Genetic control of Fusarium circinatum tolerance in Pinus patula × P. tecunumanii hybrid families

Abstract

The pine pitch canker fungus, Fusarium circinatum, has caused large-scale mortality of Pinus patula crops in South African nurseries and high in-field post-planting mortality. Tree breeders have identified selection and breeding of tolerant material as the likely long-term solution to this disease. In this study, the greenhouse artificial inoculation screening method was employed to investigate the genetic control of F. circinatum tolerance in a factorial mating design of Pinus patula × P. tecunumanii low elevation (PPTL) and high elevation (PPTH) hybrid families and their parental species. Results indicated that F. circinatum tolerance is under moderate genetic control (h² between 0.13 and 0.36) as assessed in a hybrid factorial mating design with a large number of PPTL and PPTH families. The PPTL hybrid displayed the highest level of tolerance, followed by pure P. tecunumanii LE, then the PPTH hybrid, pure P. tecunumanii HE and lastly pure P. patula. A general hybridising ability (GHA) and specific hybridising ability (SHA) analysis was also conducted to rank parent families as well as hybrid families. These breeding values can be used to identify superior families for commercial production and further breeding. A poor correlation between frost tolerance and F. circinatum tolerance was also found when compared to a previous frost tolerance study utilising the same hybrid families. The results from this study indicated that it is possible for breeders to cross selected P. patula seed parents with selected P. tecunumanii pollen parents to develop F. circinatum tolerant hybrid families for commercial production.