(MC) DEVELOPING AND SCALING UP THE NEXT GENERATION OF HEALTHY FORESTS

Southern pines (loblolly (Pinus taeda) and slash (Pinus elliottii) pine) are severely impacted by fungal pathogens such as fusiform rust (Cronartium quercuum (Berk.) Miyabe ex Shirai f. sp. Fusiforme or Cqf) and pine pitch canker (Fusarium circinatum or FC). These endemic diseases cause significant economic damage to forests each year (Powers et al. 1974). Losses from rust have been estimated to be as high as $578 per hectare (Brawner et al. 1999). Decades of tree improvement research designed to identify rust and pitch canker resistant families have led to more productive plantations (Walker and McKeand 2017) and improved financial returns for investments in planted forests (Cubbage et al. 2000). Controlled inoculation systems for rust and pitch canker have been developed through collaboration among US Forest Service's Resistance Screening Center (RSC) in conjunction with university and industry stakeholders (Cowling and Young 2013). Results from tests performed at the RSC have been supported by networks of field trials established across the SE US (Spitzer et al. 2017). Research by the University of Florida, North Carolina State University and Texas A&M University has demonstrated strong evidence for the genetic control of disease resistance and has provided a better understanding of the genes regulating resistance (Resende et al. 2012, Quesada et al. 2010, Quesada et al. 2014). Recent project work has utilized methods developed to reduce the complexity of the pine genome (Neves et al. 2013) to target resistance genes for sequencing of transcripts in infected pine tissue following inoculation at the US Forest Service Resistance Screening Center.The proposed project will develop a better understanding of molecular interactions between pathogen and pine genomes to validate hypotheses implying gene-for-gene or polygenic genetic architectures for resistance or tolerance to pathogens. Damage from pine pathogens will be less predictable as climate variability increases (Quesada et al. 2019) and a better understanding of the regulation of disease would be useful for achieving both industrial and restoration goals in future forests. The well-developed phenotyping systems for screening pine seedlings for resistance to rust and pitch canker will be used to provide empirical data to validate data analysis systems to identify disease resistant reforestation populations so that these methods may be used to address other forest health problems. For example, the system used to characterize Cqf resistance genes in loblolly pine may be extended to develop disease resistant breeds of longleaf pine (Pinus palustris) and reduce replanting requirements following Cqf-induced mortality in restoration plantings or develop disease resistant breeds of slash pine for areas where FC severely reduces timber quality.