Nobuyuki Oshima

Suppressive Effect of Benomyl on the Symptoms by Tobacco Mosaic Virus and Potato Virus Y in Tobacco Plant

Watering of 200ml 0.025-1% benomyl (50% WP) suspension per plant to the basement soil of potted Samsun tobacco plants caused very considerable reduction of the severity of TMV-L (a tomato strain of TMV) symptoms. ELISA absorbance showed that in two weeks after inoculation TMV-L concentration of upper leaves of tobacco plants treated with 200ml 0.1% benomyl suspension was a quarter of that of control plants. In one month after inoculation, however, there was no difference between those concentrations. Watering of 200ml 0.1-0.5% benomyl solution per plant to Xanthi-nc tobacco plants caused a slight reduction of the severity of PVY-T (a necrotic strain of PVY) symptoms. Combined application of benomyl and 2, 4-dioxohexa-hydro-1, 3.5-triazine (2% granules) showed no obvious effects of combination against the symptoms by TMV-L or PVY-T.

Ability of Myzus persicae Sulz. in the transmission of potato leaf roll virus

Myzus persicae Sulz. fed on potato leaf roll-infected Physalis floridana Rydb. for 30 and 60 minutes were not able to infect healthy P. floridana seedlings within 3 hours after leaving the source plants. Following feedings of 10 minutes, 1, 3, and 24 hours on infected P. floridana, the aphids were singly transferred to healthy P. floridana at 24 hour intervals for 5 days, and 0, 2.6, 12.5, and 50.0 per cent infections occurred between 24-48 hours after leaving the source plants, respectively (Table 1).The aphid vectors reared on infected Datura stramonium L. were able to transmit the virus to P. floridana within 5 minutes. A mild strain of potato leaf roll virus was more readily transmitted by the aphids than a severe strain (Table 2 and Fig. 1).Adults and nymphs of the aphid reared on Chinese cabbage were allowed to feed on infected P. floridana for 2 days, and then were serially transferred to healthy P. flaridana daily, one aphid per plant, until they died. The nymphs were more efficient vector than the adults. After the both forms of the aphid left the source plant, there was a tendency that their ability to transmit the virus gradually increased and then decreased (Fig. 2).Following acquisition feeding times of 1, 3, and 6 hours on infected P. floridana, the aphids were serially transferred to healthy P. floridana daily, one aphid per plant, until they died. As acquisition feeding times were lengthened, the rate of transmission increased and retention of inoculative ability was prolonged. However, independent of the length of the acquisition feeding times, the efficiency of transmission attained a maximum within a certain time after leaving the source plant and then declined (Fig. 3 and 4).The ability to transmit the virus was found to vary considerably with individual aphids.