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Nuananong Purente, Bin Chen, Xiaowei Liu, Yunwei Zhou, and Miao He

Mutation breeding is considered to be economic and efficient in plant improvement, and the use of chemical mutagens such as ethyl methanesulfonate (EMS) can potentially address plant breeding challenges. The aim of this study was to induce morphological mutants in C. indicum var. aromaticum using EMS treatments with different doses, and to analyze the morphological and physiological traits of obtained mutants in expectation of finding favorable mutants. Results revealed significant effects of EMS doses on seed germination. The sample germination rate significantly decreased with increasing of EMS doses. The obtained morphological mutants were two viable types, containing leaf and stem mutants. Overall leaf size was significantly larger as a result of EMS treatments. And the height of mutant plants was significantly higher. Anatomical characteristics exhibited changes in both leaves and stems of the mutant plants. The puncture strength of the bent stem from the mutant plants was low, with weak penetration resistance. The total lignin and cellulose contents of mutant plants stem decreased significantly as a result of the EMS treatments. These results demonstrate the efficiency of EMS to induce mutations in C. indicum var. aromaticum, and this method can be useful in the future to assist breeding of this plant.

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Joseph N. Wolukau, Xiao-Hui Zhou, Ying Li, Yong-Bin Zhang, and Jin-Feng Chen

Gummy stem blight incited by the fungus Didymella bryoniae is a major disease of melons worldwide. The objectives of the present study were to critically evaluate melon (Cucumis melo L.) germplasm for resistance to D. bryoniae and to characterize the genetics of resistance in the resistant accessions. Two hundred sources of germplasm (plant introduction accessions, cultivars, breeding lines, landraces, and wild relatives) were screened against a single highly virulent isolate (IS25) of D. bryoniae in a plastic tunnel. The genetics of resistance to D. bryoniae was studied in three crosses between plant introductions 157076, 420145, and 323498, resistant parents that were fairly adapted (flowering, fruiting, powdery mildew tolerance) to Nanjing conditions, and plant introductions 268227, 136170, and NSL 30032 susceptible parents, respectively. Six populations of each cross (susceptible parent, resistant parent, F1, F2, the two reciprocal backcrosses) were analyzed for their responses to D. bryoniae. Seedlings in both studies were inoculated with a spore suspension (5 × 105 spores/mL−1) of D. bryoniae at the four to six true-leaf stages and assessed for leaf and stem damage at 7, 14, and 21 d postinoculation. Results of germplasm screening indicated most germplasms reported as resistant elsewhere were confirmed resistant under our conditions. However, some plant introductions identified as highly resistant elsewhere were susceptible under our conditions, the most interesting being plant introduction 482399. This plant introduction that was considered resistant was highly susceptible in our study. We also identified other sources of resistance not reported previously, for example, JF1; a wild Cucumis from the highlands of Kenya was rated highly resistant. Analysis of segregation of F1, F2, and backcross generations of the three crosses indicated that each of the three plant introductions carry a single dominant gene for resistance to the D. bryoniae.

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Zhong-Bin Wu, Hsin-Mei Ku, Yuh-Kun Chen, Chung-Jan Chang, and Fuh-Jyh Jan

Pear plants (Pyrus pyrifolia var. Hengshen) showing symptoms of chlorotic spots on leaves were observed in orchards in central Taiwan in 2004. The sap of diseased leaves reacted positively to Apple chlorotic leaf spot virus (ACLSV) antiserum. A purified virus isolate (LTS1) from pear was characterized by host range, electron microscopy, phylogenetic analyses, serological property, and back-inoculation experiments to pear. Fifteen of 28 species of tested plants were susceptible to this virus after mechanical inoculation. Pathogenicity of ACLSV isolate LTS1 was verified by back-inoculating to pear seedlings. Filamentous virions of ≈12 × 750 nm were observed in the preparations of purified virus. Virus particles accumulated in the cytoplasm were observed in the ultrathin sections of LTS1-infected pear leaf tissue. Sequence analyses of the coat protein (CP) gene of LTS1 and the CP gene of LTS2, which originated from a distinct symptomatic pear sample, shared 81.4% to 92.6% nucleotide and 87.6% to 98.4% amino acid identities with those of the CP of 35 ACLSV isolates available in GenBank. ACLSV isolates were grouped into four clusters, i.e., Asia I, II, III, and Europe, and isolates LTS1 and LTS2 were classified as members of cluster Asia II and Asia I, respectively, based on phylogenetic data. Moreover, the variability of amino acid sequences of the CP gene of 37 ACLSV isolates showed geographically associated clustering in the phylogenetic tree. To our knowledge, this is the first study on the characterization of ACLSV causing the leaf chlorotic spot disease of pear in Taiwan. This study also provides the phylogenetic relationships among ACLSV populations based on amino acid sequences of CPs, which are correlated with their geographic origins.

