The work involved assessment of the Myzus persicae (Sulz.) capability to infect successively potato plants with PVY and PVM after a Sunspray 850 EC mineral oil application. The tests were carried out in the greenhouse, with 4-week-old, healthy potato plants possessing low ressistance to viruses, derived from in vitro (test plants). Any time, for each combination and each virus, 10 successive plants were inoculated in 6 repetitions. Virus sources were potato plants infected with PVY or PVM, kept in isolated rooms. As a result of oil application, feeding of the M. persicae specimens on plants previously treated with this oil was delayed. The highest reduction as regards PVY and PVM transmission by M. persicae was obtained in the treatment where both plants constituting virus sources and test plants were protected, because only two of ten plants were infected with PVY, and only one with PVM. Mineral oil application only on potato test plants (healthy ones) reduced to a small degree M. persicae capability to transmit PVY to six successive plants (to seven in control), whereas it was much higher for PVM – to three (to six in control). In the case when only plants constituting virus sources were oil-protected, aphid’s capability to transmit PVY was limited only to four plants, and PVM – to two. These results seem to confirm much more the hypothesis that mineral oil inactivates virus particles in the stylets of aphids while they attempt to acquire it from plants which have been previously protected with mineral oil.

Potato virus Y (PVY) is one of the most destructive viruses infecting potato in Egypt and worldwide. Recent research has shown that a necrotic PVY-NTN strain is infecting potato in Upper Egypt. Chemical control is not effective to control this viral pathogen. An alternative to control PVY infecting potato is using a mild PVY strain to elicit systemic cross protection in potato plants against infection with a severe necrotic strain of PVY. Results of this study showed that a PVY necrotic strain produced a significant lesser number of local lesions on diagnostic plants (Robinia pseudoacacia L.) when these plants were treated first with a mild PVY strain. Data obtained from greenhouse and field experiments indicated that treatment of potato plants (variety Burna) with a mild PVY strain significantly protected potato from infection with a severe necrotic PVY strain, and resulted in a significant increase in tuber yield compared with infected plants without prior treatment with a mild PVY strain. The highest increase in potato tuber yield was obtained when potato plants were inoculated with a mild PVY strain 3 days before challenging with the severe necrotic PVY strain. This study proved that using a mild strain of PVY can significantly protect potato plants from infection with a severe strain of this virus under both greenhouse and field conditions and can present a potential method to reduce losses due to infection of this virus in Assiut governorate and Upper Egypt.