Susceptibility of provenances and families of Pinus maximinoi and Pinus tecunumanii to frost in South Africa

Abstract

The future of South Africa’s most important pine species, Pinus patula, is threatened by the pitch canker fungus, Fusarium circinatum. Pinus maximinoi and P. tecunumanii represent two subtropical species that provide an alternative to planting P. patula on the warmer sites of South Africa. Extending the planting range of P. tecunumanii and P. maximinoi to include higher and colder altitude sites will reduce the area planted to P. patula and the risk of F. circinatum. During 2007 progeny trials of P. tecunumanii and P. maximinoi were planted on a sub-tropical and sub-temperate site. Shortly after the establishment of these trials, unusually cold weather conditions were experienced across South Africa (-3 C at the sub-temperate site) resulting in severe mortality. This provided the opportunity to assess the variation in survival as a measure of frost tolerance within these two species to determine whether it could be improved upon through selection. Results indicated that the variation in survival was under genetic control in P. tecunumanii (h(0,1) 2 = 0.16, hL 2 = 0.27) and P. maximinoi (h(0,1) 2 = 0.11, hL 2 = 0.23) at the sub-temperate site. Correlations in provenance ranking for survival across sites were high for both species. Moderate correlations in family survival for P. tecunumanii (r = 0.52) were found at the two sites. Improvements in cold tolerance can thus be made in both species extending their planting range to include greater areas planted to P. patula thereby limiting the risk of F. circinatum.