The Efficacy of Breeding for Brown Spot Disease Resistance in Longleaf Pine

-The study objective was to determine whether selection for brown spot disease (caused by Scirrhia acicola (Dearn.) Siggers) resistance in longleaf pine (Pinus palustris Mill.) is beneficial for areas where brown spot is not present. Two groups of selections, comprising those that performed (survival and growth) well in the presence of brown spot disease and those that performed well in its absence, were selected. These selections were made in tests planted on the Harrison Experimental Forest (HEF) in southeast Mississippi. Within selection groups, the selections were mated in a partial diallel and their progeny were planted in replicated tests on two sites at the HEF. At one site, all trees were sprayed with a fungicide to protect the trees from brown spot disease, while at the other site no protection was provided. Brown spot infection was assessed one year after planting, and survival and height were assessed at years 1, 2, 3, 4, and 7. Overall, survival was significantly lower and disease incidence higher at the unsprayed site. At 7 years, survival at the unsprayed site was 73% for families selected in the presence of brown spot and 59% for the families selected in the absence of brown spot. Brown spot infection was significantly lower in the families selected in the presence of brown spot when planted at the unsprayed site, indicating that selection for brown spot resistance was effective. At 7 years, families selected in the presence of brown spot were significantly taller at the unsprayed site, but were significantly shorter at the sprayed site. Thus, selection for brown spot resistance is beneficial for those areas where brown spot disease is present, but not for areas where brown spot is controlled or absent.