研究報告/第84号

農業・園芸総合研究所研究報告

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第84号：2016年3月発行

第84号抄録

原著

寒冷地のスプレーギク栽培に適した暗期中断用各種光源の利用可能性に関する研究

佐々木　厚

Studies on the Availability of Various Light Sources for Night-break on
Spray-type Chrysanthemum in Cool Climate Regions

Atsushi SASAKI

スプレーギクの栽培において,開花の抑制と同時に整った花房の形状を形成させることを目的として,周年にわたり暗期中断による長日処理が行われている。その暗期中断用光源としては,従来から白熱電球が用いられているが,白熱電球は消費電力が多く,寿命が短いことに加え,光変換効率が低い光源である。したがって,地球温暖化防止対策の観点からも,白熱電球の代替光源の開発と利用方法の確立が急務となっている。そこで,本研究では,宮城県を含めた寒冷地におけるスプレーギク栽培において,省エネルギーおよび低コスト生産を推進することを目的として,高圧ナトリウムランプ,電球色電球形蛍光ランプ,赤色電球形蛍光ランプ,赤色LED光源の暗期中断用光源としての利用可能性を検討した。
その結果,通常光合成促進用光源として用いられている高圧ナトリウムランプを照射面積が白熱電球の約6倍になるように設置して2時間の暗期中断を行った場合,白熱電球を用いて4時間の暗期中断を行った場合と比べて,実用上問題がない程度の花芽分化の抑制効果が認められた。このため,高圧ナトリウムランプは,暗期中断用光源として利用できることが明らかとなった。また,試作した電球色電球形蛍光ランプを用いて4時間の暗期中断を行った場合,白熱電球を用いて4時間の暗期中断を行った場合と比べて,実用上問題がない程度の花芽分化の抑制効果が認められた。このため,電球色電球形蛍光ランプは,暗期中断用光源として利用できることが明らかとなった。さらに,製品化された場合の経済性も明示された。
次に,試作した赤色電球形蛍光ランプと赤色LED光源を暗期中断用光源として用いた場合,同じ暗期中断時間で比べると,白熱電球を用いた場合より低いPPFDで商品価値の高い整った花房の形状を示す切り花を得ることができた。また,光源別に商品価値の高い整った花房の形状を示す光量の下限値を求めると,白熱電球＞赤色電球形蛍光ランプ＞赤色LED光源の順になることが示された。このため,試作した赤色電球形蛍光ランプと赤色LED光源は,暗期中断用光源として利用できることが明らかとなった。さらに,試作した赤色電球形蛍光ランプと赤色LED光源を用いた場合に,暗期中断時間と商品価値の高い整った花房の形状を示すPPFDの下限値との関係はほぼ反比例であったので,相反則が成り立っていることが明らかとなった。

〔キーワード〕暗期中断,花房形状,高圧ナトリウムランプ,スプレーギク,赤色LED光源,赤色電球形蛍光ランプ,電球色電球形蛍光ランプ

＜Summary＞

Long-day treatment is a method to inhibit flowering and to produce well-formed flower clusters (normal spray flower formation) when cultivating spray-type chrysanthemums. It involves interrupting the dark period (night-break) each night, from the time of planting seedlings or planting unrooted cuttings throughout the year until the time for short-day treatment. Incandescent lamps have conventionally been used as light sources for this treatment, but they have a high power consumption, short working life, and low light-producing efficiency rate. From the perspective of global warming mitigation, there is an urgent need to find alternatives to these lamps. For this reason and to establish energy-saving low-cost production methods, high-pressure sodium lamps, compact self-ballasted fluorescent lamps of warm white light, compact self-ballasted fluorescent lamps of red light, and red LED light sources were tested for their potential interrupting the dark period in cold climate regions, including Miyagi prefecture.

In case of autumn-flowering cultivars in light and shade cultures, when a 400-W high -pressure sodium lamp, which is normally used to promote photosynthesis, was used to interrupt the dark period each night for 2-h from the time of planting seedlings or planting unrooted cuttings until the time for short-day treatment, flower bud formation was inhibited as efficiently for practical purposes as by a 4-h dark interruption using a 75-W incandescent lamp. The 400-W lamps illuminated approximately 6 times as much irradiation area as the 75-W incandescent lamps. These results clearly show the effectiveness of high-pressure sodium lamps for interrupting the dark period. However, 
using high-pressure sodium lamps for only 1-h did not result in a level of flower bud inhibition suitable for commercial cultivation.

In case of autumn-flowering cultivars in light and shade cultures, when a 23-W compact self-ballasted fluorescent lamp of warm white light prototype, produced in collaboration with the manufacturer, was used to interrupt the dark period each night for 4-h from the time of planting seedlings until the time for short-day treatment. This treatment also inhibited flower budding to an extent sufficient for practical application. This result shows that the 23-W lamp could be used for interrupting the dark period. Furthermore, if the method used in the trial was to be commercialized, on the basis of power and depreciation costs per 10a per year, the normal power costs would be approximately 45% compared with the power costs associated with using the 75-W incandescent lamps (a 55% reduction), and for the night power costs, it would be approximately 64% (a 36% reduction).

In case of autumn-flowering and summer-to-autumn-flowering cultivars in light culture, when a 21-W compact self-ballasted fluorescent lamp of red light prototype, produced in collaboration with the manufacturer, was used for interrupting the dark period each night from the time of planting seedlings until the time for short-day treatment. The flower clusters had a well-formed shape with a high commercial value for cut-flowers; the photosynthetic photon flux density (PPFD) value was lower than that of the 75-W incandescent lamp for the same night-break time. A 6.7-W red LED light source prototype was tested on autumn-flowering and summer-to-autumn- flowering cultivars during the same growth period. The flower clusters showed a well-formed shape with high commercial value, comparable to the results of interrupting the dark period with remarkably lower PPFD value than that of a incandescent lamp for the same night-break time. The order of the light sources with minimal fluence required for well-formed high quality flowers was incandescent lamp > compact self-ballasted fluorescent lamps of red light > red LED light source. The compact self-ballasted fluorescent and red LED prototypes were clearly suitable for interrupting the dark period from the time of planting seedlings until the time for short-day treatment. When these light sources were used, the night-break time and the lower limit of PPFD value for high-value flower clusters were inversely correlated. These results indicate that the product of the lower limit of PPFD value and night-break time can be explained by the Bunsen-Roscoe law of reciprocity.

These results show that high-pressure sodium lamps, compact self-ballasted fluorescent lamps of warm white light, compact self-ballasted fluorescent lamps of red light, and red LED light sources can be used for interrupting the dark period in cut-flower spray-type chrysanthemums reared in cold climate regions from the time of planting seedlings or planting unrooted cuttings until the time for short-day treatment. In particular, red LED light source could produce flower clusters of a high commercial value at a much lower PPFD value than incandescent lamp. With its much lower power consumption, red LED light source is a promising source for interrupting the dark period.