Progress report on viruses of kiwifruit

Abstract: Kiwifruit originated in China and later introduced to international market by New Zealand. As one of the main producers of kiwifruit in the world, kiwifruit industry in China has rapidly expanded over the last decade. Pathogen is one of the key factors affecting sustainable development of kiwifruit industry.Plant pathology in kiwifruit is mainly focused on bacterial and fungal causing diseases, such as bacterial canker caused by Pseudomonas syringae pv. actinidiae. Over the last few years, outbreaks of bacterial canker on Actinidia chinensis and A. deliciosa have caused a huge impact on international kiwifruit industry.For viruses in kiwifruit, our knowledge of them is still limited. Virus which can be latent is a hidden danger in the fruit production. Mounting evidence indicates that kiwifruit viruses are widely present in fields.The first incidence of virus in kiwifruit was reported in the year of 2003 by scientists from New Zealand, who detected the presence of apple stem grooving virus in kiwifruit plants imported from China. To date, fifteen viruses have been reported worldwide, including two tobamoviruses, Ribgrass mosaic virus (RMV) and Turnip vein clearing virus (TVCV) ; a tombusvirus, Cucumber necrosis virus (CNV) ; a novel potexvirus, Actinidia virus X; a capillovirus, Apple stem gooving virus; a alfamovirus, Alfalfa mosaic virus; a cucumovirus, Cucumber mosaic virus; a nepovirus, Cherry leaf roll virus; a anulavirus, Pelargonium zonate spot virus;two vitiviruses, Actinidia virus A and Actinidia virus B; a citrivirus, Actinidia citrivirus; a novel emaravirus Actinidia chlorotic ringspots associated virus; a tospovirus, Tomato necrotic spot tospovirus; and a novel virus belonged to the family Closteroviridae. However, only few of them are documented in details. It largely remained unclear how these viruses can affect kiwifruit production. Most of these viruses are non specialists infecting a wide range of hosts. They are easily transmissible via multiple ways, by grafting, vectors and mechanical transmission. Symptoms include vein clearing, necrotic ringspots, chlorotic mosaics andmottling on leaves, but can be latent or show no obvious symptoms. It has been reported that diseases induced by Cherry leaf roll virus and Pelargonium zonate spot virus cause severe damages on kiwifruit production in orchards. A group of viruses are kiwifruit adapted as they either infect kiwifruit only or to limited host range, such as Actinidia citrivirus, Actinidia virus A and Actinidia virus B, Actinidia chlorotic ringspots associated virus, Tomato necrotic spot tospovirus. By now, there are five viruses described in China, including Actinidia virus A, Actinidia virus B, Actinidia citrivirus, Tomato necrotic spot tospovirus and Actinidia chlorotic ringspots associated virus. Recently, we carried out a survey of virus infection of kiwifruit in Henan province. A total of 68 kiwifruit samples were tested by RT-PCR. Actinidia citrivirus was the only virus detected out of 13 viruses, with an incidence rate of 17.6%. Several diagnostic tools are used for virus detection, such as herbaceous indicators, electron microscopy, ELISA and RT-PCR. Herbaceous indicators are old fashioned method for virus detection which is easy to handle, but it usually takes long time to show symptoms. It is less accurate if infected plants are symptomless or virus infection is latent. ELISA has been applied for plants virus detection since 1970 s, and now it commonly used for testing. This serologic method has high specificity which is more accurate and faster than the approach of herbaceous indicators. However, the main limitation for detecting by ELISA is a requirement of specific antibody against a particular virus. Nowadays, RT-PCR is more frequently used for virus detection, which is highly specific and sensitivity than ELISA. It also can be used for detection of viroids. China is one of the main producing countries of kiwifruits. Lack of understanding of kiwifruit viruses and their related diseases poses potential threats on kiwifruit industry. Future research should investigate the potential impacts of virus infection on kiwifruit industry and expand our knowledge of molecular mechanisms of virus infection and transmission. With rapid development of kiwifruit industry, we should raise awareness of kiwifruit viruses of growers which will help to increase understanding about the diseases in kiwifruit production. Establishment of rapid detection technology will further progress on research of kiwifruit viruses. Moreover, it is necessary to promote scientific and effective field management for improving disease control, which will minimise and prevent the spread of virus. There is a need of selecting varieties resistant to diseases, improving the quality of kiwifruits available on the market. These strategies should be implemented to ensure a safe, effective and sustainable development of kiwifruit industry which will bring social and economical benefits to our growers and consumers. In this review, it describes the viruses of kiwifruit and discusses their potential damages to kiwifruit production. This paper summarizes current research progress of viruses of kiwifruit in China, and finally reviews routine diagnostic tools commonly used for virus detection in kiwifruits.