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Funded Project

Funding Program: Regional IPM Grants (S-RIPM)

Project Title: Development of Stable and Predictable Deployment Populations of Loblolly Pine to Minimize Fusiform Rust Impacts in Southern Pine Plantations

Project Director (PD): Henry Amerson [1]

Lead State: NC Lead Organization: North Carolina State University

Research Funding: $86,900

Start Date: Jul-01-2004 End Date: Jun-30-2006

Pests Involved: fusiform rust

Site/Commodity: loblolly pine

Summary: Fusiform rust disease of pines, caused by the fungus Cronartium quercuum f.sp. fusiforme (Cqf.) is by far the most serious disease in loblolly and slash pine forests of the southern US. Deployment of resistant genotypes is the only viable strategy for controlling the devastating impacts of fusiform rust in southern pine plantations. Until recently, tree breeders believed that resistant pine genotypes were stable and reasonably predictable in performance across sites. However, we have discovered that the most resistant genotypes tend to be highly variable in resistance across different test sites (McKeand et al., 2003). Five of 6 families in that study, deemed highly rust resistant, showed much poorer predictability than the other 38 families evaluated. We hypothesize that this is due to virulence variation for major gene resistance (i.e. Fr genes) at different field locations. Understanding resistance/pathogenicity interactions will be critical for successful deployment of high-value, rust-resistant genotypes in southern pine forests. The proposed study will investigate the stability and predictability of high-yielding families that appear putatively resistant, based on limited testing. These families will be tested across multiple inoculum sources in both greenhouse (GH) and field tests. Included are families from 7 loblolly pine clones that contain 8 different heterozygous fusiform rust resistance genes, tagged with genetic markers. Markers for genes, Fr1--Fr8, will be used to examine pathogen virulence variation across the range of Cqf. and as a possible explanation for the previously observed unpredictability of resistance. Research will be conducted in two large GH tests funded by this proposal, while field studies will be funded and conducted by industry/state partners. Objectives: Specific objectives are: to develop breeding and operational deployment strategies in high-hazard rust areas, utilizing those families having stable and predictable rust resistance; to identify stable (highly resistant) but unpredictable families for site-specific or regional deployment; to identify families that are likely sources for future Fr gene discovery and genetic marker investigations; to characterize patterns of geographic virulence variation (i.e., regional vs. site to site) for each of 8 Fr genes; and to characterize virulence variation against resistance, in non-Fr families in GH studies for correlation with field studies.

Final Report:

Results PROGRESS: 2004/07 TO 2006/06 This study investigated the stability and predictability of high-yielding loblolly pine families (fams.) that appeared putatively resistant to fusiform rust disease (FRD), based on prior limited field-testing. 30 fams. previously deemed as resistant and 8 fams. deemed as susceptible, along with a susceptible checklot were inoculated with Cronartium quercuum f.sp. fusiforme spores collected from 10 sites (east TX to northeastern SC) across the range of FRD. In total more than 22,500 seedlings were inoculated at the USDA-FS Resistance Screening Center in Asheville, NC. Disease status data (gall vs. no gall phenotype) were analyzed. Seven loblolly pine selections that contain 8 different heterozygous fusiform rust resistance genes tagged with (RAPD) genetic markers (previous work Amerson and co-workers unpublished data) were included and were designated as Fr fams. RAPD markers were assessed in progeny megagametophyte DNA of the Fr fams. (approx. 4200 samples) to permit designation of each seedling as having inherited either the Rn allele (resistance allele) or the rn allele (non-resistance allele) of a given resistance gene from the mother tree The marker designated R individuals of each Fr family were used to assess virulence levels for the 8 various R alleles across the 10 inocula/sites to gain understanding of virulence variation across the survey range. In this assessment, virulence levels (percentages) were arbitrarily designated as low (0-15%), moderate (16-30%) and high (e31%). Using that scale, virulence against Fr3 resistance (plants with the Fr3 resistance allele) was uniformly low across all sites, while virulence against Fr1 resistance and Fr4 resistance typically was low or moderate with a spike for one or two sites. Virulence against Fr2 resistance was uniformly high, while virulence against Fr5 resistance was high to moderate for all sites. Virulence against Fr8 resistance, Fr6 resistance and Fr7 resistance was highly variable across sites. Although virulence against the various Fr alleles fluctuated greatly across the sites, on a family-mean basis none of the Fr fams. showed significant rank change. Summed and averaged across the 8 Fr alleles, % virulence was greatest for site 10 (northeastern SC) and least for site 6 (south central GA). Among the non-Fr fams., the 8 fams. originally considered as susceptible were again deemed susceptible. They were also predictable and displayed no rank change across the sites. In contrast with starting expectations, 7 of the 23 putatively resistant non-Fr fams. in this study were also deemed to be susceptible, while 12 of the 23 were considered to be highly resistant. Contrary to expectations, predictability among the 23 putatively resistant non-Fr fams. was also high, with only one family (on a family-mean basis) showing significant family rank change across sites. Of the 12 highly resistant non-Fr fams., 11 were predictable across sites and should be good fams. for wide deployment. In ten of these 11 highly resistant fams., where seed were available, the genetic basis of resistance, using genetic markers, is being further investigated with industry support. IMPACT: 2004/07 TO 2006/06 Fusiform rust disease is the most economically important disease of southern pines and presents major problems for plantation forestry at many locations in the southern USA. This project has enhanced our knowledge regarding pathogen virulence variation, and this information should help tree breeders and propagators produce new resistant selections. The eleven resistant and predictable high-volume families recognized in this study are suitable for wide scale deployment and should be included in current deployment strategies. PUBLICATIONS (not previously reported): 2004/07 TO 2006/06 Amerson, H.V., Kubisiak, T.L., Garcia, S.A., Kuhlman, E.G., Nelson, C.D., McKeand, S.E., Mullin, T.J. and Li. B. 2005. Interacting Genes in the Pine-Fusiform Rust Forest Pathosystem. Proc. 28th Southern For. Tree Imp. Conf. Abstr. p. 60.

Outcomes N/A

Impacts From report submitted by the PI to USDA CRIS report system Fusiform rust disease is the most economically important disease of southern pines and presents major problems for plantation forestry at many locations in the southern USA. This project has enhanced our knowledge regarding pathogen virulence variation, and this information should help tree breeders and propagators produce new resistant selections. The eleven resistant and predictable high-volume families recognized in this study are suitable for wide scale deployment and should be included in current deployment strategies.

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