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Submitted to: Plant Methods
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 9/5/2018 Publication Date: 9/11/2018 Publication URL: http://handle.nal.usda.gov/10113/6133995 Citation: Li, S. 2018. Development of a seedling inoculation technique for rapid evaluation of soybean for resistance to Phomopsis longicolla under controlled conditions. Plant Methods. 14:81. https://doi.org/10.1186/s13007-018-0348-x. DOI: https://doi.org/10.1186/s13007-018-0348-x Interpretive Summary: Phomopsis seed decay (PSD) of soybean reduces seed quality and yield worldwide. Development of effective techniques to evaluate soybean for resistance to PSD can facilitate identification of new sources of host resistance to manage the disease. This study was undertaken to develop and utilize a rapid cut-seedling inoculation technique to evaluate soybean for resistance to the causal pathogen of PSD under controlled conditions. Four experiments were conducted to test the effect of temperature, plant age, pathogen age, and different isolates of the causal pathogen on the stem lesion length. In addition, three experiments were performed to evaluate 42 soybean genotypes originating from 16 countries. Based on the results, a simple procedure developed from this study can be used to identify susceptible and resistant lines based on stem lesion length in just 14 days after challenging the plant with the pathogen. This rapid and simple technique provides a useful tool to soybean breeders and will facilitate identification of soybean with resistance to PSD without the concern of environmental effects. Technical Abstract: Phomopsis seed decay (PSD) of soybean (Glycine max L. Merr.) is caused primarily by the seed-borne fungal pathogen Phomopsis longicolla T. W. Hobbs (syn. Diaporthe longicolla). The PSD disease reduces seed quality and yield worldwide. Development of effective techniques to evaluate soybean for resistance to PSD can facilitate identification of new sources of host resistance to manage the disease. This study was undertaken to develop and utilize a rapid cut-seedling inoculation technique to evaluate soybean genotypes for resistance to P. longicolla under controlled conditions. Four experiments were conducted to test the effects of temperature, plant age, pathogen age, and different isolates of the pathogen on the stem lesion length caused by P. longicolla. In addition, three experiments were performed to evaluate 42 soybean genotypes originating from 16 countries within maturity groups III, IV, and V. Results showed that there were no significant differences in stem lesion length determined as the area under disease progress curve (AUDPC) at 24°C and 30°C. The 21 and 14-day-old seedlings appeared more susceptible than the older seedlings. Inoculation with 7 or 14-day-old pathogens caused higher values of AUDPC than older pathogen cultures. Isolates MS17-1 was the most aggressive isolate from the test of 25 isolates from seven states in the U.S. Eighteen previously reported field PSD-resistant accessions had significantly lower AUDPC than the susceptible checks and other entries (P = 0.05). This study provided rapid evaluation of soybeans for reaction to P. longicolla at the seedling stage and identification of PSD-resistant genotypes. The results were comparable to those obtained from field tests without waiting a whole growing season. Additionally, concerns about the environmental effects and uneven distribution of the pathogen in the field were ameliorated. |
