Aspergillus flavus from peanuts grown in Argentina: genetic variability and population structure

PILDAIN MARÍA BELEN; CABRAL DANIEL; VAAMONDE GRACIELA

Florianopolis, Brasil

Congreso; V Congresso Latino-Americano de Micotoxicología y IV Simposio em Armazenagem Qualitativa de Graos do Mercosul; 2006

Universidade Federal de Santa Catarina

Aspergillus flavus from peanuts grown in Argentina. Genetic variability and population structure. Pildain MB, Cabral D, Vaamonde G. Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires. Ciudad Universitaria, Pab. II, 4º piso Buenos Aires, Argentina. CP1428EHA. TE. 0054 11 4787-2706   Aspergillus flavus is well known as one of the principal producers of aspergilloses and aflatoxins, a class 1 carcinogen. Because of the importance of this mould on animal and human health, it is essential to determine their life cycles and distribution in nature. Argentina is a predominantly agricultural country and where exported grains have great acceptance in the world markets. As an attempt to contribute to the quality of those grains and improve the conditions for the agricultural workers, the objective of our study was to characterize the genetic diversity of A. flavus populations from different agroecological zones giving important information to determine which control measures are most effective in reducing A. flavus contamination. Population structure of A. flavus from stored seeds grown in different geographical areas analysed by using toxigenic potential, aflatoxin types B and G and cyclopiazonic acid (CPA) production, culture characteristics and vegetative compatibility groups (VCG) via complementation tests between nitrate-nonutilizing mutants. The A. flavus isolates were identified as members of either the L strain or S strain. In addition an effort was made to compare S strain from different countries using VCGs. The results indicated that more than 90% of the isolates (n= 196) were aflatoxin producers and almost 100% of them produce cyclopiazonic acid. The majority of the S strain produces aflatoxins type B and G. The percentage of the L strain is higher than S strain but this difference varies between agroecological zones. The results obtained indicate that genetic diversity of A. flavus in Argentina is elevated, with 0.66 VCG diversity index. This diversity was also indicated by the presence of many single-isolate VCGs as well as by the lower numer of VCGs that have members of different agroecological zones. Among 108 heterokaryotic isolates of A. flavus, 71 VCGs were found and none of the S strain from Argentina was compatible with those of other countries. Scarce VCGs contained isolates from widely separated peanut growing regions examined. S and L strains acts different, the aflatoxin producing potential of Aspergillus communities is higher when S strain is present but the conidia production is less than in L strains. The heterogeneity in the populations derived from peanut seeds at diverse locations in Argentina suggests that A. flavus populations have undergone spatial and temporal changes. Results from pairising of testers from Argentinean S strain with testers from Bénin, USA and Australia were not surprising results because of the big VCG diversity in A. flavus.Vegetative compatibility has been widely used to provide insights into the genetic structure of fungal populations and is a strong predictor of cladistics groupings. In order to accomplish the study of A. flavus in Argentina, it is necessary the identification of A. flavus isolates belonging to the same genotype or clone. The ability to characterize and monitor genetically identical strains from A. flavus populations should allow to determine how the disease is spread and which of the subpopulations are associated with aflatoxin and/or aspergilloses in our country.