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Seasonal Emanation of Ocimene from Alfalfa Flowers with Three Irrigation Treatments¹

Alfalfa (Medicago sativa L.) requires cross-pollination for economic seed production. In the arid Southwest, honeybees (Apis mellifera L.) are relied on for this pollination. The studies reported in this paper were conducted to better understand the plant and honeybee dynamics during the alfalfa pollination period. Emanation patterns of volatiles from alfalfa flowers were studied by gas chromatography during the summer seasons of 1973, 1974, and 1975. Irrigation treatments and cutting dates were varied, and observations of honey bee visitation, flowering, and plant water potential were made. Several emanation patterns of flower volatiles were noted: 1) daily aroma maxima occurred between 1100 and 1400 hours, depending on cloud cover and rainfall, 2) the June blooming period produced the highest amounts of volatiles/ flower compared to May, August, and September (gradually decreasing from June through September), and 3) a "burst" of volatiles (emanation/flower) that lasted 3 to 4 days occurred during early June each year. Irrigation treatments did not affect the amount of volatiles produced during the "burst" although adequate moisure tended to keep the volatiles/flower readings higher than the dry treatment after the "burst." The volatile "burst" may be related to a physiological "climacteric" occurring when the alfalfa plant has changed from a vegetative to reproductive state. Plant water potential and honeybee counts were not well correlated with volatile emanation changes.

Key Words: Honeybees • Pollination • Terpenes • Flower volatiles • Water stress • Climacteric • Medicago sativa L. • Apis mellifera L.

² Plant physiologist and research technician, respectively, SEA, USDA, 2000 E. Allen Rd., Tucson, AZ 85719.

Received for publication September 1, 1977.

This article has been cited by other articles:

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