|Keywords (Extracted from title, table of contents and abstract of thesis)
seed -borne fungi, sunflower, macrophomina phaseolina, rhizoctonia solani, fusarium moniliforme, f. solani, pathogenic fungi, saprophytic fungi, aspergillus flavus, a. niger, aflatoxins, mycotoxin, mycoflora
Using blotter, agar plate and deep-freezing methods as recommended, by ISTA, the seed-borne mycoflora of 20 sunflower seed samples collected from different parts of Pakistan was examined. Of the 22 genera and 38 species of fungi isolated, the pathogenic fungi encountered were Macrophomina phaseolina, Rhizoctonia solani, Fusarium moniliforme, F. solani, whereas saprophytic fungi such as Aspergillus flavus and A. niger were predominant. Component plating of sunflower seeds showed that pericarp was infected by greater number of fungi followed by seed coat, cotyledons and axis (radicle and plumule). F. Solani, H. phaseolina, R. solani were also isolated from axis of seed. Reduced number of fungal species in surface sterilized seeds indicates that most of the fungi were located on pericarp followed by seed coat, cotyledons and axis. Blotter method showed greater infection of fungi on seed parts followed by agar plate and deepfreezing methods. H. phaseolina, Fusarium spp., and R. solani showed pre and post-emergence infection of seedlings on plain water agar whereas seed inoculation and artificial infestation of soil showed highest root infection and, reduced plant growth. In pathogenicity test disease, severity increased with increasing inoculum of the pathogen in soil.
Of the different fusarium spp., F. moniliforme, F. solani, F. semitectum and F. equiesti were isolated from sunflower seed. Using TLC technique, 3% isolates of F.moniliforme produced butenloide, nectriafuran, javanicin and norjavanicin, 10% isolates of F. solani produced cisdihy drofusarubin whereas all isolates of F.equiseti and :3% isolates of F. semitectum produced nectriafuran. Of the 24 samples or sunflower seeds collected from different parts of Pakistan, 13 samples showed the presence of aflatoxin B1 including 5 in which B1 and B2 were produced. Upto 437 μg/kg of aflatoxin B1 and B2 were detected in seed samples collected from Sindh. Out of 41 isolates of A. flavus, 29 isolates produced aflatoxin B1 including 8 which also produced aflatoxin B2 where up to 467 μg/l of aflatoxin B1 and 234 μg/l of aflatoxin B2 was detected. Highest amount of aflatoxin was produced by sclerotial isolates of A. flavus as compared to non sclerotial strains. Amount of aflatoxin showed positive correlation with number of sclerotia used for inoculating the sunflower seed substrate .Sunflower seeds with 6, 10 and 15% moisture and stored at 4, 15, 20, 25, 30, 35 and 40oC showed a gradual reduction in germination of seed with increase in storage time. Infection of A. flavus and subsequent aflatoxin production was less at low temperature and low moisture. Incidence of pathogenic fungi viz., Fusarium spp., H. phaseolina and R. solani decreased with increase in storage time. At 15% moisture and 40C, production of aflatoxin 81 was 131,961 Vg/kg and 82 was present in traces as compared to 30°C where 20,115 vI/kg of aflatoxin B1 and 15,890 vg/kg aflatoxin 82 were detected. Sunflower seeds at 6 and 15% moisture when treated with propionic acid @ 250 and 000 ppm and stored at 30oC showed a reduction in A. flavus infection and aflatoxin production with increase in storage tine. Similarly, treatment of sunflower seeds with ammonia gas for 10 minutes or above reduced infection of A. flavus and subsequent aflatoxin production during storage .Seed treatment with fungicides viz., Benomyl, Captan and Bay tan reduced infection of A. flavus and other fungi with an increase in germination of seeds. Production of aflatoxin also reduced due to reduction in A. flavus infection. Seed treatment with NaC1 and Ocimum sanctum leaf powder also reduced aflatoxin production.