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The buoyant densities of bean yellow mosaic virus (BYMV) B25, pea mosaic virus (PMV) E198, lettuce mosaic virus (LMV), and potato virus YN (PVYN) were 1.318, 1.321, 1.330, and 1.326 g/ml, respectively. Their S values were 143, 140, 143, and 145 S. The particle morphology of BYMV B25, PMV E198, and LMV could reversibly be changed by magnesium ions. PVYN particles were broken in the presence of magnesium ions. The molecular weight of the coat protein subunit of the four viruses was 34,000 daltons. In many preparations also a 28,000 daltons component was present. This must be considered to be a breakdown product, derived from the 34,000 daltons component by proteolytic activity. De zweefdichtheden van het bonescherpmozaiekvirus (BYMV) B25, het erwtemozaiekvirus (PMV) E198, het slamozaiekvirus (LMV) en het aardappelvirus YN (PVYN) bedroegen respectievelijk 1,318, 1,321, 1,330 en 1,326 g/ml. Hun sedimentatiecoefficienten waren 143, 140, 143 en 145 S. De deeltjesvorm van BYMV B25, PMV E198 en LMV kon reversibel worden veranderd door toevoeging en verwijdering van magnesium-ionen. Deze induceerden het optreden van breuken in de deeltjes van PVYN. Het molecuulgewicht van de manteleiwiteenheid van de vier virussen bedroeg 34.000 daltons. In veel preparaten was bovendien een component van 28.000 daltons aanwezig. Deze moet worden beschouwd, als een proteolytisch afbraakprodukt dat ontstaat uit de component van 34.000 daltons.

Bean yellow mosaic virus, pea mosaic virus, lettuce mosaic virus, and potato virus YN were purified by homogenizing and clarifying infected leaves in a mixture of 0.1 M tris-thioglycollic acid buffer pH 9, carbon tetrachloride and chloroform, followed by differential centrifuging applying moderate centrifugal forces. Het bonescherpmozaiekvirus B25, het erwtemozaiekvirus E198, het slamozaiekvirus en het aardappelvirus YN konden worden gezuiverd door geinfecteerde bladeren te vermalen in een mengsel van 0,1 M tris-thioglycolzuur pH 9, tetrachloorkoolstof en chloroform, en de geklaarde suspensie vervolgens differentieel te centrifugeren bij matige centrifugaalkrachten.

Numbers of plants infected with bean yellow mosaic virus by aphid transmission decreased with increasing preinoculation temperature in the 15° to 33° range in some experiments. Preinoculation temperature had no effect in other experiments. The effect was related to differences in postinoculation environment other than temperature. A 2-day postinoculation exposure to 30° resulted in aboft twice as many infected plants as at 15–24° when plants were maintained at 15°, 24°, or 30°, for 2 days before inoculation.

In middles leaves of tobacco systemically infected with potato virus Y, the epidermis is far from uniform as a source of virus for aphids. Interveinal epidermis is somewhat better than that of adjacent veins; interveinal epidermis at the leaf tip is about twice as good as that at the base, the middle part being intermediate. These differences are less marked in lower leaves, which are therefore more uniform sources. In upper leaves the chlorotic lesions are good sources for aphids, but adjoining green areas are not. Availability of virus to aphids is closely related to the concentration of virus in expressed sap as measured serologically. Symptom development of virus Y in tobacco reflects both the increase of virus and its availability to aphids.

Electron microscopic observations of sections of leaf, fruit, and stem tissues of Carica papaya L. infected with papaya ringspot virus showed filament-shaped particles in the cytoplasm. In the cell they were in a somewhat parallel arrangement or completely randomly distributed. The average length of the particles was 800 ± 10 mμ, and the diameter 12 mμ. They had a channel in the center. It is believed that these particles are identical to the virus agent because they are found in naturally or in experimentally infected papayas and in mechanically inoculated squash (Cucurbita pepo L.), but not in healthy plants, and because they have the same shape and similar dimensions as particles known to cause other plant virus diseases.

