The 2011 ASHS Annual Conference

Trees of the genus, Pyrus, notably cultivars of P. calleryana Decne. (callery pear) and the species P. kawakamii Hayata. (evergreen pear), have been widely used as medium-sized, deciduous or semi-evergreen, flowering landscape trees in urban Southern California.  They are well adapted to a range of soil conditions and moderate drought, but they have serious defects that limit their use. Callery pears, ‘Bradford’ and other newer cultivars, suffer from fire blight disease (Irwinia amylovora) and narrow branch angles that cause severe splitting of main branches, while evergreen pear is highly susceptible to fire blight and can require considerable training to develop an attractive tree.  An ornamental Pyrus breeding program by the Landscape Plant Development Center (LPDC), Mound, MN, identified several Pyrus interspecific hybrids with wide-angled branch structure, good flowering, attractive fall color, and fire blight resistance.  Their parentage may also confer adaptation to warm semi-arid climates, but this trait has not been proven.   Thus, a five-year study was initiated at the University of California Riverside to determine the performance and horticultural characteristics of six advanced interspecific Pyrus selections from LPDC’s breeding program under the climate and soil conditions of warm semi-arid inland Southern California, and to compare their performance against ‘Bradford’ and evergreen pears.  Across all characteristics evaluated, none of the interspecific hybrid selections performed as well as the best overall tree in the study, evergreen pear.  However, the performance of three selections equaled ‘Bradford’.  All trees of two hybrid selections were killed by fire blight, but all hybrid selections exhibited wide branching angles and good structure.