ARS | Publication request: Pollen Viability and Pollen Tube Attrition in Cranberry (Vaccinium macrocarpon)

Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 13, 2008
Publication Date: N/A

Interpretive Summary: Cranberries require bees for pollination. More pollen is needed than expected from the numbers of resulting seeds in a berry. It was shown that cranberry pollen is largely fertile, but that about half of the pollen grains failed to generate a pollen tube that extended the length of the floral style. If this physiological inhibition or hidden incompatibility of cranberries could be at least partly overcome through breeding, then marginal pollinator service (e.g. nectaring honey bees) would be far more effective in setting cranberry fruits.

Technical Abstract: The content of mature seed in a cranberry fruit increases with stigmatic pollen load. On average, however, only two seeds result for every tetrad of pollen deposited. What then is the fate of the two remaining pollen grains fused in each tetrad? Germination in vitro revealed that most of the grains in every tetrad were viable and could initiate a pollen tube (90% of tetrads generated 3-4 pollen tubes). Using a semi-vivo technique, excised styles of receptive pistils were implanted in agar, dosed with two or four pollen tetrads, and incubated for two days. On average, the count of pollen tubes exiting the cut style tips was one quarter the count of tetrads; doubling the pollen load doubled the count of tubes, with heaped pollen loads yielding >20 pollen tubes. Gametophytic selection via pollen tube attrition in the style appears to explain the discrepancy between stigmatic pollen load and the count of mature seeds in a cranberry fruit.