Abstract
Some properties of an attenuated tomato strain (L11A) of tobacco mosaic virus (TMV) were compared with the parent virulent strain (L). Dilution end point of L11A was 10-7-10-8, while L was still infective at 10-8. L11A lost its infectivity after heat treatment at 90C for ten min while L did not. The infectivity of L11A was lost more rapidly than that of L at 70C. The shape of particles and the length distribution pattern of L11A after purification were much the same as those of L. The sap of tomato leaves infected with L11A retained about 50% of the original infectivity after a weekstorage at 25C and less than 10% after a year-storage, whereas that of leaves infected with L retained 80 and 50% of infectivity after respective periods. L11A was suspended at 3.3mg/ml either in 0.01M phosphate buffer (pH 7.0) or in the same buffer containing 2% sucrose, then lyophilized and the resultant virus powder was stored at 22-25C. The samples without sucrose completely lost their infectivities after 27 months storage, whereas the samples with sucrose were highly infectious still at the same stage of storage. To examine whether the lyophilization with sucrose affected virulence, the sample stored for 27 months was inoculated to Nicotiana tabacum cv. Xanthi nc, and the produced lesions were isolated singly. The saps from these lesions were tested separately on tomato seedlings for their virulence. Only one lesion out of 50 produced a chlorotic patch on a leaflet of tomato. All other lesions caused no symptom. The effect of temperature on the multiplication of L11A and L in tomato leaf discs was compared. The optimal temperature for L11A was 25-28C, while that for L was 28-30C. At 35C, L multiplied considerably but L11A did not. The ratio of the amount of L11A to that of L decreased consistently as the temperature was raised up to 35C.
