Susceptibility of European pear genotypes in a gene bank to pear psylla damage and possible exploitation of resistant varieties in organic farming

Since the time when Westigard et al. (1970) have discovered that Asian pear species – Pyrus betulifolia, P. calleryana, P. faurieri, P. ussuriensis, P. x bretschneideri – are resistant to the pear psylla (Cacopsylla species) there is an increasing interest towards the possible resistance of different pear genotypes against this very serious pests of pear production. Harris (1973) investigated the psylla resistance of interspecific pear hybrids and established their resistance to this pest. Although interspecific hybrids have been found to be resistant to pear psylla in other studies, too (Bell & Zwet 1998, Robert & Raimbault 2005, Bell 2009), the bad quality of their fruit limits their usefulness in breeding programmes (Robert & Raimbault 2005) and in commercial production. Quamme (1984) evaluated several pear species and also a number of European per cultivars from the point of view of psylla resistance and has found some of them to be more or less resistant to this pest. Several authors investigated great many further European pear genotypes in the past twenty five years (Quarta & Puggioni 1985, Briolini et al. 1988, Butt et al. 1988, Berrada et al. 1995, Puterka et al.1993, Kocsisné et al. 2005, Robert & Raimbault 2005, Bell & Stuart 1990, Bell 1992, 2003, Bell & Puterka 2004, Sestras et al. 2009, Bell 2009) and detected several cultivars, clones, wild seedlings, ancient and local genotypes to be resistant or highly tolerant to this pest. Most studies were made with field observations (Quarta & Puggioni 1985, Briolini et al. 1988, Berrada et al. 1995, Puterka et al.1993, Kocsisné et al. 2005, Robert & Raimbault 2005, Sestras et al. 2009, Bell 2009) and great many studies were made in the laboratory, too, by rearing psylla larvae on plant material (Harris 1973, Butt et al. 1988, Bell & Stuart 1990, Bell 1992, 2003, Puterka et al 1993, Bell & Puterka 2004). Most authors agree that commonly grown European pear cultivars are highly susceptible to the pear psylla damage (e.g. Quarta & Puggioni 1985, Robert & Raimbault 2005). No more than a minor part of the investigated genotypes have been found to be resistant or at least of low susceptibility (e.g. Quarta & Puggioni 1985, Bell & Stuart 1990, Robert & Raimbault 2005, Sestras et al. 2009). One Italian cultivar, Spina Carpi, that was found to be of low susceptibility by Quarta & Puggioni (1985), was regarded to be resistant by other authors, too (Briolini et al. 1988, Robert & Raimbault 2005). As far as the reasons of resistance to pear psylla damage are concerned Harris (1973) has pointed out that it is the consequence of ovipositional dispreference and increased nymphal mortality on resistant genotypes. Butt et al. (1988) Susceptibility of European pear genotypes in a gene bank to pear psylla damage and possible exploitation of resistant varieties in organic farming