Validation of micrografting to identify incompatible interactions of rootstocks with virus-infected scions of Cabernet Franc

Background and Aims Grafted grapevines are a key component of modern viticulture. Grafting provides not only resistance to soil-borne pests, but can also improve adaptability to the environment and can improve fruit yield and quality. Graft incompatibility induced by grapevine viruses causes damage to vineyards worldwide. The aim of the present study was to create a rapid and reliable means of evaluating graft incompatibility resulting from grafting virus-infected scions onto healthy grape rootstocks. Methods and Results Scions of Control (healthy Cabernet Franc), LR131 (Cabernet Franc infected with GLRaV-1) and LR132 (Cabernet Franc infected with GLRaV-1 and GVA) were grafted onto different rootstocks by micrografting, green grafting and bench grafting methods. All the micrografts infected with LR132 failed, while LR131 and Control micrografts had similar survival rates. The impact of LR132 was less severe on green grafted plants, followed by bench grafts. Analysis of variance showed an interaction of grafting method x virus variety x rootstock, affecting grafting survival. When grafted onto Freedom and 101-14, LR131 inhibited the growth of both scion and rootstock, but no significant impact was seen when LR131 was grafted onto St. George and AXR1. Well-established callus was visible between the surfaces of LR131 and the rootstocks. The virus GLRaV-1 was detected moving from the LR131 scion source to rootstocks 7 days after micrografting. Callus formation was delayed by LR132 between scion and rootstock surfaces, and a scion-rootstock vascular connection did not establish, resulting in the death of all micrografts. Conclusions Micrografting is a reliable and sensitive method to screen for virus tolerant graft combinations compared with green and bench grafting. Significance of the Study The results of the present study validate micrografting as a means of producing credible information for selection of virus tolerant rootstocks, and ultimately vineyards with higher rates of compatible grafts.