Tolerance of Pinus patula full-sib families to Fusarium circinatum in a greenhouse study

Abstract

The pitch canker fungus, Fusarium circinatum, has caused large scale mortality of young Pinus patula Schiede & Deppe ex Schltdl. & Cham. seedlings in nurseries in South Africa since 1990. Diseased seedlings have been inadvertently carried to the field, which in turn have died and has reduced stocking below an acceptable level. Tree breeders have suggested that the only long-term solution to limit infection by this pathogen is to identify and deploy tolerant P. patula families. A commonly used technique to identify tolerant clones is to artificially inoculate open-pollinated progeny from orchard clones with F. circinatum under greenhouse conditions. In these trials, large variation in tolerance to the pathogen among seedlings within open-pollinated families was observed and that this could be influenced by the pollen parent. Therefore, identifying individual full-sib families where both parents are known, should improve the identification of tolerant families, which can then be repeated. In this study, cuttings from control-pollinated P. patula seedling hedges were inoculated with F. circinatum in a greenhouse. The results showed large family variation where some of the full-sib families were similar in tolerance to P. elliottii Engelm var. elliottii seedlings. Therefore, it is recommended that breeders focus on identifying specific family combinations that are more tolerant to F. circinatum.