Submitted to: Walnut Research Conference
Publication Type: Research Technical Update
Publication Acceptance Date: 3/1/2010
Publication Date: 1/1/2011
Publication URL: http://walnutresearch.ucdavis.edu/2010/2010_245.pdf
Citation: Sudarshana, M.R., Mahmood, N., Rowhani, A. 2011. Characterization of R genes involved in resistance to Cherry leaf roll virus in paradox hybrids. Walnut Research Conference. pp. 245-251. Interpretive Summary:
Technical Abstract: A single dominant ‘R’ gene (clrvR), in black walnuts (Juglans hindsii) or ‘paradox’ hybrids (J. hindsii x J. regia) confers resistance to Cherry leaf roll virus (CLRV), the causal agent of blackline disease. The identification and cloning of the ‘R’ gene is expected to aid the walnut breeding program by improving the accuracy and efficiency of current PCR-based screening methods of the progenies of backcrosses and is also expected to help generate novel rootstocks tolerant to infection by CLRV. In our attempt to identify the clrvR, 37 degenerate primers were modified from previously published studies or were newly designed to amplify homologs of known ‘R’ genes from genomic DNA extracted from paradox cultivar Burbank. About 150 primer pairs were tested using gradient PCR, and amplicons specific to cultivar Burbank, but not to cultivar Chandler, were cloned, sequenced and analyzed for similarities to published ‘R’ gene sequences. Many sequences were screened and four of these showed significant similarities to other sequences in the NCBI BLAST database. Of these, the most promising sequence showed an almost 80% similarity to a published Hazelnut ‘R’ gene sequence in the database. However, subsequent screening of virus resistant back cross selections and other English walnut varieties did not find the amplified product unique to cultivar Burbank. Future studies will explore alternate strategies to identify the clrvR gene.