Uncovering <i>Fusarium</i> 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 <i>Fusarium</i> community, particularly <i>Fusarium oxysporum</i> f. sp. <i>vasinfectum</i> race 4. We investigated the diversity, distribution, and pathogenicity of <i>Fusarium</i> species in soil samples collected from 26 cotton-corn rotation fields across 10 counties. A total of nine <i>Fusarium</i> species were isolated: <i>F. incarnatum</i>, <i>F. equiseti</i>, <i>F. solani</i>, <i>F. verticillioides</i>, <i>F. proliferatum</i>, <i>F. clavum</i>, <i>F. oxysporum</i>, <i>F. flocciferum</i>, and one unidentified <i>Fusarium</i> sp. The highest species diversity (five species) was observed in Sherman County. <i>Fusarium solani</i> was the most frequently isolated species (39%) across all counties, followed by <i>F. equiseti</i> (22%), while <i>F. flocciferum</i> was the least frequently isolated species (2%). Greenhouse pathogenicity assays showed <i>F. incarnatum</i> caused significantly higher disease severity relative to non-inoculated control on aerial parts of cotton (<i>P</i>=0.0137), while <i>Fusarium flocciferum</i>, <i>F. proliferatum</i>, and <i>F. clavum</i> caused significantly higher disease severity relative to non-inoculated control on roots (<i>P</i>=0.01, <i>P</i>=0.01, <i>P</i>=0.02, respectively). On corn, differences in disease severity were not statistically significant (<i>P</i>>0.05). <i>Fusarium</i> isolates were recovered from both symptomatic and asymptomatic roots following pathogenicity trials, suggesting endophytic colonization. This study revealed a complex <i>Fusarium</i> community capable of cross-infecting cotton and corn, with implications for regional disease management. The absence of <i>Fusarium oxysporum</i> f. sp. <i>vasinfectum</i> 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.