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Funded Project

Funding Program: IPM Partnership Grants

Project Title: Developing Improved Protocols to Assess Alfalfa Varieties for Resistance to P. sclerotioides

Project Director (PD): Gary Bergstrom [1]

Lead State: NY Lead Organization: Cornell University

Undesignated Funding: $37,351

Start Date: Apr-01-2009 End Date: Mar-31-2010

Pests Involved: brown root rot, BRR, spring black stem, leaf spot, SBS, Phoma

Site/Commodity: alfalfa

Area of Emphasis: resistance

Summary: Phoma sclerotioides, an economically important fungal pathogen with widespread distribution in the Northeast, causes brown root rot of alfalfa (BRR) and contributes to alfalfa spring black stem and leaf spot (SBS). Alfalfa varieties with effective resistance to P. sclerotioides are not available. BRR resistance of alfalfa varieties appears to differ by P. sclerotioides biotype, with no variety resistant to all biotypes. All varieties are at least moderately susceptible to SBS caused by P. sclerotioides. Current breeding protocols involve the use of a single isolate of P. sclerotioides to screen for resistance to BRR and do not include P. sclerotioides when screening for resistance for SBS. The proposed study will identify the minimum set of isolates needed to breed alfalfa for effective P. sclerotioides resistance and will investigate which P. sclerotioides biotypes contribute to SBS. Controlled studies will be conducted to test the virulence of isolates of each P. sclerotioides biotype to the alfalfa varieties Peace, Starbuck, and WL 347 LH. Preliminary studies suggest that the P. sclerotioides resistance of these varieties differs by biotype. Both foliar and root inoculations will be conducted. Field surveys will be conducted in New York and Vermont to evaluate which P. sclerotioides biotypes are associated with SBS in alfalfa production fields. The study will provide breeders with the tools necessary to develop alfalfa varieties with stronger, more effective resistance to both root and foliar disease caused by P. sclerotioides. Objectives: 1. Evaluate which biotypes of P. sclerotioides contribute to SBS. 2. Identify the minimum set of P. sclerotioides isolates needed to breed alfalfa for effective resistance to P. sclerotioides. 3. Disseminate research findings. Proposal

Final Report:

Outcomes Efforts to breed alfalfa for resistance to spring black stem and leaf spot (SBS) should focus on P. medicaginis. P. sclerotioides contributes to SBS in alfalfa production fields, but it occurs at much lower levels than P. medicaginis (Table 1). Pathogenicity testing of P. sclerotioides and P. medicaginis isolates on alfalfa foliar tissues confirms this conclusion. In inoculation trials, P. sclerotioides contributed to SBS (Figures 3, 4) but, at least under the conditions tested, it caused much lower disease severity than P. medicaginis (Figures 5, 6, 7). If breeders choose to include P. sclerotioides when screening for resistance to SBS, representative isolates of all infraspecific varieties of P. sclerotioides should be used. In surveys of alfalfa production fields, P. sclerotioides var. sclerotioides was isolated from foliar tissues less much less frequently than it was isolated from root tissues and less frequently than P. sclerotioides var. viridis, var. steubenii, and var. sasktachewanii were isolated from foliar tissues. However, pathogenicity testing indicates that all infraspecific varieties of P. sclerotioides can cause SBS, and the infrequency with which P. sclerotioides var. sclerotioides was isolated from foliar tissues in the production fields may have reflected environmental conditions in spring 2009. Poor disease development in the inoculated brown root rot (BRR) trial precluded evaluation of differences in aggressiveness of infraspecific varieties of P. sclerotioides across alfalfa cultivars. Research is still needed to identify the minimum set of P. sclerotioides isolates needed to screen alfalfa for BRR resistance. Research results were disseminated at a November 2009 in-service training for Cornell University extension educators and at extension meetings in northern New York in March 2010. Survey results were published in the Canadian Plant Disease Survey (volume 90, pages 116-118), and the other research findings will be published in a manuscript that will be submitted to Plant Disease. Research conducted as a part of this grant helped facilitate the award of a $5,000 Kieckhefer Adirondack Fellowship to Michael J. Wunsch, graduate research assistant, by Cornell University to further our understanding of the relationship between phylogeny and virulence in P. sclerotioides.

Impacts Research funded by this grant will help alfalfa breeders make efficient use of scarce research dollars. The survey of alfalfa production fields and the inoculation experiments conducted as a part of this grant indicate that P. sclerotioides is not an important foliar pathogen of alfalfa, and they indicate that alfalfa breeders should focus on P. medicaginis when breeding for SBS resistance. The results suggest that few gains will be made by breeding alfalfa for resistance to foliar infection by P. sclerotioides. The research has greatly improved our understanding of the epidemiology of P. sclerotioides. P. sclerotioides infected alfalfa foliar tissues in most production fields sampled, indicating that P. sclerotioides can be spread with the movement of hay. Shortly after snowmelt in the spring, P. sclerotioides forms fruiting bodies (pycnidia) on infected crop residues from the previous year. Sporulation that occurs on lesioned alfalfa leaves dropped during use or during transport of hay will facilitate establishment of the pathogen at new sites. The results indicate that all infraspecific varieties are likely to be disseminated by movement of hay.

Report Appendices Final Report 2010 [PDF]

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