Aspergillus species and mycotoxins in figs from California orchards

Although 23 different Aspergillus spp. decayed figs in California orchards, only A. niger occurred in more than 0.2% of the figs. The black-spored Aspergillus isolates that caused the disease fig smut were classified as A. niger var. niger, A. niger var. awamori, A. japonicus, and A. carbonarius. Different fungi differed in their association with Aspergillus Section Nigri (causal agents of fig smut) infections in figs. For example, most figs infected with Aspergillus Section Flavi (potential aflatoxin producers) also had infections by Section Nigri. For other fungi, there was either no significant relationship between fig infections by these fungi and Section Nigri or simultaneous infections by Section Nigri were fewer than expected. Insect damage to the fig fruit, predominantly by navel orangeworm (Amyelois transitella), did not significantly increase the colonization of figs by Aspergillus spp. The incidences of infection by Aspergillus (Sections Nigri, Aspergillus, Flavi, and Circumdati) in figs differed little for different harvests. Figs naturally infected with A. alliaceus, A. melleus, A. ochraceus, and A. sclerotiorum of Aspergillus Section Circumdati contained ochratoxin up to 9,600 ng/g, although only 40% of the figs with these fungi had more than a trace amount of ochratoxin. Aflatoxin contamination in figs naturally infected with Aspergillus Section Flavi varied according to the species involved. No aflatoxins were detected in all figs infected with A. tamarii and in most figs infected with A. flavus. High levels of aflatoxin (>100 ng/g) were detected in 83% of the figs infected by A. parasiticus, but in only 32% of the figs infected by A. flavus. Section Flavi isolates from fig orchard soils were tested for their ability to produce the mycotoxins aflatoxin and cyclopiazonic acid. Aspergillus parasiticus isolates always produced aflatoxin but never cyclopiazonic acid; A. flavus strain S (producers of small sclerotia) isolates always produced both aflatoxin acid cyclopiazonic acid, but strain L (producers of large sclerotia) isolates frequently did not produce aflatoxin or cyclopiazonic acid; and A. tamarii isolates never produced aflatoxin but always produced cyclopiazonic acid. Aspergillus flavus was recovered from the soil, at fewer than 6 CFU/g of dry soil of every fig orchard assayed in 1992 and 1993. Although A. parasiticus was rarer in fig fruit than was A. flavus for each year, in orchard soil A. parasiticus was more frequent than A. flavus. Isolates of A. flavus strain L were much more common in the orchard soil and fig fruit than those of strain S. Figs in commercial orchards seem to be a favorable substrate for infection by and growth of Aspergillus spp.