Black aspergilli in Brazilian onions: From field to market.

The occurrence of black aspergilli in onions has been reported as frequent, and this group of fungi harbors potentially toxigenic species. In addition, Aspergillus niger has been reported as the causative agent of black mold rot, an important postharvest disease that causes damage throughout the world. Brazil stands out as one of the world's largest onion producers. However, few studies have been conducted to investigate the mycobiota in Brazilian onions. For this reason, we investigated the mycobiota of 48 market (n = 25) and field (n = 23) onion bulb samples. Nineteen soil samples were collected from the same fields and evaluated. In field onions and soil samples, Penicillium spp. was the prevalent fungal group, whereas in market samples A. section Nigri was the most frequent group. Due to the taxonomic complexity of this group, species identification was supported by phylogenetic data (CaM gene). A. welwitschiae was the most prevalent species in market samples. Black aspergillus strains were evaluated for fumonisin B2 (FB2) and ochratoxin A (OTA) production. Overall, 53% and 2.2% of the strains produced FB2 and OTA, respectively. The occurrence of FB2 and OTA was also investigated in onion bulb samples but none showed contamination with these mycotoxins.

Molecular analysis of Aspergillus section Nigri isolated from onion samples reveals the prevalence of A. welwitschiae.

The aim of this study was to isolate Aspergillus section Nigri from onion samples bought in supermarkets and to analyze the fungal isolates by means of molecular data in order to differentiate A. niger and A. welwitschiae species from the other non-toxigenic species of black aspergilli, and detect genes involved in the biosynthesis of ochratoxin A and fumonisin B2. Aspergillus section Nigri were found in 98% (94/96) of the onion samples. Based on the results of multiplex PCR (performed on 500 randomly selected strains), 97.4% of the Aspergillus section Nigri strains were recognized as A. niger/A. welwitschiae. Around half of them were subjected to partial sequencing of the CaM gene to distinguish one from the other. A total of 97.9% of the isolates were identified as A. welwitschiae and only 2.1% as A. niger. The fum8 gene, involved in fumonisin B2 biosynthesis, was found in 36% of A. welwitschiae isolates, but radH and pks genes, involved in ochratoxin A biosynthesis, were found in only 2.8%. The presence/absence of fum8 gene in the A. welwitschiae genome is closely associated with ability/inability of the isolates to produce fumonisin in vitro. Based on these results, we suggest that in-depth studies are conducted to investigate the presence of fumonisins in onion bulbs.

Isolation and Identification of Aspergillus Section Nigri, and Genotype Associated with Ochratoxin A and Fumonisin B2 Production in Garlic Marketed in Brazil.

The garlic contains sulfur bioactive compounds responsible for medicinal properties. The decrease of these compounds due to inadequate storage conditions reduces the beneficial properties and favors infection by microorganisms. Several studies have shown high frequency of garlic infected with Aspergillus section Nigri that potentially produce mycotoxin. Garlic samples were collected in markets of Brazil and a total of 32 samples (of 36) had the fungal infection with predominant genus Aspergillus (50.3%), Penicillium (34.7%), and Fusarium (11%). A total of 63% (649/1031) of infection with Aspergillus section Nigri, of which 60 isolates were selected for analysis of genetic variability that resulted in 4 clusters. Representatives of clusters were identified by the calmodulin gene. Isolates from cluster I were subdivided into A-I and identified as A. niger (16 isolates) and the isolates of clusters B-I, II, and III were identified as A. welwitschiae (43 isolates). Besides, an isolate of the IV-cluster was identified by A. luchuensis. Further, we used the multiplex PCR to verify genotypes of 59 isolates, and none of these had OTA production-associated genotype. Moreover, 19 A. welwitschiae and 15 A. niger were FB2 production-associated genotype. Our study is the first report to the incidence of garlic infection in Brazil and to show that A. welwitschiae causes most of these infections.