Greenhouse results suggest disease severity caused by Diaporthe longicolla, as a stem pathogen and as a seed pathogen, in soybean (Glycine max L.) may not be correlated

Authors: SURESHBABU, BIJULA MANKARA - North Dakota State University; Gillen, Anne; Smith, James - Rusty; MARKELL, SAMUEL - North Dakota State University; MATHEW, FEBINA - North Dakota State University

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: The fungus Diaporthe longicolla causes Diaporthe (Phomopsis) seed decay, as well as pod and stem blight in soybean in the United States. However, our understanding of the genetic basis of resistance to this fungus is limited. Therefore, this study compared the presence of stem and seed resistance associated with D. longicolla in greenhouses tests and determined that resistance on one part of the plant was not a reliable predictor of resistance on the other part of the plant. Twenty-nine soybean lines showed significantly less susceptibility to D. longicolla compared to the susceptible line 'Hawkeye' in the stem experiment, while six lines were significantly less susceptible compared to the susceptible line ‘PI 371611’ in the seed experiment. There was no significant correlation between the disease severity data obtained from the two experiments. These findings suggest that the genes responsible for resistance to D. longicolla as a stem pathogen may differ from those responsible for resistance as a seed pathogen but need further investigation. The findings of this study provide valuable insights into the presence of soybean lines in the USDA Soybean Germplasm Collection with possible resistance to D. longicolla that soybean breeders can use to develop new cultivars. Ultimately, this knowledge will greatly enhance soybean production and sustainability in regions affected by pod and stem blight and Diaporthe seed decay.

Technical Abstract: Diaporthe longicolla causes Diaporthe (Phomopsis) seed decay, as well as pod and stem blight in soybean (Glycine max L.) in the United States. However, our understanding of the genetic basis of resistance to D. longicolla is limited. Therefore, this study aims to investigate the presence of stem and seed resistance associated with D. longicolla. Separate experiments were conducted to determine stem and seed resistance, both using a completely randomized design. Thirty-nine accessions were screened against a single isolate of D. longicolla in both experiments. In the stem experiment, one mycelial plug was placed on the wound created on the stem at the second trifoliate stage, and the inoculated plants were incubated at 24±3°C with 90% humidity for seven days. In the seed experiment, seeds of each genotype were surface-sterilized, soaked in a mycelial suspension for four hours, plated on 2% water agar, and incubated at 23±2°C for seven days. Seven days post-inoculation, significant differences in disease severity were observed among the genotypes in both the stem (p<0.0004) and seed (p<0.0003) experiments. Twenty-nine genotypes showed significantly less susceptibility to D. longicolla as a stem pathogen compared to the susceptible 'Hawkeye', while six genotypes were significantly less susceptible compared to the susceptible check ‘PI 371611’ in the seed experiment. However, there was no significant correlation between the disease severity data obtained from the two experiments (p>0.05). These findings suggest that the genes responsible for resistance to D. longicolla as a stem pathogen may differ from those responsible for resistance as a seed pathogen but need further investigation.