Host resistance to pear psyllids [Cacopsylla pyri (L.), C. pyricola (Förster), and C. pyrisuga (Förster)] is a major objective of several pear breeding programs in North America and Europe (Bellini and Nin, 2002; Brewer and Palmer, 2011; Lespinasse et al., 2008). Both adults and nymphs feed primarily in the vascular tissue of the leaves, petioles, and succulent shoots. Prolonged feeding in the phloem by nymphs affects the plant directly by inducing necrosis and premature defoliation. The nymphs excrete excess sugar as honeydew, which can cause russeting of young fruit. Sooty mold fungus grows on the honeydew, resulting in reduced photosynthesis and marked fruit. The insect is also the vector of the pear decline phytoplasma (Hibino et al., 1971). In North America, C. pyricola has rapidly developed resistance to commonly used pesticides, including organophosphates and pyrethroids, and biological controls are not always sufficiently effective. Resistant cultivars would reduce grower costs and enhance the sustainability of the pear industry.
The programs seek to combine resistance from Pyrus ussuriensis Maxim, P. pyrifolia (Burm.) Nakai, and from landraces of P. communis L. (Bell, 2013; Bell and Puterka, 2004; Braniste et al., 2008). The choice of parents for breeding must take into consideration the level of resistance to pear psylla and fruit quality and production traits. Germplasm with at least medium-sized fruit have been used in preference to the small-fruited Asian species (P. betulifolia Bunge, P. calleryana Decne., P. fauriei Schneid., and smaller-fruited P. ussuriensis) that are also resistant to pear psylla (Westigard et al., 1970). The fruit traits of many of the cultivars and selections used in breeding have not been well documented with the exception of P. ussuriensis × P. communis backcross selections from the Cornell University breeding program and the European landrace cultivars (Bell and van der Zwet, 1999). In general, the Cornell P. ussuriensis × P. communis selections are characterized by small to medium-sized fruit (35 to 60 mm diameter), round to round–ovate and pyriform shape, moderate skin russeting, medium texture, coarse to moderately fine grit, and generally poor flavor with two exceptions (NY10353 and NY10354). The European landrace cultivars have larger fruit (54 to 70 mm in diameter), are more pyriform, and have less skin russet, but have generally coarse, firm texture, elevated levels of grit, and insipid to poor flavor.
Several advanced generation interspecific Pyrus communis × P. pyrifolia and Pyrus communis × P. ussuriensis backcross selections are also being used in our breeding program as sources of resistance to pear psylla. The degree of resistance to nymphal feeding of most of these selections has been characterized (Bell, 2013). The purpose of this study was to document and rank this germplasm for fruit quality traits as an aid to selecting appropriate parents for breeding.
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Brewer, L.R. & Palmer, J.W. 2011 Global pear breeding programmes: Goals, trends and progress for new cultivars and new rootstocks Acta Hort. 909 105 119
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