Effects of Ovule Positions in Fabaceous Flowers on Seed Set and Outcrossing Rates

Abstract

Linearly nonrandom seed set patterns were found in pods of bee-pollinated Lupinus nanus Dougl. (ex Benth.) and Medicago sativa L. In a mixture of different genotypes of the California blue lupine and in a white-flowered mutant of tetraploid alfalfa, seed set was highest in the second ovule position from the peduncular end of the pod and declined toward the stylar end In M. sativa there was also a lateral non-randomness with seed set being much higher (P < 0 2%) in even-numbered ovule positions, which correspond to the upper valve of the pod if the fruit is viewed from the peduncular end, than in odd-numbered positions Highly significantly unequal seed set distributions between the two fruit valves also found in pods collected from the wild, belonging to M radiata L., M polymorpha L., and M. truncatula Gaertn. In left-handed (anticlockwise coiled) Medicago pods the higher seed set occurred in the upper valve, and in right-handed pods in the lower valve (fruits viewed from the peduncular end). In both L. nanus and M sativa outcrossing rates, as verified by progeny tests of genetically marked seed parents, varied with ovule position. In the lupine this rate rose from less than 30% in the basal position to almost 70% in the stylar-most position. In alfalfa, in which total selfing amounted to less than 4%, this selfing was confined to fruit valves characterized by the higher seed set and occurred in basal and middle positions.