The management of soil-borne pathogens is nowadays complicated by the increasing restrictions in the usage of fumigants. Several factors need to be considered for a sustainable use of this practice such as the susceptibility of rootstocks against soil-borne pathogens which is age-dependent and the incomplete resistance of some of the rootstocks to one or more pathogens. There is an evidence of a pathogenic variation among some isolates of Phytophthora spp. on solanaceous crops and on rootstocks and the development of new diseases or the re-emergence of already known pathogens such as Colletotrichum coccodes after the phase out of methyl bromide. The critical aspects of grafting for soil-borne pathogens management in Italy are discussed.Keywords: solanaceaous crops, Phytophthora nicotianae, Phytophthora capsici, Colletotrichum coccodes
1.IntroductionIn Italy, 59 million vegetable plants, generally grown under greenhouse, are grafted (Morra and Billotto, 2010). In Piedmont (northern Italy) grafted plants are mostly used in tomato cropping system but is becoming more popular also in the case of bell pepper and, in some areas, on melon.Grafted tomatoes are used to reduce susceptibility against pest and root and wilt diseases and to increase yield (Louws et al., 2010;Rouphael et al., 2010). However, resistance may be broken down under high pathogen population pressure and new races of the pathogen may evolve on rootstocks. Recently, some emerging diseases on plants grafted on rootstocks have been recorded in Italy. Verticillium wilt incited by Verticillium dahliae was consistently observed on eggplant grafted on Solanum torvum (Garibaldi et al. 2005), while Colletotrichum coccodes attacks were observed on grafted tomato plants grown in several farms after repeated cropping cycles of tomato (Minuto et al. 2008). This last pathogen can infect several cultivated species, including pepper, potato, eggplant, lettuce, chrysanthemum and some species of Cucurbitaceae and Brassicaceae (Dillard, 1992;Last et al., 1966). Among Phytophthora group, both P. nicotianae and P. capsici can affect tomato (Erwin and Ribeiro, 1996). Rootstocks belonging to interspecific hybrids of Solanum lycopersicum x S. hirsutum (cvs. Beaufort, He Man) and to S. lycopersicum (cv. Energy) were Due to an increased request of grafted plants, experimental activities have been carried out to evaluate the effectiveness of grafting on resistant rootstock against emerging soilborne diseases of tomato. The rootstocks used in this study are considered resistant to many other soil-borne diseases, but their tolerance to P. nicotianae, P. capsici and C. coccodes is not known.
2.Materials and methods
Experimental layout.The first set of trials was carried out in 2010 under growth chamber conditions at Agroinnova (Univesity of Torino) to test the susceptibility of several tomato rootstocks to Phytophthora nicotianae and P. capsici under artificial inoculation conditions. The second set of trials was carried out in 2010 in a plastic tunnel at Boves (Cuneo)...