Reducing the risk of pitch canker disease (caused by Fusarium circinatum) to Pinus patula in South Africa

[摘要] The principal objective of this research has been to reduce the potential impact of Fusariumcircinatum on young and mature Pinus patula trees in South Africa. The results provide newknowledge concerning the genetic variation within P. patula, and suggest alternative species andhybrids, with resistance to infection by the pitch-canker pathogen F. circinatum. The infectionof nursery plants is the principal cause of dying seedlings after planting and controlling thedisease in the nursery is paramount to achieving good post-planting survival of P. patula. A largenumber of alternative pines, which are more tolerant to the pathogen, exist. Pinus elliottii is themost versatile alternative due to the ready availability of seed and the fact that it can be plantedon a wide range of sites. Although the species is more tolerant than P. patula, individual familiesvary in their tolerance to F. circinatum and care should be taken to eliminate the moresusceptible families. Pinus maximinoi and the low elevation (LE) source of P. tecunumanii arehighly tolerant and provide an excellent alternative to P. patula on sites free of frost. The highelevation (HE) source of P. tecunumanii, which is more tolerant of cold than the low elevationsource, is significantly more tolerant to F. circinatum than P. patula. However, large variation inthe tolerance of individual P. tecunumanii (HE) families to F. circinatum exists and tolerantfamilies of this source need to be identified before commercial deployment. Although P.maximinoi and P. tecunumanii are sub-tropical pines and sensitive to frost, meaningful variationin the tolerance of individual families to frost has been observed which indicates that thesespecies can be bred for improved frost tolerance. On the colder sites, P. pseudostrobus maybecome an important alternative to P. patula due to its excellent tolerance to F. circinatum. In allcases hybrids between P. patula and pines more tolerant to F. circinatum, are significantly moretolerant than P. patula. Of these the P. patula x P. tecunumanii hybrid is the most promising.Due to the excellent tolerance of P. tecunumanii (LE) all families of the P. patula x P.tecunumanii (LE) hybrid are tolerant of F. circinatum. On the other hand, families of the P.patula x P. tecunumanii (HE) vary greatly in their tolerance to F. circinatum and the specificcombination of the parents appears to play an important role in determining tolerance. Althoughonly 5% of the current P. patula growing stock is of similar tolerance to F. circinatum as P.elliottii heritability for tolerance to F. circinatum is high in P. patula indicating that improvements can be achieved through breeding. Good control can also be achieved byidentifying specific full-sib P. patula families that are tolerant to F. circinatum, rather than theuse of open pollinated seed. It is anticipated that large areas, currently well suited to P. patula,will in the future be replanted with pine hybrids and species more tolerant of F. circinatum.Pinus patula, which has been bred for improved tolerance to F. circinatum, will be limited to themost temperate regions of South Africa.

[发布机构] University of Pretoria