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Jianjun Zhang, Wei Zhu, Jaime A. Teixeira da Silva, Yongming Fan and Xiaonan Yu

The analysis of herbaceous peony (Paeonia lactiflora Pall.) floral bud initiation and differentiation from autumn to early spring is important because flower formation is strictly correlated with flowering in late spring. A clear understanding of peony flower development would allow management practices to be optimized for stable annual production and supply of cut flowers. The aim of this research was to study the time-sensitive characteristics underlying flower development in peony cultivar ‘Dafugui’. Flower bud differentiation was assessed by paraffin and hand-made slices, as well as stereomicroscopy. Both methods have strengths and weaknesses. Our observations are not entirely consistent with those of previous studies. Flower bud differentiation in ‘Dafugui’, which starts from late September to mid-April of the following year, is divided into differentiation of the lower parts (separate differentiation periods for the bracts, sepals, petals, stamens, and pistillodes) and upper parts (separate differentiation periods for the petals, stamens, and pistil), and is closely related to annual changes in ambient temperature. Differentiation of lower flower buds takes place before winter dormancy, whereas that of upper parts starts early in the following spring, and finally forms a double-flowered type. The three methods used in this article can be used to study P. lactiflora flower bud differentiation and can contribute to an understanding of this process in the future.

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Yan Cheng, Qian Wang, Qingyu Ban, Jianfeng Geng, Xiao Wei Zhang, Ying Yi and Xilin Hou

Quantitative trait loci (QTLs) identified so far in Brassica were mainly generated in the final stage of plant development, which did not apply to the exploitation of genetic effects that were expressed during a specific developmental stage. Thus, the objective of this study was to simultaneously identify unconditional and conditional QTL associated with plant height at various stages of nonheading Chinese cabbage. One hundred twelve doubled haploid (DH) lines developed from the cross between nonheading Chinese cabbage lines ‘SW-13’ and ‘SU-124’ were used for QTL analysis of plant height by the composite interval mapping method combined with mixed genetic model. The map we used for QTL analysis was an updated version of the first genetic map of nonheading Chinese cabbage with 48 additional markers to the same DH population. With data from 2 years, a total of 11 unconditional QTLs in six linkage groups and 23 conditional QTLs in eight linkage groups were identified for plant height. The results indicated that the number and type of QTLs and their genetic effects for plant height were different in a series of measuring stages. Each QTL can explain 7.92% to 28.25% of the total phenotypic variation. Two QTLs (ph8-4 and ph8-5) were identified to be associated with plant height using both unconditional and conditional mapping methods simultaneously in 2 years. These results demonstrated that it is highly effective for mapping QTL of developmental traits using the unconditional and conditional analysis methodology.

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Qingrong Sun, Meijuan Sun, Hongyan Sun, Richard L. Bell, Linguang Li, Wei Zhang and Jihan Tao

The organogenesis potential is different among cultivars and must be optimized for individual genotype. Shoot organogenesis capacity from in vitro leaves and root organogenesis capacity of in vitro shoots in six clonal apple rootstock cultivars were compared. The shoot organogenesis capacity was highly genotype dependent. ‘GM256’ was found to be the most responsive genotype for shoot regeneration from leaf explants among the cultivars, showing high regeneration percentage on all tested media. The effects of basal medium composition and cytokinins on shoot regeneration were different depending on rootstock genotype. Optimum regeneration occurred on Murashige and Skoog (MS) basal medium for ‘71-3-150’, and optimum regeneration occurred on Quoirin and Lepoivre (QL) basal medium for ‘60-160’ and ‘ПБ’. Thidiazuron (TDZ) was more effective than 6-benzylaminopurine (BA) for Malus prunifolia (Y), whereas TDZ and BA were not significantly different for the other cultivars. All rootstock cultivars showed high root organogenic capacity. The percentage of rooting reached more than 90% and the mean root number per plantlet ranged from three to five. The optimum rooting medium was different for different rootstock cultivars. Optimum root organogenesis occurred on half-strength QL medium for ‘GM256’ and ‘Y’, and for ‘ПБ’ and ‘JM7’ on one-quarter-strength MS medium.

