Treatment appears effective in reducing aflatoxin ByDennis Pollock
One strain of the A. flavus is nearly all toxigenic—potentially harmful—and an- other strain is roughly half toxigenic and half atoxigenic.Michailides said theatoxi- genicAF36 strainmultiplies and increases population, which displaces or competes with thepopulationof the toxigenic strain. He said it took more than 10 years of research, primarily with pistachios, to get AF36 registered by showing its efficacy andsafety. Tests showedAF36became the dominant strain in the soil where it was applied. In 2011, levels of displacement of toxigenic strains reached between 90% and 95%. AF36 reduced the aflatoxin-positive samples from treated commercial pista- chioorchards some40%,Michailides said. For cotton or corn, reduction with AF36 droppedpositive samples asmuchas 80% and 90%. Registration for pistachios came in 2012. AF36 Prevail has since been regis- tered for use in almonds. Michailides said another product, Afla-Guard GR by Syngenta, is expected to be registered soon for pistachios and almonds, and could offer better sporula- tion than AF36. He said it is important to continue to practice sanitation to reduce mummies and touse insecticides tocontrol navel or- angeworm. He said the optimumtime for thebest sporulation is inmid-July, and it’s
important to stockpile properly to avoid moisture and leaks under plastic covers. Soil samples are being taken in al- monds, and PCR analysis is speeding the process of learning the relative popula- tions of strains of aflatoxin. Research on AF36 in almond acre- age accelerated in 2019 in McFarland, Woodland, Wi l l iams, Manteca and Turlock, where 100 acres each was treat- ed and untreated. Michailides said research showed the application of AF36 Prevail greatly dis- placed the toxigenic strains of A. flavus and A. parasiticus in commercial or- chards. The plan, he said, is to expand the almond project to 5,000 acres, to get more soil samples and to increase sam- pling for aflatoxin. Bob Klein, manager of the California Pistachio Research Board, said there are fewer than 10 pistachio handlers, and af- latoxin remains a significant trade issue for all of them. The handlers subsidized applicationof AF36, whichhe saidproved inexpensive and quick and easy to apply. KleinsaidhebelievesAF36 canbemost effective if there is a region-wideapproach to itsuse, particularlybecausewindblows spores from aflatoxins among neighbor- ing almond and pistachio orchards. “AF36 is a useful tool to manage af- latoxin, but it is not a panacea,” he said, estimating it is used on 90% of
California pistachio acreage. Leighton Liesner, executive director of the Arizona Cotton Research and Protection Council, said there is a build- up of AF36 after annual treatments and, if that ceases, populations of toxigenic aflatoxin grow. “When the carrier (of AF36)—wheat or sorghum seed—comes in contact with moisture, the AF36 begins to grow and produce spores to be dispersed by wind and insects,” Liesner said. He listed the goals of the aflatoxinmit- igation program inArizona as: to expand atoxigenic strain technology; improve and simplify manufacturing; add new atoxigenic strains and effectively deliver them; ensure the long-termavailability of atoxigenic technology; andprovide atoxi- genic technology to the commodities that need it economically. In studies conducted during three years in Bowie, Arizona, average AF36 levels increased more than 380%, based on analysis of 11 samples from four pis- tachio orchards, he said. Like Klein, Liesner talked of the area- wide effect of AF36 application, noting applicationof the product in commercial cotton influences the compositionof fun- gi in both treated and nearby fields. (Denni s Pol lock i s a repor t er in F r e s no . He ma y b e c on t a c t e d a t agcompollock@yahoo.com.)
It’s a “very rare event,” an expert says, and that produces a special challenge in addressing aflatoxincontamination: find- ing ways tomake a rare event ever rarer. The almond business and others have taken extensivemeasures to control afla- toxins,whichhavebeenlinkedtolivercan- cer, and the Almond Board of California presented awebinar on the topic. Themis Michailides, plant pathologist with the University of California, Davis, and the Kearney Agricultural Research and Extension Center in Parlier, opened the webinar and said aflatoxins can be a problemnot only for almonds but also for pistachios and figs. Aflatoxins are produced by Aspergillus flavus and A. parasiticus. Regulatory limits for aflatoxins for the United State are set at 15 parts per billion for total aflatoxins, 10 parts per billion for the B1 toxin. For the EuropeanUnion, it’s 10 parts per billion for all aflatoxins and 8 parts per billion for B1. The incidence of aflatoxin inCalifornia crops are one almond nut in 25,000 to 30,000; one pistachio nut in 5,000 in an “off ” or lower production year, and one in 20,000 in an “on” or higher production year; and one fig in 5,000. Aflatoxin lives in the soil and produces spores andsclerotia insoil andmummies.
12 Ag Alert June 9, 2021
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