Management of Diaporthe-infected soybean seed
Date
2021-12
Authors
Haafke, Alexandria Jade
Major Professor
Advisor
Mueller, Daren
Munkvold, Gary
Licht, Mark
Committee Member
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Abstract
Phomopsis (Diaporthe) seed decay is a disease that causes economic losses for farmers and affects the quality of soybean for planting. In the past, it was commonly suggested to sort out diseased seed, apply a seed treatment, and plant at a higher seeding rate when planting seed lots with high amounts of Diaporthe-infected seed and low germination rates. The fall of 2018 had an unusual amount of rainfall, leading to an outbreak of this disease in the soybean growing regions of the United States. While there have been studies on Diaporthe-infected seed in the past, studies with more modern seed treatments as well as published studies on seeding rates and yield potential were lacking. Seed was collected from the harvest of 2018 and 2019 to plant in the subsequent years to test the effects of seed treatments and seeding rates on Diaporthe-infected, low germination seed and to test if yield potential of this seed was the same for healthy, high-quality seed lots. The objectives of this research were to: (1) test if seed treatments with different modes of action affected plant stand, plant health, and yield of Diaporthe-infected seed and healthy seed, (2) determine if planting at a higher seeding rate will offset the low germination of Diaporthe-infected seed, and (3) evaluate if, at the same plant stand, would Diaporthe-infected seed have the same potential as healthy seed. Three small plot field experiments were conducted in 2019 and 2020 to test these objectives.
The seed treatment experiment showed seed treated with pyraclostrobin + fluxapyroxad + metalaxyl + clothianidin, a standard base treatment, or pyraclostrobin alone typically had the greatest stand, canopy greenness, and canopy coverage regardless of Diaporthe infection or germination level. Although seed treatment helped in these aspects, yield was not affected by seed treatment in 2019 or 2020 (P = 0.078 and 0.514). In the first year of this study only, seed lot affected yield where the healthy seed lot had about 9% greater yield than the diseased seed lot (P <0.001).
In 2019 and 2020, although the plant stands of the healthy seed lot were numerically and sometimes significantly greater than the diseased seed lot, yields were similar for both seed lots (P = 0.251 and 0.226). As seeding rate increased, so did the stand, canopy greenness, and canopy coverage. Although these plant health aspects were greater in the plots with higher seeding rates, plots planted at all four seeding rates resulted in similar yields each year (P = 0.942 and 0.092).
The yield potential experiment revealed that yield was not negatively affected (P = 0.196 and 0.455) when plant stand is the same for plots planted with Diaporthe-infected seed and healthy seed at approximately 247,000 plants/hectare. There were little to no differences in the plant health or yield between seed lots in both years.
Diaporthe can infect soybean seeds, sometimes at very high levels such as the case in 2018, but seed treatments and increased planting populations can offset the impact Diaporthe seed decay. Also, once stand is established, Diaporthe did not have any long-term effect on plant health or yield. These data can help farmers and seed industry mitigate the negative impacts of DSD.
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