Multiple forms of resistance to the Phomopsis stem canker pathogens Diaporthe helianthi and D. gulyae in sunflower

Authors: Underwood, William; Misar, Christopher

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2024
Publication Date: 6/1/2024
Citation: Underwood, W., Misar, C.G. 2024. Multiple forms of resistance to the Phomopsis stem canker pathogens Diaporthe helianthi and D. gulyae in sunflower. Plant Disease. 108:1704-1749. https://doi.org/10.1094/PDIS-03-23-0610-RE.
DOI: https://doi.org/10.1094/PDIS-03-23-0610-RE

Interpretive Summary: Phomopsis stem canker disease of cultivated sunflower has become an increasing concern for US sunflower production in the major sunflower growing region of the Northern Great Plains over the past two decades. This disease can be caused by multiple species of fungi in the genus Diaporthe, but in the US, Diaporthe helianthi and D. gulyae are the most common species found to cause the disease. Phomopsis stem canker disease progression is a complex process that ultimately results in development of stem lesions on sunflower plants that cause degradation of the pith, resulting in plant wilting and death and reducing yield and oil quality. Sunflower plants can be resistant to Phomopsis stem canker disease in different ways, such as resistance to expansion of leaf and stem lesions as well as resistance to transmission of the fungus from the leaf and petiole tissue into the stem. The goals of this study were to examine different types of physiological resistance to Phomopsis stem canker disease in sunflower lines that were previously identified as partially resistant in field trials under conditions of natural infection. While these lines are known to exhibit resistance to the appearance of stem lesions in the field, the type of resistance possessed by each line was unknown. A second goal was to determine if lines are resistant to D. helianthi, D. gulyae, or both species to allow for prioritization of lines carrying resistance to both causal species. Sunflower lines possessing multiple forms of resistance to the disease were identified, along with lines possessing resistance to both Diaporthe species. These results will allow for further research to understand the genetic basis for different forms of resistance and to combine distinct modes of physiological resistance to achieve durable control of Phomopsis stem canker in sunflower hybrids.

Technical Abstract: Phomopsis stem canker of cultivated sunflower (Helianthus annuus L.) can be caused by multiple necrotrophic fungi in the genus Diaporthe, with Diaporthe helianthi and D. gulyae being the most common causal agents in the United States. Infection begins at the leaf margins and proceeds primarily through the vasculature, progressing from the leaf through the petiole to the stem resulting in formation of brown stem lesions centered around the petiole. Sunflower resistance to Phomopsis stem canker is quantitative and genetically complex. Due to the complex disease process, resistance is possible at different stages of infection and multiple forms of defense may contribute to the overall level of quantitative resistance. In this study, sunflower lines exhibiting field resistance to Phomopsis stem canker were evaluated for stem and leaf resistance to both D. helianthi and D. gulyae in greenhouse experiments and responses to the two species were compared. Additionally, selected resistant and susceptible lines were evaluated for petiole transmission resistance to D. helianthi. Lines with distinct forms of resistance were identified and results indicated that responses to stem inoculation were strongly correlated for the two fungal species while leaf responses were not significantly correlated. These results provide a basis for genetic dissection of distinct forms of sunflower resistance to Phomopsis stem canker and will facilitate combining different forms of resistance to potentially achieve durable control of this disease in sunflower hybrids.