Behaviour of Heterobasidion annosum and Heterobasidion irregulare isolates from central Italy in inoculated Pinus pinea seedlings

Abstract

Five Heterobasidion annosum and five H. irregulare isolates, collected in central Italy, were tested in order to assess the differences in their behaviour, on PDA medium and in two inoculation experiments on three-yearold Pinus pinea seedlings. In vitro the average growth rate of H. irregulare isolates was faster than H. annosum isolates at a temperature ranging between 5 to 30°C. In an inoculation test, performed at a temperature between 8 and 12°C, all the isolates had a comparable growth in the seedlings after three weeks, but successful infection was significantly more frequent with the H. irregulare isolates. Inoculation was repeated with only two individual isolates, collected from within the National Park of Circeo in disease centres that were very close to each other. This test was performed at a higher temperature (8-24°C), and observations were carried out one, two, three and six weeks later. The H. irregulare isolate always produced a more extended infection in seedlings than the H. annosum isolate. The study indicates that H. irregulare has a somewhat different behaviour versus P. pinea in comparison with H. annosum. We thus believe that the need to monitor how this situation evolves should not be overlooked.

Pathogenicity of Spanish isolates of Heterobasidion annosum s. s. in Pinus pinaster seedlings

“…However, there was no difference in the mortality rate of the infected and control seedlings treated by soil infestation. Nevertheless, rates were similar to or even higher than observed by other authors (Lehtijarvi et al 2011;Scire et al 2011), who reported low mortality rates in other pine species, such as P. pinea, P. halepensis, P. nigra, P. sylvestris and P. brutia seedlings. The mortality rates (approximately 35 and 10% for stem inoculation and soil infestation, respectively) were lower than reported for some North American pine species, such as P. elliottii, P. echinata, P. palustris, P. strobus and P. taeda (Delatour et al 1998), and, to a lesser extent, for P. sylvestris (Swedjemark and Stenlid 1995), although inoculation methods were different from those used in this study.…”

“…Moreover, seedling mortality did not occur after 3 months from the inoculations, which is consistent with previous findings of maximal mortality rates in young seedlings at between 5 and 14 weeks after inoculation, which was attributed to occlusion of the pathogen from the plant material after this length of time (Swedjemark et al 2001). Indeed, P. pinaster (also called resin pine) produces a large amount of oleoresin (62.8% of resin acids), which acts as mechanical barrier, and monoterpenes (28.7%), which may be fungitoxic (Asiegbu et al 1998;Scire et al 2011). Nevertheless, rates were similar to or even higher than observed by other authors (Lehtijarvi et al 2011;Scire et al 2011), who reported low mortality rates in other pine species, such as P. pinea, P. halepensis, P. nigra, P. sylvestris and P. brutia seedlings.…”

“…Although H. annosum has occasionally been recorded on Pinus sylvestris and Pinus nigra in Spain, the presence of the fungus on P. pinaster in association with forest decline is a very recent finding (Prieto-Recio et al 2012). This pathogen is very aggressive on Pinaceae; however, some pine species such as P. pinea and P. halepensis have shown a lesser susceptibility (Scire et al 2011). To our knowledge, pathogenicity tests have not previously been carried out with H. annosum isolates and P. pinaster.…”

Impacts of exotic forest pathogens on Mediterranean ecosystems: four case studies

“…This sudden co-occurrence is leading to genetic exchanges between the two taxa, although the European H. annosum is only sporadically present in the habitat colonized by the more assertive American species (Gonthier and Garbelotto 2011). H. irregulare has been suggested to be ecologically more adapted to the Mediterranean climate than the European native species (D'Amico et al 2007;Scirè et al 2011), but pathogenicity on Pinus sylvestris and Pinus pinea appears not to differ between North American, European and introduced North American Heterobasidion isolates . What really differs is the sporulation potential, much higher for the North American species during dry summers .…”

Predicting the activity of Heterobasidion parviporum on Norway spruce in warming climate from its respiration rate at different temperatures

“…(Rishbeth ; Brown and Webber ; Sciré et al. ) showing an optimum between 20 ° C and 30 ° C and an abrupt decrease in activity above 30°C. Cartwright and Findlay () found a nearly linear response of growth by a number of various decay fungi to temperatures in the range of 3–20 ° C, which is in agreement with our results.…”