USE OF GREEN-GRAFT INDEXING FOR EARLY DETECTION OF GRAPEVINE STEM GROWING PITTING DISEASES

Controlled growth conditions (temperature, light, raising) were developed for early and reliable symptom expression by green-graft indexing of 2 syndromes of the grapevine rugose wood complex: Kober stem grooving (KSG) and Rupestris stem pitting (RSP). Because of the young plant material, symptoms could not be revealed after peeling of the indicator trunk and so were observed by light microscopy on transverse sections of the indicator stem just below the graft point. After 6 to 8 months KSG symptoms on Kober 5BB were more marked than RSP symptoms on Rupestris du Lot and were obvious enough to establish the presence of the disease, whereas RSP diagnosis required more than a year. Despite these differences in symptom development the cytopathological effects on the indicator wood appeared very similar between the 2 syndromes. The rootstock hybrid 161-49 C used as RSP indicator showed symptoms sooner than Rupestris du Lot and, in spite of a greater variability in the responses linked to the extent of lignification of the indicator stem, generally gave a conclusive result after 8 months. The results also showed that the presence of a Vitis vinifera in the graft combination is indispensable for the expression of the KSG and RSP symptoms on the indicators. The application of green-graft indexing for KSG and RSP to sanitary selection as well as to the etiological study of these diseases has been discussed.