Callose and determination of pistil viability and incompatibility

Callose provides a useful phenotypic bioassay in plant breeding to determine: incompatibility system; gametophytic competition; and stigma and ovule viability. Callose appearance in ovules may be associated with senescence, and used to determine the effective pollination period. In incompatible matings, callose formation is specific and related to rejection phenomena. The stigma callose response is induced by informational molecules carried by the germinal line, i.e. self or interspecific pollen, but not by the somatic line. Several methods of visualizing callose are reviewed. The role of callose in pollen-stigma interactions has many analogies with host-parasite interactions, and a model is proposed based on relationships between callose, boron and inhibitor (phytoalexin-like) synthesis. The callose response provides a useful tool for the biotechnology of seed production.