| 摘要： 番石榴(Psidium guajava L.)為台灣重要熱帶果樹之一，‘珍珠拔’為國內目前主要之栽培品種，夏果品質不佳為目前產業之主要限制，但其相關生育及生理資料闕如。為瞭解及建立基礎生理資料，本研究首先對盆植‘珍珠拔’番石榴進行光合作用日變化(diurnal change)之基礎生理調查及雙乾旱復水週期試驗，觀察‘珍珠拔’於逆境之枝梢生長及生理反應，建立番石榴生育之水分閥值及生理指標，以供日後研究之參考。而後調查田間植株夏季定時遮陰、不同疏果程度及不同留果位置，對夏果番石榴品質之影響，期藉由上述技術，以提升‘珍珠拔’番石榴夏果品質及建立疏果指標，並為日後調整全株留果數、留果位置之建議。 ‘珍珠拔’之暫時凋萎點葉片水勢為-2.0 MPa，葉片相對水分含量為89%，土壤張力計讀值為-55 KPa，暫時凋萎點時光合作用速率下降主要受氣孔因子影響，且於復水後逐漸恢復與對照組無顯著性差異。達永久凋萎點時，葉片水勢為-3.0 MPa，葉片相對水分含量為80%，土壤張力計讀值為-71 KPa，此時光合作用主要受非氣孔因子影響。試驗結果顯示，雖然番石榴對乾旱逆境具若干程度之耐受力，然其碳同化物生產及新梢營養生長卻大幅下降，顯示適度灌溉仍為其經濟生產所必需。 夏果品質不佳可能與植株於果實生育期面臨強光、高溫逆境，繼而降低光合作用速率有關。本試驗採用之遮陰網遮光率可達30-59%，午間可降低氣溫3°C，遮陰後可有效提高植株午間光合作用速率及水分利用率，降低葉片與大氣蒸氣壓差，葉綠素螢光最大光合作用轉化效率ΦPSⅡ(Fv/Fm)在正午時略微降低，但處理間無顯著性差異。遮陰後不改變處理間葉綠素含量，果實品質於處理間並無顯著性差異，但果實經遮陰後可延長生育日數5-6日。 探討當季留果數(不同葉果比:<6、6-8、10-12、14-16)及不同著果位置(上幅、外幅、內膛)對果實品質之影響，夏果不論調整全株疏果或單一結果枝環剝之葉果比，其果實生育日數於各組距間無差異，但果實品質則隨葉果比之增加而提升，以14-16葉/果最佳。不同著果位置以著生於內膛果實生育日數較長，且果實品質略差。冬果試區趨勢與夏季果實相同，建議葉果比為10-12葉/果，且與14-16葉/果者無異。不同著果位置上幅果實因枝條成熟度關係，糖度表現較差。夏果植株於採收後經修剪所得之下季開花率較低，將導致晚冬/早春果之低產，如欲達穩定週年生產，應分區、異時修剪較佳，而冬果植株採收後之下季開花率高，花後應適當疏果，以提升夏果果實品質。Guava (Psidium guajava L.) is one of the most economically important tropical fruits in Taiwan. Although ‘Jen-Ju-Ba’ is the major local guava cultivar, information regarding its reproduction and physiology is limited. Additionally, poor fruit quality in the summer poses a great challenge for its cultivation. To understand and build fundamental physiological data, we first carried out a basic study of photosynthesis diurnal changes of potted ‘Jen-Ju-Ba’ and a two water withholding/recovery cycle tests to observe shoot growth and physiological responses of ‘Jen-Ju-Ba’ under drought stress to further establish the hydration threshold for ‘Jen-Ju-Ba’ reproduction. Furthermore, this study examined the effects of regular shading, degree of fruit thinning, and fruiting position on quality during the summer months. By leveraging the techniques above, this study aimed to enhance fruit quality of ‘Jen-Ju-Ba’ in the summer and establish an indicator of fruit thinning to serve as a recommendation for future production of total fruit numbers and positioning. Our results indicated that the temporary wilting point for leaf water potential was -2.0 MPa, and the leaf relative water content was 89%. In addition, the tensiometer reading was -55 KPa. The decreasing photosynthetic rate at the temporary wilting point was mainly caused by stomatal factors and showed no significant difference when compared to the control group after rehydration. When the permanent wilting point was reached, the leaf water potential was -3.0 MPa, the leaf relative water content was 80%, and the tensiometer reading was -71 KPa. The photosynthetic rate here was mainly affected by non-stomatal factors. The shoot vegetative growth stopped at the temporary wilting point and did not continue after rehydration. The shade adopted in our study could block 30-59% of sunshine and reduce air temperature by 3°C at noon to effectively raise the photosynthetic rate and water use rate as well as lower the leaf to air vapor pressure deficit. The maximum Fv/Fm value of chlorophyll fluorescence was slightly lower at noon, but there was no significant difference between treatments. Shading did not change the amount of chlorophyll between treatments nor yield a significant difference in fruit quality. However, it did prolong the reproduction of fruit for another 5-6 days. While assessing the effects of the leaf to fruit ratio (<6, 6–8, 10–12, and 14–16) and fruit position (upper, external, and internal of the canopy) on fruit quality, we showed that regardless of adjustments of the leaf:fruit ratio of the whole plant or on one bearing shoot with girdling, the number of fruit reproduction days indicated no difference across each interval. However, fruit quality was enhanced as the leaf:fruit ratio increased, with quality being the highest at a 14–16 leaf: fruit ratio. As for fruit position, internal of the canopy resulted in longer reproduction days with slightly poorer quality. Winter fruit projected a similar tendency as summer fruit, with quality highest at 10–12 or 14–16 leaf:fruit ratios, albeit with no significant differences. Upper canopy fruit position resulted in lower quality possibly due to maturity of shoots. The return blooms of the following season of summer plants trimmed after harvest was lower, causing low production in late winter and early spring. If a stable production throughout the year is to be ensured, trimming should be differentially carried out by region and time. When this occurred, the return blooms of the following season of winter plants trimmed after harvest was higher. Therefore, appropriate fruit thinning should be carried out after blooming to raise fruit quality in the summer. |
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