Comparison of the tolerance of Pinus patula seedlings and established trees to infection by Fusarium circinatum

Abstract

Since the first appearance of Fusarium circinatum in South Africa in 1990, foresters have been challenged with poor field survival of seedlings at establishment. One of the best long-term solutions is to improve the genetic tolerance of Pinus patula to infection by the pathogen. Currently, large numbers of families are routinely screened for their tolerance to F. circinatum by infecting open-pollinated seedlings from orchard clones in a greenhouse and assess-ing lesion development. In this study, nine-year-old P. patula trees from 96 families were inoculated with F. circina-tum in the field. Their levels of tolerance were assessed and compared to those observed in seedlings originating from seed harvested from the same trees. The field results were also compared with those from previous greenhouse screening trials where seedlings from a number of the same families had been inoculated with F. circinatum. The results showed that there was a strong phenotypic (r = 0.71) and genetic (rg = 0.94) correlation in the performance of the families common in both the greenhouse studies. A comparison of the tolerance of the families, screened as both seedlings and as trees, was also meaningful (r = 0.40). Furthermore, the seedlings raised from seeds collected from the infected P. patula trees, that ranked more tolerant than the mean of the P. elliottii trees, were similar in tolerance to P. elliottii seedlings in the greenhouse trial. Our results indicate that utilising seedlings from clones known to be tolerant should improve the tolerance of mature trees to infection by F. circinatum.