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    Process of Mango Infected by Colletotrichum gloeosporioides and Host Histopathology
    YU Haiying, LAN Jianqiang, LIU Lin
    Chinese Journal of Tropical Crops    2022, 43 (2): 361-368.   DOI: 10.3969/j.issn.1000-2561.2022.02.017
    Abstract4550)   HTML22)    PDF(pc) (9332KB)(92)       Save

    Colletotrichum sp. is a kind of fungus with wide geographical distribution and wide host range. It can infect plants and fruits before and after ripening, especially for mature tropical crops, causing serious economic losses and affecting the export quality of products. The infection process of C. gloeosporioides on mango fruit and the interaction between C. gloeosporioides and mango host were studied to reveal the infection mode and expansion pathway of the pathogen on fruit and leaves. After Inoculating the healthy ‘Sannian mango’ fruits and leaves with the strong pathogenic strain CG16 isolated and screened from the diseased fruit of local variety ‘Sannian mango’ in Yuanjiang, the histopathology and ultrastructure of mango fruits and leaves infected by C. gloeosporioides were studied by light microscope, scanning electron microscope and transmission electron microscopy. C. gloeosporioides formed primary hyphae 12 hours after infection, and the primary hyphae penetrating the host cell wall formed a funnel-shaped hyphal cone. It constricted at the hyphae in contact with the host cell wall, often formed a diaphragm, and expanded rapidly into normal hyphae after passing through the host cell wall. It took about one day from the inoculation of mango to the appearance of symptoms. In the process of infecting mango, C. gloeosporioides first formed the primary infection hyphae, and the host cells gradually disappeared and died with the invasion and expansion of the primary hyphae. The primary hyphae first spread between cells and continuously established new nutritional parasitic relationships in vivo. 2.5 days after inoculation, with the invasion of hyphae, the host cells finally died and dissolved, and the expanded hyphae diffused in the dead host cells gradually became thinner and more branched, and the secondary hyphae was formed. The secondary hyphae propagated and expanded in large numbers dispersing or forming mycelial bundles in the host. Four days after inoculation, a series of pathological changes occurred in host tissues and cells, including deformation of host cells, thinning of cell walls, deformity and partial disappearance of cells, disintegration of protoplasts and other organelles, necrosis and cell death. Five days after inoculation, the secondary hyphae in the vegetative stage of dead body proliferated and expanded in the dead host cells. Six days after inoculation, the conidiophores formed, and the spores began to mature and fall off 8 days after inoculation. In this study, the way of infection and expansion of C. gloeosporioides in fruits and leaves, as well as a series of pathological changes in host tissues in the process of infection were revealed, which would provide a theoretical basis for the prevention and control of the disease in production.

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    Analysis of Codon Usage Bias in the Chloroplast Genome of Ananas comosus
    YANG Xiangyan, CAI Yuanbao, TAN Qinliang, QIN Xu, HUANG Xianya, WU Mi
    Chinese Journal of Tropical Crops    2022, 43 (3): 439-446.   DOI: 10.3969/j.issn.1000-2561.2022.03.001
    Abstract1654)   HTML19)    PDF(pc) (1285KB)(188)       Save

    The codon usage bias of chloroplast genome affects the genes expression efficiency, which provides important information for chloroplast genetic engineering and species genetic improvement. To determine the codon usage characteristic of the chloroplast genome and its main influencing factors in pineapple (Ananas comosus), the codon usage pattern and its preference of pineapple chloroplast genome were analyzed using bioinformatics softwares. The average GC content of codons of pineapple chloroplast genes was 38.31%, the average GC content of codons from the first position to the third position was 46.78%, 39.61% and 28.53%, respectively, and the average GC contents at the first and second positions of codons were significantly higher than that at the third position. The value range of effective number of codons (ENC) was 38.48—61.00, and its average value was 47.21, indicating weak codon bias. GC1 was significantly correlated with GC2, GCall was significantly positively correlated with GC1, GC2 and GC3, and GC3 was not significantly correlated with GC1 and GC2. ENC was not significantly correlated with GC1, but significantly and extremely significantly correlated with GC2 and GC3, respectively. Codon number (N) was only significantly correlated with GC3, which indicating that the base composition of the third position in the three positions of the codon mainly affects codon number. RSCU analysis showed that among the 29 codons with RSCU>1, 12 codons ended with A, 16 codons ended with U, and 1 codon ended with G. Neutrality plot analysis showed that there was not significant correlation between GC12 and GC3, and the correlation coefficient and regression coefficient was 0.065 and 0.085, respectively. ENC-plot analysis showed most genes were distributed near the standard curve, and most ENC ratios were distributed in the interval of -0.05—0.05. PR2-plot analysis showed that all genes were unevenly distributed in the four regions of the PR2 plan, and the use frequency of pyrimidine T/C at the third position of codon was higher than that of purine A/G. Bias analysis of Neutrality plot, ENC-plot and PR2-plot suggested that natural selection and mutation as the main factors affect the codon usage bias of pineapple chloroplast genome. Analysis of optimal codons and RSCU showed that most of the 29 codons with RSCU>1 and the 18 optimal codons ended with A or U. The results provide scientific basis for codon optimization of exogenous genes and improvement of their expression efficiency.

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