Effects of growth stages, temperature, and vertical distribution of infested residue on soybean brown stem rot incidence and severity
Date
1997
Authors
Ramasubramaniam, Harikrishnan
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Yang, X. B.
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Abstract
Growth chamber studies were conducted to quantify the influence and the interaction of plant age and temperature on infection by P. gregata and on brown stem rot development. Growth stages of the soybean cv. 'Sturdy' ranging from VC to R1 were generated using four temperatures, 15, 20, 25, and 30 C, along with three transplanting intervals of 14, 21, and 28 days after planting. At each transplanting interval, plants were transplanted into infested and sterile soils, and maintained at 15, 20, 25, and 30 C for disease development. Temperature significantly affected both incidence and disease severity (P = 0.0001). Generally, increasing temperature decreased disease incidence, severity and amount of isolation. Disease incidence and severity were greater at 15 and 20 C than at 25 and 30 C. Data on growth stages were obtained by pooling across infection temperatures x transplanting intervals. Plants at younger vegetative stages had three times greater incidence and 30 to 50 times greater severity compared to plants in advanced vegetative stages and plants in bloom.
Disease incidence and severity decreased with increase in transplanting intervals. There was significant transplanting interval by incubation temperature interaction for disease development (P = 0.006). The intervals had a more profound effect on disease incidence and severity at 25 and 30 C than at 15 and 20 C. Our results show that both temperature and physiological age have significant influence on infection and disease development. Two greenhouse studies were conducted to determine the effects of infested soybean residue placement and size on the development of brown stem rot. Study 1 had three sizes of infested residues and four depths of placement. Study 2 had two sizes, three depths of placement, and three densities of infested residue. Results of study 1 showed no significant differences in incidence and severity across all residue sizes and depths.
However, in the second study, residue sizes and depth of placement had significant effects on both incidence and severity. Mixing at the bottom 5 cm had significantly lower incidence and severity in comparison to the other two placements with both residue sizes. There were no significant differences in disease incidence and severity among densities.
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