Differences between Self-Incompatibility and Self-Sterility

Abstract

THE term ‘self-sterile’ is used for describing plants which fail to set self-seed when they are grown in isolation or when they are self-pollinated. Silow¹ reviewed the early usage of this term and proposed the term ‘voluntarily self-sterile’ to describe Lotus plants that fail to set seed when isolated from insects and ‘artificially self-sterile’ when they still fail to set self-seed following artificial self-pollination. He observed that several Lotus species in isolation set more self-seed following artificial self-pollination than the same plants without artificial self-pollination. This difference can be accounted for by the presence of a stigmatic membrane which prevents germination and growth of any pollen. This membrane is ruptured by artificial self-pollination or by insect pollination of the flower, after which pollen can germinate and grow. The presence of a stigmatic membrane was observed by Elliott² in L. tenuis and by Giles³ in L. corniculatus. Giles³ was unable to observe any difference in germination between self- and cross-pollen once the membrane ruptured. The presence of a similar membrane was observed by me⁴ in several other Lotus species. This membrane can account for the observed voluntary self-sterility and for differences between voluntary and artificial self-sterility, but it does not account for artificial self-sterility.