Effect of summer trunk girdling on fruit quality, maturation, yield, fruit size and tree performance in ‘Mihowase’ satsumas

SummaryProblems with marginal internal quality and fruit colour exist in the South African satsuma (Citrus unshiu Marc.) industry. Timing of summer girdling from 2–11 weeks after the “physiological fruit drop” (APFD) period on fruit quality, maturation, yield, fruit size distribution and tree performance were investigated in three trials: a) girdling under deficit irrigation, b) girdling under normal irrigation, and c) consecutive (two years) girdling under deficit irrigation. The trials were carried out with ‘Mihowase’ satsuma trees on Troyer citrange rootstock in Simondium in South Africa. Girdling, applied 2–4 weeks APFD, significantly (P<0.05) improved fruit colour, total soluble solids (TSS) level and TSS/TA (titratable acidity) ratio in the first season. Consecutive girdling did not improve the above indices significantly in the second season. TA and juice percentages were not influenced by girdling at different times and during years. All girdling treatments did not affect fruit yield and size in the first season. However, consecutive girdling at eight weeks APFD significantly (P<0.05) decreased yield in the second season. Consecutively girdled trees did tend to produce smaller fruit than ungirdled trees with consecutive girdling at 5–8 weeks APFD significantly (P<0.05) decreasing fruit size. Leaf chlorophyll and N contents, six weeks after harvest, were lower in girdled trees than in ungirdled ones.