Graft union abnormality: some impacting factors

Abstract

Factors involved in incidence of abnormal, excessive graft union enlargement were investigated. Material of Sauvignon blanc, Cabernet Sauvignon, Richter 110 and 101-14 Mgt was collected. Combinations of Sb/R110, CS/R110, Sb/101-14 Mgt, and CS/101-14 Mgt were warm and cold callused. Hot water treatment/no treatment was done for each combination. After the commercial nursery phase, vines were evaluated and planted in the field using a vine by pole training system (1.5 x 1.0 m), in clayey and sandy soils, with normal and overly wet seasonal conditions, and restricted and unrestricted root volume availability for each soil type. After the nursery phase, warm callused vines had noticeably thicker graft unions; diameters of both rootstock and graft scion were larger. Graft union quality between warm and cold callused vines was similar. Generally, below- and above ground growth and graft union mass were stimulated by warm callusing, whereas graft scion mass was higher for cold callused vines. No obvious effect could be related to hot water treatment. Rootstock 101-14 Mgt realised lower root mass compared to R110, particularly with warm callusing. Differences were induced during callusing and/or in nursery. General trends over three seasons of study showed that cultivars could be separated, C. Sauvignon having thicker graft unions and rootstock diameters than S. blanc. Warm callusing would likely lead to thickest graft unions and thinnest rootstocks, irrespective of graft combination, whereas cold callusing is likely to result in thinnest graft union and thickest rootstock, therefore a more balanced vine. Rootstock diameter per se was better associated with aboveground growth than graft union diameter. Most vine deaths occurred during the second growth season and did not increase after that; large increases and highest numbers were found in clayey soil under normal and wet conditions. In clayey soil most vines died under wet conditions and in sandy soil most vines died with normal irrigation. Cane starch contents were similar. Visual evaluation of fusion/integration of vascular systems of graft unions and measurements of graft union and cane size indicated no recognisable relationship between vascular system restriction and normal or over-sized graft unions. Among various grafted plant material production techniques and vineyard management practices, warm callusing surfaced as most important impact factor on graft union abnormality. The study indirectly addressed the economic viability of young vineyards and sustainability of production.