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In previous abstracts (HortScience 23:707;24:121), ABA when added throughout the in vitro production cycle, reversed the tissue culture-induced rejuvenation of the day neutral strawberry `Fern'. Compared to benzyl adenine (BA) proliferated plants, ABA treated tissue culture-produced plants flowered earlier and had more adult leaf patterns. In the present study, we analysed endogenous ABA concentrations in the apices and unexpanded leaves of BA treated tissue culture-propagated plants, selved seedlings and propagated adult runner tip plants at 3, 7 and 15 weeks ex vitro, after germination or after runner tip propagation. Using pentadeuterated standards and single ion monitoring, ABA concentrations in tissue culture produced and juvenile seedling plants were significantly lower than adult plants at 3 and 7 weeks. By 7 weeks, only the adult plants were flowering. At 15 weeks, no differences in ABA concentration were significant and all three types flowered.
Polyembryony is an important characteristic for citrus that allows them to be propagated clonally through seed. Even when it is genetically controlled by a quantitative trait, the environment in which the seed is developed can affect it. The aims of this investigation were to evaluate polyembriony in two citric rootstocks in two harvest cycles and embryo germination of polyembrionic seeds. Embryos of 300 seeds of Citrus volkameriana and C. amblycarpa were counted and measured in Summer-Fall and Winter 1998 and 1999, respectively; embryo of 50 seeds of both rootstocks were germinated in vitro. The number of embryos per seed was 1.9 and 1.6 in C. volkameriana and 4.7 and 5.7 in C. amblycarpa. In C. volkameriana, we observed 42% of monoembryonic seeds during summer-fall and 67% in winter, whereas in C. amblycarpa 5.0 and 4.1% were detected, respectively. Only embryos that were larger than 1 mm long germinated. Even when germination takes similar time (5 to 6 days), further growth is faster in larger embryos (5 to 10 mm) than smaller ones. Therefore, size of embryos would need to be considered for propagation purposes.
This research was supported in part by U.S. Dept. of Agriculture Capacity Building Grant No. 92-38814-7490. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore
Research was initiated in 1990 to study spore viability, spore germination in vitro, and methods of controlled environment culture for the endangered Aleutian shield-fern, Polystichum aleuticum. Examination of spores using scanning electron microscopy revealed from 24% to 78% deformed and possibly nonviable spores per plant. Normal spores germinated in 30-45 days on both Knop's solution and Hoagland's No 2 solution in aseptic culture. Germination was most rapid on cultures with less than 6 g/1 agar. Cultures with no agar were susceptible to contamination by algae, and sporophyte losses during transfer to greenhouse media were high. Germination rate and subsequent appearance of the first leaf stage did not differ significandy within a medium pH range of 4.7 to 7.0. Spores exhibited a thermodormancy at 25°C, but germinated well at 18°C and required light for germination. Sporophyte transfer from aseptic culture was most successful after true fronds beyond the first leaf stage had developed. A commercial bedding plant mix composed of Sphagnum sp. peat and perlite provided an optimum rooting medium for the ferns.
Distichlis spicata var. stricta (Torrey) Beetle is a native grass that tolerates salt, high pH, and some heavy metals. It has been proposed for use in several challenging environments, including mine spoils and salt-impacted areas of golf courses. But, its widespread use has been hindered by several factors, one of which is poor seed set. Because chromosome numbers are variable and some genotypes are aneuploids, there was concern that pollen viability in some genotypes was low. Pollen from several genotypes failed to germinate in vitro on four artificial media prepared with various levels of osmoticum. However, hand pollination in vivo resulted in profuse pollen germination for all genotypes tested. Germination on pollinated stigmas was observed at intervals beginning 2 h after pollination with a fluorescence microscope using aniline blue and acridine orange stains and in bright field using toluidine-O stain. Very young stigmas seemed unreceptive and, while pollen would germinate, the pollen tubes would not grow down through the style. On receptive stigmas, many pollen tubes grew down toward the egg and some reached it within 24 h. There was no evidence of impaired fertility. Aniline blue was the best method for observing pollen tube growth through the style, although toluidine-O was adequate for observing germination on the stigmatic surface.
. Asymbiotic germination is a useful technique to propagate and conserve several endangered orchid species ( Arditti and Ernst, 1993 ; Fay, 1992 ; Pritchard, 1989 ), whereas some terrestrial orchids are relatively difficult to germinate in vitro ( Rasmussen
2 Current address:Lab. Plant breeding, Fac. Life and Environmental Science, Shimane University, Matsue 690-8504, Japan. This research was funded by INTA–JICA project `The Horticulture Development Project in
High temperatures during flowering have been implicated in reducing seed set and fruit set in tomatoes (Lycopersicon esculentum). Pollen viability and vigor were studied by measuring in vitro germination and pollen tube development in pollinated pistils of four processing tomato cultivars under normal (25° C day/15° C night) and high (32° C day/23° C night) temperatures. Preliminary studies were carried out to determine the length of pollen tubes in styles collected in times ranging from 3 to 48 hours after pollination. Under normal temperatures the pollen tubes reach the end of the style between 12 and 18 hours. At high temperatures there are fewer pollen tubes moving through the style and the time to reach the end of the style is longer. In pollen vigor studies, crosses were made between pollen and pistils of plants grown under different temperature treatments, then pollinated pistils were collected at 4, 8 and 12 hours after pollination. There were differences in in vitro pollen germination percentage and pollen tube length in the pollinated pistils, suggesting that high temperatures act to slow down pollen activity.
Abstract
Seedlings were obtained from incompatible crosses and seifs of certain African and Indian Impatiens by culturing excised embryos and ovules in vitro after fertilization in vivo. Selfed seedlings of I. campanulata Wight, I. epiphytica G. M. Schulze, I. hookeriana Am., and I. pseudoviola Gilg. were obtained by embryo and ovule cultures. Hybrid seedlings of I. hookeriana × I. campanulata were derived from embryo culture. Few to several hybrid seedlings each of I. flaccida alba Arn. × I. repens Moon, I. uguenensis Warb. × I. epiphytica, and I. uguenensis × I. flaccida alba were developed from cultures of 5- to 16-day-old ovules. Some ovules from 11 out of 57 incompatible crosses cultured in vitro grew and germinated. Except for I. hookeriana selfed progenies resembled their parents in gross morphology and breeding behavior. I. hookeriana selfed seedlings had smaller flowers and less pollen than their parents. Most hybrids exhibited blended parental characteristics, and all were sterile. Four interspecific hybrid progeneis are reported for the first time.