利用益收生長素改善東方型百合之上位葉病變

Abstract

東方型百合生產栽培過程中，會發生由於鈣元素不足造成花苞附近葉片焦枯變形的現象，稱之為“上位葉病變 (Upper leaf necrosis, ULN)”，俗稱“葉燒”，此病變常發生於 ‘葵百合’、‘Acapulco’ 等品種。本研究藉由益收生長素抑制植株的快速生長，降低植株在ULN感病時期對鈣的大量需求。無論處理方式為種球種植前浸泡，或是在ULN感病期初噴施於葉面，皆可改善植株ULN嚴重程度並降低葉片壞疽面積。 以 ‘葵百合’ 為參試栽培種，植株生長於人工氣候室日夜溫20/15 ˚C自然光照室，以及無環控設備的塑膠棚溫室。當種球種植前浸泡益收生長素濃度由125 mg∙L^-1增加至1000 mg∙L^-1，植株ULN罹病率及感病程度皆降低，然而花苞消蕾數劇增，植株高度嚴重矮化。因此以花苞安全性為前提，決定種球浸泡益收生長素濃度為125 mg∙L^-1。無論栽種環境日夜溫度、試驗種球產地、種球種植前萌芽長度，甚至是品種的不同，種球浸泡125 mg∙L^-1益收生長素不但降低植株ULN嚴重程度，對株高的抑制在實用上亦無太大不良影響。然而，益收生長素在葵百合植株內作用的時效性約為三星期，因此種球種植後地上部萌芽出土所需天數越長，益收生長素對植株ULN改善效果越有限。 此外在葵百合植株ULN感病初期，葉面噴施1000 mg∙L^-1益收生長素，可抑制感病期間的植株快速生長，明顯降低植株ULN罹病率、感病程度及植株高度，且對花苞消蕾影響小 (每株0.1朵)，無論噴施的天數在21 DAP (Days after planting) 或是受溫度影響植株生長速度而延至28 DAP。然而，若植株ULN病徵顯露時才葉面噴施1000 mg∙L^-1益收生長素，會降低ULN改善的效果。將益收生長素的處理方法以種球種植前浸泡搭配葉面噴施，可延緩植株ULN感病初期噴施益收生長素的短暫關鍵時期，達到減輕植株ULN目的。 另外有許多因子會影響葵百合ULN嚴重程度。日夜溫30/25˚C環境下，植株的地上部生長極為快速、葉片相互包裹抑制蒸散作用的時間短，因此ULN罹病率和感病程度低；而20/15˚C環境植株不但展葉所需天數多、根部生長量又不足，因此ULN罹病程度最嚴重。至於利用較高的冷藏溫度，促使葵百合種球在種植前有較長的芽以及些許的stem roots生長，並未觀察到有改善植株ULN的效用。 益收生長素處理確定可降低東方型百合ULN嚴重程度：種球種植前浸泡125 mg∙L^-1益收生長素，對花苞安全性及株高抑制無太大影響，可適用於切花生產模式；而植株ULN感病初期葉面噴施1000 mg∙L^-1益收生長素，或是與種球種植前浸泡相互搭配，不僅對ULN改善有極大助益，更降低植株高度、縮小花徑，適用於盆花生產。

Upper leaf necrosis (ULN) is a calcium (Ca) deficiency disorder, commonly observed as leaf tipburn, occurred on some Oriental hybrid lilies, such as ‘Star Gazer’ and ‘Acapulco’. This research tried to use ethephon as a novel control agent for suppressing ULN, by decreasing plant growth rate and consequently Ca demand of leaf tissue. Ethephon significantly reduced ULN severity regardless application methods, i.e., pre-plant bulb dip or foliar sprays. Lilium ‘Star Gazer’ was grown in a phytotron with day/night temperature of 20/15˚C and a plastic house without temperature control. Both ULN incidence and severity were dwindled, as concentration of ethephon in pre-plant bulb dip increased from 125 to 1000 mg∙L^-1. However, aborted buds increased and plant height shortened greatly at higher concentrations. Hence, under the premises of regular cut flower quality, the ethephon concentration of pre-plant bulb dip was suggested to be 125 mg∙L^-1, of which plants height were not influenced. Furthermore, the ability of 125 mg∙L^-1 ethephon bulb dip to reduce ULN severity was not affected by temperature regimes, bulb producing areas, pre-plant shoot length, and cultivars. Efficacy of pre-plant bulb ethephon dip was approximately three weeks. As a result, the longer it takes Lilium ‘Star Gazer’ to emerge from media, the less ethephon was effective on controlling ULN. Foliar spray of ethephon at 1000 mg∙L^-1 significantly reduced ULN as well; best result was obtained when application was performed at the start of susceptible period. Such early application suppressed plant growth rate without sacrificing flower counts. Since lily growth depends on temperature and storage duration, dates of early applications varied from 21 to 28 days after planting among experiments. The degree of ULN reduction was reduced when application date was delayed. In addition, combinations of pre-plant bulb dip and foliar sprays with ethephon, not only ULN was reduced, but the proper period of foliar sprays was also extended. Several other factors might affect ULN occurrence. Lilium ‘Star Gazer’ grew rapidly in a phytotron with day/night temperature of 30/25˚C; ULN severity was reduced because the period of leaf overlapping was shortened. Shoot length (and thus stem roots growth) at planting was not a factor associated with ULN. It was concluded that the use of ethephon successfully suppressed ULN in Oriental lilies to an acceptable level. Foliar spray with 1000 mg∙L-1 ethephon at the start of susceptible period, with or without combination with pre-plant bulb dip in 125 mg∙L^-1 ethephon, reduced both ULN and plant height, a practice suited for pot lily production. For cut lily production, pre-plant bulb dip with 125 mg∙L^-1 ethephon was recommended, since ULN was reduced but plant height was not affected.