Masters Theses

Date of Award

5-1999

Degree Type

Thesis

Degree Name

Master of Science

Major

Ecology and Evolutionary Biology

Major Professor

Ralph W. Dimmick

Abstract

At Ames Plantation in western Tennessee, unharvested soybeans are left in the field over winter as a supplemental food source for northern bobwhite quail (Colinus virginianus). Studies conducted at the Plantation show that soybeans comprise approximately 70% of the winter diet of bobwhites. The production of mycotoxins in soybeans could adversely affect the health and reproductive performance of bobwhite quail. The objective of this study was to determine the effect of late winter precipitation on the production of Bi, B2, Gi, and Ga aflatoxin and T-2 toxin in soybeans left in the field over winter at Ames Plantation.

During March and April of 1997 and 1998, experiments were conducted to measure aflatoxin and T-2 toxin production in soybeans exposed to 3 weather treatments: (1) ambient weather; (2) simulated dry condition; and (3) simulated wet condition. Aflatoxins and T-2 toxin were detected in treatment samples collected during all experimental periods except April 1998. The majority of the samples containing aflatoxins were wet and ambient samples. Aflatoxins were detected in dry samples during March 1997 only. In April 1997, mean levels of AFB], APB2, and AFGi were significantly higher (P < 0.05) in the wet treatment samples. These results suggested that aflatoxin production in soybeans is dependent on late-winter precipitation.

In contrast, data from this study suggested that the level of T-2 toxin produced in soybeans was not significantly dependent on amount of rainfall. During all experimental periods except April 1998, T-2 toxin was produced in soybean samples in all 3 weather treatments; the levels of toxin produced did not differ significantly (P > 0.05) among the treatments.

The level of T-2 toxin produced in soybeans was related to air temperature. T-2 toxin formation is enhanced by temperatures fluctuating between freezing and thawing. The mean level of T-2 toxin in March treatment samples was significantly higher (P < 0.05) in 1998 (431ppb) compared to 1997 (167 ppb). Daily temperatures below 0 C occurred on no more than 2 consecutive days during March 1997, but occurred for 5 consecutive days during March 1998.

To determine the natural occurrence of aflatoxins and T-2 toxin in soybeans left in the field over winter, samples of Hutcheson, Tennessee 5-95, and Laredo variety soybeans were collected during March and April of 1997 and 1998. Samples were collected from the pods of standing plants and from the ground. Seven percent of 70 samples collected from pods contained aflatoxins ranging from 32 to 164 ppb. Furthermore, 17% of the 70 samples collected contained T-2 toxin at either 500 ppb or 1,000 ppb.

The prevalence of aflatoxin and T-2 toxin in soybeans in the pod was dependent on variety. Only 1 of 39 Hutcheson samples contained aflatoxin and no aflatoxins were detected in any of the Tennessee 5-95 samples. In contrast, 16% of 25 Laredo samples contained aflatoxin. Laredo variety soybeans were more resistant to T-2 formation than Hutcheson soybeans. T-2 toxin was detected in 21% of 39 Hutcheson samples but occurred in only 12% of 25 Laredo samples.

Although the prevalence of aflatoxins in Hutcheson pod samples was extremely low, 42% of 43 ground samples contained aflatoxins ranging from 16 to 1,032 ppb. Likewise, the percentage of ground samples containing T-2 toxin (37%) was higher than the percentage of pod samples (21%). These data suggested that the pods of Hutcheson soybeans limited mycotoxin contamination, possibly by protecting seeds from fungal invasion and moisture exposure.

The levels of aflatoxins and T-2 toxin detected in soybeans at Ames Plantation probably were too low to cause toxic effects in wild quail and would not significantly affect the overwinter survival of bobwhites. Therefore, managing for mycotoxin contamination in soybeans would not be necessary. If toxic levels are detected in overwintering soybeans, then removal of this food source would be an appropriate management strategy.

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