Lack of pollen dispersal was noted in various sites and cultivars of sweet cherry (Prunus avium) following one of California's warmest recorded winters (≈550 hours @ 7°C in the Central Valley). `Bing' cherry is thought to require 850 to 880 hours for adequate budbreak and bloom development. Cross pollination is required by most sweet cherry cultivars for fruit set, including `Bing'. Complete anther dehiscence averaged 13% in `Bing' trees sampled, compared to 52% in `Rainier', 65% in `Brooks', 84.5% in `Burlat', 33% in Van, 23% in `Larian', and 86% in `Black Tartarian'. A range of degree of dehiscence from none to half-open was widely apparent, again by cultivar. Many partially dehiscent anthers did not shed pollen normally but appeared to have the mass of pollen completely adherent inside the pollen sacs. `Black Tartarian', `Larian', and `Burlat' shed pollen readily, however, pollen from dehiscent anthers of other cultivars generally appeared to stick together on the everted locule walls and required direct manipulation to be withdrawn from the pollen sac. Anther morphology ranged from normal size to half normal size, anthers appearing to be without pollen altogether that shriveled on drying, and lobes that were aborted. Pollen germination was low overall: 19% `Bing', 18% `Rainier', 20% `Brooks', 57% `Burlat', 14% `Van', 48% `Larian', and 48% `Black Tartarian'. Poor fruit set in low chill years is often attributed to lack of bloom overlap with pollenizers, however, inadequate chilling also may contribute to low fruit set by inhibiting anther and pollen growth and development. The implications of a critical chilling requirement for normal floral differentiation are that in cherry-growing areas where low chill years are common, pollen may not be viable or transferrable from pollenizers and female gametophytic development also may be impaired.
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