Breeding for PVY resistance in tobacco LJ911 using CRISPR/Cas9 technology

Strain-specific hypersensitive (HR) and extreme resistance (ER) phenotypes elicited in potato plants by three Potato virus Y (PVY) isolates in strain groups PVYO (BL and DEL3) and PVYD (KIP1) were studied. PVYO and PVYD isolates elicit HR genes Ny or putative Nd, respectively, and all three isolates elicit ER gene Ry. They were inoculated to 39 Australasian, European, or North American potato cultivars released over a 117-year period and harvested tubers were replanted. Both primary and secondary symptoms were recorded. Two European cultivars always developed ER following sap and graft inoculation and, thus, carried comprehensive PVY resistance gene Ry. One Australasian and two European cultivars always developed susceptible phenotypes and, thus, lacked genes Ry, Ny, and putative Nd. Sap inoculation with isolate KIP1 elicited localized HR (LHR) in 31 cultivars and both LHR and systemic HR (SHR) in three others; thus, all carried putative Nd. Isolates BL and DEL3 both elicited susceptible phenotypes in 11 of these 34 cultivars but LHR alone, SHR alone, or both LHR and SHR in the other 23 which, therefore, all carry Ny. With these two isolates, SHR expression ranged from very severe to very weak, with the greatest numbers of isolate–cultivar combinations occurring in the severe category with BL (n = 11) and moderate category (n = 12) with DEL3. Within the same isolate–cultivar combination, overall, SHR symptom expression was weaker with secondary than primary infection. With both primary and secondary infection, SHR expression was most severe with KIP1 and weakest with DEL3. Genes Ny and putative Nd were present in cultivars released between 1939 and 2010 or 1893 and 2010, respectively, occurring in cultivars from all three world regions. These findings have important implications concerning breeding new PVY-resistant potato cultivars, especially for countries lacking healthy seed potato stocks, or where subsistence farmers cannot afford them. An alternative to including gene Ry is incorporating as many strain-specific PVY resistance genes as possible.

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Characterization of a Novel Resistance-Breaking Isolate of Potato Virus Y in Nicotiana Tabacum

International Journal of Phytopathology ◽

10.33687/phytopath.003.01.0376 ◽

2014 ◽

Vol 3 (1) ◽

pp. 01-10

Author(s):

Jae-Hyun Kim ◽

Young-Soo Kim ◽

Soo-Won Jang ◽

Yong-Ho Jeon

Keyword(s):

Potato Virus ◽

Potato Virus Y ◽

Biological Properties ◽

Systemic Movement ◽

Pvy Resistance ◽

Resistance Breaking ◽

Systemic Vein ◽

Vein Necrosis ◽

Tobacco Cultivar

Potato virus Y (PVY) was identified from a PVY-resistance flue-cured tobacco variety KF120 showing vein necrosis at Buron province, Korea. Biological properties of the isolate named PVY-ToBR1 was characterized using various host plants with another isolate PVY-ToJC37. The isolated PVY-ToBR1 induced systemic vein necrosis symptoms on a PVY-resistant tobacco cultivar (VAM) harboring potyvirus resistant va gene, though tissue printing showed the systemic movement of virus was slightly delayed. By contrast, the isolate PVY-ToJC37 failed to infect VAM plants and the virus was not detected on inoculated leaf and systemic leaves in VAM plants. Similarly, the isolated PVY-ToBR1 induced distinctly systemic vein necrosis symptoms on PVY-resistant tobacco cultivars (V.SCR, PBD6, TN86, TN90, Virgin A Mutant, NC744, and Wislica) that have the recessive potyvirus resistance gene va, but PVY-ToJC37 did not infect systemically infect these tobacco cultivars, suggesting that PVY-ToBR1 is a novel resistance-breaking isolate in tobacco. The coat protein (CP) genes of PVY-ToBR1 and PVY-ToJC37 were amplified using RT-PCR assays with specific primers for PVY isolates and nucleotide sequences of the CP genes were determined. The isolate PVY-ToBR1 showed 88.4% - 99.4% and 86.6% - 99.4% CP identities to the 46 different PVY isolates at the nucleotide and amino acid, respectively. Phylogenetic relationship from CP comparisons showed that PVY-ToBR1 isolate clustered with PVYNTN isolates and PVY-ToBR1 isolate more closely related to the isolates from European than from North American PVY NTN.

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