葉面噴施尿素促進‘Tifblue’兔眼藍莓落葉及其對萌芽、開花及結果之影響

Effects of defoliation with urea spray on budbreak, flowering and fruiting in‘Tifblue’rabbiteye blueberry(Vacciniumvirgatum Aiton)

落葉果樹於亞熱帶低海拔地區常因冬季低溫不足，而無法順利打破芽體休眠，栽培上可藉由強制落葉克服此一問題。本研究探討於休眠末期以葉面噴施尿素強制‘Tifblue’兔眼藍莓(Vaccinium virgatum Aiton)落葉，對萌芽、生長與開花結果之影響。於2016年3月1日及2017年2月7日，以0.5%或3%尿素水溶液，對植株進行葉面噴施，另以噴施清水做對照組。兩年試驗結果顯示，3%尿素處理可使植株提早落葉，但後續新梢數量、枝條總生長量及各次梢長度在處理間無顯著差異。2016年試驗以二種尿素處理後第4週，植株之累積花芽萌芽率達50%，較對照組提前2週。尿素處理之最終累積花芽萌芽率亦高於對照組。2017年試驗以3%尿素處理植株於處理後第6至10週間之累積花芽萌芽率高於其它二處理。2016年試驗中，尿素處理雖可提早萌芽、開花及著果，但採收期並未提早。3%尿素處理之產量較集中，但總產量、果徑、單果重、果實內可溶性固形物含量與其它二處理無顯著差異，推測與2016年尿素處理之植株於開花期遇連續大雨，導致授粉不良所致。2017年試驗以3%尿素處理可提早萌芽、開花及著果，並使產期提前，產量亦顯著高於對照組，但果徑、果重及果實之可溶性固形物含量則處理間無顯著差異。此外3%尿素處理顯著降低果實酸度與增加果實糖酸比，果實品質較佳；0.5%尿素處理在2017年試驗中並無法提早落葉與萌芽，產量與對照組無顯著差異。綜合兩年試驗結果，在休眠期葉面噴施3%尿素水溶液，能加速兔眼藍莓‘Tifblue’落葉，提早花芽萌發，使花期與其它品種一致，有利授粉，可增加產量與果實品質，且對樹體營養生長無影響，為一簡單安全的催花方式。

Insufficient chilling temperatures received by deciduous fruit trees in the subtropical lowland often lead to poor spring budbreak. Defoliation is a common practice to overcome this problem. In this study, the effects of forcing defoliation by foliar sprays with urea solution at a late dormant stage on budbreak, growth, and fruiting in container grown‘Tifblue’rabbiteye blueberries (Vaccinium virgatum Aiton) were investigated. The bushes were sprayed with 0.5% or 3% urea solution on March 1, 2016and February 7,2017and the control group was sprayed with water. In both years, defoliation after 3% urea spray occurred earlier than the control group. However, the urea sprays did not affect the number of new shoots, cumulative shoot growth, or length of new shoots. In the 2016trial, 50% accumulative floral budbreak on urea sprayed bushes was registered four weeks after treatment, two weeks earlier than the control. The final rate of accumulative floral budbreak was also higher in urea sprayed bushes. In 2017, higher accumulative floral budbreak was also recorded in the 3% urea sprayed bushes during the 6th to 10th week after treatment. Defoliation treatments resulted in early bloom and fruit set but not early harvest in 2016.Totalyield, number of berries, berry diameter, berry weight and total soluble solids content were not significantly different among treatments. Although 3% urea spay advanced blooming in 2016, the final yield was not affected, possibly due to heavy rainfall during the full bloom period. In 2017,flower budbreak, flowering, fruit set and harvest in bushes subjected to 3% urea sprays were all earlier and final yield higher than the control. The number of berries, berry diameter, berry weight and total soluble solids content were not significantly different among treatments within harvest periods. In addition, 3% urea spay reduced berry acidity and increased sugar/acid ratio, thus improving berry quality. In contrast,0.5%urea spray had little overall effects on defoliation, budbreak or fruit yield in 2017.In conclusion,3% urea solution spray on‘Tifblue’rabbiteye blueberries in the late dormant stage promoted defoliation, flower bud break, and increased yield and fruit quality without negative effect on vegetative growth. It is therefore, recommended as an easy and safe practice for blueberry growers in the subtropical region.