Abstract: A study was undertaken to find the biodiversity of Fusarium spp. on stored cereal grains (maize, sorghum and paddy) collected from different places of Karnataka State, India by testing seed health. Altogether ten Fusarium species were found to be associated with different cereals such as, F. moniliforme (25.35%), F. graminearum (15.5%), F. proliferatum (14%), F. oxysporum (12.68%), F. avenaceum (9.86%), F. subglutinans (8.45%), F. semitectum (5.63%), F. poae (4.22%), F. sporotrichiodes (2.81%) and F. anthophilum (1.40%). The occurrence of Fusarium species were higher in maize 43.66%, followed by sorghum 38.02% and very low in paddy 18.31%. Among them F. moniliforme, F. avenaceum, F. subglutinans, F. semitectum, F. graminearum and F. oxysporum were common on all the three cereal grains.
Introduction
Biodiversity is a unique characteristic of living organisms. One of the most fascinating and attractive aspects of the microbial world is its extraordinary diversity (Prescott et al., 1996). Molds are ubiquitous in nature and domestic environments (Langseth et al., 1993). As a result fungi can easily contaminate raw food materials both during their growing period and after harvest.
Food is the first and foremost source of nutrition. Cereals and millets form the staple food of the human race. More than 70% of the total food is served by the plant and plant products-cereals and millets (Pitt et al., 1985). These include rice, maize, wheat, barley, oats, rye, sorghum, pearl millets, ragi and many other types of millet. The role of fungi (molds) in the loss of stored products (cereals & millets) can not be ignored. Besides Aspergillus, Penicillum and Alternaria; Fusarium also attacks the stored cereal grains. Members of the genus Fusarium are among the most widespread and important plant pathogens in the world. Most of the crops are invaded by one or more species of Fusarium. Members of this group of fungi are known for producing mycotoxins in cereal grains (Bacon et al., 1992 and Marin et al., 1998).
However, studies on biodiversity of Fusarium Liseola species on maize grain are very limited (Marin et al., 1998). Not much work has been done to know the biodiversity of Fusarium spp. in cereal grains at Karnataka State, India. Hence the present piece of work was undertaken to identify the associated species of Fusarium and their occurrence in different stored cereal grains.
Materials and Methods
The experiment was conducted at the Laboratory of Department of Studies in Microbiology, Mysore University, India during the period from August 2000 to June 2001.
Collection of sample: Freshly harvested seed sample of maize, sorghum and paddy comprising of about 250 grams were collected from different places of Karnataka State, India. Then the seeds were kept in brown paper bag and stored at normal room temperature in the laboratory of Department of Studies in Microbiology, Mysore University, India over a period of 3 months.
Seed health test: Three replicated samples of maize, sorghum and paddy comprising 200 seeds were drawn randomly for seed health analysis following blotter method (ISTA, 1996).
Identification of Fusarium spp.: All the seed samples were assayed for the presence of fungal pathogen using stereo-binocular microscope. Identified Fusarium spp. under stereo-microscope were transferred to Potato Dextrose Agar (PDA) medium and then incubated for 4-7 days at 28 °C ±3. After incubation, temporary slides were mounted and examined under compound microscope with the help of relevant taxonomic books identified till species level according to the methods of Gilman (1956), Booth (1971) and Nelson et al. (1983).
Results and Discussion
The findings on this investigation for the occurrence of biodiversity of Fusarium spp. on stored cereal grains are in Table 1 & 2 and Fig. 1 & 2. Ten Fusarium spp. such as F. moniliforme, F. proliferatum, F. subglutinans, F. avenaceum, F. semitectum, F. oxysporum, F. graminearum, F. anthophilum, F. poae and F. sporotrichiodes were detected. The occurrence of these Fusarium spp. varied significantly depending on the type of cereals. Percent yielding Fusarium species were higher in maize followed by sorghum and very low in paddy. Distinguishable characteristics of Fusarium spp. obtained from the stored cereal grains are presented in Table 2.
