Transmission Modes Of Cucumber Green Mottle Mosaic Virus And Selection Of Resistance Inducers

Cucumber Green Mottle Mosaic Virus(CGMMV; genus Tobamovirus) is one of the mosteconomically important viruses of cucurbit crops worldwide, particularly in Asia. It is also present butusually less dramatic in Europe and the Middle East as well as South America, and it has been recentlydescribed in North America where it seems to have been introduced through infected seeds. CGMMVhas a narrow host range and mainly infects cucumber(Citrullus sativus L.), watermelon(Citrulluslanatus(Thunb.) Matsum. et Nakai), melon(Citrullus melo L.) and bottle gourd(Lagenaria siceraria(Molina) Standl. Var. Clavata Hara). The typical symptom of CGMMV is a mosaic pattern of infectedleaves.CGMMV has stable virus particle and its transmission modes are complicated. The virus can betransmitted by seed, soil, water and contact, so it has the potential risk of worldwide distribution. It ispresumed that seeds may be the major primary infection source of CGMMV for long distancetransmission. The soil contaminated with infected plant debris is also recognized as the major primarysource. The plants can be infected by CGMMV in contaminated water throughout the field. CGMMV isreadily contact-transmitted virus and easily spread indirectly from infected plants to healthy bysap-contaminated. To understand how CGMMV spreads is fundamental to designing strategies to blockspread and thereby prevent disease. The transmission modes of CGMMV were researched in thisdissertation.CGMMV infects grafted watermelon frequently and widely in China. To investigate thetransmission modes and their efficiency is urgently needed to understand the factors contributing toepidemiology of the disease. In the present study, the results showed that the occurrence of CGMMV inbottle gourd seed production base reached 100%, while the contamination rate and transmission ratewere 100% and 0.92% respectively. The bottle gourd plants showed obvious mottle symptom on leavesstarting 36 days after seed sowing. The long latent period of CGMMV in seedlings implies a potentialrisk to use contaminated seeds in the production of grafted watermelon. This virus could overwinter insoil with debris of infected plants and the infection rate of CGMMV from contaminated soil was10.30%. CGMMV could be transmitted from infected watermelon plants to healthy ones by pruning atleast to the ninth plant during the whole growing season. The transmission distance was 1.87 m(thesecond next to infected plant) by dip irrigation and 2.31 m(the third next to infected plant) by flowirrigation. The results suggested that contaminated seeds, contaminated soil, pruning and irrigationtransmitted CGMMV at different efficiency, all contribute to the epidemiology of CGMMV.The four chemicals 2.1.3-benzothiodiazole(BTH), brassinolide(BL), chitosan oligosacharide(CTS) and salicylic acid(SA) were applied to bottle gourd, to compare their effectiveness in inducingresistance against CGMMV. The relatively good level of resistance were induced by the four chemicalsat the concentrations of 0.05 g·L-1 for BTH, 5×10-5 g·L-1 for BL, 1.0 g·L-1 for CTS and 0.138 g·L-1 forSA respectively after an induction phase of 3 days(time elapsed between treatment and CGMMVinoculation). The best induction phases were 1 d for BTH, 3 d for BL, CTS and SA respectively. Amongthe 4 compounds, the greatest efficacy reached 70.39% after treatments with BL at concentration of5×10-5 g·L-1 3 days before CGMMV inoculations. Those four chemicals showed potential in applicationto grafted watermelon industry to reduce CGMMV damage.