Variations of abscisic acid contents in various organs of grapevine infected by the eutypa dieback fungus, Eutypa Lata
In grapevine, eutypa dieback is a disease induced by ascomyceta fungus, Eutypa lata. At present, eutypa dieback is considered as the most serious deterioration disease of grapevine. The external symptoms of this disease are most conspicuous during the first months of the annual growth cycle and include dwarfed shoots with smaller and necrotic leaves and unfavourable development of grapes. All these symptoms were still suggested an hormonal perturbation in grapevine organs. The aim of this work was to determine the effects of eutypa dieback on abscisic acid contents in flower buds, flowers, young berries, leaves and internodes of grapevine. This study was also performed to determine the relationship between this growth regulator and disease development. The study was performed using organs (1) from healthy vines, (2) healthy appearing organs from vines with one symptomless arm and one diseased arm, and (3) moderately and (4) strongly diseased organs. From flowers buds separated to bunch of grapes closed stages, free abscisic acid (ABA) and the glucose esters of this acid (ABA-GE) were analysed in Vitis vinifera L. cv. Cabernet Sauvignon which is sensitive to E. lata.
In the healthy appearing organs, growth and development as well as water and ABA contents were not changed by eutypa dieback fungi. Whereas eutypa dieback induced a decrease of water content and the rate of growth increase in diseased organs. During all the period studied in leaves and since fruit set stage in the internodes, the ABA and ABA-GE contents were increased by eutypa dieback proportionally to symptoms. The ABA levels increase in leaves and internodes were not seem to be produced by ABA-GE hydrolysis since increase in ABA-GE levels were also observed in response to eutypa dieback. The maximum of ABA characterising grapevine flowers was delayed by eutypa dieback and their level was reduced with increasing symptoms severity. In flower buds, flowers and young berries, this disease induced a decrease of ABA-GE contents during all period studied proportionally to symptoms severity. The mycelium of two E. lata isolates cultured in Errikson and Petersson medium culture can synthesize ABA. A part of this growth regulator was diffused in medium culture. It was suggested that increase of ABA levels in diseased organs must have many origins: perturbation of (1) ABA-GE translation, (2) synthesis of ABA by grapevine caused by water stress and (3) synthesis of ABA by the fungi. The possible relationship between increased ABA content in the diseased organs and expression of eutypa dieback symptoms is discussed.
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