Studies on the inheritance of leaf shape in Nicotiana tabacum L.

Variation in leaf shape of tobacco depended mainly on three independently segregating gene-pairs with intermediate heterozygotes. Br-br acted on the leafbase only, giving broadly and narrowly winged (sessile and petioled) leaves. Pt- pt and Pd-pd were cumulative, and acted on the amount of mesophyll. The effect of Pt was twice that of Pd. From ptptpdpd to PtPtPdPd, the leaf-base or petiole became longer, the angle of lateral veins more acute and the leaf-blade narrower, but the length of the midrib and the lateral veins stayed the same.

Among sessile (BrBr) types, variation due to Pt-pt and Pd-pd was continuous, so that the sessile first filial generations must be test-crossed with petioled (brbr) types, to enable classification for petiole length, which was the main criterion. Even then, allowance must be made for the number of leaves, since a higher number induced an upward extension of the region of increasing petiole length, and consequently increased the maximum petiole length of the plant.

The data of previous authors were analysed and, where necessary, reinterpreted. This analysis confirmed that variation in leaf shape of tobacco could be explained in terms of the three gene-pairs.