Influence of soybean cultivar, seed quality, and temperature on seed exudation and Pythium disease development

Seedling diseases may cause a 100% reduction in seedling stand in a disease favorable conditions. Among soilborne pathogens that cause soilborne diseases pythium spp. are the most common fungal pathogen and are found in all arable soils in the world. Pythium can cause seed rot, and pre- and post-emergence damping-off. Different Pythium spp. are active at different temperature ranges. Seed exudates, exude during seed germination and seedling growth contain carbohydrates which are mainly sugars, amino acids, vitamins, hormones, and organic acids. The quantity of carbohydrates and other nutrients in exudates and Pythium disease development has a positive correlation. Experiments consisted of two soybean cultivars (Archer and Hutcheson) and three seed quality levels (high: above 80%, medium: 60 to 79%, low: below 60% germination). Temperatures 10, 15, 20, 25, 30, and 35°C were used to test the effect of temperatures on disease development in different seed treatments. Five Pythium treatments: P. vexans, P. aphanidermatum, P. ultimum, P. irregulare, and noninfested were used. Data were collected on average root, shoot, and seedling dry weight, seedling emergence, and root discoloration. Seed exudates were collected from each seed treatments for 72 hours and Capillary Gas Chromatography was used to analyze sugars and organic acids. The study concluded that Archer was more resistant than Hutcheson to Pythium spp. at all temperatures tested. Also, the total carbohydrates and organic acids in exudates of cultivar Archer was lower than that of Hutcheson, and decreasing seed quality increased the amount of nutrients in seed exudates of both cultivars.;Amount of nutrients in seed exudates had a negative correlation for percent live seedlings and a positive correlation with percent root discoloration. Also, this study showed that P. ultimum was active at low temperatures (at 10°C) and P. aphanidermatum was active at high temperatures (at 30 and 35°C). P. vexans and P. irregulare were active at a wide temperature range.