Abstract
An attenuated virus isolate named Pa18 was successfully selected from the pepper plants in which the parent isolate P6 of tobacco mosaic virus pepper strain (TMV-P) has been inoculated and subjected to the subsequent heat treatment according to Holmes. The attenuated isolate Pa18 induced very mild symptoms on sweet pepper plants, and completely protected the plants from the infection by the parent isolate (P6) if the former was inoculated 10 days before the inoculation of the latter. The isolate Pa18, however, did not completely protect the plants from infection by tomato strain, yellow mosaic strain or another strain of TMV. The symptoms on sweet pepper caused by the isolated Pa18 remained mild throughout the growth period of the plant. The host range of the isolate Pa18 was found to be identical to that of the parent isolate (P6) which is infectious to 24 plant species belonging to 5 families. These host plants excepting Nicotiana megalosiphon, N. benthamiana and Physalis floridana failed to show symptoms or developed only faint mottling. Practical utilization of Pa18 for the control of the mosaic disease of sweet pepper was evaluated in the field. The growth of the plants infected with Pa18 was quite similar to that of the uninoculated control, while the growth of P6-infected plants was considerably poorer than that of Pa18-infected plants. The yield of the plants inoculated with TMV-P (P6) decreased as much as 36% of the uninoculated control, while that of Pa18-infected plants was almost the same as that of the uninoculated control. The yield of the plants inoculated with Pa18 and challenged by P6 decreased about 18% of that of the uninoculated plants, whereas the yield of the Pa18-infected plants increased 21.6% over that of plants inoculated with P6. In addition, the inoculation of the isolate Pa18 resulted in the suppression of mosaic symptoms on the fruit caused by the isolate P6. These results indicate that the attenuated isolate Pa18 may be effectively utilized for the control of mosaic disease caused by TMV-P in pepper plants.
