concentrations were high for 18-day-old plants with a significant reduction at 30 days. Electrical resistance increased significantly between 18- and 30-day-old plants with a significant reduction between 30- and 55-day-old plants.;Average populations of rhizosphere bacteria and actinomycetes were the same for 18- and 30-day-old plants with significant increase for 55-day-old plants. The trends for rhizoplane microorganisms were just the opposite of the rhizosphere microflora populations.;Changes in ratios of rhizosphere-rhizoplane microorganisms occurred as the plants matured with significant differences occurring between 30 and 55 days.;Short term collection of root leachates fro 18-, 30-, and 55-day-old cotton plants showed significant cultivar differences in electrical resistance, carbohydrate and cation concentrations.;Calcium and sodium concentrations had the greatest overall associations with root zone microflora populations and ratios for 18-day-old plants. For 30-day-old plants, the most consistent root leachate components for root zone microflora models were calcium, potassium, carbohydrate, and electrical resistance. Calcium and magnesium were associated with root zone microflora from 55-day-old plants.;Statistical models indicated that calcium from 18-day-old plants was negatively associated and sodium and magnesium were positively associated with high incidence of damping-off. The effects of calcium and sodium were simulated in in vitro experiments with unsterilized field soil artificially infested with R. solani. A high ratio of rhizoplane bacteria to rhizoplane actinomycetes from 18-day-old plants was associated with high incidence of damping-off.;Low root pH, high calcium concentration, and low magnesium concentrations from 18-day-old plants were associated with good stands. Increased numbers of rhizosphere and rhizoplane actinomycetes from 18-day-old plants were associated with good stands.;High root leachate electrical resistance from 18-day-old plants, and low potassium concentrations from 30-day-old plants were associated with high yield. Low numbers of rhizosphere bacteria from 18-day-old plants, low numbers of rhizoplane bacteria from 30-day-old plants, a high ratio of rhizoplane actinomycetes to rhizosphere actinomycetes from 30-day-old plants, and a low ratio of rhizosphere bacteria to rhizosphere actinomycetes from 55-day-old plants were associated with high yield.;Low concentrations of potassium from 18- and 30-day-old plants, high root weight and high carbohydrate from 30-day-old plants, low root pH and high electrical resistance from 55-day-old plants were associated with earliness.;Low root pH and high electrical resistance from 18-day-old plants, low electrical resistance and high carbohydrate concentrations from 30-day-old plants, low potassium and high magnesium concentration from 55-day-old plants were associated with resistance to Verticillium wilt. A high ratio of rhizoplane actinomycetes to rhizosphere actinomycetes from 18-day-old plants was associated with resistance to Verticillium wilt.;High root pH from 30- and 55-day-old plants was associated with susceptibility to Phymatotrichum root rot. A high ratio of rhizoplane actinomycetes to rhizosphere actinomycetes from 30-day-old plants and high numbers of rhizopshere actinomycetes from 55-day-old plants were associated with lower incidence of Phymatotrichum root rot.