Severity of Phomopsis Seed Decay, Seed Quality Evaluation, and Field Performance of Soybean
- Gonzalo Zorrilla,
- Allen D. Knapp and
- Denis C. McGee
The ability of seed quality tests to predict field performance of soybean seed lots with different incidences of infection by the causal agents of phomopsis seed decay (PD), was evaluated. Different seed infection levels were induced in one ‘Corsoy 79’ soybean seed lot by exposing naturally infected pods to 0, 3, 4, or 5 d at >95% relative humidity and 25 °C. Seeds were then removed from pods and dried. Seed quality wase valuated by germination tests on creped cellulose wadding (Kimpac), rolled towel, and sand and by cold, accelerated aging (A.Aging), tetrazolium (TZ), and conductivity tests. Field emergence of these seeds was evaluated at two locations and two 1991 planting dates in Iowa. Differences between laboratory germination test results for seeds with low (6.4 and 11.5%) infection levels were minor. At higher infection levels (18.2 and 32.4%), test differences were as large as 23%.P homopsis-diaporthine fection was located primarilyin the seed coat with lesser infection levels in cotyledons. Cotyledonary infection was not associated with variation in test results, but seed coat infection was, as evidenced by greater numbers of infected-abnormal seedlings in Kimpac and towel tests than in other tests. Field emergence declined with increasing PD seed infection at all sites and planting dates. Kimpac, towel, sand, A.Aging, and cold tests gave good estimates of field emergence at seed infection levels to 18.2%, but at 32.4% infection, Kimpac and towel tests underestimated field emergence. Tetrazolium and conductivity tests overestimated seed quality at low and high infection levels.
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