Abstract
The pollination biology of Impatiens cuspidata, a rare and endemic balsam from the Western Ghats, has been studied with special reference to phenology, pollination, pollen-pistil interactions, breeding experiments and stigma receptivity. It flowers at night between 2330 and 0430 hr; flowering days extend up to 160 days in a year. The anther dehisced one day before anthesis, which confirmed the protandrous condition of the flower. Pollen-ovule ratio was calculated as 1729:1. Hawk moths, honeybees, flies and butterflies are the major pollinators of Impatiens cuspidata. Pollen grains are oval, having an average diameter of 28.24μm. Pollen viability by FCR test confirmed that 82% pollen grains are viable on the day of anthesis. Best pollen germination along with 1636μm tube development was achieved in Brewbakers medium. Stigma was more receptive (up to 80%) on the first day of flower opening. It chiefly reproduced by means of cross pollination, where the fruit set was only 40%, but artificial cross-pollination through xenogamy enhanced fruit set up to 80%. The plant is an obligate out-crosser and self incompatible, as confirmed by various hand pollination experiments. Seed germination in natural and controlled conditions was only 20%. Its dependence on a specialized habitat, bottlenecks in sexual reproduction, low percentage of seed germination and other abiotic factors could be reasons for its limited distribution and endemism.
Highlights
Pollination biology provides a framework to test a diverse array of paradigms in several subdisciplines of biology (Bawa et al 1993)
A comprehensive study on pollination biology of Impatiens was fundamental to investigations into its reproductive syndrome, systematics and evolutionary biology
A comprehensive study on pollination biology of endemic balsams has not been made so far due to their habitat specificity, island biogeography, delicate nature and explosive fruits. One such wild ornamental balsam namely Impatiens cuspidata has been selected for the present investigation on pollination biology encompassing phenology, pollination, pollinator behaviour, pollen viability, stigma receptivity and breeding behaviour to find out possible reasons for its limited distribution in the Western Ghats
Summary
Pollination biology provides a framework to test a diverse array of paradigms in several subdisciplines of biology (Bawa et al 1993). The genus contains over 206 species in India (Vivekananthan et al 1997; Vishwanathan & Manikandan 2003; Bhasker 2006), half of which occur in southern India and more than 86 are endemic to the Western Ghats (Nair 1991) Due to their restricted distribution, nearly 30 species of Impatiens are already threatened with uncertain future (Vajravelu & Daniel 1983; Pandurangan & Pushpangadan 1997; Sreekala et al 2008). A comprehensive study on pollination biology of endemic balsams has not been made so far due to their habitat specificity, island biogeography, delicate nature and explosive fruits Against this background, one such wild ornamental balsam namely Impatiens cuspidata has been selected for the present investigation on pollination biology encompassing phenology, pollination, pollinator behaviour, pollen viability, stigma receptivity and breeding behaviour to find out possible reasons for its limited distribution in the Western Ghats
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