The Relationship of Gin Date to Aflatoxin Contamination of Cottonseed in Arizona

Aflatoxins are potent mycotoxins produced by fungi in Aspergillus section flavi. The toxic effect of aflatoxins on humans and other animals is well known (7); thus, many countries regulate the quantity of aflatoxins allowed in foods and feeds (17). Aspergillus flavus Link:Fr. infects many oilseed crops and is frequently, as with cottonseed, the primary cause of aflatoxin contamination (13). When cottonseed is crushed for oil, the remaining meal then competes with other vegetable meals in the livestock feed market. During crushing, toxin is concentrated about twofold in the meal. In the U.S., both cottonseed and cottonseed meal may be sold at a premium for dairy feed only if the aflatoxin content does not exceed 20 ppb (17). Seed and meal exceeding 300 ppb aflatoxin may not be used for beef cattle feed. In the southwestern U.S., aflatoxin contamination of cottonseed frequently occurs in furrow-irrigated cotton. Irrigation can influence aflatoxin contamination, particularly if continued into the harvest season (19). Indeed, field plot and laboratory observations suggest crops harvested later tend to have greater contamination (8). Cotton is indeterminate; the first bolls to mature and open are exposed to the environment while later bolls are developing. Bolls produced closer to the ground frequently contain the greatest aflatoxin contamination (3). These bolls are both the first to open and the closest to irrigation water (19). Contamination is thought to occur in two phases (4,8): the first occurs prior to seed maturity; the second after maturity. Insect damage, particularly pink boll worm damage (Pectinophora gossypiella Lepidoptera: Gelechiidae) is associated with the first phase. Bolls infected during this phase frequently produce seed that exhibit bluegreen-yellow-fluorescence (BGYF) of the lint (3,12). The second phase occurs after seed maturity, and involves direct infection of the seed by A. flavus. This process is favored by warm, moist conditions (4,16). Contamination of some bollworm-resistant Bt cottonseed lots in 1995 was attributed to the second phase of contamination (11). During the second phase, the aflatoxin content of seed initially infected during the first phase may also increase. Thus, harvest date may be an important factor influencing final aflatoxin content. The harvest season in Arizona typically extends over several months. Increased costs of late irrigation and pest control and losses associated with crop weathering may offset benefits of increased yield accrued from continued crop development. It is not clear how harvest date impacts aflatoxin contamination in the commercial setting. During 1995 and 1996, collaboration with a commercial gin afforded the analysis of the impact of gin date on aflatoxin content. The result is a clear association between harvest date and seed aflatoxin content that should be considered when developing integrated management systems for the control of aflatoxin contamination of cottonseed.