| The disease caused by Rice black-streaked dwarf fijivirus (RBSDV) is one of the most important diseases in corn production in the world. RBSDV is transmitted in nature by Laodelphax striatellus Fallen. Severe plant dwarfing, leaf greening, enations on the underside of the leaves, and distortion of the plants are the characteristic symptoms of the disease.Artificial inoculation of RBSDV on maize through virulent vector, Laodelphax striatellus Fallen, was carried out in screenhouse. Symptoms were recorded after inoculation through the whole growth period and the younger stem was measured in the tasseling stage. The histological observation of the cross and longitudinal sections under fluorescence microscope of leaves and stems revealed that the phloem cells from diseased leaves and stems remarkably increased and the morphology was abnormal and disorganized comparing with the healthy ones. Longitudinal section observation of last third internode from the top of maize stem indicated that the cell expansion was inhibited and the cell length of the diseased stems were shorter than the healthy ones. It was concluded that symptoms of gall formation (enations) in the abaxial epidermis of leaves correlated to the phloem cell increase, abnormal and disorganized morphology; stunted plants associated with the inhibition of stem cell expansion.ID-ELISA for detecting RBSDV and the endogenous hormone contents was adopted to find out the correlation of the symptoms and the endogenous hormones. In the study,two high-susceptble maize inbred lines of Ye 478 and Ye107 from Reid group were used and the artificial inoculation of RBSDV onto the seedlings through the virulent vectors of Laodelphax striatellus Fallen was done in greenhouse and screenhouse. Samples infected by RBSDV in the field were also collected. Three different tissues of young shoot, young leaves and roots from the infected plants and un-inoculated controls of maize plants at the seedling stage, jointing stage, big trumpet stage, stooling and booting stages were collected for the assay of four kinds of endogenous hormone contents. The four tested endogenous hormones were gibberellin (GA ), indole-3-acetic acid ( IAA), abscisic acid (ABA) and zeatin riboside (ZR). The results were summaried as follows. In young shoot tissue, the contents of GA, ABA, IAA and ZR were no significant difference in heathy and infected plants during seedling stage to jointing stage. In root, GA contents in infected plants were obviously lower than those in the healthy ones through the four growth stages,besides the more stunted plants were, the lower GA contents detected. The contents of ABA of severe infected plants were higher than healthy ones. In leaves, GA contents showed similar changes with the ones in roots. ABA contents kept higher in diseased than in healthy ones through the whole growth stages. Moreover, ABA contents increased more as the symptoms developed. While IAA contents showed higher at the beginning and forming periods of enations (seedling to jointing stages) in the diseased than in the healthy controls. By big trumpet growth stage, it showed obvious difference between diseased and healthy ones. At late growth stage (stooling and booting stages), the healthy ones contained higher IAA than the diseased plants. There were higher ZR levels in healthy than in diseased ones.By analyzing the symptom development and endogenous hormone contents, it was concluded that the lower levels of GA in infected root and leaves could be the main cause for the reduced root growth, stunted stem and leaf darkening. The rapid accumulation of ABA brought about declining and dying back of the diseased plant. The higher level of IAA in diseased than in healthy plants might related to the formation of the enations. It indicated that the symptoms appearance and development were strongly correlated to the endogenous hormone contents. The results can provide the bases for further molacular study and set the management strategy to control maize rough dwarf disease in corn production. |
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