A study of five mechanically transmissable cherry virus isolates with herbacous hosts

Five virus isolates RS 2, RS 25, RS 26, RS 28 and RS 29, were transmitted by juice-inoculation technique from sour and sweet cherry trees to cucumber. Four isolates were obtained from trees growing in the Kootenay cherry district of British Columbia. Another one was isolated from a tree growing in the coastal area of this province. Viruses known to occur in the source trees are Necrotic Ring Spot Virus, Sour Cherry Yellows Virus, Twisted Leaf Virus and Little Cherry Virus. The relationship and the complexity of the virus isolates was studied with herbaceous hosts, using a mechanical transmission technique. Pincherry (Prunus pennsylvanica L.) was inoculated by the same technique as a means for provisional identification of the virus isolates. The cucumber syndrome of isolate RS 25 was very mild, that of isolate RS 2 mild, that of isolate RS 29 was of medium severity and those of isolates RS 26 and RS 28 were very severe. Inoculates RS 2 and RS 29 varied greatly in symptom expression on cucumber, whereas the symptom expression of the other isolates was less variable. Isolate RS 29 was characterized by symptomless systemic infection of Nemesia sp.. var. Triumph. Isolates RS 26 and RS 28 both infected Petunia hybr., var. Blue Bee, without expressing symptoms, whereas the other isolates did not infect this species. Other host species too carried the isolates without expressing symptoms, whereas symptoms were produced on cucurbit hosts. Isolates RS 2, RS 26, RS 28 and RS 29 appeared to consist of more than one virus. Strains of a virus P occur in all isolates and isolate RS 25 itself is also a strain of this virus. All five strains of virus P express similar very mild symptoms on cucumber, whereas a characteristic severe savoying type of symptom is produced on squash (var. Table Queen). Species susceptible to virus P are cucumber, pincherry, squash, sweet pea, tobacco (under conditions of long day) and other species. Lathyrus odoratus L. and Lens culinaris Medic. are species useful in separating virus P from the other viruses occurring in isolates RS 2, RS 26, RS 28 and RS 29. It is possible that virus P is related to cucumber-mosaic virus as suggested by symptoms on squash and tobacco. In previous work by other investigators a strain of cucumber-mosaic virus was also isolated from Prunus hosts. On pincherry (P. pennsylvanica L.) isolate RS 28 caused acute symptoms of necrosis and shothole. The plants recovered but symptoms of mottling were systemic. Necrotic Ring Spot Virus caused similar symptoms on Prunus hosts and this virus and Sour Cherry Yellows Virus was present in the original source tree. The other isolates in pincherry all caused similar symptoms of mottling on the young leaves. A few necrotic lesions were produced also. On reisolation from pincherry virus P was obtained in case of isolates RS 2, RS 26 and RS 29. No virus was reisolated in the case of isolate RS 25. The complete parent isolate was reisolated in case of isolate RS 28. The results with pincherry suggest that virus P is responsible for the mild symptoms whereas virus P in conjunction with an additional virus as in isolate RS 28 incites the severe shock symptoms. The identification of the viruses present in the isolates can be carried out by scion inoculation of a set of suitable Prunus indicator hosts.Land and Food Systems, Faculty ofGraduat