A STUDY OF SIZE DIFFERENCES IN TWO STRAINS OF CUCURBITA PEPO L.: I. GROSS SIZE DIFFERENCES

Abstract

Size differences were studied in vegetative organs of two purebred strains of Cucurbita pepo L. which differ greatly in size by their genotype.The growth pattern of plants of the selected strains was found to be essen tially the same in the two types. The two strains exhibited great differences in mature organ size, but only small differences in number of organs.No correlation was found between embryo size and mature size. In the early stages of primary shoot development, however, a correlation was found between embryo size and the rate of new organ initiation. This correlation disappeared during the later stages of plant development. The parental strains had similar rates of organ formation, while the crosses showed hybrid vigor with respect to rate of new organ formation.Sizes of the apical meristems and organ primordia were essentially the same in the large and small strains and did not appear to determine mature organ size differences.Development of size differences between the same organs of the two strains and the crosses was found to be mainly due to duration of organ growth. Rates of organ growth differed only slightly between the strains. Increase in size of successively formed organs of the same strain was also found to be mainly due to duration rather than to rate of organ growth.