Studies on cucumber mosaic virus

Abstract

A comprehensive description of the symptoms caused by cucumber mosaic virus (CMV) on various hosts is given, as observed on naturally affected plants as well as mechanically inoculated plants with several strains of CMV.Infection with CMV gives generally a stunting effect on the host plant. In tomato, Linaria bipartita, etc., rosette symptom has been occasionally noted. As foliage symptoms, mosaic is the most common. Before mottle, there usually appears vein-clearing, vein-banding or chlorotic spot. Bright yellow spots have been observed frequently in infected plants of pansy and celery. Sometimes on red pepper and gladiolus, white mottling occurred. Mosaic symptoms are usually associated with distortion of the leaves. In extreme case, CMV causes fern-leaf in tomato, Linaria, etc. Distinct ruffling is seen on the leaves of Datura, Japanese radish and others. Inoculations with the isolates from pansy showing yellow ring spot, and from Galega officinalis, produced ring spot on tobacco. A noticeable, virulent strain has been isolated from a markedly yellowed plant of pansy; the virus produces systemic necrosis on tobacco, petunia, etc. and eventually kills the top (Fig. 7).Enations have been observed on leaves of naturally affected plants of petunia, scabiosa and cucumber. In case of cucumber, the symptom was reproduced by inoculation. The cucumber variety, Shin aonaga-jibai, seems to be liable to develop enations. An isolate of CMV from chrysanthemum produced on leaves of tobacco peculiar outgrowths (Fig. 10), similar to those observed by Smith (1951).The most usual symptoms on the flower were break of petals, and mottle of calyx. In primula, color of petals, as a whole, turned pale. In tobacco and petunia, affected with isolates from chrysanthemum and from Japanese radish, prominent malformation of flower was observed in addition to break (Fig. 11 and 12).Symptoms on fruits of cucumber are usually not conspicuous. This may be explained by the tolerance to CMV in the commercial varieties of cucumber in Japan. Chlorotic spots appear often at the stem-end of fruit. The most pronounced symptoms have been found on a squash variety, Tokyo (Cucurbita maxima); the fruits are distinctly mottled and warted. In red pepper and tomato, yellow mosaic may occur on the fruits. Fruits of eggplant sometimes are suppressed in colouring and turn whitish.On inoculating mechanically, local lesions developed on the inoculated leaves of plants in 20 species covering 9 families. Local lesions may be in the form of necrotic solid spot, necrotic ring, grayish spot with brown border, concentric ring, or chlorotic ring, as illustrated in Figs. 14 to 18. The type and development of lesions depend on the strains of the virus, kind of host plant and season of the year. In Chenopodium anthelminticum and C. album, no further development than local lesion was observed, whereas in legumes and tobacco, local lesions caused by certain strains of CMV were followed by streak along the vein, extending to stem, or by systemic mottling.There has been found no symptomless carrier. X-bodies were not observed in trichomes and epidermis of tobacco, tomato, cucumber and corn leaves infected with CMV.