Study on Fumonisin Accumulation in Different Grain Sorghum and Maize Genotypes in Iran
Fusarium verticillioides is one of the agents causes fusarium ear rot of corn and grain mold of sorghum too. Fusarium isolates obtained from different maize and sorghum fields were identified based on the morphological characters by using valid mycological keys. To confirm the morphological identification results, 17 F. verticillioides isolates were tested by species- specific primers and standard isolates as mating type testers for this fungus. To choose the most aggressive isolates their pathogenicity variation were evaluated in a greenhouse test based on a randomized completely design with three replications and 36 treatments. Susceptible maize stems were inoculated with infected toothpicks and were evaluated based on the length of necrosis after 10 days. In order to evaluate the reaction of different maize and sorghum genotypes to F. verticillioides and Fumonisin accumulation in their kernels, 10 maize and 10 grain sorghum genotypes were evaluated based on a RCBD with three replications at four locations during two years in separate trials. Maize ears were inoculated by Nail Punch method with a mixture of spore suspension (106 spore/ml) of seven virulent isolates. Sorghum panicles were also inoculated by spraying the mixture of spore suspension at 50% flowering stage and covering them with paper bags for two weeks. Evaluation was done using Disease Severity Index (%DS) two months after inoculation. Finally data analyzed by SAS software and means were compared by Dunkan test at 5% level. In this survey total fumonisin produced on different maize and sorghum kernels were analyzed by ELISA kits. The results of analysis of variance of pathogenicity test showed that there are significant statistically difference among isolates based on their virulence on maize stems. The results of maize experiments at all locations during two years demonstrated that genotypes 2 and 3 with 40.9% and 35.9% DS respectively were the most susceptible and genotypes 1 and 7 with 13% and 18.9% DS respectively were determined as the most resistant genotypes. Also genotypes 2 and 3 had the highest level of fumonisin with 72.6 and 65.3 ppm respectively and genotype 1 (K18) had the least level of fumonisin (8.9 ppm) in comparison to the other maize genotypes. There was a appropriate correlation between fumonisin contamination and disease severity measured on different maize genotypes (r = +0.93**). The results of sorghum experiments at all locations during two years demonstrated that genotypes 1 and 3 with 42.8% and 39.7% DS respectively were the most susceptible and genotypes 7 with 27.2% DS was determined as the most resistant genotype. As fumonisin analysis for sorghum kernels was done only in 2011, the results of sorghum experiments at all locations in this year demonstrated that there are significant statistically difference among genotypes based on fumonisin production although this range was so low in comparison to maize genotypes. There was a low correlation relationship between fumonisin contamination and disease severity measured on different sorghum genotypes. This is the first report of fumonisin analysis of sorghum hybrids in Iran.
Keywordsó Maize, Grain Sorghum, Fumonisin, Fusarium verticillioides.