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CROP PHYSIOLOGY & METABOLISM

Effect of Flower Color and Sampling Time on Volatile Emanation in Alfalfa Flowers

^a Istituto Sperimentale per le Colture Foraggere, viale Piacenza 29, 26900 Lodi, Italy

iscfbred{at}telware.it

Flower volatile compounds of alfalfa (Medicago sativa L.) are involved in attractiveness to pollinating insects, and thus influence seed set. This study investigated differences in volatile emanation in this species by varying flower color of the sampled material or time of flower collection. Chemical determinations were made by gas chromatography and gas chromatography–mass spectrometry analyses. The first investigation examined volatile concentration in clones characterized by seven different color ratings. Significant variation among colors was found with a trend for greater emanation from dark- than from light-colored flowers. This trend could bear an evolutionary significance to compensate for the possibly lower visibility of dark flowers in a stand. The second investigation analyzed volatiles from intact inflorescences and from florets and rachises taken separately. A substantial similarity of volatile amount and composition among the three kinds of samples was observed. The final investigation assessed the volatiles produced at different times of the day in each of the first three flowerings of the growing season, during which alfalfa pollination was expected to take place. Confirming previous evidence, temporal patterns of emanation were observed, with a sharp increase from the flowering in May to those in July and August and a strong time-of-day effect during the two summer flowerings (burst of volatiles around midday). The marked seasonal effect appeared somewhat related to temperature increase while the daily variation of emanation in summer paralleled that of solar radiation. There seems to be a coincidence between conditions for maximum volatile emanation and reported optima for insect foraging activity.

Abbreviations: GC, gas chromatography • MS, mass spectrometry