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Zhi-li Suo, Xiao-qing Zhao, Jian-peng Zhao, Xiao-chong Zhao, and Fu-fei Chen

Large natural genetic diversifications have occurred among Chinese tree peony cultivars under the natural and artificial selections on the flower for ornamental and medicinal uses in the past over 1500 years in China. Paeonia suffruticosa ‘Zi Mei You Chun’ X.Q. Zhao & J.P. Zhao & X.Z. Zhao & X.C. Zhao & Q.X. Gao & Z.Q. Zhao & J.X. Zhao & Z.L. Suo (Paeoniaceae) is a unique cultivar possessing side flowers and bicolored floral disc belonging to the Central Plains tree peony cultivar group of China. This natural mutant is not only an outstanding ornamental, but also a valuable material for scientific research on evolution of tree peony cultivars, metabolic pathways of pigments in the floral disc, origin of floral disc in Paeoniaceae, and other issues in plant evolutionary and developmental genetics.

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Yihui Cui, Peng Zhao, Hongqiang An, Nan Lv, Zifeng Zhang, Wei Pei, and Wanjun Wang

To find the characteristics of somatic embryogenesis of orchids and elucidate the mechanism, we had previously established an efficient plant regeneration system via somatic embryogenesis in Dendrobium candidum Wall ex Lindl. In this study, a detailed cytological investigation was carried out on the initiation and developmental process of somatic embryogenesis. Based on our observations, the somatic embryogenesis in D. candidum originated from the transition of an embryonic callus cell to the initial somatic embryo cell, and the somatic embryos initiated from those cells. During the transition process, condensation and devacuolation successively occurred in the cytoplasm of the embryonic callus cells, giving rise to the formation of a typical initial somatic embryo cell with dense cytoplasm and a clear nucleus. One of the two pathways in somatic embryogenesis is the single-cell-derived somatic embryo which is generated from an inner initial somatic embryo cell in embryonic callus and develops into a globular somatic embryo in a way similar to zygotic embryogenesis and then keeps developing into a protocorm-like body (PLB). The other is a multiple-cell-derived somatic embryo which is generated from peripheral grouped initial somatic cells in embryonic calli and directly forms globular embryo or multicellular somatic proembryo, lacking the typical early stages of embryogenesis. Both pathways were observed in the somatic embryogenesis system, indicating that the culture system in D. candidum can be a useful tool for investigating the mechanisms underlying orchid embryogenesis.

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Tingting Zhao, Dawei Li, Lulu Li, Fei Han, Xiaoli Liu, Peng Zhang, Meiyan Chen, and Caihong Zhong

Kiwifruit (Actinidia chinensis Planchon) is an economically important fruit, and its flowering and production are affected by the chill accumulation in winter. In this study, the chilling requirements of nine kiwifruit cultivars with three ploidy levels (diploid, tetraploid, and hexaploid) were analyzed by using the Dynamic Model, Utah Model, and chilling hours (CH) Model. The chilling requirements for vegetative budbreak of these kiwifruit cultivars were 24–55 chill portions (CP), 316–991 chill units (CU), and 222–853 CH, and the chilling requirements for floral emergence were 45–69 CP, 825–1336 CU, and 655–1138 CH. The chilling requirements for vegetative budbreak and floral emergence were significantly lower for diploid than hexaploid cultivars with tetraploid cultivars intermediate. Pearson correlation analysis indicated that ploidy levels were positively correlated with chilling requirement, with the cv of 0.74 and 0.82 for vegetative budbreak and floral emergence chilling requirements, respectively. In conclusion, these results provide some novel insights of kiwifruit varieties of various chilling requirements, which is beneficial for kiwifruit cultivar selection for different climates and environments.

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Changwei Shen, Yifei Ding, Xiqiong Lei, Peng Zhao, Shuo Wang, Yangchun Xu, and Caixia Dong

A field experiment was conducted over three growing seasons (2012–14) to study the effect of the foliar application of different potassium (K) fertilizers [potassium phosphate monobasic (KH2PO4), potassium nitrate (KNO3), and humic acid potassium (HAK)] on the fruit growth rate, yield, and quality of ‘Kousui’ japanese pear (Pyrus pyrifola) trees. Except the first year of study, foliar application of K fertilizers generally led to an increase in the concentration of fruit total soluble sugar, titratable acidity (TA) and sweetness, along with an elevated K accumulation in leaf and fruit at maturity. In 2013 and 2014, compared with the control, KNO3 treatment led to an average 16% higher yield, and HAK led to an average 15% higher soluble solid content (SSC). Furthermore, HAK resulted in 26% higher yield in 2014. KNO3 treatment showed 19% higher leaf K concentration, 38% leaf K accumulation, and 43% fruit K accumulation in maturity than the control in 2014. Different effects were found on the concentration of specific types of sugar and organic acid, of which fructose and malate were consistently increased by the K application. With regard to the amino acids, KNO3 and HAK treatments led to a significant increase in the concentration of aspartic acid, which was 12% and 22% higher than the control, respectively. In conclusion, foliar application of KNO3 is an efficient way to increase ‘Kousui’ japanese pear fruit yield, whereas spraying HAK is an effective way to improve the fruit quality.