蓮霧果萼端木栓化生理障礙與果實水分生理之研究

蓮霧(Syzygium samarangenes)為臺灣重要經濟果樹，於屏東沿海地區栽培之蓮霧‘大果’種，常於果實成熟時發生果萼端木栓化(Corky Calyx End, CCE)生理障礙，造成經濟損失。根據田間觀察，CCE好發於較大的果實或大果型的品種，以新梢旺盛植株較嚴重，且果園土壤鈉濃度或電導度值偏高。CCE果實萼片較短而薄、果萼周圍果皮環狀白化，病徵部位果肉維管束褐化及空洞化，果肉薄壁細胞叢狀死亡而遺留空胞。CCE被認為是果實缺鈣相關生理障礙，CCE果實近果蒂端及近果萼端的鈣濃度皆較正常果實低。於好發CCE之蓮霧‘大果’種果園進行噴施鈣肥試驗，探討其對CCE之影響。於CCE好發之2013年產季，於謝花後至小果套袋前之果串，每週噴施一次0.2%硝酸鈣或0.2%氯化鈣+0.1%硼砂，連續處理4週，成熟果之CCE比率分別為1.1%及1.2%，遠低於對照組之24.0%；噴施0.2%硝酸鈣處理並不影響果重及品質相關特性。2014年之試驗對照組CCE發生率僅0.8%，噴鈣處理果實皆無CCE徵狀，各項品質特性與對照組無顯著差異。探討蓮霧果實發育期間果實內木質部功能衰退樣態與發育期間鈣的累積及成熟果實中鈣濃度分布間的關聯，以了解果萼端鈣的獲得的時機。蓮霧‘大果’種果實的生長為典型的單S形曲線，相對生長速率及果實含水量高峰出現於吊鐘期進入轉色期時(盛花後第28至34天)，之後總可溶性固形物及果皮花青素含量快速增加，同時可滴定酸含量降低。近果萼端果肉木質部功能於相對生長速率高峰時驟降，轉色期後持續降低，至成熟時完全失去功能；鈣濃度於盛花後13天內增加，於相對生長速率高峰(盛花後第28至34天)時驟降，之後至成熟(盛花後第59天)前呈緩慢下降趨勢，然而果實總鈣含量至果實成熟前仍持續增加。成熟果實果皮和果肉鈣濃度皆由果蒂端往果萼端梯度下降，以果萼端果肉的鈣濃度為最低，此部位亦為CCE徵狀起始的區域，顯示果實內鈣濃度與木質部輸導功能變化有關。為探討果實發育期間蒸散速率的變化是否造成木質部輸導阻礙，測試果實不同發育階段表皮蒸散速率之差異。發育中的蓮霧‘大果’種果實表面積可用果徑(D)推估，果實表面積估計值A=5.13 x D1.71。隨果實由胚仔期發育至成熟期，果實表面積由10.3增加至122.6 cm2，胚仔期至合臍期間，單位表面積蒸散速率由1.33 mg·cm2·h-1降至1.05 mg·cm2·h-1，之後緩慢增加，至果實成熟期為1.71 mg·cm2·h-1。果實轉色期後，果皮蒸散速率並未下降，顯示果皮蒸散作用非造成木質部輸導功能衰退的原因。為了解果實鈣獲得的競爭力，探討果實和植株間的水分關係。蓮霧‘大果’種果實於吊鐘期(盛花後第29-35天)有明顯的日間果徑縮小現象，約於每日1400HR時達到當天果徑最小值，1600HR後果徑開始回升；果徑日間縮小現象於轉色期(盛花後第36-45天)後逐漸消失。樹冠噴霧處理對於果徑縮小幅度無顯著影響，而果實轉色期以前，若植株新葉旺盛，植株蒸散需求量大可能使果徑縮小更為明顯，應避免培育過多的新梢並應提早適量疏除嫩梢，以避免果實嚴重的暫時性缺水，影響鈣的獲得。

