Submitted to: Journal of Crop Improvement
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 27, 2012
Publication Date: September 12, 2012
Citation: Bellaloui, N., Mengistu, A., Zobiole, L.H. 2012. Phomopsis seed infection and time of harvest effects on seed phenol, ligin, and isoflavones in maturity V soybean genotypes differing in phomopsis resistance. Journal of Crop Improvement. 26:693-710. Interpretive Summary: Phomopsis is a major soybean seed decay disease in the midsouth USA, resulting in poor seed quality. Currently, there are no phomopsis resistant cultivars available in the market. Therefore, looking for other alternative to control the disease is essential. Phenolics are natural compounds that are produced by plants and have been reported to be involved in disease resistance and plant defense mechanism against diseases. Also, phenolic compounds such isoflavones have been reported to have antioxidant properties and beneficial health effects to human. Therefore, understanding the production and response of these compounds to phomopsis in the Early Soybean Production System is crucial. Seed production and quality of phenolic compounds (total phenol, lignin, and isoflavones) were evaluated in seed of soybean genotypes susceptible, moderately resistant, and resistant to phomopsis under irrigated and nonirrigated conditions. The concentration of seed phenolic compounds was significantly higher in moderately resistant and resistant genotypes than susceptible genotypes under irrigated and nonirrigated conditions. Moderately resistant and resistant genotypes with higher phenolic compounds had also higher boron concentration, indicating a possible involvement of boron in phenolic compound production and structural support of soybean plants. The current research demonstrated that genotypes with higher phomopsis seed infection had lower phenolic compounds, suggesting that the level of phenolic compounds is involved in defense mechanisms and associated with the level of resistance to phomopsis. Soybean breeders may be able to use phenolics as biomarkers for selecting soybean genotypes for higher resistance to phomopsis and also for higher desirable seed phenolics such as isoflavones under biotic and abiotic stress environment.
Technical Abstract: The objective of this research was to evaluate phenolic compounds (total phenol, lignin, and isoflavones) in seed of susceptible (S), moderately resistant (MR), and resistant (R) soybean genotypes to phomopsis seed decay disease under irrigated and nonirrigated conditions. Seeds were evaluated at physiological maturity stage (R8) and 15 days later to test for weathering effects. Results showed that the concentration of seed phenolic compounds were significantly (P=0.05) higher in R and MR genotypes than S genotypes under irrigated and nonirrigated conditions. Seed phenolic compound concentrations were significantly lower in S genotype than MR or R genotypes. Cell wall boron percentage was significantly higher and total boron was significantly lower is S genotypes than MR and R genotypes. The current research demonstrated that genotypes with higher phomopsis seed infection had lower phenolic compounds. The higher cell wall percentage in S genotypes indicated a possible involvement of boron in defense mechanism against phomopsis disease. The decrease in phenolic compounds concentrations, especially in S genotypes in seed collected 15 days after R8 indicated the weathering effects on seed coat and cell wall deterioration, may be due to nutrients leakage. Soybean breeders may be able to use phenolics as phenotypic trait and biomarkers for selecting soybean genotypes for higher resistance and for higher seed nutritional qualities.