On the Vinifera variety Mission and the hybrid grapevine Baco 22A, growing on their own roots, spring growth was delayed by grapevine leafroll virus. Cane and root growth of Mission vines was considerably reduced by the virus, but it had little effect on growth of Baco 22A. Leafroll virus reduced fruit yield of Mission vines by an average of 66 percent and sugar content of grapes by 30 percent, corresponding figures for Baco 22A being 44 percent and 9 percent respectively. Tartaric acid content of grapes at harvest was not appreciably affected by the disease. Pigment concentration in wine made from grapes of infected vines of the red-fruited Mission variety was approximately half that in wine made from grapes of healthy vines.

Apple rubbery wood virus (RWV) is widespread in apple and pear varieties in New Zealand, having been found in some trees of all varieties examined. Of 278 apple trees tested, 75 percent were infected; and of 43 pear trees indexed, 70 percent carried the virus. The virus has been found to cause symptoms on two New Zealand produced apple varieties, 'Gala' and 'Splendour'. Symptoms on the former are nearly as severe as those on 'Lord Lambourne'; on the latter they are less pronounced, being comparable with those on 'Golden Delicious'. Rubbery

Apple green crinkle has been recorded on 22 cultivars in New

Field surveys of vineyards in the major vine-growing districts indicate that grapevine fanleaf and leafroll viruses are widespread and of high incidence in New Zealand, and that enation disease, which is possibly caused by a strain of fanleaf virus, and yellow mosaic, a strain of fanleaf virus, are present but of low incidence. Field diagnoses of fanleaf and leafroll viruses have been confirmed by transmission to indicator varieties.

A leal infection index was used to express in numerical terms the severity of apple mosaic virus (AMV) symptoms. It was demonstrated that mild strains of AMV gave apple trees a high level of protection against infection with severe strains of the same virus. It was also shown that scions carrying a mild strain when worked to trees carrying a severe strain were effectively protected against invasion by the severe strain. Although there was some breakdown in protection in the first and second years after working, in subsequent years protection became more firmly established.The cross-protection reaction provides a useful technique for detecting mild or symptomless strains of AMV. It is suggested that cross-protection could be used to protect orchard trees in areas where field spread of AMV occurs and that it could be used to regenerate apple trees stunted by severe strains of the virus.