Rates of pitch canker induced seedling mortality among Pinus radiata families varying in levels of genetic resistance to Gibberella circinata (anamorph Fusarium circinatum)

Abstract

Pitch canker, caused by Gibberella circinata Nirenberg & O’Donnell, is a problem for pines in both native and planted stands. The aerial phase of the disease results in shoot and canopy dieback, whereas soil or seedborne inoculum can cause damping off of emerging seedlings. Based on the extent of lesion development on inoculated shoots, families of Pinus radiata have been shown to differ significantly in resistance to pitch canker. This study was undertaken to determine if these same families also differ in mortality caused by G. circinata at the seedling emergence stage. For this purpose, seeds treated with a suspension of G. circinata spores were planted in a greenhouse and rated for pitch canker induced mortality. Variation between families, in mortality of emerging seedlings, was significant but the observed variation was not significantly correlated with measures of resistance based on stem inoculation tests. This suggests that mechanisms limiting the development of stem lesions do not confer measurable resistance to the seedling phase of the disease and therefore that early exposure to the pathogen may compromise selection for resistance to pitch canker in stands of Pinus radiata.