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Y. Wang, Y. Liu, P. He, O. Lamikanra and J. Lu

Resistance to grape anthracnose [Elsinoë ampelina (de Bary) Shear] was evaluated in 13 known Vitis species and five taxonomically undescribed grapes native to China. One hundred and eight clones of Chinese Vitis species were tested under field conditions between 1990 and 1992. Berry infection did not occur in these species. Leaves displayed strong resistance to anthracnose, although intraspecific variations were observed. There was no relationship between anthracnose resistance and geographical origin of the species. Results from this study indicate that oriental grape species are useful for disease-resistance breeding.

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Yu Hong, D. Creech, Wang Chuanyong, Gu Yin and He Shanan

Blueberries are now the hot point of fruit development in China. Researches conducted in the past since 1980s include mainly introduction and propagation. More than 30 cultivars of rabbiteye blueberries and southern highbush blueberries were introduced successfully in the Nanjing Botanical garden in late 1980s. For dormant cuttings of 4 rabbiteye blueberry cultivars Gardenblue, Tifblue, Climax, and Premier the rooting percentage could reach 84%, 52%, 62%, and 79% respectively under interrupted misting. Lignification of the cuttings seemed the key point for rooting. For soft cuttings the rooting percentage can reach 90% to 95% with chemical treatments. Seedling selection has been conducted and some promising individuals are under observation. So far, there were little experiments on cultural practice under taken. But looking at the difference of soils between the blueberry growing areas in the US and China it seems that there are a series of aspects should be researched in the future.

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Yu Hong, D. Creech, Wang Chuanyong, Gu Yin and He Shanan

The native species of Vaccinium are distributed in both northeast and south of China but more species are in the South. Ecologically, there is a vast territory in the South with acidic soils and plenty of precipitation and warm weather. On the other hand in the northeast regions temperature in winter is usually a problem for cultivated blueberries and protection from freezing is necessary for young plantations. Based on the result of introduction of cultivars, including rabbiteye, southern highbush and lowbush blueberries, in both northern and southern parts in China during the last 2 decades authors suggested that the most prospective regions for blueberry growing could be mostly in south of China. In the between of the two regions the natural ecological conditions are not appropriate for blueberry growing but plantations under plastic film appeared relatively vigorous. 12 rabbiteye blueberry cultivars have been tested in the south and the performance of growth and fruiting are good. It is expected that the average of yield could reach about 15 t·ha–1. The quality of fruits is similar to that of the natives in North America. Up to now there are less insects and diseases damages. It seems that the regions in the south of Changjiang (Yangtze) River provide good conditions for blueberry commercial growing.

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Riqing Zhang, Fangde Lv, Fang He, Bixia Xie and Lingdan Wang

Pecan [Carya illinoinensis (Wangenh.) C. Koch], a world-famous nut tree native to North America, was introduced to China in the early 1900s. However, little success had been recorded in terms of its nut production. Based on comparative studies of the geoclimate, soil conditions, and growth and performance of the pecan crop between southeastern U.S. and China, as well as in 12 other countries with successful pecan cultivation, it is feasible to grow pecan in China within the latitudes 25–35°N. In these areas, the summer temperatures range from 25–35°C with lower DIF. The annual precipitation is 500–1500 mm. Further studies using the Dendroclimate Predicative Analysis of water and heat conditions in the U.S. Pecan Belt, which is composed of seven factors, including the annual mean and extreme low temperatures, annual frost-free days, and annual precipitation, concluded that four pecan cultivation regions should be designated in China. These regions were the Favorable Region (I), the Northern and Southern Suitable Regions (IIa, IIb), the Northern and Southern Marginal Regions (IIIa, IIIb), and the Northern and Southern Undesirable Regions (IVa, IVb). The Favorable Region is along both sides of the Yangtze River in-between latitudes 25–35 °N and longitudes 100–122 °E. Some areas with microclimates, such as western Yunnan, nourish several pecan cultivars and have demonstrated a promise of pecan production. The demand for pecan is high in China, and this regionalization of pecan cultivation will ultimately enhance further collaboration on pecan production between horticulturists in China, United States, and other countries. Future research will result in the introduction of much better pecan cultivars to the different cultivated regions in China.

