Transmission of Mulberry Ringspot Virus by Longidorus martini Merny

Abstract

When mulberry seedlings were planted in soils brought from mulberry fields where mosaic disease was severe, the seedlings showed ringspot and enation symptoms on the leaves 6 to 17 months after planting, reconfirming Okabe's conclusion (1959) that mosaic is a soil-borne disease.From the leaves showing enation and/or ringspot symptoms of these experimentally infected seedling, a virus was isolated by juice inoculation to cowpea, Chenopodium amaranticolor, C. quinoa, and C. murale. In electronmicroscopy, the virus was found to be spherical, about 22mμ in diameter. The virus reacted with antiserum to mulberry ringspot virus prepared by Dr. T. Tsuchizaki, but not with antiserum to tomato black ring virus sent from Dr. B.D. Harrison, Scotland. The virus was identified as mulberry ringspot virus reported by Tsuchizaki et al. (1970).The infected soil lost its transmissibility when dried for 7 days. Many nematodes belonging to Longidorus were collected by sieving technique from soil around roots of infected mulberry trees in the fields. The species was identified as L. martini Merny by Mr. Y. Oshima.Lots of 10 to 56 L. martini sieved from soil in which diseased mulberry trees had been growing were placed near the roots of 31 potted healthy mulberry plants. After 3 to 12 months, 10 of these plants showed symptoms, and the virus was detected from these 10 plants by juice inoculation to test plants. No infection occurred in 8 control mulberry plants grown in soil free from L. martini.Transmission tests using Xiphinema sp. sieved from soil in which diseased mulberry had been growing gave negative results.The symptoms on mulberry plants incited by the nematode transmission were ringspots, enations and some vein necrosis, and no fern-leaf and yellow leaf symptoms were observed.