Diversity of toxic and phytopathogenic Fusarium species occurring on cereals grown in Karnataka state, India

A total of 198 cereal samples (53 maize, 54 sorghum, 37 paddy and 54 wheat) were collected from 11 districts of Karnataka to understand the percent infection (PI), relative density (RD) and their frequency (Fr) caused by Fusarium spp. All samples were screened by agar plating method using MGA 2.5 agar media and incubated at 25 ± 2 °C for 3-5 days. The study revealed the association of 10 different Fusarium species known trichothecene producers such as Fusarium acuminatum, F. avenaceum, F. crookwellense, F. culmorum, F. equiseti, F. graminearum, F. nivale, F. poae, F. sambucinum and F. sporotrichioides along with non-trichothecene producers like F. anthophilum, F. oxysporaum, F. proliferatum, F. semitectum, F. solani, and F. verticillioides. All the ten isolated potential trichothecene producing Fusarium species were analyzed for their ability to produce trichothecenes by using thin layer chromatography method. The highest infection of Fusarium spp. in maize was by F. verticillioides with PI of (2.95 %), with RD of (15.16 %) and highest Fr was by F. graminearum (79.24 %) and the lowest was F. avenasium with PI of (0.13 %). For sorghum maximum PI was by F. verticillioides (3.02 %), with F. graminearum having highest RD (14.39 %) and with F. verticillioides highest Fr. (72.22 %). In paddy highest PI was by F. verticillioides (3.21 %) and the least was by F. avenaceum (0.09 %). Similarly in wheat the highest PI was by F. verticillioides (2.76 %) while lowest was by F. avenaceum (0.10 %). The highest Fr was with F. graminearum (79.62 %) while the lowest was by F. avenaceum (3.70 %) and the highest RD was by F. graminearum (22.04 %) and lowest was by F. solani (0.72 %). The manually identified Fusarium spp. were further confirmed by PCR-based detection using ITS1 and ITS4 primers followed by sequencing of the PCR amplicons. PCR studies confirmed that all the tested fungal isolates belongs to Fusarium spp. with the amplicon size of 600 bp. Sequencing and the blast data from NCBI data base confirmed the sequence similarity of 99 % to the genus Fusarium and accession numbers were obtained. Chemotyping studies showed that the isolated Fusarium species are known to produce different types of trichothecenes. The study revealed the diversity in phytopathogenic Fusarium spp. in major cereal crops growing in different agro-climatic regions of Karnataka, India.