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Weining Wang, Yanhong He, Zhe Cao and Zhanao Deng

Garden impatiens (Impatiens walleriana), a very important floricultural crop in the United States, has been devastated by impatiens downy mildew (IDM) in recent years. This study was conducted to determine if induced tetraploidy could improve impatiens resistance to downy mildew. Tetraploids were induced by colchicine and confirmed by chromosome counting. Compared with diploids, induced tetraploids showed significant morphological changes, including larger and thicker leaves with larger and fewer stomata; thicker and fewer stems; larger and fewer flowers; and larger pollen grains with higher stainability. In detached leaf and in vivo inoculation assays, tetraploids exhibited improved downy mildew resistance, with lower disease severity, disease incidences, and sporangia densities. Plasmopara obducens, the causal agent of IDM, underwent a similar development process in the leaf tissue of diploids and tetraploids. These results suggest that induced tetraploidy can result in significant changes in impatiens leaf and plant morphology and can increase impatiens resistance to downy mildew to a certain extent.

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Mengmeng Zhang, He Huang, Qing Wang and Silan Dai

Conventional crossbreeding remains an effective technique for chrysanthemum (Chrysanthemum ×morifolium Ramat.) breeding. However, there are always many problems when breeding chrysanthemum because of its complex genetic background, such as difficulty matching parents, selecting superior hybrid progenies, quantitatively describing certain target traits, and evaluating breeding results. A recent mathematical analysis method is an effective method for evaluating plant breeding progress. In this study, we used 505 multiflora chrysanthemum germplasm resources as test materials; we divided the flowering time into five groups using a grading analysis method, including extremely early group (genotypes that flowered when daylength was longer than 13.5 hours), early group (genotypes that flowered when daylength was 13.5–12.0 hours), medium group (genotypes that flowered when daylength was 12.0–11.0 hours), late group (genotypes that flowered when daylength was 11.0–10.0 hours), and extremely late group (genotypes that flowered when daylength was shorter than 10.0 hours). Moreover, the breeding objective was to breed early-flowering genotypes. Using 15 phenotypic characters as evaluation factors, 37 excellent genotypes, including four early-flowering genotypes, were screened out from the aforementioned resources according to an analytic hierarchy process (AHP) and weighting of the gray relational grade. We selected one early-flowering genotype and eight medium-flowering genotypes from these 37 genotypes and matched six hybridized combinations based on the genetic distance between genotypes calculated by the Q cluster analysis method. We used a comprehensive evaluation method combining AHP and the gray relational analysis (GRA) method for the evaluation of 367 progenies. Moreover, we screened out 52 superior hybrids, including 36 early-flowering hybrids. The results of this study demonstrate that the mathematical analysis method is an immensely effective method to breed new cultivars of early-flowering multiflora chrysanthemum. This study also provides an effective method to define and improve the flowering time of other cultivated plants.

Open access

Xinyi Chang, Junli Sun, Lianling Liu, Wang He and Baolong Zhao

Wild jujube (Ziziphus acidojujuba) and cultivated jujube (Ziziphus jujuba) belong to the family Rhamnaceae. Jujubes have marked drought- and salt-tolerant properties. After salt stress, wild jujube seedling growth was inhibited and photosynthetic efficiency was reduced. A bioinformatics approach was used to analyze the transcriptomics data from wild jujube seedlings grown under salt stress, and the genes differentially expressed under the salt stress were identified to provide a theoretical basis for the development and use of wild jujube plantations in salinized soil. The transcriptome sequencing from leaves of wild jujube seedlings was carried out using second-generation sequencing technology. The effects of salt stress on the differential expression of photosynthesis-related genes in wild jujube seedlings were analyzed. Transcriptome sequencing revealed a total of 5269 differentially expressed genes (DEGs), of which 2729 were up-regulated and 2540 were down-regulated. DEGs were mainly enriched with respect to photosynthesis, photosynthetic antenna proteins, glyoxylic acid and dicarboxylic acid metabolism, linolenic acid metabolism, cysteine and methionine metabolism, and porphyrin and chlorophyll metabolism. Among them, the photosynthesis pathway-related DEGs were most highly enriched. Further analysis of porphyrin and chlorophyll synthesis and photosynthesis-related pathways revealed that they were significantly enriched by 97 photosynthesis-related DEGs. The DEGs in the photosynthesis and photosynthetic antenna protein pathways were down-regulated, whereas the DEGs glutamyl-tRNA reductase (HEMA), ferrochelatase (HEMH), and pheophorbide a oxygenase (PAO) in the porphyrin and chlorophyll synthesis pathways were up-regulated, with the remainder being down-regulated. The nuclear gene encoding Rubisco, the key enzyme in the photosynthetic carbon fixation pathway, was also down-regulated. The results showed that the photosynthetic rate of wild jujube seedlings decreased following exposure to salinity stress, an effect that was related to the increased synthesis of 5-aminolevulinic acid and heme, and the up-regulation of expression of a gene encoding a chlorophyll-degrading enzyme, and was related to the down-regulation of gene expression in photosynthesis-related pathways such as light energy capture and carbon fixation. Selection of nine DEGs related to photosynthesis and chlorophyll biosynthesis by quantitative real-time-PCR confirmed that expression changes of these nine DEGs were consistent with the transcriptome sequencing results.

