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-year-old 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.