Occurrence, epidemical regularity and control strategies for grape trunk diseases

Abstract: Grape trunk Diseases (GTDs) is a general term for the grape trunk diseases caused by a vari-ety of pathogenic fungi, includes ESCA complex disease, Eutypa dieback, Botryosphaeria dieback,black foot disease and Diaporthe dieback. At present, GTDs happen in grape production area both at home and abroad, and it leads to a gradual increase in the risk of global grape yield and quality decline in case of lacking of efficient prevention and control technology. This paper provides a comprehensive review of the occurrence and damage of grape trunk diseases worldwide, their symptoms, pathogenic species, occurrence pattern and control measures, as well as an outlook on future research directions for grape trunk diseases. Firstly, this review documented most of reports of grape trunk disease from thirty-six countries in world, eight countries have found five kinds of GTDs, which are France, Spain, Ameri-ca, Australian, South Africa, Italy, Czech Republic and China, and seventeen countries have reported two or four kinds of GTDs. The more details were described in section one. Secondly, we listed typical symptoms of five main grape trunk diseases and their related pathogens. Thirdly, the epidemical regular- ity of each kind of GTDs is in detail documented and their developmental conditions (air temperature,relative humidity, rainfall, etc.) are described. Their main pathogens can be detected at the wound area caused by pruning or curved for covering with soil. Spore maturation and sporulation need humid envi-ronmental conditions and a wide temperature range from 5 to 40 ℃. After successive rains, conidia and sporangium of four kinds of GTDs spread through the air, except for black foot disease. Campylocar- pon spp. and Cylindrocarpon spp. are the main pathogens of black foot disease, which lives in free wa-ter of the soil. Wounds at root site and interface of grafting position are probably the entrance for patho-gens to infect black foot disease. Wounds caused by pruning supplied infection sites for the pathogens  of other four kinds of GTDs. Moreover, integrated control strategies of GTDs were highlighted in fourth part. Some preventive strategies include advance or delay the pruning time and spray pesticides on the wound area, which aims to avoid peak period of spore releasing and reduce the contact between tree wounds and pathogens. Hot water treatment is also a commonly used method to reduce pathogens in plants. Once GTDs happens, cutting off the infected branches, injection of hydrogen peroxide into the canes, usage of wooden pegs inoculated with endophytic strains of Trichoderma atroviride to insert the infected parts of the canes are effective to control GTDs. In last part, we discussed biological and abiotic stresses (drought stress and water stress) related to GTDs. The stresses maybe induce the patho- gens to change from latent state to pathogenic state. The expression of symptoms caused by stress is probably due to the reduction of host resistance. Other host stress factors, including freezing damage, damage to roots by transplanting, infestation of pathogenic nematodes, and non-optimal environmental conditions for growth (malnutrition or high-salt soil) are also related to GTDs symptoms of a variety of hosts However, some areas lack of a more detailed and in- depth understanding, for example, initial pathogen source and invasion conditions. Looking forward, field spore monitoring, molecular identifica-tion technology and X-ray scanning equipment can assist in quantifying the amount of field spores and judging whether the pathogen has successfully invaded. The cytological and genetic knowledge of fun-gal pathogenicity and toxicity can greatly promote the research on GTDs, clarify the role of pathogens in the occurrence and development. More important, genomics technology has been widely studied due to its pathogenic mechanism and excellent germplasm resource mining. This technology can also be ap-plied to the analysis of important pathogenic factors or to screen out genetic loci or materials resistant to GTDs as a method to improve grape’s resistance. In summary, GTDs widely happen in world and lead to heavy loss. The research on the occurrence, epidemic pattern and action mechanism of GTDs are important to understand how to control them and also other fruit trunk diseases in the future.