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Zhang Qixiang

On the basis of investigating pollination habits of 45 cultivars of Mei Hua, interspecific hybridization between Mei Hua and apricot (Prunus armeniaca). David's peach (P. davidiana) as well as siberian apricot (P. sibirica) were made from 1982 to 1991. With total number of pollination flower 17,050, 168 hybrid seed and 75 hybrid seedlings were obtained. Embryo culture in vitro was used for undeveloped young hybrid embryos. Test of freezing resistance both in artificial freezing and in overwintering for the hybrid seedlings showed that there were 5 hybrids with double and nice flower to be very hardy to low temperature. They were able to tolerate as low as -35C for 30 days in open ground, and now they were planted in northwest China's Gansu province and northeast China's Liaonin province without cold injury.

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Natalie Anderson, David H. Byrne, Jonathan Sinclair, and A. Millie Burrell

Embryo culture techniques are employed to germinate seed of early ripening peach and nectarine [Prunus persica (L.) Batsch] cultivars. Generally, the embryos in these genotypes do not mature by the time the fruit matures, thus rendering normal stratification procedures ineffective. In 1998 and 1999, immature embryos from multiple peach genotypes were cultured in an embryo rescue medium (Woody Plant Medium, 3% sucrose, 0.065% agar) at 5 °C for 45 days in the dark. Embryos were then placed under lights at either a cool-temperature (18 °C in 1999 and 20 °C in 1998) or a warm-temperature (30 °C in 1999 and 28 °C in 1998) treatment with a photoperiod of 12 hours for germination and initial growth. After 2-4 weeks, embryos were rated for germination, root number, and top growth. The embryos incubated at the cool-temperature regime not only had better germination, but also had a higher rate of greenhouse survival.

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David H. Byrne, Natalie Anderson, Jonathan Sinclair, and A. Millie Burrell

Embryo culture techniques are employed in early ripening peach and nectarine cultivars. Generally, the embryos in these varieties are not mature by the time the fruit matures, thus rendering normal stratification procedures ineffective. In 1998 and 1999, immature embryos from multiple peach genotypes were cultured in an embryo rescue media (WPM, 3% Sucrose) at 5 °C for 45 days in the dark. Embryos were then placed under lights at either a cool temperature (18 °C in 1999 and 20 °C in 1998) or a warm temperature (30 °C in 1999 and 28 °C in 1998) treatment with a photoperiod of 12 h for germination and initial growth. After 2 to 4 weeks embryos were rated for germination, root number, and top growth. The embryos incubated at the cool temperature regime not only had better germination, but also had a higher rate of greenhouse survival.

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Jonathan W. Sinclair and David H. Byrne

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.

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R.W. Robinson

Cucurbita ecuadorensis is a valuable source of multiple virus resistance. It is resistant to zucchini yellow mosaic virus (ZYMV), papaya ringspot virus (PRSV), watermelon mosaic virus, tobacco ringspot virus, squash mosaic virus, and cucumber mosaic virus (CMV). Its virus resistance can be transferred to squash and pumpkin, but sterility barriers must be overcome. The cross Cucurbita maxima× C. ecuadorensis can readily be made, and there is no need for embryo culture. Pollen fertility of the hybrid is somewhat reduced, but sufficient for producing F2 seed. Segregation for sterility occurs in the F2, but selection can be made for fertile plants that are homozygous for virus resistance. Cucurbita ecuadorensis is much more distantly related to C. pepo than to C. maxima, and there are more formidable barriers in this interspecific cross. The cross is very difficult to make with some C. pepo cultivars, but other cultivars are more compatible. Viable seed were not produced, but hybrid plants were obtained by embryo culture. Although both parents were monoecious, the hybrid was gynoecious. Male flower formation was induced by treating the hybrid with Ag or GA, but they were male-sterile. F2 seed was not obtained, but backcross seed was easily produced by using the interspecific hybrid as the maternal parent in crosses with C. pepo. The most refractory barrier was achieving homozygosity for ZYMV resistance. Disturbed segregation occurred in succeeding generations and the progeny of most resistant plants segregated and were not uniform for resistance. This and other barriers to interspecific gene exchange were overcome and a summer squash variety homozygous for resistance to ZYMV, PRSV, and CMV is being released this year.

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Dirk Vuylsteke, Rodomiro Ortiz, Shaun Ferris, and Rony Swennen

. International mailing address: IITA, c/o L.W. Lambourn & Co., Carolyn House, 26 Dingwall Rd., Croydon CR9 3EE, England. We thank Leo Oragwa, Julian Osuji, and Josephine Okoro for assistance in embryo culture, chromosome counting, and data processing

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Dirk Vuylsteke and Rodomiro Ortiz

embryo culture and chromosome counting, respectively. We acknowledge the International Network for the Improvement of Banana and Plantain for making available the diploid male parent. IITA is a nonprofit organization and is a member of the Consultative

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Dirk Vuylsteke, Rony Swennen, and Rodomiro Ortiz

Oragwa for technical assistance in embryo culture and Gillian Eggleston and Mike Ogburia for undertaking the preliminary consumer acceptability studies. We acknowledge the International Network for the Improvement of Banana and Plantain for making

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Rodomiro Ortiz and Dirk Vuylsteke

.W. Lambourn and Co., 26 Dingwall Road, CR9 3EE, England. Paper no. IITA/96/JA/63. The authors thank Mr. Leo Oragwa for assistance in embryo culture and the crew led by Ms. Josephine Okoro for data collection. We acknowledge the International Network

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Ching-yeh Hu, Lee Wang, and Bernard Wu

Embryo culture can by-pass yew (Taxus) seed dormancy and produce large population of seedlings to be screened for the anticancer drug, taxol, production. Immature linear embryos from seeds of T. baccata, T. brevifolia. T. cuspidata, and T. media were dissected and cultured. B5 medium supported the best embryonic growth during the initial two week's culture for T. cuspidata and T. baccata. T. brevifolia grew faster on MS medium. Weak embryo dormancy was encountered in T. brevifolia and T. cuspidata from the mature seeds but not from the immature ones. No embryonic growth had been observed in T. media dissected from mature seeds due to strong dormancy. Developing embryos were subsequently transferred to 1/2X B5 medium for germination. Rooting percentage in the mature seed derived T. brevifolia embryos increased from 12.5 to 63.6 when 30 μM GA3 was added to the initial medium. Several hundreds of seedlings of T. baccata. T. brevifolia and T. cuspidata had been acclimatized to the greenhouse conditions. The taxol content of resultant T. cuspidata seedlings was 0.027% (dry weight), while that of T. brevifolia obtained from the wild twig was 0.030%.