關鍵字

質體外染劑追蹤法；缺鈣生理障礙；日間果徑縮小；線性位移感測器；表面積估算；蒸氣壓差

並列摘要

Wax apple (Syzygium samarangense Merr. Perry) is an economically important fruit crop in Taiwan. Corky calyx end (CCE) is a physiological disorder in ‘Big Fruit’ varietiey that commonly occurs in the coastal area of Pintung, Taiwan and often causes economic losses. Vigorous trees bearing large fruit and in orchards with high soil sodium concentration or electric conductivity value are prone to CCE. CCE fruits have shorter and thinner calyx lobes and discolored fruit skin around the calyx end. The vascular bundle tissue is browning and hollowing, and clusters of dead empty cells were observed in the corky flesh. CCE has been associated to calcium deficiency, as the calcium concentrations in the calyx and pedicel end of a CCE fruit were lower than normal. The effects of calcium spray on CCE of ‘Big Fruit’ were investigated in a CCE susceptible orchard. Four-time weekly application treatments of 0.2% Ca(NO3)2 or 0.2% CaCl2+0.1% borax four times to fruit clusters from petal fall to small fruit bagging stage resulted in incidence of CCE at 1.1% and 1.2%, respectively, at harvest, significantly lower than the control at 24.0%. Spray of 0.2% Ca(NO3)2 did not affectefruit weight or quality. The CCE incidence in 2014 was negligible at 0.8%, and no CCE fruit was observes in all the calcium spray treatments. Fruit quality characteristics was not affected by calcium spray treatments. To understand the timing of calcium uptake and xylem function within wax apple fruit, calcium accumulation and allocation during fruit development were investigated. The growth of wax apple ‘Big Fruit’ fruits expressed a typical single sigmoidal curve against time. The highest relative growth rate (RGR) and water content were observed at the onset of breaker stage (28-24 DAFB). Total soluble solids and skin anthocyanin content increased rapidly accompanied by the decrease in titratable acidity after breaker stage. A sharp functional decline in xylem toward the calyx end of the fruit was also observed, resulted in a complete loss of xylem function by harvest. Calcium concentration was highest on 13 DAFB, it dramatically declined at the peak of RGR (28-34 DAFB) and gradually declined afterward. However, total calcium content continued to increase by harvest. A mature fruit expressed a high to low calcium concentration gradient from the pedicel to the calyx end. The calcium concentration in the flesh of the calyx end was the lowest, which was also the initial site of CCE symptom. The distribution was also consistent with the result of the decline of xylem function inside fruit. To documnet the relation between fruit transpiration and xylem function, the fruit surface area and transpiration rate of developing wax apple fruit were investigated. In developing ‘Big Fruit’ fruits, surface area was estimated by fruit diameter (D) using a simplified model, A= 5.13*D1.71. The surface area of a young wax apple fruit increased from 10.3 to 122.6 cm2 at full maturity, while the transpiration rate decreased from 1.33 to 1.05 mg·cm2·h-1 at small fruit stage, then slowly increased to 1.71 mg·cm2·h-1 at full maturity. The high fruit transpiration rate after breaker stage suggested no relation between fruit transpiration and xylem function decline after breaker stage. The water relation between fruit and plant was investigated to understand the competitiveness of fruit for obtaining calcium. Diurnal fruit contraction was detected in wax apple ‘Big Fruit’ at Bell stage (29-35 DAFB), with a minimum diameter recorded at approximately 1400HR and a recovery and growth after 16:00HR. The diurnal contraction phenomenon gradually diminished after the breaker stage (36-45 DAFB). Canopy misting before the breaker stage did notaffect diurnal fruit contraction. It appears that before the Breaker stage, a vigorous tree with abaundant new leaves might have increased canopy transpiration and water demand, thus causing more significant diurnal fruit contraction. It is recommended that moderate tree growth or early shoot thinning could avoid temporary daily water shortage and facilitate calcium transport to fruit.