1984. Effect of white clover mosaic virus infection on various processes relevant to symbiotic N, fixation in red clover. Can. J. Bot. 62: 38-43. The effect of white clover mosaic virus infection on several factors relevant to syn~biotic N, fixation was determined in nodulated red clover (Trifoli~lm prntensc L.) plants at 10-leaf, preblooming, blooming, and flower-senescence stages of growth, corresponding to 3, 6, 9, and 12 weeks after virus inoculation, respectively. Virus infection caused a significant ( P s 0.01) reduction of plant growth (top and root weight), nodulation (number and weight of nodules), rhizobial population, nitrogenase activity, and leghemoglobin concentration in the nodules. The presence of a high concentration of virus within nodules at all harvest times was indicated by infectivity assays. The leghemoglobin was shown to be localized in the peribacteroidal space by a cytochemical technique. A significant increase in inducible nitrate reductase activity was associated with virus infection of plants. KHADHAIR, A. H., R. C. SINHA et J. F. PETERSON. 1984. Effect of white clover mosaic virus infection on various processes relevant to symbiotic N2 fixation in red clover. Can. J. Bot. 62: 38-43. Les effets d'une infection par le virus de la mosaique du trkfle blanc sur plusieurs facteurs pertinents h la fixation symbiotique d'azote ont Ct C determinis chez des plants nodulCs de trkfle rouge (Trifoli~ltn prcrterzse L.) aux stades de croissance suivants: 10 feuilles, prCfloraison, floraison et sknescence des fleurs; ces stades correspondent respectivement h 3, 6, 9 et 12 semaines aprks I'inoculation du virus. L'infection virale provoque une diminution significative ( P 5 0,Ol) de la croissance de la plante (poids des parties aCriennes et des racines), de la nodulation (nombre et poids des nodules), de la population rhizobienne, de I'activitC nitrogknasique et de la concentration de IeghCmoglobine dans les nodules. Des tests d'infectivite montrent une concentration ClevCe de virus h toutes les rCcoltes. Une technique cytochimique rCvkle que la IeghCmoglobine est IocalisCe dans les espaces pCribactCro'idiens. Une augmentation significative de I'activitC de la nitrate riductase est associec h I'infection virale des piantesT [Traduit par le journal]

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A virus‐like disease of apple was observed for the first time in Canada in 1974 in a three year old planting. The disease was characterised by stem pitting, necrosis and breaking or separation of scion/rootstock at the graft union. Foliage was sparse and leaves were chlorotic and diffusely mottled. Using both frozen and freshly harvested leaves of infected apple trees from rootstock suckers as inoculum, a virus was transmitted to herbaceous indicator hosts. Based on host range symptoms, serology and electron microscopy, this virus was identified as tobacco ringspot virus. Initial counts of nematodes in the rhizophere of apple trees affected with union necrosis showed high densities of Xiphinema americanum Cobb., a known vector of nepoviruses. Reports of similar symptoms have indicated that the disease, apple union necrosis and decline was associated with the recovery of tobacco ringspot virus from infected rootstocks. This is the first report associating a union incompatibility condition of apple and tobacco ringspot virus.

(Wilkinson et al. 1954) and somewhat resembled a boiling water extraction method described by Habermann (1967 The amount of fungal growth was measured on a Reichert Visopan projection microscope.The growth of each disc was scored on a scale from I to 4, with 4 for profuse growth. Also, the longest hyphal strand was measured from the cut edge of the disc to the tip of the hypha. RESULTS AND DISCUSSIONThe amount of chlorogenic acid in each of the four tobacco cultivars was compared with the susceptibility of the plants to verticillium wilt (Fig. l)