ISHS Acta Horticulturae 235: XIV International Symposium on Fruit Tree Virus Diseases
CORRELATION OF PEAR NECROTIC SPOT WITH PEAR VEIN YELLOWS AND APPLE STEM PITTING, AND A FLEXUOUS FILAMENTOUS VIRUS ASSOCIATED WITH THEM |
| Authors: | H. Yanase, H. Koganezawa, P.R. Fridlund |
| Abstract:
Pear necrotic spot (PNS) is a graft-transmissible disease which occurs in Japan. Some popular varieties of Japanese pear are susceptible to the disease. The characteristic symptoms of the disease are necrotic spots which develop on mature leaves. The inoculation tests of PNS, pear vein yellows(PVY) and apple stem pitting(ASP) to their indicators demonstrated that PNS was closely correlated with PVY and ASP. PNS-diseased pear trees were always infected with PVY. Eleven of 20 American PVY isolates induced symptoms of PNS on the indicator of PNS(Pyrus serotina var. culta HN39) and 17 isolates also induced symptoms of ASP on the indicator of ASP(Malus sieboldii MO-65). Three of four American ASP isolates caused symptoms on HN39 and an indicator Nouveau poiteau A filamentous virus was always transmitted from PNS, PVY and ASP-infected trees to Nicotiana occidentalis subsp. obligua No.1. This virus had a somewhat restricted herbaceous host range. Celosia cristata, Sesamum indicum, Tetragonia expansa, Gomphrena globosa and Chenopodium murale showed symptoms. Leaf extracts lost infectivity between 9–24 hr at 25C, 10 min at 50–55C and after dilution 10-2-10-3. A ASP isolate was purified by acidification and calcium phosphate clarification, two cycles of ultracentifugation using sucrose cushion, and rate zonal sucrose density gradient centrifugation. The size of the virus particle is 12–15 nm wide and 800 nm long. The virus particles formed easily end to end aggregations. Prominent peaks in length distribution of virus particles appeared in 800, 1 600, 2 400, and 3 200 nm in dip preparation of diseased N. occidentalis subsp. obligua No.1. These results suggest that these pear and apple diseases are caused by different strains of the same filamentous virus. Back-transmission of the purified virus to pear or apple is in progress to elucidate that this virus causes the three diseases. | |
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