Status of Phytophthora and Huanglongbing Diseases of Citrus Causing Decline in Coorg Mandarin in India

Abstract

Coorg mandarin is a famous ecotype of mandarin grown in multi-tier cropping system in coffee and pepper plantations in Coorg region of India. The roving survey indicated disease incidence of huanglongbing (HLB) and Phytophthora ranging from 35%-64.2% and 22.5%-35.6% in different places of Coorg region. A total of 177 Phytophthora infected (plant roots 59, soil 118), and 576 greening or HLB infected Coorg mandarin samples were collected from 184 Coorg mandarin orchards, of these 111 Phytophthora isolates were isolated and characterized in this study on the basis of colony growth patterns and morphological structures. Based on the virulence, only 52 of 111 Phytophthora isolates were amplified by PCR using universal internal transcriber spacer (ITS) primers, cloned and sequenced. The sequences analysis of Phytophthora isolates revealed more than 97% nucleotide (nt) similarity within themselves, except eight isolates of P. palmivora and four isolates of P. nicotianae had varied nt identity (70.6% to 97.4%) with other Phytophthora species compared. Similarly, 523 of 576 Coorg mandarin samples were confirmed the presence of HLB infection by PCR using 16S rRNA gene specific universal primers. The representative five of 523 Coorg mandarin isolates showed nt identity ranged from 94.4% to 95.3% with Candidatus Liberibacter asiaticus (AB008366) isolate infecting citrus in Asia and one isolate of HLB shared nt identity of 96.9% with Ca. L. asiaticus (KJ944269).