Self-incompatibility in Prunus is widespread. Most commercial almond (Prunus dulcis) and sweet cherry cultivars (Prunus avium) are self-incompatible, and some are cross incompatible. Thus, they require a specific pollen source other than themselves to bear fruit. Plums (Prunus domestica) can be self-compatible, self-incompatible or partially self-compatible. Partial self-compatibility means that fruit set from self-pollination can occur, but success is usually low, less than 15%.

The sour cherry (Prunus cerasus) industry in the United States is a monoculture of the cultivar Montmorency, thus it has been considered self-compatible. Beginning in 1983, cultivars of cherries have been introduced from Europe into breeding programs, and many of these are self-incompatible. Consequently, self-incompatible sour cherry cultivars are now being released.

Researchers at Michigan State University tested several cherry cultivars to determine their compatibility rating. ‘Tschemokorka’ and ‘Crisana’ sour cherries are self-incompatible. This was shown by observing pollen germination and pollen tube growth in the pistil. If the pollen is incompatible, the pollen might germinate, but it is killed as it grows down the style of the pistil. In ‘Meteor’ and ‘Montmorency’ sour cherries, pollen germinates, and growth begins down the style, but a large amount of pollen is killed as it grows. Some gets through and fertilizes the ovule, but a lot gets stopped along the way. The researchers labeled this as partial self-incompatibility.

What this means for Alaska sour cherry growers is that pollination intensity is extremely important to fruit set in ‘Meteor’ and Montmorency’ sour cherries.

Excerpted from HortScience 1990. 25(12): 1636-1638. A preliminary analysis of self-incompatibility in sour cherries, by A. Lansari and A. Iezzoni.