Free access

Zhi Quan, Bin Huang, Caiyan Lu, Yi Shi, Yanhong Cao, Yongzhuang Wang, Chuanrui He, Guangyu Chi, Jian Ma, and Xin Chen

Much nitrogen (N) is lost in high-input protected cropping systems mainly via leaching of not only nitrate-N but also extractable organic N (EON), but the role of EON in this process is poorly appreciated. A consecutive 3-year plot experiment was conducted to investigate the impact of co-application of manures with chemical N fertilizer on N accumulation and loss in a greenhouse soil rotationally planted with cucumber or tomato and lettuce. Application of manures significantly enhanced the average contents and stocks of NO3 -N, EON, and total N (TN) in 0- to 60-cm soil layer, although EON accumulated within growing season, while NO3 -N accumulated with fluctuation, and TN accumulated gradually throughout the 3-year experiment. With application rate at 120 or 180 t dry manures per hectare per 3 years, the corresponding apparent N surplus was 2710 or 3924 kg⋅ha−1 per 3 years. Due to little increase of biomass N uptakes during vegetable seasons, the accumulated N in soil profile would be a potential loss source, largely via leaching of both nitrate and EON. Application of manures slowed soil acidification but intensified secondary salinization of the greenhouse soil. Considering the manures-induced high soil N accumulation and loss, well-balanced evaluation of the role of manures in high-input agricultural ecosystems is needed.

Free access

Hai-Fang Yang, Hye-Ji Kim, Hou-Bin Chen, Jillur Rahman, Xing-Yu Lu, and Bi-Yan Zhou

Litchi trees flower at the apex of terminal shoots. Flowering is affected by the maturity of terminal shoots before growth cessation occurs during the winter. In this study, we focused on changes of flowering in three important cultivars, Guiwei, Feizixiao, and Huaizhi, from Dec. 2012 to Mar. 2013 under natural winter conditions. Flowering rate, carbohydrate accumulation, and expression of the flowering-related genes were determined at three different developmental stages of terminal shoots with dark green, yellowish green and yellowish red leaves, respectively. The results showed that the total soluble sugar and starch contents in the dark green leaves were the highest, whereas those in the yellowish red leaves were the lowest. Trees with dark green terminal shoots had the highest flowering rates, whereas those with yellowish green or yellowish red shoots had relatively lower flowering rates. SPAD was highest in dark green leaves and lowest in yellowish red leaves at the start of the trial. The SPAD value of yellowish red leaves slightly increased but did not reach the levels of the dark green leaves, whereas levels of the other leaf stages remained fairly constant. Expression level of the litchi homolog FLOWERING LOCUS C (LcFLC), the floral inhibitor in yellowish red leaves, increased from 16 Jan., whereas that in dark green leaves declined to a level lower than the yellowish red leaves on 4 Feb. Expression level of the litchi homolog CONSTANTS (LcCO), the floral promoter in dark green leaves, was higher than that of yellowish red leaves before 26 Jan. Expression level of the litchi homolog FLOWERING LOCUS T 2 (LcFT2), encoding florigen, was higher in dark green leaves than in the other two leaf types. Our results suggest that terminal shoots should be matured and leaves should turn green for successful flowering. Mature leaves had higher expression levels of the floral promoter and florigen. In litchi production, leaves of the terminal shoots (potential flowering branches) should be dark green during floral induction and differentiation stages, and winter flushes should be removed or killed.