Symptoms

After its entry into the plant , the virus particles get into the pholem tissue and move along the direction of food particles and thus spread to all parts of the plant . The first symptoms appear on young leaves as mottles , chlorotic streaks , ring -spots or colour-breaking in flowers . In extreme cases malformation of leaves and flowers , crinkling and twisting may result.

CyMV produces the typical mosaic mottle on young leaves of Cymidium which may later turn brown and necrotic . Severely affected leaves may drop prematurely . In Cattleya it produces necrotic spots which appear as sunken spots on the underside of leaves. Sometimes after the initial manifestation the plant may remain normal . Cattleya and Phalaenopsis are more susceptible to this disease than Cymbidium .

TMV-O produces chlorotic steraks on the leaves of cymbidium which may later turn brown . In Cattleyas , it causes colour breaking in flowers ,which is the appearance of patches and streaks of higher pigmentation on a lighter background . Concentration of virus particles would be higher in areas where there is colour -breaking than in normal parts.

Originally it was believed that CyMV and TMV -O when present together , produces the " blossom -brown -necrotic streak " in Cattleya. This is a serious malady and completely ruins the appearance of the flower . Teh lesions appear a few days after flowers have opened as brown streaks which are more apparent in white flowers than in coloured ones. Lawson (1970b) is of the opinion that the assumption that this disease is caused by the combined action of the two viruses is wrong and CyMV alone can produce the disease in Cattleya .

CyMV shows lesions a fortnight after infection has occured but TMV-O does not spread so rapidly . Lawson (1970b) reports that flowers produced in Cattleya plants six months after inoculation of the virus did not show colour-breaking but in the second year they did.

ORsV affects mostly Odontoglossum grande producing the characteristic ring spots which are concentric rings of dead and green tissue appearing on leaves. In Cymbidium leaves it produces the " diamond mottle " or " heioglyphic chlorosis " and in Cattleya a mild form of colour -breaking .