Heterobasidion annosum and Armillaria ostoyae significantly reduce radial growth during three years before stem death in infected Pinus pinaster

Butt and root-rot diseases caused by Armillaria sp. and Heterobasidion sp. are highly destructive to conifers worldwide. These diseases lead to loss of growth, wood degradation, and tree mortality, often necessitating premature logging. However, little is known about the effect of infection on the growth and mortality of adult pines during forest development. In this study, mature maritime pines were sampled from two forest sites in south-west France. In 2013, the Sanguinet site provided both healthy (asymptomatic) and Heterobasidion annosum-infected pines, while in 2019 the Mano site also provided Armillaria ostoyae-infected pines. Radial growth dynamics were compared between healthy and infected pines using two complementary approaches taking into account the diameter of each tree: 1. Compensation over 10 years and year by year comparisons of mean (dendrochronogram) between groups of pines with same Last Year of Radial Growth (LYRG); 2. Analysis of covariance by modeling the relationship between basal area increment and basal area in healthy or infected pines for each LYRG. Our results indicate that symptomatic trees infected by Heterobasidion annosum are characterised by a rapid reduction in radial growth across the entire tree circumference. The covariance method was more efficient to show that the radial growth of infected trees was significantly lower (between 25% and 72% loss) in the three years preceding the year of growth arrest, on both sites, i.e., for two different periods of years. For Armillaria ostoyae, growth data shows the same trends than for H. annosum, with a sharp decline over the last 2–3 years of growth. Covariance results for LYRG 2018 and 2019 reveal that infection symptoms significantly reduces the radial growth of infected trees compared to asymptomatic trees over the last three years of growth. These results show that infection of maritime pine by butt and root-rot fungi can lead to a rapid decrease in radial growth, and this decrease is independent of the calendar year of cambial death at breast height.