Pollen deposition on the stigmatic surface of blueberry pistils was studied with regard to maximum pollen load and stigmatic fluid production (stigma receptivity). Three hybrid southern highbush cultivars (Vaccinium corymbosum L. with V. darrowi Camp, V. ashei Reade, and/or V. angustfolium Aiton), two northern highbush cultivars (V. corymbosum), and one hybrid half-high cultivar (V. corymbosum with V. angustifolium) were selfand cross-pollinated with counted pollen tetrads until saturation of the stigmatic surface occurred. Stigmatic saturation generally required 200 to 300 tetrads and was characterized by the cessation of stigmatic fluid production and the inability to absorb further tetrads. The loss of stigmatic receptivity was irreversible. Cross-pollination resulted in cessation of stigmatic fluid production at lower levels of tetrad deposition than did self-pollination, suggesting a potential pollen-stigma recognition phenomenon. Northern highbush, half-high, and southern highbush cultivars required 7% to 10%, 12% to 17%, and 14% to 21%, respectively, more self-pollen to develop the stigmatic saturation condition. The potential relation of the pollenstigma phenomenon to self-incompatibility mechanisms is discussed.
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