DETECTION AND CHARACTERIZATION OF CITRUS GREENING BACTERIUM (Candidatus Liberibacter asiaticus) IN PUNJAB
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Date
2018
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Punjab Agricultural University, Ludhiana
Abstract
The present study was conducted on the greening disease of citrus in the Department of Plant Pathology, PAU, Ludhiana during the year 2015-17. Surveys were conducted in the citrus growing districts- Bathinda, Fazilka, Hoshiarpur, Ludhiana and Sri Muktsar Sahib of Punjab. The incidence of the disease ranged between 5% to 60% in all the cultivars with mean incidence of 17.9%. The disease incidence was highest in Ludhiana (23.4%) and lowest in Sri Muktsar Sahib (16.2%). Interveinal chlorosis, green island and blotchy mottle of leaves and bi-coloured fruit symptoms of disease were observed during the surveillance on Kinnow mandarin, Sweet orange and Daisy cultivars of citrus. Of the three agro-climatic zones of Punjab, maximum incidence was recorded in Central zone (23.4%) as compared to Arid-irrigated (17.63%) and Sub-mountainous (16.5%). The incidence of disease was 17.34% in Kinnow, 17.24% in Sweet orange and 40% in Dasiy. The presence of greening bacterium (Ca. Las) was confirmed through PCR in 39 symptomatic Kinnow leaf samples from Fazilka, Hoshiarpur and Ludhiana. The HLB bacterium was also detected in 15 and 25 batches of adult psyllid vector (Diaphorina citri Kuwayama) through PCR indicating an association of psyllid vector with the bacterium. The isolation of Ca. Las on Liber A medium was tried but unable to culture HLB bacterium from the leaves of greening infected PCR positive Kinnow plants. The disease was characterized by sequencing of 16S rRNA from four Kinnow isolates (PLK-NO, PLK-HO, PHK-MG and PFK-KW) which showed 98% to 100% similarity with reported isolates of Candidatus Liberibacter asiaticus from Asia. All the four isolates showed 99-100% nucleotide identity.
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