Occurrence of Phaeomoniella chlamydospora on grapevine planting material in Sardinia and its control with combined hot water and cyproconazole treatment.

Abstract

The occurrence of Phaeomoniella chlamydospora was investigated during the propagation process of an Italian nursery, and combined hot water and cyproconazole treatments were carried out to limit its spread in nursery plants. In the three–year period 2005–07, cutting and graft samples (scion cv Sangiovese, rootstock cvs 140Ru in 2005 and 1103P in 2006–07) were taken during the propagation process at several infection risk stages in order to assess the presence of P. chlamydospora. Moreover, in 2005 and 2006 cuttings from esca–symptomatic grapevines (scion cv Sauvignon blanc, rootstock cvs 140Ru in 2005 and 1103P in 2006) were treated at different stages of the propagation process. In 2007, artificially infected 1103P cuttings were treated after inoculation with P. chlamydospora (107 conidia ml-1). Cuttings and callused graftlings were treated by dipping in a hot water bath at 50°C for 30 min (HWT) or in a cyproconazole suspension (0,1 g a.i. l-1) for at least 12 h, in different combinations. At each stage of infection risk and at each treatment woody material was collected and grown in pot, avoiding accidental contamination, or in the field nursery for one season and then destructively examined. DNA was extracted from wood collected at different points along the plant and analysed by nested PCR with Pch-specific primers. One-mm thick woody slices from artificially inoculated cuttings were plated on MEA plus antibiotics and fungicides. Despite the extended wood discoloration, P. chlamydospora occurrence on nursery plants was scarce in the three–year period. Planting material contamination may have resulted from infected mother plants (from 0.0 to 6.7 % of infected cuttings were obtained directly from non-symptomatic mother plants) or from the propagation process, particularly during the stages following grafting (0.0 to 23.3 % of infected grafts). Canes from esca–diseased mother plants were always contaminated, but in quite different percentages (about 30 % of the cuttings examined in 2005, from 1.9 to 4.1 % in 2006 and 2007). However, no final conclusion could be drawn about which stages played a major role in the contamination of nursery plants, due to the low and irregular infection frequencies detected in the propagation process. As regards P. chlamydospora control, HWT performed on cuttings before or after cold storage influenced vegetative growth depending on both the cultivar and the growth conditions, but it was deleterious on callused graftlings. Natural contamination on nursery material in 2005 and 2006 was insufficient to assess the effectiveness of treatments. In 2007, HWT and cyproconzole treatments alone were not effective in reducing the percentage of infection in cuttings that were artificially inoculated. Only cyproconazole immediately followed by HWT significantly reduced the number of infected cuttings, but it was not sufficient to eradicate the pathogen.