SPLS Seminar: Factors influencing biocontrol efficacy and mycotoxin contamination risk in Texas corn

Abstract: Grain corn is an important crop in Texas valued at over $1.2 billion. However, mycotoxin contamination is a perennial problem in Texas that results in significant economic losses for corn growers. Aflatoxin produced by Aspergillus flavus and related species and fumonisin produced by Fusarium verticillioides and F. proliferatum are the two major mycotoxins contaminating corn in Texas. Recommended mycotoxin mitigation tactics include minimizing biotic (insect injury, disease) and abiotic (drought, soil fertility) stresses to the corn crop. In addition, biological control using naturally occurring non-aflatoxigenic A. flavus genotypes to outcompete aflatoxin producers is an effective strategy to limit aflatoxin contamination, but there is no biocontrol for fumonisin. Climatic conditions where corn is grown vary in Texas, ranging from cool and dry conditions in the north to warmer and wetter conditions in the south. In general, cool temperatures (20-25℃) favor fumonisin contamination while warmer temperatures (25-35℃) favor aflatoxin production. Though some factors contributing to aflatoxin biocontrol efficacy and mycotoxin risk and have been previously characterized, knowledge gaps still exist that limit the ability of corn growers to mitigate crop losses due to aflatoxin and fumonisin contamination. Thus, the objectives of the current study are to 1) elucidate area-wide, multi-year effects of applying single-strain versus multi-strain aflatoxin biocontrol products; 2) compare the size and composition of mycotoxigenic fungal communities among different agroecological regions in Texas; 3) identify biotic and abiotic factors that influence growth of mycotoxigenic fungi and severity of mycotoxin contamination; and 4) collect field data to contribute to development of predictive models for mycotoxin contamination risk. In 2024, fields located in different regions of Texas and with variable biocontrol application histories were sampled. Fields treated with single- and multi-strain products all had high frequencies of biocontrol genotypes in soil and on the crop at harvest, but frequencies of individual genotypes within the multi-strain mixture varied from field to field. High frequencies of biocontrol genotypes in fields that did not receive an application in 2024 suggests biocontrol strains displace aflatoxigenic A. flavus in both treated and non-treated fields and persist in soils for several years. Fumonisin-producing Fusarium spp. and A. flavus were the most frequent kernel-infecting fungi, but incidence varied among different regions of Texas. Likely due to biocontrol applications, aflatoxin concentrations in grain were generally low (below the FDA action level of 20 ppb), while fumonisin concentrations were frequently above the FDA advisory level (2 ppm) in central and northern regions of Texas. Both Aspergillus and Fusarium ear rot severity correlated with ear injury caused by insect feeding. In addition, mycotoxin concentrations correlated with insect feeding style with aflatoxins correlated with chewing injury while fumonisin correlated with piercing injury. Relationships between soil factors, weather variables, mycotoxigenic fungal populations, and severity of mycotoxin contamination are currently being evaluated and will be used for development and validation of models to predict aflatoxin and fumonisin contamination risk in Texas. A better understanding factors influencing the long-term efficacy of aflatoxin biocontrol applications and mycotoxin contamination risk will allow corn growers to make more effective and economical mycotoxin management decisions.