Inheritance of leaf area and hooked trichome density of the first trifoliolate leaf in common bean (Phaseolus vulgaris L.)

Hooked trichomes on common bean (Phaseolus vulgaris L.) plants are known to function as a plant defence against phytophagous insects and rust disease, and wide genotypic variability exists for trichome density. A bean cross between small-leafed, low-trichome-density cv. Harokent (P1) and broad-leafed, high-trichome-density cv. California Dark Red Kidney (P2) was analyzed to determine the inheritance of leaf area and trichome density of the first trifoliolate leaf under controlled environments. The F1 hybrids had leaf areas similar to those of the broad-leafed parent P2, had a trichome density similar to that of P1, and had fewer trichomes per leaf than the mid-parental value. Frequency distribution of the characteristics for the F2 and backcross P1F1 were skewed toward P1 but displayed continuous variation, with means around the mid-parental values. Generation-means analysis suggested control of the characteristics by additive, dominance and epistatic gene interactions. Low narrow-sense heritability estimates were obtained for these characteristics. Significant correlations between leaf area and trichome abundance and between trichome abundance and density were obtained, but leaf area and trichome density were not correlated. Selecting small leaves with high trichome density may be accomplished, since they are independent. These two characteristics are desired in small white pea bean cultivars. However, several cycles of recurrent selection in large populations may be required to combine these two desired characteristics. Key words: Common bean, Phaseolus vulgaris, inheritance, trichomes, plant defence