Factorial Balance in the Determination of Fruit Shape in Cucurbita

Abstract

Several independent genetic factors tending to flatten fruit shape in Cucurbita have been isolated. Their recessive allelomorphs produce various elongate shapes. Other elongate types are evidently not due to factors of this sort but to others which either produce shape elongation directly or inhibit the operation of flattening factors. Genetic analyses of certain pure lines of Cucurbita with elongate fruits, based on a study of crosses between these and flatter lines of known constitution, are described. These indicate that in certain lines there is 1 elongating factor of this sort, whereas others evidently possess 2 or more. A specific fruit shape seems to be the resultant of a balance between a series of factors differing in the degree and direction of their effect. Shapes which are phenotypically identical may be very [diverse genotypically. These shape factors evidently operate through their influence on growth correlations.