Walnut grafting success and bleeding rate as affected by different grafting methods and seedling vigour

Different grafting and/or budding methods were compared in terms of grafting success in 2004 and in 2005. Generally, the optimum period of grafting, under our experimental conditions, was limited to the early Spring and late Summer. Modified bark grafting in mid- April was the most convenient and reliable grafting method for 2- to 3-year-old walnut seedlings, with 80 - 93 % grafting success. The method consisted of collecting dormant scions in March, cutting the seedling rootstocks back 1 - 2 weeks before grafting in mid-April, and temporarily covering the graft area with moist sawdust for about 3 weeks before waxing. A higher rate of xylem bleeding in early Spring was a major factor in graft failure. Therefore, in the following experiments (2006), the effect of vigour of the different seedlings and methods of bleeding control were investigated for their effects on the bleeding rate, grafting success, and scion growth. Regardless of seedling vigour, temporary covering of the graft area with moist sawdust resulted in the highest grafting success (>80%) mainly by providing suitable conditions required for better callus formation. Scion growth at the end of the growth season (tree height) was significantly less (P <= 0.01) on seedlings of low vigour compared to high-vigour seedlings (62.31 vs. 125.20 cm height), underlining their potential importance in the reduction of tree size for high-density planting systems. Xylem bleeding was also reduced in seedlings of low vigour, although this reduction was not significant during the graft healing period.