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Zhiyong Hu, Min Zhang, Qigen Wen, Jie Wei, Hualin Yi, Xiuxin Deng and Xianghua Xu

Seedlessness is of commercial importance in citrus (Citrus L.). Seedless ‘Ougan’ mandarin (C. suavissima) was selected from a bud sport mutation that occurred in ‘Ougan’ mandarin. We analyzed their pollen viability through KI-I2 and FDA staining, and examined the anthers of wild-type (seedy) and seedless mutant ‘Ougan’ mandarin using histological and cytochemical methods to characterize the process of pollen development. No pollen fertility was detected in this mutant. Pollen abortion in anthers of the mutant occurred at the tetrad stage of microspore development, and almost all the tetrads were abnormal. The mutant had heterogeneous microspore populations, including monads, dyads, triads, tetrads, and polyads in the same microsporangium. Pollen grain number per anther of the mutant was 21.9% less than the wild type. Morphology of mature pollen grains using SEM showed that the shape of mature pollen grains from both wild type and mutant is similar, but the microsporangia of the latter contained pollen grains of more variable sizes. At the early mature pollen grain stage, abundant starch grains and lipids appeared in the wild type's pollen, but fewer amounts were observed in the mutant. Moreover, the tapetal cells of the wild type accumulated lipids, but not those of the mutant. Results indicated that the abnormal development of the microspore led to pollen abortion in the mutant, and this could be the reason for its seedlessness. However, the genetic reasons for the aberrant tetrads are not clear and are under investigation.

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Shutian Tao, Danyang Wang, Cong Jin, Wei Sun, Xing Liu, Shaoling Zhang, Fuyong Gao and Shahrokh Khanizadeh

Lignin is the main component of stone cells, and stone cell content is one of the crucial factors for fruit quality in chinese white pear (Pyrus ×bretschneideri). The lignin biosynthesis pathway is complex and involves many enzymatic reactions. Cinnamate-4-hydroxylase [C4H (EC.1.14.13.11)] is an essential enzyme in lignin metabolism. This study was conducted to investigate the effect of bagging on lignin metabolism during fruit development in chinese white pear. The study showed that bagging had little effect on stone cell content, lignin content, C4H activity, and C4H gene expression and that there was a positive correlation between C4H gene expression and lignin content as well as stone cell content. Moreover, a full-length complementary DNA (cDNA) encoding C4H (PbrC4H, GenBank accession number KJ577541.1) was isolated from chinese white pear fruit. The cDNA is 1515 bp long and encodes a protein of 504 amino acids. Sequence alignment suggested that the deduced protein belongs to the P450 gene family and that C4H might be located subcellularly in the cell membrane. The results indicate that bagging cannot change the lignin and stone cell content significantly and that C4H catalyzes a step in lignin biosynthesis. These findings provide certain theoretical references and practical criteria for improving the quality of chinese white pear.

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Li Ma, Chang Wei Hou, Xin Zhong Zhang, Hong Li Li, De Guo Han, Yi Wang and Zhen Hai Han

Understanding of root growth patterns and architecture of apple (Malus ×domestica Borkh.) trees is very important for commercial apple production. Most commercial apple trees are usually a grafted complex consisting of the scion and the rootstock, each of which is a different genotype. Recently, rootstocks of dwarf tree species have been used extensively to meet the convenience in management; however, this practice appears to negatively impact root development. Using minirhizotrons, we investigated root dynamics, root spatial distribution, and shoot growth in ‘Red Fuji’ scion grown: 1) directly on dwarf and vigorous root stocks and 2) on a dwarf root stock placed in between the non-dwarf scion and non-dwarf rootstock (hereinafter referred to as an interstem). The results showed that: 1) one or two peaks in total root length density (TRLD) were observed in each scion/rootstock combinations every year; 2) the greatest TRLD peaks were always observed in between May and December. The peaks of shoot growth were always asynchronous with that of white root length density; 3) compared with scion/vigorous rootstock combinations, inserting a dwarfing interstem between the scion and vigorous seedling rootstock reduced the TRLD; 4) scion/vigorous rootstock combinations had a relatively deep, widespread and large root system. Scion/dwarfing rootstock combinations had a root system distributed in a small region; and the root systems of scion/dwarfing interstem/vigorous rootstock combinations tended to be intermediate between those of scion/vigorous rootstock and scion/dwarfing rootstock. This implies that the insertion of interstems altered the root architecture by not only the quantity of roots, but also the spatial distribution.

