Occurrence, molecular diagnosis and suitable time of detection of citrus greening disease in sweet orange

Huanglongbing (HLB), previously known as citrus greening disease (CGD) is one of the most destructive disease of citrus and responsible for decline of citrus orchards in Andhra Pradesh (A. P) and other citrus growing areas in the country. A preliminary survey on prevalence of HLB associated with citrus was carried out in three major sweet orange growing districts of A. P and the results revealed that a high incidence of 14.5% was recorded in Prakasam district followed by Kadapa (13.18%) and Nellore (12.59%). The DNA extracted from different plant parts of acidlime, i.e. bark, midrib, vein and lamina by CTAB and SS Tris-EDTA methods were subjected to PCR amplification. An amplification product of 1150 bp was observed in bark, midrib and vein. However, no amplification was observed in leaf lamina. Between CTAB and SS Tris-EDTA method, DNA from SS Tris-EDTA method yielded bright band compared to CTAB method. Detection of HLB in sweet orange was done from December 2004 to April 2005 at fortnight interval. It was observed that an excellent amplification product of 1150 bp was observed from December 2004 to February 2005. From March onwards a mild amplification of 1150 bp was observed in both the methods. So it can be concluded that winter season will be the suitable period for detection of the pathogen. Between these two methods of DNA extraction CTAB method was useful for detection of HLB in midrib and veins while SS Tris-EDTA method was useful for detection in bark of sweet orange