First Report of Plum bark necrosis stem pitting-associated virus in Stone Fruit Trees in China.

Plum bark necrosis and stem pitting disease was first observed on a 'Black Beaut' plum (Prunus salicina Lindl.) in the United States in 1986 and later is several other countries. Plum bark necrosis stem pitting-associated virus (PBNSPaV; genus Ampelovirus, family Closteroviridae), the putative causal agent of the disease, infects many stone fruit species and causes decline, gummosis, flattening of scaffold branches, and stem necrotic pits in some diseased trees (1,3). An investigation of the incidence of PBNSPaV on stone fruit trees in China was conducted during 2009 and 2010. Leaf samples were collected from 47 trees, including peach (P. persica L. Batsch), nectarine (P. persica L. var. nucipersica Schneider), plum (P. domestica L.), ornamental plum (P. cerasifera Ehrb), sweet cherry (P. avium L.), and flowering cherry (P. serrulata L.), grown in Hubei, Henan, and Shandong provinces in central and northern China. Most of sampled trees showed trunk gummosis or stem pitting. The presence of PBNSPaV was tested by reverse transcription (RT)-PCR using primer set PBN195F/PBN195R (5'-CTGGTCTTCCTGCTACTCCTT-3'/5'-AAGCCCACAATCTCAGAGCG-3') designed for the detection of the coat protein (CP) gene of the virus. Total RNA was extracted from leaves using a CTAB protocol reported by Li et al. (2). Products of the expected size of 190 bp were amplified from 20 samples, including seven cultivated peach, four ornamental peach, one nectarine, two plum, one ornamental plum, three sweet cherry, and two flowering cherry samples. All trees positive for PBNSPaV showed stem pitting symptoms on the base of the trunk. To further confirm these results, a 590-base region of the heat shock protein 70 homolog (HSP70h) gene was amplified by RT-PCR using primers HSP-P1/HSP-P2 (5'-GGAATTGACTTCGGTACAAC-3'/5'-TCGAAAGTACCACCACCGAA-3'). Amplicons of the expected size were cloned into the vector pMD18-T (TaKaRa, Dalian, China) and sequenced by Genscript Corp. (Nanjing, China). Sequences of 18 PBNSPaV isolates were deposited in GenBank with Accession Nos. JF810177-JF810194. Sequence comparisons showed that the partial HSP70h gene from the Chinese PBNSPaV isolates shared 82.2 to 100% nucleotide (nt) and 94.0 to 100% amino acid (aa) similarities between them and 83.6 to 99.1% nt and 94 to 100% aa similarities with the corresponding region of the other PBNSPaV isolates deposited in GenBank. In July 2010, peach GF305 seedlings were inoculated by side grafting with budwoods from two PBNSPaV-positive ornamental peach plants. In June 2011, grooving symptom was observed on the stems of the seedlings and the virus was detected by RT-PCR. The results further confirmed PBNSPaV infection in China. These results show that PBNSPaV and the associated disease occur in main cultivated and ornamental Prunus species in China. Given the importance and the devastating symptoms of the disease, it is important to prevent virus spread by using virus-tested propagation materials. References: (1) M. Al Rwahnih et al. Arch. Virol. 152:2197, 2007. (2) R. Li et al. J. Virol. Methods 154:48, 2008. (3) D. B. Marini et al. Plant Dis. 86:415, 2002.