| Summary: | 碩士 === 國立臺灣大學 === 園藝學研究所 === 95 === 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<sup>-1</sup>. 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<sup>-1</sup>, of which plants height were not influenced. Furthermore, the ability of 125 mg∙L<sup>-1</sup> 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<sup>-1</sup> 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<sup>-1</sup> 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<sup>-1</sup> ethephon was recommended, since ULN was reduced but plant height was not affected.
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