Molecular diversity of “Huanglongbing” pathogens in endosymbionts, parasitoids and predator of psyllids in Coorg mandarin ecosystem in Western Ghats, India

Abstract

The Coorg mandarin is a key ecotype citrus species cultivated in multi-tier cropping systems within coffee and pepper plantations in the Coorg region of India and faces considerable challenges from “huanglongbing” (HLB) transmitted by psyllids. Surveys showed that the HLB incidence ranges from 35 % to 64.2 % in Karnataka, 40 %–70 % in Tamil Nadu, and 30 %–60 % in Kerala among both seed-grown and grafted plants. This study identified four groups of psyllids, their associated endosymbionts (Wolbachia and ‘Candidatus Profftella armatura’), and two parasitoids (Tamarixia radiata and Syrphophagus aphidivorus), along with a predator (Allograpta nasuta), potentially influencing HLB dynamics. HLB detection in Coorg mandarin samples, based on vector and plant diagnostics, revealed four distinct groups (G1–G7) sharing over 97 % nucleotide identity with ‘Candidatus Liberibacter asiaticus’ strains infecting citrus globally. Further analysis of genetic variability through tandem repeat numbers (TRN) in the CLIBASIA_01645 locus showed TRN variation from 0 to 21 across the southern states, indicating significant genetic diversity among ‘Ca. L. asiaticus’ populations adapted to the specific ecological niche of Coorg mandarin groves. This is the first report characterizing psyllids, associated endosymbionts, parasitoids, and predators in the Coorg mandarin ecosystem.