|Jaime Garcia, Ramon|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/30/2004
Publication Date: 6/15/2004
Citation: Jaime-Garcia, R., Cotty, P.J. 2004. Aspergillus flavus in soils and corncobs in South Texas: Implications for management of aflatoxins in corn-cotton rotations. Plant Disease. 88:1366-1371. Interpretive Summary: Aflatoxins are dangerous toxic chemicals that contaminate many crops. The fungus named Aspergillus flavus causes aflatoxin contamination of both cottonseed and corn. Farmers commonly rotate corn and cotton crops in South Texas where reduced tillage frequently results in long-term residence of corncobs on soil surfaces. A. flavus can grow and survive on corn cobs. We studied the potential of corncobs as sources of A. flavus in cotton and corn crops in South Texas from 2001 to 2003 in order to gain insights into potential methods for preventing contamination. The results indicate that corncobs are an important source of crop exposure to A. flavus. Corncobs from the previous season contained, on average, over 190 times more A. flavus propagules than soil from the same field, and two-year old corncobs still retained 45 times more propagules than soil. The quantity of A. flavus in corncobs decreased with corncob age. Delaying harvest of corn causes an increase on both the incidence and quantities of A. flavus on pre-harvested corncobs. The results suggest that aflatoxin management should include prompt harvest and techniques to reduce the period cobs remain in the field such as incorporation under the soil. This research is beneficial to researchers and crop growers.
Technical Abstract: Aspergillus flavus causes aflatoxin contamination in both cottonseed and corn. Cotton/corn rotations are common in South Texas where reduced tillage frequently results in long-term residence of corncobs on soil surfaces. Corncobs are colonized by A. flavus either prior to harvest or while in the soil. This study sought to determine the potential of corncobs as sources of inoculum for cotton and corn in South Texas. A. flavus communities in corncob and soil samples were collected during the planting seasons of 2001 to 2003 from 29 fields extending from Calhoun and Victoria Counties in the north to the Rio Grande Valley. In order to assess persistence of A. flavus in corncobs, A. flavus communities in corncobs and soil were contrasted every 2 to 3 months in four fields throughout the three-year study to assess long-term variation and in two fields on a biweekly basis to assess seasonal variation. The results indicate that corncobs are an important source of A. flavus inoculum. Corncobs from the previous season contained, on average, over 190 times more A. flavus propagules than soil from the same field, and two-year old corncobs still retained 45 times more propagules than soil. There was no significant difference in the incidence of A. flavus strain S on corncobs and soil. The quantity of A. flavus in corncobs decreased with corncob age (r2 = 0.54, P = 0.002). Delaying harvest caused an increase in both the incidence and quantity of A. flavus on preharvested corncobs.