GROWTH OF EXCISED ROOTS OF POLYPLOID TOMATOES

Abstract

LINDSTROM (1929) described a haploid mutant of tomato which originated spontaneously in 1926. The absolutely homozygous diploid was obtained from the haploid by the decapitation-callus method (Lindstrom and Koos, 1931; Lindstrom, 1940), and the homozygous tetraploid in turn was derived from the diploid (Lindstrom and Koos, 1931). This unique series offered an opportunity to explore the effect of autopolyploidy on the growth of excised roots. The experiments reported here are a contribution to such a study. MATERIAL AND METHODS.-Through the courtesy of Dr. E. W. Lindstrom plants of the haploid tomato were received together with seed of the diploid and tetraploid derived from the haploid. Characteristics of the plants.-The haploid tomato is of the dwarf type, smaller in height and in spread of plant than the diploid. It grows rather luxuriantly, putting out many short axillary branches, and cuttings from these are easily rooted. Its dwarfness is apparent in a shorter internodal length and in leaves smaller both in length and in breadth. The main stalk is decidedly smaller in circumference than that of the normal diploid; the flowers also are distinctly smaller (Lindstrom, 1929). The haploid is highly sterile (Lindstrom, 1940); the autodiploid is quite fertile. Comparative measurements of stem, leaves, and flowers prove the haploid to be approximately 70 per cent of the size of a typical diploid (Lindstrom and Koos, 1931). The leaves of the tetraploid are noticeably thicker and broader than those of the diploid. The flowers are conspicuously larger, being fully 40 per cent larger than those of the standard diploid. The pollen grains of the tetraploid are larger and more variable in size (Lindstrom and Koos, 1931). The tetraploid is highly sterile (Lindstrom, 1940), though less so than the haploid. According to Lindstrom (by letter), the tetraploid roots less readily than the haploid or diploid and is slower in axillary sprouting. The In form is always lowest in dry weight, the 2n highest, and the 4n is between. Excised roots. The haploid excised roots were derived from a single cutting as described below. The diploid and tetraploid roots were obtained from germinating seeds. Of ten clones of excised roots of the tetraploid, five were primary tips and five were secondary root tips. No marked difference was noted in the responses in culture of these two types of root tips. The diploid excised roots were all primary root tips. Sterile excised roots from seeds.-These were obtained by surface-sterilizing seed with a 1-1000 solution of mercuric chloride, or with the azochlora-