Pollen-ovule ratios in seven species of Vaccinium (Ericaceae) and stamen structure in Vaccinium myrtilloides and Vaccinium vitis-idaea

Pollen-ovule (P/O) ratios were determined for five Vaccinium species (Ericaceae) native to eastern Canada (Nova Scotia: V angustifolium, V. boreale, V. caespitosum, V. corymbosum, V. uliginosum), one in western Canada (Saskatchewan: V myrtilloides), and one (V vitis-idaea) from both provinces. Pollen, released at maturity as tetrads, was converted to total pollen grains per flower to yield P/O ratios ranging from 238 (V caespitosum) to 2008 (V vitis-idaea), but 736 for the latter in Saskatchewan. These P/O ratios are indicative of facultative autogamy to facultative xenogamy. Additionally, the structure of mature stamens and pollen tetrads was studied in V myrtilloides and V vitis-idaea. Each anther was functionally bilocular; had a single-cell thickness (i.e., epidermis) with regularly occurring papillae; lacked an endothecium; and possessed two distal, hollow tubules each terminating in a pore. Overall pollen grain viability was 76%-97% (V myrtilloides) and 51%93% (V vitis-idaea), with about 20% of tetrads having only 1-3 grains viable, and 12% and 27% of tetrads entirely nonviable in V myrtilloides and V vitis-idaea, respectively. Pollen tetrads occasionally were connected by a sticky substance resembling pollenkitt, but viscin threads were absent. One instance of precocious (in situ) germination of tetrads was recorded within anthers of V myrtilloides. Key words: pollen-ovule ratios, pollen tetrads, pollen viability, poricidal anther, stamen structure, Vaccinium. Les auteurs ont determine les ratios pollen-ovule (P/O) chez 5 especes de Vaccinium (Ericaceae) indigenes de l'Est canadien (Nouvelle-Ecosse: V. angustifolium, V. boreale, V. caespitosum, V. corymbosum, V. uliginosum), une de l'Ouest canadien (Saskatchewan: V. myrtilloides)etle(V. vitis-idaea), provenant des deux provinces. Ils ont converti le pollen libere a maturite en tetrades, en terme de total de grains de pollen par fleur et ainsi obtenir des ratios P/O allant de 238 (V caespitosum) a 2,008 (V vitis-idaea), mais seulement 736 pour cette derniere en Saskatchewan. Ces ratios sont l'indication d'une autogamie facultative a une xenogamie. Ils ont de plus etudie la structure des etamines matures et des tetrades de pollen chez le V myrtilloides et le V vitis-idaea. Chaque anthere est fonctionnellement biloculaire, montre une seule couche de cellule (i. e. epiderme), avec la presence reguliere de papilles, sans endotheque et avec deux tubules distaux vides se terminant par un pore. Dans l'ensemble la viabilite du pollen etait de 76-97% (V myrtilloides) et 51-93% (V vitis-idaea), environ 20% des tetrades possedant seulement 1-3 grains viables, et 12% et 27 % des tetrades entierement non viables, chez les V myrtilloides et V vitis-idaea respectivement. Les tetrades de pollen sont occasionnellement reliees par une substance collante ressemblant a un pollenkitt, mais sans la presence de filaments de viscine. On a observe un cas de germination precoce de tetrades (in situ) dans les antheres du V myrtilloides Mots-cles : ratios pollen-ovule, tetrades de pollen, viabilite du pollen, anthere poricidique, structure des etamines, Vaccinium. [Traduit par la Redaction]
Introduction Vaccinium L. is a well recognized and widely distributed genus in the family Ericaceae. Although primarily known for its edible fruit-yielding temperate species such as blueberry and cranberry, the [...]