INFLUENCE OF PLANTING DATE AND SEED TREATMENT ON EMERGENCE AND PREHARVEST SEED INFECTION IN SORGHUM

Abstract

Low seed germination, early seedling death and infection of seeds by fungi before harvest are major problems in sorghum. Seeds of four sorghum cultivars treated with three fungicides were planted at different dates to determine if seed treatment and planting dates influenced seed germination, post emergence seedling death and preharvest seed infection. Germination was significantly lower when seeds were planted at soil temperature less than 20(DEGREES)C. Seed treatment with fungicides increased germination of the four sorghum cultivars when seeds were planted at low temperatures, but not at high soil temperature. The effect of seed treatment on germination at higher soil temperature was inconsistent. Post emergence seedling blight was higher when seeds were planted at higher temperature. Seed treatment with fungicide did not consistently reduce post emergence seedling death for all cultivars. Planting date influenced preharvest seed infection by various fungi and subsequent seed germination. Seeds obtained from May planting had significantly lower germination than those from June planting dates. Of the fungi isolated; Alternaria spp. and Fusarium spp. especially F. moniliforme, were the most prevalent. The incidence of Fusarium spp., was significantly higher on seeds from May than from June planting. Correlation analysis indicated that incidence of Alternaria spp. and seed germination were positively correlated, whereas the incidence of Fusarium spp. and germination of seeds from May plantings were negatively correlated. Greenhouse study of seedlings grown from Fusarium or Alternaria infected seeds showed that seedlings derived from Fusarium infected seeds were stunted, with reduced root and shoot growth; symptoms similar to post-emergence seedling blight in the field. Histopathological and scanning electron microscope studies showed that seed infection in the field by F. moniliforme is more damaging to sorghum than infection by other fungi. Of the sorghum cultivars, IS4225 was resistant to Fusarium seed infection. The results show that planting sorghum at soil temperature above 20C improves germination. At lower soil temperature, seed treatment with fungicides increased emergence. Seedborne Fusarium spp. reduces seed viability and might be involved in post emergence seedling blight