Pollination and Pollen Tube Growth in Relation to Cranberry Fruit Development

Pollination and pollen tube growth were evaluated in two years as potential factors suppressing cranberry ( Vaccinium macrocarpon Ait.) fruit set. Supplementing insect pollination with hand pollination increased fruit set from ≈30% to ≈38% in both years. The number of flowers per unit area was an important contributor to fruit set variation in one year. Cranberry uprights exhibited a temporal decline in fruit set when flowers were pollinated sequentially; the first flowers to open had a higher probability of fruit development than flowers opening later. Examination of stigmas indicated flowers receiving low amounts of pollen (<10 tetrads), or pollen that fails to germinate, are more likely to abort. An inadequate number of pollen tubes and lack of subsequent fertilization provides a partial explanation of fruit abortion in cranberry. Cranberry fruit set under existing field conditions appears to be limited, in part by insufficient pollination and pollen tube growth, with the latter apparently the result of intraplant competition for resources. Providing supplemental hand pollination increased cranberry yields in both years, 48% over natural insect pollination when the number of flowering uprights per unit area was high (≈3000/m 2 ). A significant amount of yield variation was explained by the number of flowering uprights per unit area in both years.