MOLECULAR CHARACTERIZATION OF VIRUS ASSOCIATED WITH YELLOW MOSAIC DISEASE IN HORSE GRAM
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Date
2024-05-06
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Acharya N G Ranga Agricultural University
Abstract
In this study, begomovirus associated with YMD of horsegram in
Andhra Pradesh was studied based on diseased samples collected from
Anantapuramu, Chittoor and YSR Kadapa districts. Based on PCR
amplification and sequencing analysis, it was confirmed that all five samples
infected with HgYMV indicating its predominance in horse gram growing
areas of AP. Whole genome was determined for all the five isolates using
overlapping primers for amplification of DNA-A and DNA-B components of
HgYMV.
The size of DNA-A in five isolates ranged from 2733-2736 nucleotides
whereas for DNA-B, it was found to be 2670-2726 nucleotides in length.
Complete genome analysis and sequence identity of HgYMV DNA-A and
DNA-B of five isolates shared maximum nucleotide identity ranged from
95.5-98.7% for DNA-A and 94-98.2% for DNA-B with other HgYMV
infecting pulses from different places. Among DNA-A and DNA-B
components shared more than 94% identity among themselves, thus provining
five isolates of HgYMV belong to same variant of the HgYMV. The
recombination analysis revealed that DNA-A and DNA-B of HgYMV under
present study is a recombinant, which is a derivative of known virus.
The sequence analysis of IR region of HgYMV DNA-A and HgYMV
DNA-B yielded broad range of identity (50.8-98.8% and 27.4-98.7%
respectively) with HgYMV infecting other legumes. The IR region of all five
isolates contains conserved TATA box, Nanomer and Ori sites.
Nucleotide analysis of six ORFs of HgYMV DNA-A component with
other begomoviruses was attempted. ORFAV1 and ORFAV2 shared 95.3 to
100% and 81.8 to 100% identity respectively with compared HgYMVs
different isolates of HgYMV. A high similarity was also observed for other
ORFs AC1 (95.0-100%), AC2 (80.7-100%), AC3 (83.5-99.2%) and AC4
xviii
(92.8-100%). When compared with other begomovirus the closest association
was found for MYMIV (80.6-86.6%), MYMV (82.2-84.5%) for DNA-A and
MYMIV (60.3-68.4%), MYMV (60.5-68.3%) for DNA-B and less similarity
was observed for DoYMV, VbGMV and FbLCV.
The nucleotide analysis of ORFs of DNA-B component showed that
high similarity (94.1-100%) was observed for BV1than BC1 (77.8-100%)
which indicates BC1 is a divergent (KDP and TPT isolates).
Bemisia tabaci populations were collected from four districts of
Andhra Pradesh (YSR, Anantapuramu, Chittoor, Nellore) for identification
biotypes and genetic groups. The existence of two genetic groups was
revealed based on partial mtCOI gene sequence analysis. KDP and NLR
belong to Asia-II-1 genetic group. Asia-II-8 genetic group was 1st time
reported in AP identified in ATP and TPT B. tabaci population.
The association of secondary bacterial endosymbionts with Bemesia
tabaci populations was studied using16S rRNA/23S rRNA gene sequences.
Wolbachia, a s-endosymbiont was identified in all four isolates which belongs
to super group B. Whereas the association of Cardinium and Arsenophonus
was observed from Kadapa B. tabaci population. The phylogenetic analysis
identified Cardinium connected to C2 subgroup and Arsenophonus to A2
subgroup. Rickettesia was absent in all B. tabaci populations. Thus, Asia -II-1
genetic group from KDP was found in association with Wolbachia,
Cardinium and Arsenophonus, while Asia-II-8 genetic group associated with
only Wolbachia.
A total of 37 Horse gram genotypes were screened for identifying
resistance against Horse gram yellow mosaic virus. The PDI values of 37
genotypes ranged from 0-97.2%. Eighteen genotypes were found resistant
under natural disease screening methods. Eight genotypes exhibited higher
degrees of susceptibility (30.85-97.2%). The apparent rate of infection which
depicts disease progression indicated that slow progress in resistant type
genotypes (BSP21-3, r:0.20), whereas faster rate of spread disease in
susceptible genotypes Indira Kulthi (r:0.45) and BSP21-5 (r:0.454).