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Liang Cheng, Ning Zhang and Bingru Huang

The accumulation of 1-aminocyclopropane-1-carboxylate (ACC), which is a precursor for ethylene production, in plant roots exposed to salinity stress can be detrimental to plant growth. The objectives of this study were to determine whether inoculating roots with bacteria containing deaminase enzymes that break down ACC (ACC-deaminase) could improve plant tolerance to salinity in perennial ryegrass (Lolium perenne) and to examine growth and physiological factors, as well as nutrition status of plants affected by the ACC-deaminase bacteria inoculation under salinity stress. Plants of perennial ryegrass (cv. Pangea) were inoculated with either Burkholderia phytofirmans PsJN or Burkholderia gladioli RU1 and irrigated with either fresh water (control) or a 250 mm NaCl solution to induce salinity stress. The bacterium-inoculated plants had less ACC content in shoots and roots under both nonstressed and salinity conditions. Salinity stress inhibited root and shoot growth, but the bacterium-inoculated plants exhibited higher visual turf quality (TQ), tiller number, root biomass, shoot biomass, leaf water content, and photochemical efficiency, as well as lower cellular electrolyte leakage (EL) under salinity stress. Plants inoculated with bacteria had lower sodium content and higher potassium to sodium ratios in shoots under salinity stress. Shoot and root nitrogen content and shoot potassium content increased, whereas shoot and root calcium, magnesium, iron, and aluminum content all decreased due to bacterial inoculation under salinity treatment. ACC-deaminase bacteria inoculation of roots was effective in improving salinity tolerance of perennial ryegrass and could be incorporated into turfgrass maintenance programs in salt-affected soils.

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Yan Zhang, Cuiyue Liang, Yan Xu, Thomas Gianfagna and Bingru Huang

The objective of the study was to determine whether the expression of a cytokinin (CK) biosynthesis gene encoding adenine isopentenyl transferase (ipt) would delay or suppress leaf senescence induced by nitrogen (N) or phosphorus (P) deficiency in a C3 grass species, creeping bentgrass (Agrostis stolonifera). The ipt gene was ligated to a senescence-associated promoter, SAG12, and was transferred into creeping bentgrass using an agrobacterium (Agrobacterium tumefaciens)-mediated transformation technique. Plants from an SAG12-ipt transgenic line (S41) and a null transformant (NT) control line were grown in nutrient solutions with all essential elements or without N (−N) or P (−P) for 21 days. Significant declines in leaf photochemical efficiency (Fv/Fm) and chlorophyll content of mature leaves were detected in NT and SAG12-ipt plants exposed to N or P deficiency. Compared to the NT control line, SAG12-ipt plants had higher levels of Fv/Fm, chlorophyll, and CK contents in leaves, and these differences between the NT control and SAG12-ipt line became more pronounced with treatment duration. The ipt expression was detected in the −P-treated and the −N-treated plants after 21 days, although the level of expression decreased under N or P deficiency. Under −P treatment, root acid phosphatase activity was greater in SAG12-ipt line than in the NT control line. No significant differences in nitrate reductase activity were detected in leaves or roots between the SAG12-ipt and the NT control lines. Our results demonstrated that SAG12-ipt expression suppressed leaf senescence induced by N or P deficiency in a perennial grass species. The suppressing effects on leaf senescence under P deficiency may be related to CK regulation of more efficient use of P in roots of the SAG12-ipt plants.

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Xuejuan Chen, Ming Sun, Jianguo Liang, Hui Xue and Qixiang Zhang

Chrysanthemums have beautiful flowers with high ornamental value and rich genetic diversity. Amplified fragment length polymorphism (AFLP) markers were used to detect the relationships among 12 wild accessions and 62 groundcover chrysanthemum cultivars. Nineteen EcoRI/MseI primer combinations revealed 452 informative polymorphic bands with a mean of 23.8 bands and 71.5% polymorphic rate per primer pair. Jaccard’s coefficient of similarity varied from 0.64 to 0.89, indicating much genetic variation in chrysanthemums. The 74 accessions were classified into two major groups by unweighted pair group method with the arithmetic averages (UPGMA). The dendrogram showed that AFLP variability was closely correlated with both geographic distribution and traditional classification of the wild accessions. Among all accessions, genetic relationship was the most relevant factor in AFLP-marker clustering, whereas petal type was also informative. AFLP technology could be very efficient for discriminating species of chrysanthemum and its related genera and reconstruct their genetic relatedness.

