Abstract:

A new behavioral outbreeding mechanism, “flexistyly”, was found in some species of the genus Amomum and Alpinia (Zingiberaceae). In this paper, the floral and pollination biology of Alpinia oxyphylla were studied in two populations at the South China Botanical Garden in Guangzhou during the 2002-2003 flowering seasons. The objectives of this study were to determine whether A. oxyphylla showed the same flexistyly pollination mechanism as that in other species of Alpinia previously reported and to examine the breeding system. According to our observation, flowering of A. oxyphylla took place from late February to late April. The flowering period of inflorescence lasted on average about 16-26 d, with most individuals at 23-26 d, and anthesis of a single flower lasted 1 d. Generally, populations of A. oxyphylla had two floral morphs that differed in flowering behavior: the cataflexistylous morph in which the stigma is held erect above the dehiscent anther when anthesis begins in the morning and becomes curved under the anther in the afternoon, and the anaflexistylous morph in which the receptive stigma is curved under the indehiscent anther in the morning and moves into a reflexed superior position above the anther as it begins to shed pollen in the afternoon. The stylar movements in the two floral morphs were synchronous, and they had similar traits to those found in other Alpinia species previously reported. However, our observations indicated that if the maximal air temperature was under 18 ℃, the anthesis of a single flower was prolonged to 2 d, and the populations of A. oxyphylla showed only a single floral morph, viz., the cataflexistylous morph, in which the stigma was held erect above the dehiscent anther when the flower starts to open in the morning and begins to curve under the anther until the second day at 6:30-11:00 a.m. During the flowering period, both the stigma acceptability (H₂O₂ test) and pollen viability (MTT test) held high levels (>96%) and even retained levels above 75% until 9:00 a.m. on the second day when the flower withered. The P/O ratios of the two floral morphs were different: the cataflexistylous morph had lower pollen grains and P/O ratio than that of the anaflexistylous morph, but approximately equal ovules. Field experiments indicated thatA. oxyphylla was self-compatible. The seed sets were significantly high in both out-crossed and artificial self-pollinated flowers, while no seed set occurred in bagged emasculated flowers and bagged flowers indicating that there is no apomixes. There were significant differences in the seed set between the self-pollination and cross-pollination treatment on anaflexistylous morph. However, no significant differences were found in the seed set between the self-pollination and cross-pollination treatment on the cataflexistylous morph. Our results showed that the breeding system of A. oxyphylla is xenogamy and dependent upon insects for fertilization. The effective pollinators were solitary bees and the honeybee, which visited the flowers mostly for nectar. Uhe pollen is starchy and the flower produced ample nectar, 8.37-15.79 μl, with a sugar concentration of 30.12%-32.83%, which was the main reward for pollinators. During the day, the nectar volume augmented with time and attained a peak (15.79±5.7) μl at about 14:00 p.m., after which it descended to (11.22±8.11) at about 18:00 p.m.; however, the nectar sugar and amino acid (0.031±0) mg·ml^-1 concentrations were steady. Our observations also showed that the labellum with red stripes, which act as a “honey guide”, may be an indirect advertisement, and nectar may be a direct advertisement in attracting pollinators.

Key words: Alpinia oxyphylla, Flowering, Flexistyly, Pollination, Breeding system