Uncovering Fusarium species diversity, distribution and pathogenicity associated with cotton-corn rotation fields in recently expanded cotton-growing areas of the Northern High Plains of Texas

The recent expansion of cotton acreage in the Northern High Plains of Texas has raised concerns about the occurrence of a diverse Fusarium community, particularly Fusarium oxysporum f. sp. vasinfectum race 4. We investigated the diversity, distribution, and pathogenicity of Fusarium species in soil samples collected from 26 cotton-corn rotation fields across 10 counties. A total of nine Fusarium species were isolated: F. incarnatum, F. equiseti, F. solani, F. verticillioides, F. proliferatum, F. clavum, F. oxysporum, F. flocciferum, and one unidentified Fusarium sp. The highest species diversity (five species) was observed in Sherman County. Fusarium solani was the most frequently isolated species (39%) across all counties, followed by F. equiseti (22%), while F. flocciferum was the least frequently isolated species (2%). Greenhouse pathogenicity assays showed F. incarnatum caused significantly higher disease severity relative to non-inoculated control on aerial parts of cotton (P=0.0137), while Fusarium flocciferum, F. proliferatum, and F. clavum caused significantly higher disease severity relative to non-inoculated control on roots (P=0.01, P=0.01, P=0.02, respectively). On corn, differences in disease severity were not statistically significant (P>0.05). Fusarium isolates were recovered from both symptomatic and asymptomatic roots following pathogenicity trials, suggesting endophytic colonization. This study revealed a complex Fusarium community capable of cross-infecting cotton and corn, with implications for regional disease management. The absence of Fusarium oxysporum f. sp. vasinfectum race 4 indicates it may not yet have been introduced into the Northern High Plains; however, continued surveillance is warranted given its detection in New Mexico and adjacent counties in Texas.