Scanning electron microscopy studies were made on pollen samples from several small fruit crops: 3 selections of blueberry (Vaccinium), 4 Vitis spp. (V. vinifera L., V. cinerea Engelm., V. rupestris Scheele, and V. amurensis Rupr.), 2 cultivars of raspberry (Rubus), 5 cultivars of blackberry (Rubus), and several species and ploidy levels of strawberry (Fragaria) including 54 cultivars of F. × ananassa Duch., as well as pollen of Duchesnea and Potentilla.
Pollen size and exine characteristics were similar for 4 grape species examined. Polyploid blueberry selections were separable from the diploid selection by pollen grain size. Raspberry and blackberry pollen differed in size, exine ridging or reticulation, and presence of borderless or collared pores. Strawberry pollen is characterized by exine ridging and absence of pores. Cultivars of Fragaria × ananassa could be categorized into 4 groups according to exine ridge patterns. Cultivars exhibited broad longitudinal ridges or were characterized by less prominant to indistinct ridges. One cultivar was unique in that anastomosing ridges were present between adjacent ridges.
Pollen grains of diploid F. vesca L., F. vesca fma. semperflorens Duch., and F. nubicola Lindl, ex Lacaita; a tetraploid clone of F. vesca; the hexaploid F. moschata Duch.; and octoploid F. × ananassa, F. chiloensis (L.) Duch., and F. virginiana Duch. are broadly elliptical, tricolporate and moderately to prominently ridged. Size of pollen and prominance of exine ridges appeared to correspond with ploidy level. Pollen of F. nipponica Mak. differed in that grains are subprolate to sphaeroidal and exine is ornamented with minute, rounded to subconical verrucae arranged in rows. Pollen of the related genera Duchesnea and Potentilla were very similar morphologically to those of octoploid Fragaria spp., except that pollen of D. indica (Andr.) Focke are larger and the exine of P. recta L. exhibits an extremely minute pore structure.
Received for publication February 23, 1977. Mention of a trademark name or a proprietary product does not constitute a guarantee or warranty of the product by the USDA, and does not imply its approval to the exclusion of other products that may also be suitable.
Research Plant Pathologist, Fruit Laboratory, Plant Genetics and Germ-plasm Institute. Assistance with SEM photography by Gordon Carpenter is gratefully appreciated.