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Yanhong Lou, Liang Chen, Qingguo Xu and Xunzhong Zhang

Tall fescue is an important cool-season grass widely used for forage and turf, and its genotypic variation for morphological traits has not been well documented. One hundred and fifteen tall fescue accessions, including 25 commercial cultivars, were divided into five groups based on their origination. The morphological traits, including plant height, spike length, pulvinus distance, spikelet count, branch count per spike, spike count per plant, and spike weight in different accessions were determined under field conditions in 2013 and 2014. There was significant genotypic variation in morphological traits among the 115 tall fescue accessions. Wild accessions exhibited a greater variation in the morphological traits than commercial cultivars. Close correlations were found among plant height, spike length, pulvinus distance, and spikelet count. The results of this suggest plant height, spike length, pulvinus distance, and spikelet count could be used as key morphological traits for evaluating all fescue germplasm effectively.

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Zhengrong Hu, Erick Amombo, Margaret Mukami Gitau, Aoyue Bi, Huihui Zhu, Liang Zhang, Liang Chen and Jinmin Fu

Bermudagrass (Cynodon dactylon) is a typical and widely used warm-season turfgrass. Low temperature is one of the key environmental stress limiting its utility. However, little information is available about the differences of cold response between bermudagrass genotypes. Here, we analyzed antioxidant defense system and fatty acid composition in cold-resistant genotype WBD128 and cold-sensitive genotype WBDg17 exposed to chilling stress. Low temperature (4 °C) significantly decreased the relative water content, whereas increased the H2O2 and O2 contents, more profoundly for WBDg17. Under chilling condition, WBD128 had higher anti O2 activity than WBDg17. Besides, the contents of total glutathione, reduced glutathione (GSH) and its oxidized form (GSSG) were markedly increased by low temperature in both genotypes, whereas WBD128 had significantly higher values of GSH, total glutathione, and GSH/GSSG ratio than WBDg17. Moreover, chilling stress increased saturated fatty acids (SFAs) percentage (palmitic acid and stearic acid) in WBDg17. After chilling treatment, the proportion of linoleic acid decreased in both genotypes, particularly in WBDg17. As for unsaturated fatty acids (UFAs), the percentage of linolenic acid was increased in WBD128. In addition, chilling treatment decreased the values of double bond index (DBI), UFA/SFA ratio as well as degree of unsaturation in WBDg17. Finally, chilling stress altered the expression patterns of the genes, which encode one kind of late embryogenesis abundant proteins (LEA), superoxide dismutase (Cu/Zn SOD) C-repeat-binding factor/DRE-binding factor (CBF1), and peroxidase (POD-2). Collectively, our results revealed that natural variation of chilling tolerance in bermudagrass genotypes may be largely associated with the alterations of antioxidant defense system and fatty acid composition.

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Ji-Yu Zhang, Zhong-Ren Guo, Rui Zhang, Yong-Rong Li, Lin Cao, You-Wang Liang and Li-Bin Huang

This study examined the ability to vegetatively propagate 1-year-old pecan (Carya illinoinensis) through the rooting of hardwood cuttings. Cuttings were treated with varying concentrations of different auxins and different combinations of media and ambient temperatures. Under different temperature conditions, all auxin treatments induced the rooting of cuttings but did not promote sprouting. The effectiveness of the induction of adventitious roots was as follows: 1-naphthalene acetic acid (NAA) > indole 3-butyric acid > indole 3-acetic acid. The base of the parent shoot treated by NAA at a concentration of 0.09%, planted in substrate with bottom heat was the most effective, with 82% rooting, 8.3 roots/cutting and root lengths of 7.3 cm. These findings suggested that auxin and substrate/air temperature differences are both indispensable in the process of adventitious roots formation in pecan. This study revealed that the propagation of hardwood cuttings derived from branches of 1-year-old pecan is possible.

