Occurrence of Phaeomoniella chlamydospora on grapevine planting material in Sardinia and effect of combined hot water and cyproconazole treatments on its control

The occurrence of Phaeomoniella chlamydospora was investigated during vine propagation in an Italian nursery, and combined hot water (HWT) and cyproconazole treatments were carried out to limit the spread of the fungus in nursery vines. In the three-year period 2005–07, cutting and graft samples (scion cv. Sangiovese, rootstock cv. 140Ru in 2005 and 1103P in 2006–07) were taken during propagation at several infection risk stages, and the occurrence of P. chlamydospora was assessed by nested PCR. In 2005 and 2006, cuttings from esca-symptomatic grapevines (scion cv. Sauvignon blanc, rootstock cv. 140Ru in 2005 and 1103P in 2006) were treated at different stages of the propagation process. In 2007, artificially infected 1103P cuttings were treated with HWT and cyproconazole after being inoculated with P. chlamydospora, and the fungus was detected by isolation on agar medium. The effect of HWT on the growth of 1103P, 779P, Sangiovese and Cabernet franc cuttings was also assessed. Despite extended wood discoloration, P. chlamydospora was scarce in nursery vines during the three-year period. The contamination of planting material may have resulted from already infected mother plants (0.0 to 6.7% of infected cuttings) or may have started during the propagation, particularly after grafting (0.0 to 23.3% of infected grafts). Canes from esca-diseased mother plants were always infected, but the incidence of infection of the cuttings varied widely (about 30% in 2005, from 1.9 to 4.1% in the other years). However, no final conclusions could be drawn about the stage or stages at which the nursery vines mainly became infected, because the infection frequencies detected in the propagation process were too low and irregular. As regards control of P. chlamydospora, HWT of cuttings performed before or after cold storage influenced plant growth, depending on both the cultivar and the growing conditions, but HWT was harmful to callused graftlings. Natural contamination of nursery material in 2005 and 2006 was insufficient to allow the effectiveness of treatments to be assessed. In 2007, HWT and cyproconzole alone did not reduce the percentage of infection in artificially inoculated cuttings. Only cyproconazole immediately followed by HWT significantly reduced the number of infected cuttings, but this procedure did not eradicate the pathogen.