Field evaluations of soybean lines from a new source of resistance to Phomopsis seed decay, 2012

Authors: Gillen, Anne; Mengistu, Alemu; Bellaloui, Nacer

Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/22/2013
Publication Date: 8/14/2013
Citation: Gillen, A.M., Mengistu, A., Bellaloui, N. 2013. Field evaluations of soybean lines from a new source of resistance to Phomopsis seed decay, 2012. Plant Disease Management Reports. 7:FC126.

Interpretive Summary: Phomopsis seed decay is an important disease which causes large soybean quality losses when environmental conditions favor its growth, and harvest is delayed due to wet field conditions. High humidity, free water and warm temperatures during pod development favor Phomopsis seed decay development and are common in Mississippi. No commercially available soybean cultivars have a significant level of resistance to this disease. The objective of this research is to develop soybean lines with resistance to Phomopsis seed decay, high yield potential and good agronomics, focusing on breeding lines derived from PI 423941, a new source of resistance, shown to highly reduce seed infection. A field trial of experimental soybean breeding lines, parental lines, and susceptible and resistant varieties was conducted in 2012 to assess disease in seed collected at maturity and 15 days after normal maturity. Initial results indicate that the varieties thought to be resistant were actually only moderately resistant to moderately susceptible under Mississippi conditions. However, several of the experimental lines showed lower levels of Phomopsis infection than their susceptible parent. This indicates that PI 423941 may have contributed some genes for resistance in these breeding lines.

Technical Abstract: Phomopsis seed decay (PSD) is an important disease which causes large soybean quality losses when environmental conditions favor its growth, and harvest is delayed due to wet field conditions. High humidity, free water and warm temperatures during pod development favor PSD development and are common in Mississippi. No commercially available soybean cultivars have a significant level of PSD resistance. Seventeen breeding lines derived from PI 423941, a new source of PSD resistance which was shown to highly reduce seed infection percentage, were screened in 2012 in an innoculated field trial that was irrigated using overhead sprinklers. The checks included PI 423941(resistant parent), resistant checks SS93-6012 and SS93-618, two susceptible parental lines, a maturity group 5 susceptible breeding line and a maturity group 4 susceptible breeding line. Seed was collected at normal harvest and 15 days after normal harvest (delayed harvest). Infection of the seed with Phomopis longicolla, the primary causal agent of PSD, was evaluated using a plated seed assay. The susceptible parents had higher levels of seed infection at delayed harvest (PSD2) than the resistant checks, but they were not always significantly different from SS93-6012 and SS93-6181. SS93-6012 and SS93-6181 had similar PSD2 scores to the suscptible maturity group 5 check. This indicates that SS93-6012 and SS93-6181 are not highly resistant in Mississippi. Three experimental lines had scores significantly lower than their susceptible parent. This indicates PI 423941 has contributed some resistance genes to these lines.