The Effect of Pythium ultimum and Soil Flooding on Two Soybean Cultivars

Abstract

The effect of flooding and Pythium ultimum on soybean, Glycine max, was determined in a series of greenhouse experiments using the cultivars Hutcheson and Archer. Seeds were planted into pasteurized soil either not infested or infested with sand-cornmeal inoculum of P. ultimum and either flooded at emergence for 2 days or at the four leaf node stage (V4) for 5 days. A nonflooded control was included in each experiment. Seeds placed directly into infested soil resulted in little or no stand for Hutcheson regardless of flood treatment, whereas stand was reduced for Archer only in the flooded infested soil treatment. Additional experiments were conducted by placing seed onto a 2- to 5-mm layer of pathogen-free soil on top of the infested soil. Flooding at emergence reduced plant height, growth stage, and top dry weight for Hutcheson and root fresh weight for both cultivars. Greater reductions for Hutcheson in root weight, and top dry weight in P. ultimum-infested soil in the soil layer experiments, also indicated that Hutcheson was more susceptible than Archer. Flooding alone decreased root weights, and infestation with P. ultimum reduced weights further resulting in an additive effect. This also was the case for plant height, growth stage, and top dry weight for Hutcheson for flooding at emergence. Root discoloration was greatly increased for both cultivars in infested soil flooded at emergence. Similar results were found when plants were flooded at V4; however, the effect was not as great as with flooding at emergence. These studies indicate that Pythium damping-off and root rot may account for a portion of the negative response of soybean to flooding. The results also indicate that Archer has some resistance to P. ultimum.

Root rot and damping-off of Aleppo pine seedlings caused by Pythium spp. in Algerian forest nurseries

“…Liquid cultures of fungi were prepared by adding inoculum discs and grass blades to sterile water in a Petri dish at 25°C. Inoculum was produced as described earlier (Kirkpatrick et al 2006) by adding 5 mm plugs of each isolate to a previously sterilized 500 ml flask containing 237.5 g of sand, 12.5 g of cornmeal and 80 ml of deionised water. Isolates were allowed to grow on the medium for 9 days, and the flasks were shaken every other day to disperse the inoculum evenly.…”

Resistance to Pythium Seedling Disease in Soybean

“…Placing seed directly on P. ultimum inoculum severely reduced stands of Hutcheson in non-flooded soils and there was no stand in flooded soils. (Kirkpatrick et al 2006a). With Archer, placing seed directly on the inoculum did not affect stand unless the plots were flooded and then stands were reduced by almost 65%.…”

“…Table 3. Plant stand for two soybean cultivars at seven days, after termination of flooding at emergence, when seed were planted directly into soil infested with P. ultimum or noninfested soil a (Kirkpatrick, et al 2006a). …”

“…Under these experimental conditions, most of the seedling disease was probably due to seed rot. In order to determine the effect of P. ultimum on root rot, Kirkpatrick et al (2006a) separated the seed from the inoculum with 2 to 5 mm of sterile soil (Table 5). This thin layer of sterile soil allowed the seeds to germinate before contacting the pathogen.…”

Pathogenicity of Pythium species causing seed rot and damping-off in soybean under controlled conditions

“…in causing seed rot involves placing seeds directly on a Pythium culture growing in a Petri dish (Broders et al 2007;Brown and Kennedy 1965;Dorrance et al 2004;Thomson et al 1971;Zhang and Yang 2000). Pre-emergence damping-off is commonly assessed using a pot assay, in which inoculum is mixed with soil or another growing medium and seeds are subsequently planted in the medium (Ali-Shtayeh et al 2003;Bates et al 2008;Broders et al 2007;Kirkpatrick et al 2006aKirkpatrick et al , 2006bZhang and Yang 2000). Alternatively, a plug of Pythium isolate can be placed directly on the hypocotyl to induce infection (Rosso et al 2008;Thomson et al 1971).…”