Genetic basis of trichome production in Arabidopsis lyrata

Leaf trichomes may protect plants against herbivorous insects, and may increase tolerance to drought and UV‐radiation. The perennial herb Arabidopsis lyrata (Brassicaceae) is polymorphic for trichome production and occurs in a glabrous and trichome‐producing form. In addition, there is quantitative variation in trichome density among trichome‐producing plants. To examine the genetic basis of glabrousness, we conducted controlled crosses with plants originating from two natural populations in Sweden (one polymorphic for trichome‐production, and one consisting of glabrous plants only). In addition, we estimated the heritability of trichome number from parent‐offspring regressions for plants originating from the polymorphic population. Crosses between glabrous plants resulted in glabrous offspring only, whereas crosses between glabrous and trichome‐producing plants, and crosses between trichome‐producing individuals, resulted in either all trichome‐producing offspring or both phenotypes. In segregating crosses between trichome‐producing plants, the ratio of glabrous:trichome‐producing offspring did not deviate significantly from 1:3, while in segregating crosses between glabrous and trichome‐producing individuals the ratio did in most cases not deviate from 1:1. Within‐ and between‐population crosses gave similar results. The heritability of trichome number estimated from regression of offspring on mid‐parent was high (h2±SE, 0.65±0.15). The results suggest that glabrousness is inherited in a simple Mendelian fashion, with the allele coding for trichome production being dominant over that for glabrousness. They further indicate that glabrousness is due to a mutation at the same locus in both populations.