Resistance to Pear Psylla Nymphal Feeding of Germplasm from Central Europe

Pear psylla (Cacopsylla pyricola Foërster) is the most serious pest of the European pear (Pyrus communis L.) in the production regions of Europe and North America. Nine plant germplasm introductions of pear from Central Europe recently released from plant quarantine were evaluated for nymphal feeding antixenosis, a primary mode of resistance known to be correlated with ovipositional antixenosis and antibiosis (i.e. nymphal mortality and reduced developmental rate). Five single-shoot budded trees were grown in the greenhouse without pesticide application. The top two youngest fully expanded leaves were infested with ten 2nd and 3rd instar nymphs from a young laboratory colony. The number of surviving nymphs and the number of actively feeding nymphs was recorded after two days. Three cultivars from Yugoslavia, ‘Karamanka’, ‘Jerisbasma’, and ‘Vodenjac’, plus NY 10353 (a resistant control of P. ussuriensis Max. ancestry) were significantly more resistant to nymphal feeding than the susceptible control, ‘Bartlett’, and the cultivars ‘Junsko Zlato’, ‘Lida’, ‘Orlovskaya’, ‘Oranzhevaja’, ‘Nadejda’, and the selection IV 12. These objective data confirm field observations made in Europe of the Yugoslavian cultivars, and increases the number of psylla-resistant genotypes available for breeding new cultivars. INTRODUCTION The pear psylla (Cacopsylla pyricola Foërster syn., Psylla pyricola Foërster, P. pyri L., and P. pyrisuga Foerster) is a serious insect pest of the cultivated European pear (Pyrus communis L.) in the production regions of North America and Europe. The insect has rapidly developed resistance to most of the pesticides employed for control and biological controls alone have rarely provided sufficient control for commercial production. The annual cost of chemical control exceeds $300 per acre. Cultivars with durable resistance would enhance the economic and environmental sustainability of pear production by reducing producer costs and pesticide use. These species of pear psylla and their host apparently coevolved in Europe. Early investigations of western European cultivars identified only a single moderately resistant cultivar, the old Italian pear ‘Spina Carpi’ (Quarta and Puggioni, 1985). Pomologists and breeders have been collecting wild germplasm and landrace cultivars in order to identify diverse sources of resistance for use in the development of new, but psylla-resistant, cultivars. The present research is a continuation of an investigation of the Pyrus gene pool of eastern and central Europe as a source of resistance (Bell, 1991, 1992; Bell and Stuart, 1990; Puterka et al., 1993). MATERIALS AND METHODS Germplasm Nine recent germplasm introductions of pear from central Europe, plus ‘Bartlett’ as a susceptible control and NY 10353 (a P. ussuriensis × P. communis BC1 hybrid) as a resistant control (Table 1). Proc. XXVI IHC – Genetics and Breeding of Tree Fruits and Nuts