Summary

Chemicals capable of selectively inhibiting pollen development and thus blocking male fertility have been known for some time. Most were identified in screening programs designed to discover chemical hybridizing agents (CHAs) for the large-scale commercial production of hybrid seed, particularly in small grains. Driven by practical requirements, this research has identified newer generations of CHAs with increasingly better selectivity and effectiveness. However, research into the mode of action of these substances has lagged their practical applications in breeding and hybrid production. Compounds are known that cause a range of effects, including feminization of male florets and inhibition of early anther development, interference with tapetal functions and microspore development, and defective germination of the mature pollen. Several CHAs also have demonstrated a stimulatory effect on the induction of androgenic plants from anther cultures derived from treated plants. The strength of this response varies among genotypes. The molecular and physiological mechanisms of these effects are unknown. The purpose of this review is to encourage further research with these substances.

Introduction: Tools and insights into pollen development

The study of complex natural events requires development of tools suitable for their analysis and manipulation. Effective use of such tools then becomes the basis of practical new technologies. So it is with efforts to probe the development and function of the male gametophyte. Descriptive methods have led just so far into understanding the development of pollen and the process of pollination. Beyond description, one must functionally separate its essential from its accidental elements and identify the points of regulation. The classic analytical tools for dissection and disruption of developmental processes are surgical, chemical, and genetic. This discussion considers chemical methods.