SEED-BRONE MYCOFLORA OF IMPORTANT CROP PLANTS WITH SPECIAL REFERENCES TO TOXIGENTIC SPECIES OF FUSARIUM

Abstract

Seed samples of wheat, com, millet, sorghum and barley obtained from various parts of Pakistan were studied for seed-borne mycoflora by simple blotter method and deep freezing method. Of the seed-borne fungi, 12 genera and 21 species from 19 samples of wheat, 10 genera and 20 species from 35 samples of corn, 15 genera and 31 species from 25 samples of millet, 14 genera and 23 species on 27 samples of sorghum and 11 genera and 17 species from 14 samples of barley were isolated and identified. Fusarium proliferatum, Fsubglutinans, Stemphylium sp., Aspergillus sulphureus, A.candidus and Drechslera halodes on corn; Rhizoctonia solani and Fsubglutinans on wheat; D.halodes, Fequiseti, F. clamydosporum, Flongipes, F proliferaium, Fsubglutinans, F pallidoroseum, F. solani, Chalara sp., Choanephora sp., D.tetramera, Trichothecium sp., Cladosporium herbarull1, Trichoderma sp., Cephalosporium sp., and Stemphyliull1 sp., on millet: Fsubglutinans, Piptocephalis sp., and Synrephalastrum receillosuill on sorghum and Aspergillus niger, Cephalosporium sp., Cladosporium herbarum, Drechslera dematioidea, Stemphylium sp., and Ulocladium sp., on barley are new records from Pakistan. Phytotoxic effect of Fusarium spp., on seedling growth of wheat, corn, millet and sorghum, and on leaves and roots of wheat seedlings was observed. Effect of Fusarium culture filterates decreased growth of seedlings. The effect of temperature, moisture content and storage period on seed-borne mycoflora was examined where 19% moisture content of barley and 13% of wheat, corn and sorghum at 20°C was found to be most favourable for the growth of storage fungi. Interaction of Fusarium spp., with other fungi in vitro was also studied. In dual culture plate assays, Trichoderma hamatum showed inhibition in growth of Fusarium oxysporum. F. pallidoroseum, F. sporotrichioides, F. moniliforme, Fsubglutinans, F.proliferatum, Fequiseti, Flongipes, Fscirpi and F. solani producing zone of inhibition. Trichoderma hamatum showed antagonistic activity against Fusarium spp., in vivo. Thin layer chromatography technique was used to investigate mycotoxins and other secondary metabolites of Fusarium spp. Derivatives of zearalenone were detected from F.equiseti, F moniliforme, F.oxysporum, F proliferatum, F. pallidoroseum. F. solani, F.sporotrichioides and Fsubglutinans. Among naphthaquinone pigments cis-dihydrofusarubin from Flongipes, F. moniliforme, F. oxysporum, F. proliferatum and Fsubglutinans; nectriafurone from Fequiseti, F. moniliforme, F. oxysporum. F. pallidoroseum, F. solani and F. Subglutinans; isomarticin from F.equiseti and F. pallidoroseum; marticin from. F pallidoroseum and F solani; bostrycoidin from F moniliforme and javanicin from F pallidoroseum were detected. F.moniliforme and Fsubglutinans were found to produce consistently a characteristic reddish orange and a dark brown pigment respectively. These pigments could be useful in identifying the two species. Preparative thin layer chromatography was used to isolate the secondary metabolites produced by Fusarium spp. From F moniliforme five compounds were separated at different Rf values. The molecular weigh. and elemental formulae of these compounds were identified. A simple dichotomous key has been proposed for the identification of the 11 Fusarium spp. The key is based on the TLC profiles of secondary metabolites of Fusarium spp., and their growth response to the presence of tannin.