DETECTION, IDENTIFICATION AND MANAGEMENT OF SEED-BORNE FUNGAL PATHOGENS ON FARMER-SAVED SOYBEAN (Glycine max (L.) Merrill) SEEDS

ABSTRACT

Soybean is afected by a wide range of diseases, many of which are seed-borne. Infection by seed-borne pathogens leads to seed rot, low seedling vigour and reduction in plant growth. Seed-borne fungal pathogens on farmer-saved seeds of soybeans were investigated by examining a total of eleven (11) seed samples from two districts (Saboba and Yendi) in the Northern region and one from CSIR-Savanna Agricultural Research Institute (CSIR-SARI). Appearance quality of farmer-saved soybean seed samples revealed the main categories of damaged seeds as shrivelled (ranging from 6% to 10.5%), discolored (8.3% to 12.5%), broken and cracked (5.5% to 12.5%). Four hundred seeds (400) from each seed sample were used. Seed sample obtained from Sunsong-Gbung in the Yendi district were found to have the highest proportion of discolored seeds (12.5%). Seed samples obtained from Zang district were observed to have the highest proportion (12.5%) of broken and cracked seeds. The blotter and agar plate incubation methods as described by International Seed Testing Association (ISTA) were used to identify fungi associated with the seed samples. A Completely Randomized Design with four replications was used. Two hundred (200) seeds from each seed sample were used with fifty (50) seeds per replication. A total of nine fungi were found to be associated with the soybean seeds evaluated using blotter and agar plate methods. Out of this number, four of them were identified as pathogenic on soybean and had high prevalence level before seed treatment applications as follows: Alternaria spp. (ranging from 9.0% to 14.2%), Cercospora spp. (9.0% to 11.9%), Fusarium spp. (9.8% to 15.2%) and Macrophomina phaseolina (7.8% to 13.4%). The other five fungi species were identified to be saprophytic. They had a high prevalence levels as well in the seed tested before seed treatment as follows: Aspergillus flavus (9.0% to 12.9%), Aspergillus niger (7.0% to 13.5%), Curvularia spp. (9.0% to 13.2%), Penicillium spp. (9.0% to 14.1%) and Rhizopus stolonifer (16.9% to 21.5%). Pathogenicity tests conducted on

iii

the four fungal isolates; Alternaria spp., Cercospora spp., Fusarium spp. and Macrophomina phaseolina to fulfil Koch’s postulate proved to be positive. A Completely Randomized Design with three replications was used. Nine potted plants were used for each treatment. All soybean plants inoculated with fungal isolates developed disease symptoms one week after inoculation. Re-isolation of fungal pathogens from diseased plants confirmed they were the causal organism of the symptoms that were observed. The use of Insector T 45 (Imidacloprid 350g/kg and Thiram 100g/kg), Monceren GT 390 FS (20% Imidaclopride) and 20% Pencycuron), Garlic extract (Allicin) and Neem (Azadirachtin) seed extract as seed treatments over a period of 90 days, led to a decrease in prevalence of fungal as well as an increase in seed germination and seedling vigour compared with the untreated seeds. Seeds treated with Monceren GT 390 FS over a period of 90 days had the highest reduction in fungal as well as high germination (85.0%) and seedling vigour (1360.1). Further studies should be conducted to determine bio-efficacy of the neem seed and garlic extract which have been proved to have some degree of antifungal effect in the study. Farmers should be educated on seed treatment measures before storage to prevent the build-up of seed-borne fungi which results in higher prevalence of fungi and poor seed germination.