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Shanshan Seng, Jian Wu, Jiahui Liang, Fengqin Zhang, Qiuyan Yang, Junna He and Mingfang Yi

Starch accumulation is important during com development. ADP-glucose pyrophosphorylase (AGPase) is the rate-limiting enzyme in starch synthesis. AGPL is the large subunit of AGPase. Here, we isolated and characterized the large subunit of AGPase gene GhAGPL1 in gladiolus (Gladiolus hybridus). GhAGPL1 was highly expressed in sink organs (cormels and corms). The expression of GhAGPL1 was induced by glucose, sucrose, and mannitol, and it was repressed by abscisic acid (ABA). Overexpression of GhAGPL1 in the arabidopsis (Arabidopsis thaliana) apl1 mutant resulted in complementation of AGPase activity and thus starch synthesis. Silencing GhAGPL1 in gladiolus decreased the transcript level of GhAGPL1 and GhSus, and resulted in the reduction of AGPase activity and starch content in gladiolus corm and cormel. Meanwhile, sucrose content was higher in GhAGPL1-silenced corm. Surprisingly, silencing GhAGPL1 in gladiolus produced smaller corms and fewer number of cormels. Overall, GhAGPL1 contributed to the quality and quantity of gladiolus corms and cormels.

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Chunyu Zhang, Xuesen Chen, Hongwei Song, Yinghai Liang, Chenhui Zhao and Honglian Li

Volatile compounds have a tremendous impact on fruit quality. We evaluated the volatile compound profiles of ripening wild apple fruit (10 Malus baccata accessions and three Malus prunifolia accessions) in the National Field Genebank for Hardy Fruits at Gongzhuling, China. Alcohols, esters, aldehydes, terpenes, hydrocarbons, ethers, heterocycles, carboxylic acids, and ketones were detected in the M. baccata and M. prunifolia fruit, with the first four being the main volatile compounds present. Of the 92 volatiles detected, esters were the most diverse (49 compounds). This wide range of abundant volatile compounds suggests that M. prunifolia is a good resource for breeding apple cultivars with novel and interesting flavors. The M. baccata accession ‘Zhaai Shandingzi’ and the M. prunifolia accession ‘Bai Haitang’ had the widest range of volatile compounds and the highest volatile compound contents of the accessions examined, and will therefore be good breeding materials for developing commercial lines with enhanced flavor and for widening the genetic diversity. The number of different ester compounds present was significantly positively correlated (r = 0.877) with the cube root of the weight of an individual ripe fruit. Principal component analysis (PCA) showed that the contents of ester compounds could be used to distinguish between M. baccata and M. prunifolia species. Therefore, ester compounds could be used as a reference of parental choice in apple breeding.

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Rui Zhang, Fang-Ren Peng, Dong-Liang Le, Zhuang-Zhuang Liu, Hai-Yang He, You-Wang Liang, Peng-Peng Tan, Ming-Zhuo Hao and Yong-Rong Li

Scion wood of ‘Caddo’ and ‘Desirable’ pecan (Carya illinoinensis) was grafted onto the epicotyl of 1-month-old, open-pollinated ‘Shaoxing’ pecan seedlings for evaluation as a grafting technique to reduce the time to produce grafted trees. The results showed that seedlings grafted with “base scions” had higher survival than those grafted with “terminal scions” for both ‘Caddo’ and ‘Desirable’. Also, grafting with paraffinic tape could achieve greater success rate than that with medical tape. The most ideal time to perform this grafting was late April in Nanjing, China, when pecan seedlings were about 35 days old. This study demonstrated that the technique yielded successful epicotyl grafting of >70%, and it could thus be applied in practice.

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Rui Zhang, Fang-Ren Peng, Pan Yan, Fan Cao, Zhuang-Zhuang Liu, Dong-Liang Le and Peng-Peng Tan

Root systems of pecan trees are usually dominated by a single taproot with few lateral roots, which are commonly thought to inhibit successful transplanting. This study aimed to evaluate early growth and root/shoot development of pecan seedlings in response to taproot pruning. Taproots of ‘Shaoxing’ seedling pecan trees were mildly (1/3 of the total length of the radicle removed) and severely (2/3 of the total length of the radicle removed) pruned at different seedling development stages shortly after germination. At the end of the first growing season, top growth was measured and then trees were uprooted so that root system regrowth could be evaluated. The results showed that root pruning had no impact on increases in stem height or stem diameter. However, pruning the taproot could stimulate primary growth in taproot branches. Root weight and the number of taproot branches per tree increased with decreasing taproot length. This study indicated that severe root pruning when three to five leaves had emerged resulted in root systems with more taproot branches and the greatest root dry weight after one growth season, which may increase survival and reduce transplanting shock.