CHARACTERISTICS OF ALFALFA FLOWERS AND THEIR EFFECTS ON SEED PRODUCTION

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Abstract
Several characteristics and properties of the alfalfa flower were studied to determine their role in seed setting and to provide a basis for the evaluation of mutant flowers for pollination by honeybees. Ease of tripping varied with plant and with age of floret. Nectar was secreted at a uniform daily rate for 4–5 days after the flowers opened. Nectar absorption was similar to secretion for 2 days but then accelerated. Removal of nectar had no effect on seed setting. Ovules were viable from opening to wilting of the flowers. Age of floret did not affect seed production after self-fertilization but, after cross-fertilization there was a gradual decline after 3 days. Pollen from untripped florets decreased slightly in germination with age, but remained viable after 10 days’ storage in a honeybee colony. Pollen-collecting honeybees effectively cleaned themselves of pollen in 2 days. Seed production was not increased by repeated visits of honeybees to tripped flowers, and cross-fertilization was not increased by dusting pollen on plants before tripping. Ovules of florets with exposed stigmas remained fully functional for up to 6 hours but then declined rapidly to llmost 0 at 48 hours. Foreign pollen was still 50% effective when applied 24 hours after self-pollination. Self- and cross-fertilized seeds were intermingled in the pods but self-fertilized seeds did not occur beyond the fourth position from the proximal end. It is suggested that extent of honeybee pollination may be improved by providing an alfalfa flower either with an exposed stigma or with a vestigial standard petal combined with delayed sell-tripping.

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