Studies on the Simultaneous Detection of Citrus Huanglongbing Pathogen,Citrus exocortis viroid, Citrus tristeza virus by Multiplex RT-PCR Studies on the Simultaneous Detection of Citrus Huanglongbing Pathogen,Citrus exocortis viroid, Citrus tristeza virus by Multiplex RT-PCR Quick Detection of Citrus exocortis viroid (CEVd) by One-step RT-PCR Quick Detection of Citrus exocortis viroid (CEVd) by One-step RT-PCR Simultaneous and Rapid Detection of Four Important Graft\|transmissible Pathogens of Citrus by Multiplex PCR