修剪和GA3處理建構‘玉荷包’荔枝開花溫量模式之研究

Abstract

‘玉荷包’荔枝(Litchi chinensis Sonn. ‘Yu Her Pau’)結果率低，目前農民多以人工修剪花序來確保產量，但花序修剪的效果不穩定，且需耗費大量工時。本研究首先探討花序長度和結果量間之關係，並從處理時期及濃度來了解GA3對‘玉荷包’荔枝開花及結果之影響，最後建立開花模型，用以剖析荔枝開花階段及最適處理GA3的時機。試驗結果顯示，‘玉荷包’荔枝花序長度與寬度間成一定比例，20公分左右之花序能有最高結果量，且這個最適花序長度不因修剪、開花時期、年份等影響。於花序誘導前期，即頂芽感受到低於20°C達230小時，或誘導程度達2,000個誘導溫量(inducing unit)時，葉面噴施100 mg L-1 GA3能產生最高比例之帶葉花序，但濃度提高至1350 mg L-1則無法產生更多帶葉花序，且帶葉花序比例隨誘導程度增加而降低；帶葉花序的形成會縮短純花序部位長度，進而提高單一花序平均結果量，但若帶葉花序上葉片過晚成熟則無法提高結果量。於花序可見後處理GA3，會抑制花序上各小穗分枝及小花形成，故同樣能提高‘玉荷包’荔枝結果量，且以濃度1350 mg L-1處理之抑制效果最佳。由修剪對荔枝開花影響之結果，可建構兩個推估‘玉荷包’荔枝開花過程的溫量模型，當以23.42°C為基礎溫度(base temperature)，達5,778 誘導溫量時，可看見花序產生；另以19.32°C做為基礎溫度，達2,397 開花溫量(flowering unit)時，‘玉荷包’荔枝第一朵小花會綻放；以花序萌出至小花綻放間之誘導溫量可推估花序長度。以GA3處理並輔以開花溫量，可以將荔枝開花區分為四個階段，分別為(1)花序誘導期(inflorescence induction)、(2)花序伸長及分枝期(inflorescence elongation & branching)、(3)小花分生組織形成和小花發育期(forming floral (floret) meristem & floret development)、(4)小花開放期(anthesis or flowering)。

‘Yu Her Pau’ litchi (Litchi chinensis Sonn.) has a high fruit drop rate. Inflorescence pruning has become an essential horticultural operation to ensure the production in Taiwan. However, manual inflorescence pruning has instable effects and entails very high labor cost. We have found out the relationship between the length of inflorescence and fruit set, and we also have clarified the effects of GA3 application on inflorescence induction, flowering and fruit set via different treating timings and concentrations. Therefore, we established a model of inflorescence flowering process and recommendations of the best treating timing of GA3 application during inflorescence development. Our results showed there was a strong correlation between the width and the length of inflorescence. The optimum size of inflorescence in ‘Yu Her Pau’ litchi in length of fruit set was about 20 cm, independent of pruning, flowering time or year. GA3 application during inflorescence induction increased the ratio of leafy inflorescence, decreased the length of inflorescence, and increased the average number of fruit set per branch. However, leaves on the leafy inflorescence flush matured too late depressed the fruit set. The treating timing of GA3 application decided the ratio of leafy inflorescences. It was the best timing for GA3 application when apical bud sensed the temperature under 20°C for 230 hours or the level of inducing degree reaching 2,000 inducing units, and the ratio of leafy inflorescence flushes was the highest. The decreasing ratio of leafy inflorescences resulted from the induction level increasing when 100 mg L-1GA3 application, but raising concentration to 1350 mg L-1GA3 did not affect the ratio. GA3 application after inflorescence bud breaking inhibited the differentiation of side branches and florets. The inhibition resulted in an increment in fruit set. The 1350 mg L-1 GA3 using, the more fruit set would be harvest. We established two models of degree-hour to deduce the flowering process of ‘Yu Her Pau’ litchi. We defined the iv accumulated temperature affecting flowering process as ‘inducing unit’. The initiation of inflorescence will be induced by reaching 5,778 inducing unit with the base temperature as 23.42°C. The breaking of flower buds will be induced by reaching 2,397 inducing unit with the base temperature as 19.32°C. The inducing units between the initiation of inflorescence and flower buds breaking can deduce the length of inflorescence flush. The correlated relationship of the length of inflorescences and the average number of fruit set per branch leads the evaluation of the fruit set of ‘Yu Her Pau’ litchi. We clarified the 4 stages during litchi’s flowering process by GA3 application and calculation of inducing units. The 4 stages of litchi anthesis were (1) Inflorescence induction, (2) Inflorescence elongation & branching, (3) Forming floral (floret) meristem & floret development, and (4) Anthesis or flowering.