Mycofloral relations and interactions with Rotylenchulus reniformis on cotton

Thirty-seven genera representing 58 species of fungi were isolated from roots, petioles, leaves and bolls of cotton grown in Alabama. Common pathogens included 9 species of Fusarium, Pythium ultimum, P. aphanidermatum, Rhizoctonia solani, Thielaviopsis basicola, Alternaria alternata, Macrophomina phaseolina, Nigrospora oryzae, and Phoinopsis gossypii. Principal component analysis (PCA) factors derived from weather data for temperature variables accounted for 61% of the total joint variation among fungal occurrence. The second principal component, which was related to the moisture variables, accounted for 19% of the variation. Incidence of select seedling disease fungi, including R. solani and F. semitectum, was highly correlated (r = 0.85; r = 0.85) with PCA factor values for temperature and moisture, respectively. The abundance of N. oryzae was correlated with the PCA factor values for moisture (r = −0.78). The incidence of P. gossypii was correlated with PCA factor values for temperature (r = 0.78) and moisture (r = 0.74). Alternaria alternata was the most common fungus encountered, accounting for 19% and 10% of the total fungi isolated in 2000 and 2001, respectively. The incidence of A. alternata was correlated with PCA factor values for temperature (r = 0.76) and moisture (r = −0.96). Twenty species of fungi were reported for the first time colonizing upland cotton tissues.; Based on the high incidence of multiple Fusarium species associated with cotton tissues in Rotylenchulus reniformis infested fields, the relationship between these pathogens was assessed. The impact of R. reniformis and ten Fusarium species on seedling disease, plant growth, and nematode population densities was examined in a greenhouse. Further, it was determined if soil condition, autoclaved or natural, influenced the impact of Fusarium species and R. reniformis on seedling disease, plant growth, and R. reniformis population densities. Fusarium oxysporum f. sp. vasinfectum, F. solani, R. solani, and T. basicola consistently displayed extensive root and hypocotyl necrosis that was more severe and resulted in greater root hypocotyl disease index values in the presence of R. reniformis. Cotton seedling height and dry weight were reduced by R. reniformis; however, reductions were greater in the presence of select seedling disease fungi. For plant height this was most prominent and recorded in both experiments for F. lateritium, F. moniliforme, F. solani, R. solani, and T. basicola. Seedlings growing in autoclaved soil infested with fungi resulted in greater disease and reduced growth more than in natural soil. Rotylenchulus reniformis reproduction on cotton seedlings was greater in natural soil compared to autoclaved soil. This study suggests the importance of Fusarium species and R. reniformis on cotton seedling disease.; A species of Phomopsis was implicated in various diseases of cotton, including a necrotic leaf-spot disorder and premature boll rot. Its taxonomic and nomenclatural history was reviewed, as were aspects of its symptomatology. Some account of host/pathogen relationships was included. Commentary was made on the systematics of the Phomopsis-complex, particularly with regard to better defining species. (Abstract shortened by UMI.)...