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Chenping Zhou, Ruiting Chen, Yaqiang Sun, He Wang, Yi Wang, Ting Wu, Xinzhong Zhang, Xuefeng Xu and Zhenhai Han

Bridge grafting is widely applied in trunk-wounded apple trees. In this study, we carried out semigirdling and ring girdling on the trunk of ‘Nagafu 2’/Malus baccata (L.) Borkh apple trees to simulate trunk injury. We then bridge grafted a M9 self-rooted rootstock on the injured trunks to study the effects of bridge grafting on flowering, fruit-set, tree vigor, and fruit characteristics in ‘Nagafu 2’ apple. The results showed that both semigirdling and ring girdling due to the large wounded area caused significant decrease in flowering, fruit-set, and tree vigor (estimated by measuring leaf area, leaf gas exchange, tree height, and shoot growth); in addition, ring girdling increased flesh and peel firmness. However, bridge grafting of M9 self-rooted rootstock on semigirdling and girdling apple trees resulted in partial recovery of tree vigor (leaf area and photosynthesis) and maintaining the reduction of vegetative growth, thereby increasing flowering, fruit-set, yield, fruit weight, and peel firmness.

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Min Wang, Wenrui Liu, Biao Jiang, Qingwu Peng, Xiaoming He, Zhaojun Liang and Yu’e Lin

Heat stress (HS) negatively influences plant development and growth, especially production and quality. Cucumber is a widely cultivated plant in the gourd family Cucurbitaceae that is often exposed to high temperatures during summer and protected cultivation. In this study, we performed whole-genome re-sequencing of two pools, one heat-tolerant and one heat-sensitive, of the F2 population derived from L-9 (heat-resistant) and A-16 (heat-sensitive). The genetic analysis showed that the heat resistance of L-9 cucumber seedlings was controlled by a single recessive gene. By combining bulked segregant analysis (BSA) technology, the crucial gene related to HS was preliminarily mapped to a 1.08-Mb region on chromosome 1. To fine-map the locus, Indel markers were designed according to the genomic sequence. Finally, the gene was narrowed to a 550-kb region flanked by two Indel markers, namely Indel-H90 and Indel-H224, that contained 56 candidate genes. Re-sequencing results indicated that 10 candidate genes among the 56 in the candidate region showed single base pair differences in the exons. Quantitative reverse-transcription polymerase chain reaction showed that 6 genes among the 10 candidate genes were significantly decreased when exposed to high temperatures. These results not only were useful for the isolation and characterization of the key genes involved in HS but also provided a basis for understanding the mechanism of heat tolerance regulation.

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He Li, Cheng-Jiang Ruan, Li Wang, Jian Ding and Xing-Jun Tian

Sea buckthorn (Hippophae rhamnoides) is an ecologically and economically valuable species that has been widely cultivated as a new berry crop rich in nutritional and medicinal compounds. RNA Sequencing (RNA-Seq) simple sequence repeat (SSR) markers were developed to evaluate the genetic relationships among 91 plants of 31 cultivars from two subspecies, mongolica and sinensis, as well as intraspecific hybrids between them. A total of 7540 RNA-Seq SSRs were identified as potential molecular markers, in which AG/CT (27.57%) was the most abundant unit type. AT/AT (9.93%), and AAG/CTT (11.95%) are the other main repeat motifs. A total of 110 primer pairs were randomly selected for validation of amplification. Seventeen SSR loci, located in genes encoding metabolic processes and cellulose synthases, were identified to be polymorphic among different sea buckthorn cultivars. These SSR loci generated 48 alleles, ranging from 2 to 5 per locus. Cluster analysis based on the proportion of shared alleles and unweighted pair group method with arithmetic average (UPGMA) algorithm divided all the genotypes into two main groups, with all of the ssp. sinensis cultivars (native to China) and hybrids in one group and ssp. mongolica cultivars (introduced from Russia) in the other group, which was in good agreement with their taxonomic classification. The RNA-Seq SSRs developed in this study have a potential use in the conservation of sea buckthorn germplasm and marker-assisted breeding (MAB).