SEARCH FOR MOLECULAR MARKERS LINKED TO FIRE BLIGHT RESISTANCE IN PEAR (PYRUS COMMUNIS)

Randomly amplified polymorphic DNA (RAPD) and resistance gene analog (RGA) were used to search for molecular markers linked to fire blight resistance in Pyrus communis) ‘Old Home’ and ‘Seckel’. Genomic DNA from these fire blight resistant cultivars and the susceptible ‘Bartlett’ were used as templates.
To obtain RGAs, degenerate primers based on conserved regions in NBS-LRR and protein kinase-type resistance genes were used to amplify bands of ~550 and ~600 bp, respectively, from ‘Old Home’ and ‘Seckel’. Cloning and sequencing twenty of these PCR products revealed that all had different sequences, and all, except for two, of the clones were similar to RGAs from other plant species and had high similarity to several R genes.
Parsimony analysis of the predicted protein sequences of the pear RGAs and their most similar characterized R genes showed that pear RGAs clustered with known R genes.
Sequence characterized amplified region (SCAR) primers designed from these RGA sequences revealed no PCR length polymorphisms.
Sequencing two PCR products from ‘Bartlett’ showed that they had ~98% identity to the original sequences from ‘Seckel’. RAPD analyses of ‘Bartlett’, ‘Seckel’ and ‘Old Home’ revealed a high similarity (~92-93%) between the three cultivars.
Four polymorphic PCR products were cloned and sequenced, and RAPD-SCAR primers were designed.
No PCR length polymorphisms were found, and sequencing of a PCR product from ‘Bartlett’ and ‘Seckel’ using the same RAPD-SCAR primer pair showed that they had 90% nucleotide identity.
These results show some of the challenges in finding markers linked to fire blight resistance among different pear cultivars, which have a high degree of similarity to one another.

X International Workshop on Fire Blight

M.R. Afunian, P.H. Goodwin, D.M. Hunter

RAPD, resistance gene analogs, SCAR, NBS-LRR

https://doi.org/10.17660/ActaHortic.2006.704.89