Population Structure and Genetic Diversity within Peach latent mosaic viroid Field Isolates from Peach Showing three Symptoms

摘要

To gain insight into the molecular basis of field isolates inducing the symptoms of leaf yellowing, discolouration along leaf sides and leaf mosaic, six isolates from peach showing the three different symptoms in the field were studied by single-strand conformation polymorphism analysis and nucleotide sequence analysis. Results revealed that each Peach latent mosaic viroid (PLMVd) isolate is composed of a population of genetically related variants (haplotypes), one being predominant with frequencies from 32% to 57%, and most of others having a low frequency of 4-5%. Each predominant haplotype was sequenced, as well as some non-predominant haplotypes selected randomly for comparative purposes. In each isolate, sequence alignment among the predominant and non-predominant haplotypes demonstrated that the predominant haplotype had the least variation with others among them, and its sequence was identical to the consensus sequence, which inflected that the predominant haplotype displayed a wide representative of sequence for others in a PLMVd isolate. The similarities and genetic distance between the predominant sequences from peach showing the same symptoms were higher and smaller, respectively, than that with different symptoms; they were more than 98.8% and <1%, respectively, between the predominant sequences with same symptomatic source, and were <98.5% and more than 1%, respectively, between the predominant sequences with different symptomatic source. Some particular variations were indicated for these isolates, and it revealed that the isolates with the symptom of discolouration along leaf sides on their source peach trees had a G or U in position 169 nt, and the isolates with the symptom of leaf yellowing had U and C in 115 and 116 nt, respectively, and the isolates with the symptom of leaf mosaic showed diversity at (3 nt: delete C; 5 nt: A and 54 nt: U).