| Table 1: | Occurrence of Fusarium spp. on stored cereal grains in Karnataka State, India |
Occurrence of Fusarium spp. on stored cereal grains: The occurrence of Fusarium species was higher in maize 43.66%, followed by sorghum 38.02% and very low in paddy 18.31% (Fig. 1). Bacon et al. (1992) found similar results as he observed mean level of infection by Fusarium of 8.4% to 36.2% in maize, which was the highest among other grains, including wheat, rice, barley and oats. Fusarium is a contaminant of 88 - 100% of the corn-based products for animal consumption as whole corn kernels, screening, and feeds (Marin et al., 1998). An extensive study by Sala (1993) on Spanish feed samples revealed that Fusarium species contaminated 14 of 15 samples of maize, 3 of 8 of wheat, 7 of 17 of barley, and 14 of 17 sorghum.
| Table 2: | Distinguishable characteristics of Fusarium spp. obtained from the stored cereal grains in Karnataka State, India |
| Fig. 1: | Percent yielding Fusarium spp. obtained from different stored cereals in Karnataka, India |
| Fig. 2: | Different isolates of Fusarium spp. obtained from stored cereals in Karnataka, India |
The occurrence of F. moniliforme was the highest (25.35%) in stored cereal grains followed by F. graminearum (15.5%), F. proliferatum (14%), F. oxysporum (12.68%), F. avenaceum (9.86%), F. subglutinans (8.45%), F. semitectum (5.63%), F. poae (4.22%), F. sporotrichiodes (2.81%) and significantly lowest F. anthophilum (1.40%) (Fig. 2). Study of Sala (1993) revealed that almost 100% of the Fusarium strains from maize, wheat and other feed samples were of F. moniliforme and F. proliferatum, while in barley the percentage was 60%. F. moniliforme strains that occur on cereals and especially as a major fungal contaminant on maize (Castella et al., 1999).
Maize sample was found to be infected by F. moniliforme (61.11%), F. proliferatum (70.0%), F. subglutinans (50.0%), F. avenaceum (14.29%), F. semitectum (25.0%), F. oxysporum (22.22%), F. graminearum (36.36%), F. anthophilum (100%), F. poae (33.33 %) and there was no infection of F. sporotrichiodes.
Sorghum sample was found to be infected by F. moniliforme , F. proliferatum, F. subglutinans, F. avenaceum, F. semitectum, F. oxysporum, F. graminearum, F. anthophilum, F. poae and F. sporotrichiodes, 27.78, 30.0, 33.33, 28.57, 25.0, 44.44, 54.55, 0, 66.67 and 100% respectively (Table 1). However, in sorghum F. sporotrichiodes was found the most prevalent (100%) but F. anthophilum was absent.
Paddy sample was found to be infected by F. moniliforme , F. subglutinans, F. avenaceum, F. semitectum, F. oxysporum and F. graminearum with 11.11, 16.67, 57.14, 50, 33.33 and 9.09%, respectively (Table 1). In paddy, F. avenaceum was found highest (57.14%) followed by F. semitectum (50%) while F. proliferatum, F. anthophilum, F. poae and F. sporotrichiodes were absent.
The predominant species isolated from samples of maize, sorghum and paddy was F. moniliforme. These results are very much similar to those of previous investigations of Castella et al. (1999) and Marin et al. (1999).
F. moniliforme, F. proliferatum and F. subglutinans were the most commonly associated fungi with maize production in North America and many other temperate regions of the world (Munkvold et al., 1997). Species of F. moniliforme and F. proliferatum have been frequently (8 to 36%) isolated from maize (Marin et al., 1999). Again Fusarium spp. are capable of causing seedling diseases, root rots, stalk rots, and ear rots of maize, as well as damaging stored grains by producing mycotoxins (Cotton et al., 1998 and Munkvold et al., 1997). In addition to corn, F. moniliforme has been isolated from grains, including wheat, rice and oats (Marin et al., 1999).
Identified characteristics of Fusarium spp.: The identified characteristics of different Fusarium spp. are presented in Table 2 based on the manual of Gilman (1956) and Nelson et al. (1983). However, biodiversity is very important to know the nature of the organisms associated with the cereal grains which could pave the urgency of molecular studies of the organisms.