Relationships between fruit set, pollen-tube growth, and S-RNase concentration in the self-incompatible Japanese pear

Abstract

Fruit set after self-pollination varied from 0.6 to 15.2% and the growth rate of self pollen-tubes in the style also varied from 0 to 39% among the Japanese pear cultivars ( Pyrus serotina Rehd.); the former data were calculated using the results reported by several workers at different locations during several years, and the latter were our experimental results using a stylar culture technique in vitro. Cultivar differences in fruit set matched well with differences in the tube growth ( r=0.852 **, n=12) ( **; significant at 1% level by t-test). Concentration of the sum of two S-RNases in the style was cultivar-dependent, and it showed a negative relation to fruit set ( r=−0.764 *, n=7) ( *; significant at 5% level) or pollen-tube growth ( r=−0.888 **, n=18). The correlation coefficients between the pollen-tube growth and S 1-, S 2-, S 3-, S 4-, or S 5-RNase concentration were; −0.714 ( n=5), −0.242 ( n=6), −0.560 ( n=4), −0.701 * ( n=9), or −0.948 ( n=4), respectively. Cultivar differences in the expression of self-incompatibility may, thus, be present in the Japanese pear and regulated, at least in part, by the concentration of S-RNase differentially produced in the style of each cultivar.