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Kai Zhao, Feng Zhang, Yi Yang, Yue Ma, Yuexue Liu, He Li, Hongyan Dai and Zhihong Zhang

GA20-oxidase (GA20-ox) is a key enzyme involved in the biosynthesis of gibberellic acid (GA). To investigate its role in plant growth and development, we suppressed MdGA20-ox gene expression in apple (Malus domestica cv. Hanfu) plants by RNA interference (RNAi). After 20 weeks of growth in the greenhouse, significant phenotype differences were observed between transgenic lines and the nontransgenic control. Suppression of MdGA20-ox gene expression resulted in lower plant height, shorter internode length, and higher number of nodes compared with the nontransgenic control. The expression of MdGA20-ox in transgenic plants was significantly suppressed, and the active GA content in transgenic lines was lower than that in the nontransgenic control. These results demonstrated that the MdGA20-ox gene plays an important role in vegetative growth, and therefore it is possible to develop dwarfed or compact scion apple cultivars by MdGA20-ox gene silencing.

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Liu Yang, Zhongkui Xie, Zhijiang Wu, Yajun Wang, Zhihong Guo, Yubao Zhang and Ruoyu Wang

The oriental hybrid lily (Lilium oriental cv. Sorbonne) is an economically important flower noted for its pink petals. Flower quality is determined by plant height, number of flowers per plant, and flower diameter. The commercial value can be increased by improving flower quality through cultural practices such as exogenous application of hormones; however, information on this practice is unavailable for this lily hybrid. In the present study, we soaked lily bulbs for 24 hours in one of four concentrations of abscisic acid (ABA) or one of three concentrations of the ABA biosynthesis inhibitor fluridone before subjecting the bulbs to a cold storage treatment at 4 °C. During cold storage, bulbs were sampled and buds were collected every 10 days for 80 days (that is, lasting eight times). The ABA and gibberellic acid 3 (GA3) contents of buds of treatments that showed a significant difference with the control were measured in a 10-day interval. Greenhouse experiments with different cold storage durations of bulbs that measured height, flower number per plant, and flower diameter were conducted. The interaction of hormone treatments and cold storage duration played nonsignificant roles in parameters of flower quality. Exogenous fluridone application to bulbs at 12 mg·L−1 improved flower quality: height and flower number increased significantly compared with the control, but flower diameter did not change. ABA had no effect on flower quality. Because the fluctuation of endogenous GA3 is more remarkable than ABA after the application of fluridone that led to the improvement of flower quality, it can be inferred that this influence on flower quality is achieved through fluridone’s regulation on the content of endogenous GA3. A low endogenous GA3/ABA ratio was associated with improved flower quality: 12 mg·L−1 fluridone decreased the GA3/ABA ratio in most times of the cold treatment. In addition, cold storage duration affected flower quality; the 50-day cold storage can achieve the highest height, the most flower number, and bigger flower diameter simultaneously. The results of the present study suggest that soaking bulbs in 12 mg·L−1 fluridone before cold treatment followed by 50 days of cold storage before planting will increase plant height and flower number per plant.

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Zhihong Gao, Weibing Zhuang, Liangju Wang, Jing Shao, Xiaoyan Luo, Binhua Cai and Zhen Zhang

Estimating chilling requirements is crucial for identifying appropriate cultivars for a given site, for timing applications of dormancy-breaking chemical agents, and for predicting consequences of climate change. For temperate-zone fruit species such as japanese apricot, productivity is reduced when chilling requirements are not adequately satisfied. In our study, we obtained chilling and heat requirements for flowering of six japanese apricot cultivars, which spanned the range of flowering times in this species for three successive years. Different methods for determining chilling requirements were evaluated and compared, and correlations among chilling requirements, heat requirements, and flowering date were established. The dynamic model proved to be the best for determining the chilling requirements of japanese apricot. The results showed a range of chilling requirements ranging from 26.3 to 75.7 chill portions and a narrow range of heat requirements, from 1017.7 to 1697.3 growing degree-hours (GDH). A very high correlation (R = 0.9797) between flowering date and chilling requirements and a low correlation (R = 0.4298) between flowering date and heat requirements suggest that flowering date in japanese apricot is mainly a consequence of the chilling requirements of the different genotypes, whereas heat requirements contribute a limited effect to the variation in flowering dates. Chilling requirements and heat requirements were positively related with a low correlation coefficient (R = 0.4211).

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Zhi-Hong Gao, Zhi-Jun Shen, Zhen-Hai Han, Jing-Gui Fang, Yu-Ming Zhang and Zhen Zhang

Sequencing amplification fragments produced using simple-sequence repeat (SSR) primer pairs pchgms2 and UDP96008 in `Dayezhugan' japanese apricot showed that SSRs obtained included a microsatellite locus originally identified in peach. The microsatellite sequence homogeneity between UDP96008 in japanese apricot in this study and UDP96008 in the peach in GenBank was 98%. Twenty-four japanese apricot genotypes originating in diverse geographic areas had been identified with 14 SSR primer pairs developed in different species of Prunus. In total, 129 alleles were obtained and per primer pairs detected 2.5 alleles on the average. The results from cluster analysis showed that the genetic distance between `Nanhong' and `Zhonghong' was the closest, and cultivars from China and from Japan could not be separated completely.

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Cui-ping Hua, Zhong-kui Xie, Zhi-jiang Wu, Yu-bao Zhang, Zhi-hong Guo, Yang Qiu, Le Wang and Ya-jun Wang

The autotoxicity of root exudates and the change of rhizosphere soil microbes are two important factors that affect the quality and yield of Lanzhou lily (Lilium davidii var. unicolor). Phthalic acid (PA) is a major autotoxin of the root exudates in Lanzhou lily. In this study, we treated plants with different concentrations of PA from the Lanzhou lily root exudates and then analyzed the effects of autotoxins on fresh weight, shoot height, root length, and Oxygen Radical Absorbance Capacity in root. The diversity of soil fungi in Lanzhou lily soil was analyzed using MiSeq. The results showed that PA induced oxidative stress and oxidative damage of Lanzhou lily roots, improved the level of the membrane lipid peroxidation, reduced the content of antioxidant defense enzyme activity and the nonenzymatic antioxidant, and eventually inhibited the growth of the Lanzhou lily. We found that continuous cropping of Lanzhou lily resulted in an increase in fungal pathogens, such as Fusarium oxysporum in the soil, and reduced the size of plant-beneficial bacteria populations. The results in this study indicate that continuous cropping would damage the regular growth of Lanzhou lily.