RESEARCH ARTICLES/INFORMATION

Research Category: Soybean Disease and Insect Control Year: 2004 Researcher: Allen Xue Institution: AAFC Topic: Control of phomopsis seed rot of soybean in Ontario Funding: $10,000 Research Details: Phomopsis-Diaporthe complex (PDC), caused by Diaporthe phaseolorum var. sojae, D. phaseolorum var. caulivora, and Phomopsis longicolla, is an important soybean disease in Ontario. The objectives of the present project are to compare and select effective seed treatments, to evaluate variety resistance in soybean, and to determine the predominant species of the pathogens in Ontario. Field trials were conducted using 3 seed size lots to evaluate 19 seed treatments and treatment combinations at 2 locations in Ottawa in 2003, the second field season of a 3-year studies. Of the 3 seed sizes, large and medium seed had the greater emergence and yield than the small seed. There were no statistical differences among the three seed sizes in root rot severity and thousand seed weight (TSW). The results generally agree with the findings of 2002. All of the 19 seed treatments significantly reduced root rot severity, compared to the untreated controls. Nine treatments increased emergence significantly, of these, Allegiance FL + Vitavax FL was the best, increasing emergence by 8.1%. The other treatments increased emergence ranging from 3.8-5.2%. Dividend XL RTA is the only treatment showing a significant effect on yield, increasing yield by 6.7%. None of the treatments increased TSW significantly compared to the untreated checks. A total of 463 sobyean varieties/lines were evaluated at 10 locations in 5 crop heat unit (HU) regions in 2002. Sixty five varieties and lines were tentatively identified with resistance to PDC. All three PDC pathogens were isolated from the infected plants. Stem infection was common, at 20-30%, pod and seed infection was low, at 1-3% and <1.5%, respectively. The recovery of PDC pathogens was not affected by HU in Ontario. Phomopsis longicolla was the predominant species of the three PDC pathogens, representing 63% of the population. File: