Diagnosis of Citrus Greening (Huanglongbing) Disease by Pcr and Citrus tresteza Virus by Das- Elisa Techniques from Different Parts of Nepal

Abstract

Citrus species are highly nutritious sub-tropical fruits of Rutaceae Family. The climatic and geographical conditions of Nepal are suitable for citrus cultivation. However, the productivity of citrus in Nepal is only (10-11mt/ha) which is very low compared to that of developed countries. In present scenario there has been a growing awareness on the occurrence of virus and virus like disease in crops of Nepal. Plant viruses damage almost all parts of plant. Most of the citrus farms are affected by citrus greening disease (Huanglongbing) and Citrus tresteza virus (CTV) causing citrus decline. Due to this cause, farmers face huge economic loss and search for preventive and curative actions. There are more than 30 virus and virus like disease of citrus known in the world of which Huanglongbing and CTV are the most destructive. The PCR reaction specific for Asian Citrus psyllid was done by using 703 bp long fragment of ribosomal protein genes (rpl-PCR) in the rplKAJL-rpOBC (β-operon) using primer A2 and J5 (Hocquellet et al., 1999). Among 9 samples tested 7 samples gave PCR positive reaction detecting Huanglongbing (Asian Citrus psyllid), from Lamjung and Kathmandu District. . In vivo leaves samples of Junar ( C. sinensis), kagati, (C.aurantifolia ), mandarin orange (C. reticulata nibuwa (C. limon), vogate, [C. grandis), and trifoliate orange(Poncirus trifoliata) collected from four districts Lamjung, Gorkha, Dolakha and Kathmandu and in vitro shoot tip and node cultured samples of infected mandarin orange and trifoliate orange were tested for CTV by DAS-ELISA technique. All cultivars except C. grandis, in vivo were infected by CTV. Similarly, seedling grown samples tested from screen house nursery and tissue cultured samples showed negative reaction to CTV. Virus free citrus plant production technique is only the effective method for saving citrus trees and to get optimum production. There are numerous disease-transmitting vectors in open or uncontrolled environment that can easily attack the immature young plants. Pathogens of Huanglongbing and CTV are graft transmissible and vector borne. So they can easily transmit from infected scion and in open environment. Grafting with virus free trifoliate rootstock with virus free scion of different citrus cultivars of seedling plant in controlled environment (screen- house) to produce certified citrus plant is the most effective technique to control the declining condition of citrus production in Nepal. Citriculture of mandarin orange (up to 60% of total citrus plants) and Junar (20%) can enhance productivityup to 20 Mt/ha in Nepal. This can be achieved by completely removing the old plants of problematic farms with disease-free indexed plants.