Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2006
Publication Date: 2/3/2006
Citation: Bent, A.F., Hoffman, T.K., Schmidt, S., Hartman, G.L., Xue, P., Tucker, M.L., Hoffman, D.D. 2006. Disease- and performance-related traits of ethylene-insensitive soybean. Crop Science. 46:893-901. Interpretive Summary: Soybean cyst nematode (SCN) is the most economically damaging pathogen of soybean causing an estimated annual loss of one billion dollars to the soybean crop in the USA. The plant hormone ethylene plays an important role in many plant defense responses. To determine how ethylene responses contribute to defense against diseases of soybean, an ethylene-resistant mutant was tested against several soybean diseases, including nematodes. Disease responses are complex and often greenhouse and laboratory experiments differ from field trials. Therefore, several soybean diseases and ethylene responses were observed under laboratory, greenhouse and field conditions. In regard to nematodes, although it might be expected that a fully functional ethylene response would increase resistance to nematode infection, ethylene resistant plants showed the opposite response. The ethylene resistant mutant had fewer successful nematode infections than control plants. A better understanding of the role ethylene plays in plant defenses will greatly improve the ability of scientists and industrial partners to increase disease resistance in crop plants.
Technical Abstract: The plant hormone ethylene controls many beneficial plant responses, but because ethylene can promote undesirable chlorosis, senescence, disease severity and fruit over-ripening, plant lines that exhibit reduced ethylene responses have been developed for a number of species. Published studies of these lines have often used plants grown in a growth chamber or glasshouse. We previously isolated and characterized ethylene-insensitive soybean lines. The present study combined laboratory-based experiments with field performance trials. Lab experiments had indicated a slight increase in susceptibility to Septoria glycines in ethylene-insensitive soybean, but this was not detected in field plots. White mold (Sclerotinia sclerotiorum) disease severity in the field was increased in the ethylene-insensitive lines. Lab tests with soybean cyst nematode revealed reduced cyst formation. Ethylene-insensitivity strongly reduced ethylene-activated leaf chlorosis and abcission in lab tests of healthy middle-aged leaves. However, no differences were detected in leaf chlorophyll content in the field, and late-season leaf senescence occurred at similar rates in an ethylene-insensitive line and its normal ethylene-sensitive parent, suggesting that ethylene-mediated processes are not a predominant in determinant of late-season senescence of soybean leaves. Soybean yield of the ethylene-insensitive lines was notably undependable, being similar to the parental line in some field locations but severely reduced in other environments.