MOLECULAR VARIABILITY AND MANAGEMENT OF XANTHOMONAS CITRI SUBSP. CITRI CAUSING CITRUS BACTERIAL CANKER
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Date
2024-06-14
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UHF Nauni
Abstract
The present investigation entitled “Molecular variability and management of Xanthomonas citri subsp. citri
causing citrus bacterial canker” was undertaken to record the amount of molecular variability exists in different isolates of the
pathogen and different management strategies were assessed for the management of the disease. Different isolates of the
pathogen were collected from four districts (Hamirpur, Una, Sirmour and Kangra) of Himachal Pradesh and one was collected
form Punjab and one from Karnataka. The isolates were isolated from different hosts such as Citrus sinensis, C. reticulata, C.
aurantifolia, C. limon and C. jambhiri. The isolates exhibited variable colony colour from yellow, light yellow, dark yellow and
pale colour on nutrient agar medium. The variation in incubation period of isolates ranged from 2.2 to 4.4 days, in final symptom
development period ranged from 19.6 to 24 days and in per cent disease index ranged from 40 to 90 per cent in detached leaf
pathogenicity assay. The isolates showed variation under attached leaf pathogenicity assay on seedlings of sweet orange and
incubation period ranged from 7.2 to 10.4 days and final symptoms development ranged from 32.4 to 40 days and per cent
disease index varied from 37.50 to 79.17 days. Molecular identification confirmed the presence of single band in all isolates for
16S rDNA at 591 bp, for glpF gene two isolates with a single band at 690 bp and for species specific rpf gene in seven isolates
producing single band near 581 bp. Moleclar variability among isolates was confirmed by using RAPD and ISSR markers which
showed high amount of genetic variability among the isolates and both markers were polymorphic in nature. Both the markers
clustered the isolates in three groups and combined clustering grouped them in two groups. For disease management, different
resistance inducing chemicals at three different concentrations were analysed and salicylic acid, β-amino butyric acid,
acibenzolar -S- methyl and potassium chloride were effective and effectiveness increased from low to high concentration of
chemicals. All these chemicals were found to improve the plant’s phenolic and chlorophyll content and the peroxidase,
polyphenol oxidase and phenylalanine ammonia lyase activity was also enhanced with their application in comparison to
inoculated control, un-inoculated control and other treatments. Green silver and copper nanoparticles using leaf extract exhibited
the effectiveness for inhibition of the pathogen as well as disease under semi-controlled conditions with highest efficacy in green
silver nanoparticles of Ocimum sanctum and Tagetes erecta followed by green copper nanoparticles of Eucalyptus hybrida. Metal
nanoparticles were effective in disease management under controlled conditions and pathogen inhibition under in vitro
conditions.