Effects of Boron and Paclobutrazol on Growth, Fruit Set, Nutrient Uptake, and Alternate Bearing of Muye Red Bayberry

Alternate bearing, resulting mainly from boron (B) deficiency, and excessive fruits in the alternate years of red bayberry trees are the most important limiting factors for production. This investigation was conducted on 18-year-old Muye red bayberry trees (Myrica rubra Sieb. et Zuca) in a commercial red bayberry orchard located in Laxi County, Zhejiang Province in 2006–2007.The results indicated that foliar application of paclobutrazol (PB) significantly increased the vegetative growth parameters (i.e., spring shoot incident and spring shoot length). Spring shoot incidents and spring shoot lengths of red bayberry were increased with increasing PB concentrations, but the optimum fruit yield and quality were obtained from foliar-applied PB at 100–200 mg L⁻¹ at full bloom. Foliar application of PB increased the contents of N and K in the leaves with increases of PB concentrations up to 300–600 mg L⁻¹. Fruit quality of red bayberry trees treated with PB or and boron fertilizer (BF) was improved at full bloom. Foliar application of PB reduced the percentage of fruit set by 62.1% in the year after treatment with PB but increased the yield by 49.0% the following year. Foliar application of PB at 100–300 mg L⁻¹ gave the most significant improvement in fruit quality: increase in fruit weight, soluble solid content, and the ratio of soluble solids (SS) / total acidity (TA) and decrease in total acidity. Foliar application of BF slightly reduced the fruit yields in the current year but significantly increased those the following year. Combined application of BF and PB or application of PB alone markedly reduced the fruit yields in 2006 by 40.5% and 43.8%, respectively, but markedly increased those by 44.6% and 17.8% in 2007, respectively. The effects of alleviating alternate bearing of red bayberry for different treatments followed the order of combined application of FB + PB > PB > BF > control. It is suggested that PB and BF can be used to alleviate alternate bearing.