Green peach aphids infective with potato virus Y were made noninfective by exposing the tips of their stylets to ultraviolet radiations in the 2537 Å wave band. Similar results were obtained when the area around the aphid was ventilated during irradiation to carry away the ozone produced by the radiations passing through the air. This irradiation did not appear to harm the aphid even though much of its body was irradiated at the same time. Nor did it affect the infectivity of aphids when their stylets were enclosed by the labium, or when most of the length of the stylets except the tips was exposed to the radiations. Irradiation did, however, reduce the ability of aphids immediately thereafter to acquire potato virus Y during a brief feeding puncture, but this was so whether the tips of the stylets were irradiated or not. Furthermore, an hour after being irradiated, aphids acquired the virus during a brief feeding puncture as readily as did unirradiated controls. It is concluded that irradiation of the tips of the stylets of M. persicae inactivated potato virus Y that otherwise would have been transmitted to the test plants. Only virus near the tips of the stylets appeared to be transmitted even after more than the tips had been inserted into infected tobacco plants.

Purified cauliflower mosaic virus (CIMV) could be transmitted only by aphids which had probed leaves infected with an aphid-transmissible isolate of CIMV before they probed into the purified virus. Aphids which had probed healthy leaves or leaves infected with a non-aphid-transmissible isolate of CIMV or aphids which first probed into purified virus and then into infected leaves did not transmit the purified virus. These results suggest that aphids obtain a factor (acquisition factor) from leaves infected with a transmissible isolate, which enables them to acquire, and to subsequently transmit, purified virus. The acquisition factor was shown not to be the virion of the transmissible isolate. Aphids which obtained the acquisition factor from CIMV infected leaves could transmit purified CIMV but not purified viruses of the potato Y (potyvirus) group; aphids which probed leaves infected with potyviruses could transmit other purified potyviruses but not purified CIMV.

Potato virus X abd Y on potato crops in Mendoza. The presence of potato viruses X (solanum virus 1 SMITH; Annulus dubius HOLMES) and Y (Solanum virus 2 SMITH; Marmor upsilon HOLMES) on potato crops (Solanum tuberosum L. var. White Rose and var. Up-to-Date) is determined. The virus Y had not been reported up to the present in any host in Mendoza, while the virus X was reported on tomato (Lycopersicon esculentum MILL.), and, exclusively on sintomatological observations bases, on potato crops. The methods followed are described and the results are analized. Se determina la presencia de los virus X (Solanum virus 1 SMITH; Annulus dubius HOLMES) e Y (Solanum virus 2 SMITH; Marmor upsilon HOLMES) en los cultivos de papa (Solanum tuberosum L. var. White Rose and var. Up-to-Date) de Mendoza. El virus Y no habías sido señalado hasta ahora para Mendoza en ningún hospedante; el virus X, en cambio, se encontraba señalado en tomate (Lycopersicon esculentum MILL.) y en base exclusivamente a observaciones sintomatológicas, en papa. Se indican los métodos empleados y se analizan los resultados obtenidos. Fil: Pontis, Rafael E.. Universidad Nacional de Cuyo. Facultad de Ciencias Agrarias Fil: Feldman, José M.. Universidad Nacional de Cuyo. Facultad de Ciencias Agrarias

Potato virus Y (PVY) is the prototype of the potyvirus group (Harrison et al. 1971). The group is characterized by particles of diameter about 15 nm. and a length of 720 to 800 nm. and by the presence of pin-wheel inclusion bodies in infected tissues. Because of their low concentration in infected sap and tendency to aggregate during purification, few viruses of this group have been obtained in sufficient quantity for physical or chemical characterization. Tobacco etch virus (TEV) is the most extensively studied virus of the group. PVY has been recently purified (Delgado-Sanchez & Grogan, 1966; Damirdagh & Shepherd, 1970a). Its amino acid composition has been determined and compared with that of TEV (Stace-Smith & Tremaine, 1970). The present investigation was undertaken to determine the molecular size of protein subunits of PVY. A combined method of amino acid analysis and cyanogen bromide cleavage was used for this purpose.