GEORGIA

Dave Wilson

Dave discussed proposed new FDA guidelines for threshold fumonisin levels; 5 ppm for horses, 10 ppm for pigs, 1 ppm for humans, and 15 ppm for everything else. Dave presented some information on fungal successions and mycotoxins of stored pearl millet. Presence of Fusarium moniliforme in millet grain is similar to corn and grain sorghum microflora. Dave also discussed the occurrence of fumonisins and aflatoxins in the south Georgia corn survey, 1996 to 1999. The survey reported the following mean aflatoxin levels from 43 counties: 1996 – 42 ppb, 1997 – 8 ppb, 1998 – 236 ppb, and 1999 – 29 ppb. In the same survey mean fumonisin levels were: 1996 – 7 ppm, 1997 – 7 ppm, 1998 – 12 ppm, and 1999 – 1 ppm. When data from 1996 to 1999 was combined, ear damage was correlated with both fumonisin and aflatoxin content and there was a significant positive correlation between fumonisin and aflatoxin contamination. However, there was little correlation between fungi. Both A. flavus and F. moniliforme occupy the same damage area on the ear, but do not compete with each other. A. flavus dominates during hot periods and on dryer ears, while F. moniliforme dominates in cooler weather and on wetter ears. Night temperatures, net evaporation, and insect damage are the primary factors that influence aflatoxin accumulation.

Dave also mentioned that problems increase in pigs and horses, including brain lesions in horses, when fumonisin levels reach 20-30 ppm. Recent research in Missouri and Georgia has shown that the Bt gene does not affect aflatoxin levels as it did in Iowa and Indiana studies. Additional research is needed for the different Bt types and for the insects involved.

Wellington Mubatanhema

Wellington discussed the Georgia corn survey. Preharvest corn samples were collected from 41-43 counties in south Georgia from 1996 to 1999. Fusarium species and A. flavus groups were the dominant species on most samples. The mean percentage infection by A. flavus was consistently higher than to A. parasiticus each year.

Neil Widstrom discussed a six-year corn planting date test, which showed a decrease in aflatoxin as planting date was delayed. This may have been partly due to lower temperatures, particularly night temps, during the critical grain fill period. Higher temperatures enhance the activity of A. flavus and insects. Neil mentioned that the worst aflatoxin year was 1977, with the mean aflatoxin level of 622 ppb. Only two years out of the last 23 years has the mean aflatoxin level dropped below 20 ppb (1994 and 1997). Neil also mentioned that tropical corn hybrids may have less aflatoxin because they can be planted late and have excellent husk coverage. Some of the Cargill tropical hybrids have performed well at Tifton.

Dave Wilson added that there was a good correlation between bacterial diseases in pigs and aflatoxin, as well as decreased poultry and egg production.

Bazuo discussed insect resistance in corn. Maysin found in corn silk has insecticidal activity against corn earworm larvae. A study was conducted to identify corn chromosome regions associated with maysin synthesis in silks. This information will be eventually utilized for marker-assisted selection in transferring maysin genes into elite lines with resistance to A. flavus. In cross of GE37 and 65, a major QTL was detected on chromosome 3L and may be a regulator gene in maysin pathway.

Neil discussed pyramiding ear resistance to insects and invasion by Apergillus  spp. for control of preharvest aflatoxin contamination in corn. A two-year field experiment demonstrated that protection of corn ears against aflatoxin contamination is dependent on several traits, including resistance to fungal infection and ear-feeding insects, and excellent husk coverage and tightness. A highly significant correlation was found between corn earworm injury and aflatoxin contamination of corn grain. Silk maysin and husk traits can influence resistance to insect feeding. Thus, a three-prong approach is being used. High silk-maysin and excellent husk coverage can provide protection against insect entry and damage to the kernels, while chemical resistance is needed to reduce Aspergillus  invasion and production of aflatoxin. Genetic mapping of the cross GT-A1 X GT119 was completed for silk-maysin concentration and husk tightness. GT-A1 contributes the allels for low aflatoxin contamination, while GT119 contributes alleles for husk tightness. Data from these and other experiments will be used to conduct marker-assisted selection in a corn population to be generated and used for selection of inbreds with resistance to Aspergillus spp infection and ear-feeding by insects.

Neil mentioned that the early introduction of mid-West hybrids in the South provided yield advantage, but insect damage increased. Hybrids grown in the South now have better insect resistance than hybrids 20 years ago. It will be extremely difficult to completely eliminate the aflatoxin problem. Good management can reduce the problem. A Georgia software program is being developed which will aid growers in making management decisions that will reduce risk from aflatoxin contamination.

Dave Wilson mentioned that actual fumonisin levels have decreased with the newer hybrids. Dave also mentioned that breeding programs for aflatoxin and fumonisin need cheaper tests for determining toxin concentrations. ELISA kits manufactured in 1999 erroneously gave high fumonisin levels (150 ppm) in North Carolina. Poor quality control resulted in these high levels (many false positives). European Union has established a 2 ppb threshold level for corn being used for human consumption, which is driving the market.

LOUISIANA

MISSISSIPPI

The Mississippi report was given by Bruce Manning, Gary Windham, and Hamed Abbas. Dr. Ed King, USDA-ARS Associate Area Director for the Mid-South, was also in attendance.

Bruce reported on 1999 mycotoxin research with channel catfish. Aflatoxin feeding studies were conducted to evaluate the effect of feeding channel catfish diets containing corn contaminated with aflatoxin and clean corn. Results of an aquarium study showed no effects on growth, feed efficiency, and hematocrit values after feeding corn with aflatoxin concentrations of 110 and 220 ppb. Similar results occurred in a pond study. An aquarium study conducted for eight weeks found no effect on feed consumption, growth, hematocrit values, survival and liver weights when DON (deoxynivalenol) was fed at rates ranging from 0 to 10 ppm. Results of a pure T-2 toxin study indicated that the lowest addition of T-2 toxin (2.5 ppm) caused an 84% reduction in growth of juvenile catfish.

Gary introduced Martha Wilcox, who was recently hired to replace Georgia Davis. Gary mentioned that there were few problems with aflatoxin around the state in 1999. Mississippi corm acreage decreased from 600,000 acres in 1998 to 300,000 acres in 1999. Gary presented commercial corn hybrid screening data for 1998 and 1999. Entries were needle inoculated seven days after silking. Aflatoxin levels across hybrids were much lower in 1999 compared to the previous year, ranging from 13 to 913 ppb in 1999 compared to 110 to 10,018 ppb in 1998. Data for aflatoxin contamination of 19 inbreds was also presented for 1999. Aflatoxin concentrations ranged from 18 ppb form Mp715 to 1,070 ppb for SC212M. Gary mentioned the cooperative research agreement between Pioneer and Dekalb seed companies. Researchers at the USDA-ARS unit at Starkville screen elite material from these seed companies for aflatoxin resistance.