DEVELOPMENT OF THE SEED OF SOLANUM PHUREJA

DNYANSAGAR, VISHNU R., AND DELMER C. COOPER. (U. Wisconsin, Madison.) Development of the seed of Solanum phureja. Amer. Jour. Bot. 47(3): 176-186. Illus. 1960.-Ontogeny of the seed of Solanum phureja Juz. et Buk. is described. The megagametophyte, during the course of its development, ruptures the nucellus and at maturity lies in direct contact with the inner layer (endothelium) of the single massive integument. The mature megagametophyte, a 7-celled structure, consists of a 3-celled egg apparatus, an endosperm mother cell with fused polar nuclei and 3 persistent antipodals. Both 2and 3-celled mature pollen grains are formed within anthers of the same flower; hence this character cannot be considered of any taxonomic value. Double fertilization occurs between 24 and 72 hr. after pollination. A cellular endosperm is formed, the peripheral layer acting as an absorbing tissue during the early ontogeny of the seed. Later this layer becomes organized as an aleurone layer and thereafter the source of nutrients is via the basal portion of the endosperm immediately adjacent to the apical end of the vascular tissue of the developing seed. Embryo development follows the Nicotiana variation of the Solanad type. The mature testa is composed of an outer layer of thick-walled epidermal cells, an inner layer of thin-walled cells and an intervening mass of disorganized tissue. In those instances where the ovule or young seed aborts, the endothelial cells of the integuiment become hyperactive and proliferate to such an extent that the space formerly occupied by the gametophyte or the developing endosperm and embryo becomes completely filled with endothelial tissue. THE FAMILY Solanaceae contains some 2,000 species, three fourths of which belong to the genus Solanwn (Benson, 1957). Detailed analyses of the developiment of either the seed or the embryo in this largest genus are sparse and almost negligible in the Section Tuberarium, which is economically important (Schnarf, 1931; Johansen, 1950; Beamish, 1955; Walker, 1955; Williams, 1955; Wangenheim, 1957; and Lee and Cooper, 1958). None of the investigations on the Section Tuberarium gives a detailed account of the endosperm development and particularly of the embryogeny with respect to aspects as the architecture of embryo, destination of proembryonal cells and furidamental regions of the embryonic body, and laws of embryonic development. Several wild and cultivated diploid tuber-bearing species of Solanum possess desirable features not found in the common potato, S. tuberosum. S. phureja (2n -24) is one which is of interest to potato breeders, since it matures early, possesses general virus resistance and is immune to the "Y" virus. A detailed study of normal development of seed in such a species may prove helpful in methods of overcoming difficulties of hybridization. It m-ay also be of value in furnishing a basis for determining various genetic and environmental influences on the endosperm and embryo development and in embryo-culture. 1Received for publication June 27, 1959. Paper No. 755 from the Department of Genetics, University of Wisconsin, Madison. 2 The first author expresses his gratitude to Dr. R. W. Hougas for suggestions and facilities at the greenhouse. Thanks are also due to the Ministry of Education, Government of India for award of a scholarship. MATERIALS AND METHODS.-S. phureja (Hawkes, 1956 ) (S. rybinii of U.S.D.A. Plant Int. P. I. 225682.2) and S. phureja (P. I. 205561.1) were used as the seed and pollen parents respectively. The plants were grown in the greenhouse at a temperature of 70?F. Daily collections of ovaries or developing fruits were made for 30 days starting 24 hr. after pollination. The material was fixed either in formalin-acetic-alcohol or Randolph's modification of Navashin's fluid (Johansen, 1940). Carpels for the study of pollen tubes were collected for 4 days following pollination and fixed in the latter fixative. After embedding in paraffin, sections were cut at 10-16 ju and stained with either Harris' haematoxylin, Delafield's haematoxylin, or with safranin and fast green. Styles dissected for study of pollen tubes were stained with either acetoorcein or acetocarmine. OBSERVATIONS.-Ovule and inegagametophyte.Ovules are either anatropous or campylotropous and attain the maximum length of 0.15 mm. at the time of fertilization. The nucellus is usually completely utilized during the course of development of the megagametophyte, so that the latter lies in direct contact with the innermost layer (endothelium) of the single massive integument (fig. 5). Occasionally, remnants of the nucellar tissue persist in some ovules. The endothelium consists of radially elongated cells with dense cytoplasm and prominent nuclei and persists as a tapetum-like, nutritive layer adjacent to the embryo-sac. Some of the cells of the funiculus at the chalazal end of the ovule elongate and differentiate into a vascular strand thus establishing a connection with the vascular tissue of the placenta. The megagametophyte (fig. 6) consists of 7