Factors affecting the Abscission of Reproductive Organs in Yellow Lupms (Lupinus luteusL.)

Abstract

Abscission of flowers in Lupinus luteus L. (var. Weiko II) without growth of ovaries is followed by abscission of small pods (15–20 mm. long). Normally flower abscission is much more pronounced than pod abscission. Abscission was delayed on plants from which laterals or their terminal and axifliary buds were removed. Flower abscission was not affected, but pod abscission increased as a result of defoliation. When flowers at the base of the main inflorescence were replaced by auxins and anti-auxins flower abscission was induced in either an auxin pattern in which most of the flowers near the site of application dropped, and pods developed on the apical whorls, or an anti-auxin pattern in which pods developed on basal whorls near the site of application but not higher up. The anti-auxin pattern was similar to the pattern of abscission normally induced by developing pods on basal whorls. α-Naphthylacetic acid (NAA) was much more effective in inducing abscission than β-indolylacetic acid (IAA). 2:3:5-triiodobenzoic acid (TIBA), NAA, and IAA applied in mixtures at various concentrations acted mainly antagonistically, i.e. the abscission-inducing effect of NAA and LAA was depressed in basal whorls, and in apical whorls the effect of TIBA was less prevalent. Consequently the effect of the mixtures on the total number of pods was about equal to that of the most active component by itself. All growth substances seemed to move much more efficiently in acropetal direction than in basipetal direction in the flower stalk. Transport in lateral direction was very limited. The effect of growth substances applied on laterals was enhanced by defoliating the main 8tem. The influence of assimilates on flower and pod abscission and transport of growth substances is discussed.