Bunch thinning and its influence on the shoots growth dynamics in some syrah wine variety clones

During the period 2020-2022, an experiment was conducted in the experimental vineyard of the Agricultural University – Plovdiv, and four clones of the wine variety Syrah, numbered 100, 174, 470 and 524, grafted on the SO4 rootstock were selected as the study object. During the „pea size“ phase, the green pruning operation – bunch thinning was applied. The shoots growth starts from the vegetation phase „first leaf appearance“ and ends at the „veraison“. The average duration is about 100 days, covering the period of May, June and July. It was found that the vine shoots from a clone 470 reached the greatest average length, V3 – 285, 265, 290 cm and V7 – 359, 336, and 380 cm, and those from a clone 100 were distinguished by the weakest growth, V1 – 197, 203 and 205 cm and V5 – 240, 228 and 245 cm. Differences were proven between the variants, both in the non-reduced (V1, V2, V3, and V4) and in those with reduced yields (V5, V6, V7, and V8), as after reducing the number of bunches, the length of the shoots was longer – high in all vines from the used Syrah clones. This study provides information on the relationship between the applied green pruning operation (bunch thinning) during the growing season and its effects on the vegetative growth. Balancing the vines bud load by controlling yield during the growing season is a preferred viticultural practice for increasing the grape quality. Keywords: Clones, Syrah, green pruning, bunch thinning, shoot growth