Epidermal traits may be the key to resistance of brown spot needle blight in loblolly pine

Loblolly pine (Pinus taeda) is crucial for the economic stability of the southeastern United States and has been the focus of tree breeding programs for 80 years. Lecanosticta acicola, which causes brown spot needle blight (BSNB), has recently caused significant mortality to loblolly pine across the region. The fungal pathogen enters needles through stomata, making epidermal traits such as cuticle thickness or stomatal abundance vital for disease resistance. In other pathosystems, it has been shown that thicker cuticles enhance resistance, while fewer stomata provide fewer entry points for infection. Our objective was to assess the impact of breeding on epidermal traits in 17 loblolly pine families. One-year-old seedlings were grown in a shade house, and needles were harvested. The cuticle was removed with chloroform for average cuticle weight measurements, and additional metrics included needle length, width, and needles per fascicle count to get surface area. Results showed differences in cuticular wax among families, with some having about 20% more per unit area than others. This increased cuticular wax may improve disease resistance. Stomatal row analysis under a microscope revealed family variability, ranging from an average of 12 to 18 stomatal rows. Future steps will delve deeper into stomatal traits and investigate how these epidermal characteristics differ among loblolly pine families affected by BSNB in natural stands. This work aims to help landowners choose more resilient families to safeguard against BSNB.