Inheritance and distribution of trichome phenotypes in Datura wrightii

Glandular trichomes in plants often confer resistance to herbivorous insects. The native plant species Datura wrightii (Solanaceae) Is polymorphic with regard to trichome morphology, Some mature plants are covered primarily with nonglandular trichomes, while others possess glandular trichomes that excrete a sticky exudate, Both phenotypes were found in nearly all southern California plant populations surveyed, The frequencies of glandular (sticky) and nonglandular (velvety) phenotypes, however, varied significantly among populations. By employing reciprocal hybridization and backcross designs, we showed that trichome phenotype is inherited largely in a Mendelian fashion. The allele coding for the sticky phenotype was dominant over that for the velvety phenotype, The expression of the recessive gene was age dependent; velvety phenotypes produced glandular trichomes on their cotyledons and the first five true leaves. Thereafter these plants produced nonglandular trichomes on all newer leaves, We hypothesize that feeding by herbivorous insects and/or water stress may play a role in maintaining this polymorphism in natural plant populations.