Improving initiation, genotype capture, and family representation in somatic embryogenesis of Pinus radiata by a combination of zygotic embryo maturity, media, and explant preparation

The principal aim of this investigation was to improve somatic embryogenesis initiation and to enhance representation of families and genotypes within those families of Pinus radiata D. Don. A total of 19 open-pollinated seed families, many with unrelated and weakly related parents, were tested. Optimum stage of cone maturity for initiation success was tested by five collections made at 1 week intervals, spanning the developmental period from pro-embryo to cotyledonary embryos. Two media were compared; embryo-development media (EDM6) and a modified Litvay medium (Glitz). Two zygotic embryo explant-preparation techniques were tested; embryos with retained megagametophytes and excised embryos. Proliferating embryogenic tissues were obtained from all four treatments (2850 explants per treatment, 570 per collection time) for the 19 families. The best initiation rates were achieved with a combination of Glitz medium with excised zygotic embryos, with 55% of explants from all collections and all families combined giving rise to proliferating embryogenic tissue. At the optimal collection time for each of the families, this treatment gave a range of 47%–97% initiation success with an average of 70% per family.

077 In Vitro Growth of Immature Peach [Prunus persica (L.) Batsch] Embryos Related to Carbohydrate Source

Carbohydrate energy source of various tissue culture media has an effect on growth and survival of the explants. Sucrose is the standard carbohydrate used in most tissue culture systems. The objective of the study was to determine the effect of five carbohydrate sources (fructose, glucose, maltose, sorbitol, and sucrose) at two levels (2% and 3%) on germination, growth, and survival of immature peach embryos (9.7 to 14.7mm) in vitro. Five cultivars were used. Overall, fructose, maltose, and sucrose each stimulated germination and growth as the primary carbohydrate energy source of peach embryo culture to the same degree; glucose and sorbitol were inferior. However, fructose was superior to sucrose in one cultivar. In general, sugar level did not affect survival, although cultivars did vary somewhat. Survival was found to be highly dependent upon embryo maturity.

Selection against sprouting damage in wheat. II.* Harvest ripeness, grain maturity and germinability

Examination of grain development in two white-grained (non-dormant) and two red-grained (varying dormancy) wheat genotypes has clarified concepts of maturity with respect to grain dehydration, harvest ripeness, embryo maturity, base α-amylase activity and dry weight growth. Each maturity trait had a different pattern of development. The net level of grain maturity at harvest ripeness depended on the relative progress of the maturation traits at the time at which harvest ripeness was defined. Harvest ripeness is defined as the first attainment of 12½% moisture during primary dehydration of the grain, this being closely related to fitness for harvest. The effects of adopting other definitions of harvest ripeness (at 17½% and 20% grain moisture) are discussed. Significant differences amongst genotypes in development patterns, temporal placement, and harvest ripeness level were found in each maturity trait, and the differences were not parallel across traits. Differences in maturation did not coincide with differences in putative dormancy or grain colour. Results indicated that grain maturation was a multi-faceted process, with flexible synchronizations amongst maturation traits at any point in time, such as at harvest ripeness. Germination tests or a-amylase assays on progeny grain samples, at some time after harvest ripeness, measure differences in maturity as well as putative differences in dormancy. Interpretation only in terms of dormancy could be misleading. Adjustment for immaturity is discussed. ____________________ *Part I, Aust. J. Agric. Res., 28: 583 (1977).

Ovule and seed development in Pinus radiata: postmeiotic development, fertilization, and embryogeny

Development of ovule tissues in Pinus radiata after meiosis, fertilization, and embryogeny is comparable with that of other pines, but P. radiata takes longer to develop. Fertilization occurs 15 months after pollination and morphological embryo maturity is reached 5 months later. In ovules harvested in spring after meiosis, a curved band of small cells with dense cytoplasm extends from the chalazal end of the ovule to the vascular tissue of the ovuliferous scale. It is interpreted as a procambial strand, which in the next year, differentiates basipetally into elongated, thick-walled cells with degenerated nuclei.