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Wei Hu, Ju-Hua Liu, Xiao-Ying Yang, Jian-Bin Zhang, Cai-Hong Jia, Mei-Ying Li, Bi-Yu Xu and Zhi-Qiang Jin

The banana, a typical climacteric fruit, undergoes a postharvest ripening process followed by a burst in ethylene production that signals the beginning of the climacteric period. Postharvest ripening plays an important role in improving the quality of the fruit as well as limiting its shelf life. To investigate the role of glutamate decarboxylase (GAD) in climacteric ethylene biosynthesis and fruit ripening in postharvest banana, a GAD gene was isolated from banana, designated MuGAD. Coincidently with climacteric ethylene production, MuGAD expression as well as the expression of the genes encoding the Musa 1-aminocyclopropane-1-carboxylate synthase (MaACS1) and Musa 1-aminocyclopropane-1-carboxylate oxidase (MaACO1) greatly increased during natural ripening and in ethylene-treated banana. Moreover, ethylene biosynthesis, ripening progress, and MuGAD, MaACS1, and MaACO1 expression were enhanced by exogenous ethylene application and inhibited by 1-methylcyclopropene (1-MCP). Taken together, our results suggested that MuGAD is involved in the fruit ripening process in postharvest banana.

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R. Karina Gallardo, Eric T. Stafne, Lisa Wasko DeVetter, Qi Zhang, Charlie Li, Fumiomi Takeda, Jeffrey Williamson, Wei Qiang Yang, William O. Cline, Randy Beaudry and Renee Allen

The availability and cost of agricultural labor is constraining the specialty crop industry throughout the United States. Most soft fruits destined for the fresh market are fragile and are usually hand harvested to maintain optimal quality and postharvest longevity. However, because of labor shortages, machine harvest options are being explored out of necessity. A survey on machine harvest of blueberries (Vaccinium sp.) for fresh market was conducted in 2015 and 2016 in seven U.S. states and one Canadian province. Survey respondents totaled 223 blueberry producers of various production sizes and scope. A majority (61%) indicated that their berries were destined for fresh markets with 33% machine harvested for this purpose. Eighty percent said that they thought fruit quality was the limiting factor for machine-harvested blueberries destined for fresh markets. Many producers had used mechanized harvesters, but their experience varied greatly. Just less than half (47%) used mechanical harvesters for fewer than 5 years. Most respondents indicated that labor was a primary concern, as well as competing markets and weather. New technologies that reduce harvesting constraints, such as improvements to harvest machinery and packing lines, were of interest to most respondents. Forty-five percent stated they would be interested in using a modified harvest-aid platform with handheld shaking devices if it is viable (i.e., fruit quality and picking efficiency is maintained and the practice is cost effective). Overall, the survey showed that blueberry producers have great concerns with labor costs and availability and are open to exploring mechanization as a way to mitigate the need for hand-harvest labor.

Open access

Sangho Jeon, Charles S. Krasnow, Gemini D. Bhalsod, Blair R. Harlan, Mary K. Hausbeck, Steven I. Safferman and Wei Zhang

Pythium species incite crown and root rot and can be highly destructive to floriculture crops in greenhouses, especially when irrigation water is recycled. This study assessed the performance of rapid filtration of recycled irrigation water for controlling pythium root rot of poinsettia (Euphorbia pulcherrima) in greenhouses. Two greenhouse experiments investigated the effect of filter media type (sand and activated carbon), fungicide application (etridiazole), and pathogen inoculum source (infested growing media and infested irrigation water). Rapid sand filtration consistently controlled pythium root rot of poinsettia. Significant improvements in height, weight, root rot severity, and horticultural quality were observed for the plants in the sand filter treatment, compared with the inoculated control plants. However, the activated carbon filter removed essential nutrients from the irrigation water, resulting in plant nutrient deficiency and consequently leaf chlorosis, thus reducing plant weight, height, and horticultural quality. The etridiazole application did not completely prevent root infection by Pythium aphanidermatum, but plant weight, height, and horticultural quality were not negatively affected. P. aphanidermatum spread from infested growing media to healthy plants when irrigation water was recycled without filtration. Rapid sand filtration appears to have the potential to limit the spread of P. aphanidermatum that causes root rot of greenhouse floriculture crops.