Conservation, Disease-indexing and Utilization of Pathogen-free Citrus and Banana Genetic Resources in Taiwan

Abstract

Virus and virus-like diseases (greening) of citrus and banana have been causing considerable damage to fruit production worldwide due to their systemic invasion and common spread through infected budwoods, vegetatively propagated seedlings, and transmission by insect vectors. The heat-tolerant form of greening locally known as Huanglungbin (HLB) in China has seriously affected citrus trees in the tropical/ subtropical regions of Asia, and recently in the North and South America. The HLB caused great damage to the citrus industry by shortening tree lifespan and lowering fruit quality. Citrus tristeza virus (CTV) is the most common and destructive virus in the western hemisphere, and has a worldwide distribution. Citrus tatter leaf capillovirus (CTLV) has a potential to become prevalent when trifoliate orange and its hybrids are used as rootstocks. The citrus exocortis viroid (CEV) occurs in many countries, and its commercial effects are primarily on trees grafted on trifoliate orange and some its hybrids, and Rangpur lime. The bunchy-top virus (BBTV) disease has been the common and destructive virus disease of banana since the beginning of this century in Asian and Pacific regions. The banana mosaic caused by CMV has become epidemic after common cultivation of tissue-culture plantlets. Banana streak badnavirus and bract mosaic potyvirus have newly spread to many banana areas in the Pacific regions in recent years. These systemic diseases have become one of the serious constraints for the industry of citrus and banana in the Asian and Pacific region. These diseases are generally controlled by the integrated control measures including cultivation of pathogen-free seedlings, elimination of inoculum sources and prevention of secondary spread by vector insects. In view point of germplasm utilization, establishment of pathogen-free nursery system is primarily important for preventing prevalence of these diseases. National scheme of citrus pathogen-free nursery system is consist of PF citrus foundation in Chia-Yi Agriculture Experimental Station repository and the approved nurseries in private sector and fruit cooperative. The production and utilization of PF-citrus seedlings has been performed under citrus sapling certificate regulation. The virus-free banana cultivars of economic importance obtained through virus-indexing and tissue culture under heat-therapy temperature have been kept in the foundation screen-house for mass production of PF banana TC-plantlets in Taiwan Banana Research Institute. The PF citrus and banana seedlings are commonly cultivated for improving the agro-industry in Taiwan. The precise and rapid indexing techniques are indispensable for management of pathogen-free nursery system and health management of citrus and banana plants in the field. Development and application of molecular diagnostic probes including monoclonal antibodies, DNA probes, and primer pairs for polymerase chain reaction (PCR) were made for formulating indexing techniques including ELISA, rapid diagnostic strips, PCR and RT-PCR to be discussed in this presentation . The establishment of virus-free nursery system for controlling citrus and banana virus diseases has been properly performed through shoot-tip micro-grafting, and tissue culture via virus-free stock indexing and heat-therapy with tissue culture in Taiwan.