Fungal communities associated with almond throughout crop development: Implications for aflatoxin biocontrol management in California

Abstract

Interactions between pathogenic and nonpathogenic fungal species in the tree canopy are complex and can determine if disease will manifest in the plant and in other organisms such as honey bees. Seasonal dynamics of fungi were studied in an almond orchard in California where experimental release of the atoxigenic biopesticide Aspergillus flavus AF36 to displace toxigenic Aspergillus strains has been conducted for five years. The presence of the vegetative compatibility group (VCG) YV36, to which AF36 belongs, in the blossoms, and the honey bees that attend these blossoms, was assessed. In blossoms, A. flavus frequencies ranged from 0 to 4.5%, depending on the year of study. Frequencies of honey bees carrying A. flavus ranged from 6.5 to 10%. Only one A. flavus isolate recovered from a blossom in 2016 belonged to YV36, while members of the VCG were not detected contaminating honey bees. Exposure of pollinator honey bees to AF36 was detected to be very low. The density of several Aspergillus species was found to increase during almond hull split and throughout the final stages of maturation; this also occurred in pistachio orchards during the maturation period. Additionally, we found that AF36 effectively limited almond aflatoxin contamination in laboratory assays. This study provides knowledge and understanding of the seasonal dynamics of Aspergillus fungi and will help design aflatoxin management strategies for almond. The evidence of the low levels of VCG YV36 encountered on almond blossoms and bees during pollination and AF36’s effectiveness in limiting aflatoxin contamination in almond provided additional support for the registration of AF36 with USEPA to use in almond in California.

Present Status and Perspective on the Future Use of Aflatoxin Biocontrol Products

“…Aflatoxin contamination of economically important food and feed crops occurs frequently in tropical and subtropical regions [1,2]. Susceptible crops include maize, groundnut, cottonseed, tree nuts, figs, and chilies, among others [3][4][5]. Aflatoxins are synthetized alone or with other mycotoxins by several Aspergillus species, most of them belonging to section Flavi (Table 1) [6].…”

Aflatoxin in Chili Peppers in Nigeria: Extent of Contamination and Control Using Atoxigenic Aspergillus flavus Genotypes as Biocontrol Agents

“…Aflatoxin biocontrol using atoxigenic fungi is a technology developed by the United States Department of Agriculture—Agricultural Research Service (USDA–ARS) [33]. The technology has been used for decades in the US where it is registered for aflatoxin mitigation of cottonseed, maize, pistachio, almond, fig, and groundnut [33,34,35,36]. The International Institute of Tropical Agriculture (IITA), USDA–ARS, and several partners have adapted and improved the technology for use in Nigeria and other SSA nations under the trade name Aflasafe [17,37].…”

Molecular Analysis of S-morphology Aflatoxin Producers From the United States Reveals Previously Unknown Diversity and Two New Taxa

“…Aflatoxin producers within Aspergillus section Flavi can infect a wide range of food and feed crops, such as maize, sorghum, groundnuts, cottonseed, chilies, tree nuts, and insects (Shotwell et al, 1969;Shetty and Bhat, 1997;Rodrigues et al, 2009;Kachapulula et al, 2017Kachapulula et al, , 2018Singh and Cotty, 2017;Ortega-Beltran et al, 2018). Infection frequently results in contamination of the host with aflatoxins, both through ramification of hyphae in host tissue, and production of immense numbers of aflatoxincontaining conidia (Mehl and Cotty, 2010).…”