IDENTIFICATION OF MOLECULAR MARKERS FOR ROOT KNOT NEMATODE RESISTANCE IN CHILLIES
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Date
2008
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ACHARYA N.G. RANGA AGRICULTURAL UNIVERSITY, RAJENDRANAGAR, HYDERABAD
Abstract
A survey of chilli grown areas of Andhra pradesh was undertaken to
identify the predominant nematode race. The soil samples were collected and
processed for nematode isolation and identification. Seven of the samples
showed nematode infection of roots which were multiplied on the susceptible
tomato cultivar, Rutgers for further race identification using host differentials.
Chilli (Capsicum annuum L.) production is seriously affected by root
knot nematode disease to which no resistant source is available in the
cultivated germplasm. Degenerate primers based on the conserved motifs of
plant disease resistance (R) genes were used to isolate analogous sequences
called resistance gene candidates (RGCs) from cultivated Capsicum species.
The NBS, LRR and kinase domain are characteristic features of many
plant resistance genes. The NBS domain has many conserved amino acid
sequences among different R genes. NBS domain was analysed in the present
study on chilli using degenerate primers designed to the conserved region after
PCR amplification. The PCR amplified DNA fragments were cloned. Of the
27 clones obtained, 12 clones were sequenced and 9 of them showed
significant sequence homology both at nucleotide and amino acid levels with
the known R genes and resistance gene analogs isolated from other dicots and
monocots on BLAST search. The RGCs isolated from chilli showed sequence
similarity with the NBS region of other known R genes viz.
RPM1,CaMi,RPS2, N ,L6,Lettuce R gene, and RPP5. Multiple alignment of
isolated chilli RGCs using CLUSTALW grouped these into two classes. An
amino acid signature in the conserved motifs comprising the NBS domain
clearly distinguishes the two classes. All chilli RGCs belonged to the class of
R gene with LZ (leucine zipper) domain in the NBS region and TIR domain
and three RGCs (CaRGC4, CaRGC8, CaRGC10) of chilli showed separate
grouping.
To identify the resistant and susceptible germplasm of chilli, 60 RAPD
markers were analyzed by bulk segregant analysis. Of the 60 RAPD markers
analyzed, none gave any polymorphism between the bulks.
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Keywords
IDENTIFICATION, MOLECULAR, MARKERS, ROOT, KNOT, NEMATODE, RESISTANCE, CHILLIES