Effect of time of harvesting, storage and fungicide seed dressing on soybean seed health and germinability

Abstract

A key constraint to soybean (Glycine max) production worldwide is the rapid loss of viability after harvest. This study examined effects of time of harvesting, moisture content, storage period and germicide treatment on the fungal flora infection and germinability of two local soybean cultivars (Nam 1 and Nam 2). At maturity (R8 stage), a portion of the soybean crop was randomly selected from each of six fields and divided into three sections that were harvested at 90, 97 and 104 days after planting (DAP). After harvesting, seeds were dried to two moisture levels, 9.5% and 12%. For each moisture content, the seeds were divided into 2 sub-samples, the one treated with Vitavax 200 FF fungicide at rate of 3 ml kg-1, and the other was left untreated (control). Each sub-sample was then packed in polythene bags and tightly sealed and stored at room temperature (25 ± 2°C) and subsequently assayed every 30 days for three months using International Seed Testing Association procedures to determine levels of fungal flora infection and seed germinability. Results indicated that time of harvesting and fungicide treatment significantly influenced incidence of fungal flora and seed germinability, regardless of the season of growth and variety. The highest percentage germinability was recorded from the earliest harvested seeds (R8) compared to the late harvested seeds (7 - 14 days after R8). Seed dressing with Vitavax 200 FF significantly reduced levels of seed-borne fungi and improved germinability compared to the untreated seeds, although this varied with seed moisture content in storage. However, storage period had no significant effect on soybean seed germinability and incidence of most fungal micro-flora. Varietal and seasonal effects were also not significant for most fungal microflora species, except Cercospora kikuchii and Penicillium spp. The fungal microflora identified were, Aspergillus flavus, A. niger, Alternaria spp., Cercospora spp., Cercospora kikuchii, Fusarium spp., F. equiseti, F. oxysporum, F. moniliforme, F. semitectum, Phoma spp., Phomopsis spp., Penicillium spp., Cladosporium, Curvularia spp. and Colletotrichum truncatum. These results imply that soybean should be harvested at R8 stage, and seeds dressed with a fungicide so as to reduce fungal microflora incidence and increase germinability.