SNP DISCOVERY IN CANDIDATE GENES CONFERRING RESISTANCE TO PITCH CANKER AND FUSIFORM RUST IN LOBLOLLY PINE.

¹ Environmental Horticulture, University of California -Davis, Davis, CA, 95616, US

² School of Forest Resources and Conservation, University of Florida, Gainesville, FL 32611, US

³ Institute of Forest Genetics, Pacific Southwest Research Station, USDA Forest Service, Davis, CA, 95616

Loblolly pine is the most commercially important forest tree species in the US. The fungal disease Pitch Canker, caused by the necrotrophic fungus Fusarium circinatum, has been detected in loblolly pine plantations since 1974 where it causes extensive mortality associated with excessive pitch production of the host. Fusiform rust, caused by the biotrophic fungus Cronartium quercuum spp. fusiforme, has been a major disease of southeastern conifer plantations since early 1920's. Both diseases cause millions of dollars in losses to growers annually and thus demand for resistant varieties is high. The challenge, however, is that the genetic basis of stable resistance to both diseases is quantitative, rather than simple, gene for gene resistance (i.e R-Avr gene pathosystems) common in other plant-pathogen systems. Our objective is to identify single nucleotide polymorphisms in candidate genes conferring resistance to these fungal pathogens, which will be tested for association with quantitative resistance phenotypes. Candidate genes are categorized as: Positional Candidates, referring to candidate genes that are near QTLs for cell wall chemistry like pheylpropanoid pathway genes and cellulose synthase genes, Expression Candidates, referring to genes that are being identified by expression analyses (chitinases and PR10), Functional Candidates, referring to genes and regulatory regions whose roles in disease resistance have been identified in other plant systems and related to loblolly pine system through sequence homology and bioinformatics(myb and wrky class transcription factors,peroxidases, pinene synthases, terpene synthases, etc). Progress to date on candidate gene and SNP discovery will be presented.