Date Published: February 13, 2016
Publisher: Springer Berlin Heidelberg
Author(s): H. Nagaraja, G. Chennappa, K. Poorna Chandra Rao, G. Mahadev Prasad, M. Y. Sreenivasa.
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.
Cereals are mainly cultivated for food, feed and fodder. These are grown in greater quantities worldwide than any other crop to provide food energy as staple crops. The cereal grains such as maize, sorghum, wheat, rye, barely and paddy are commonly contaminated with fungi. Fungi are one of the major contaminants of food and feed grains causing biodeterioration. These grains are highly nutritious and as such they are prone to get contaminated at any point of time from harvest to storage. A wide range of fungal species including Aspergillus, Fusarium, Penicillium, Alternaria, Cleviceps, Monascum, Cephalosporium, Drechslaria, Nigrospora, Trichoderma have been reported to infect to cereal grains (Bhattacharya and Raha 2002).
Fungal contamination of cereals with trichothecene producing Fusarium spp. is a global problem and it has been reported from different parts of the world. Scientific concern has been bestowed to understand the diversity, incidence and management of trichothecene producing Fusarium spp. in wheat and other cereals. However, data on diversity of trichothecene producing Fusarium spp. on cereal grains are very limited in Karnataka, India. In order to collect more information on this, a total of 198 samples were collected covering different districts of Karnataka. Mycological examination of 53 maize, 54 sorghum, 37 paddy and 54 wheat samples, revealed the occurrence of 10 different trichothecene producing Fusarium spp. including F. avenaceum, F. crookwellense, F. culmorum, F. equiseti, F. graminearum, F. nivale, F. poae, F. sambucinum and F. sporotrichioides. However, the other three Fusarium species reported in the present study such as F. verticillioides, F. proliferatum and F. anthophilum are known as the potential producer of fumonisins (Sreenivasa et al. 2008). Occurrence of these species varied between cereals with respect to their diversity and differences were observed in percent incidence, frequency and relative density.