Analysis of Inter-Specific Incompatibility Using Fruitset, PCR-RFLP and Pollen Tube Growth in Pear

Interspecific hybridization is a popular breeding method employed to introduce effective factors into crops. To evaluate the potential of this method to enrich the quality of pear fruits, we carried out crosses between P. pyrifolia and other species using the pollens of 'OPR114' and 'OPR260' of P. betulaefolia, 'Dangshansuli', 'Xuehuali', and 'Yali' of P. bretschneideri, 'OPR125', 'OPR195', and 'OPR249' of P. calleryana, 'Bartlett', 'Bosc', 'Canal pear', and 'Max Red Bartlett' of P. communis, and 'Chuhwangbae' of P. pyrifolia to pollinate flowers of P. pyrifolia 'Niitaka'. Fruit set in 'Niitaka' pear after artificial pollination was investigated under both field and controlled conditions, which encompassed temperature control and use of water-cuttings of winter twigs. To assess compatibility of hybridizations, pollen tube elongation was analyzed in squashed styles under controlled temperature, and the self-incompatibility (SI) gene pattern was validated by PCR. Under field conditions, crosses of 'Niitaka' with 'OPR114' of P. betulaefolia and 'Bosc' and 'Canal pear' of P. communis resulted in incompatibility, as the fruit set was low. However, when 'Niitaka' was pollinated by 'Xuehuali', some of the pollen tubes reached the ovary but they then arrested and appeared swollen in the middle part of the style. PCR confirmed the incompatibility of these crosses, as the gene product from pollens was a different size from that of the 'Niitaka'. However, interspecific hybridization under controlled conditions resulted in fruit production. We show that interspecific hybridization with P. pyrifolia and other species was feasible under controlled conditions. Suggesting that self-incompatibility of crosses was dependent on environmental factors rather than genetic predisposition.