Effects of Nitrogen and Night Temeperature on the Physiology of Flower Induction in Pineapple

Verawudh, Jindarath
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Three experiments were conducted to examine the effects of nitrogen (N) and night temperature on the physiological status and susceptibility of pineapple plants [Ananas comosus (L.) Merrillj to inflorescence initiation (forcing) with ethephon. Plants with 2.05% leaf N or exposed to a 30 C night temperature had significantly lower levels of starch and total soluble sugars in the leaves at 5:00 p.m. than plants having lower leaf N or exposed to lower night temperatures. Leaf chlorophyll concentration increased linearly with increasing levels of leaf N and the two were highly correlated (r = 0 .88). After application of 5.0 mg ethephon, ethylene evolution from plants on the first one or two days was significantly higher from high-N plants or from plants held at a 30 C night temperature than from low-N plants or from plants held at lower night temperatures. Ethylene evolution decreased over time and reached minimum levels three to four days after ethephon application. Ethylene evolution from the plants was assumed to be mostly from breakdown of the applied ethephon. Plants with high N or exposed to a 30 C night temperature had a lower percentage forcing than plants with lower levels of N or exposed to the lower temperatures. The interactions between night temperature (20, ambient with a mean of 22.5, and 30 C) and leaf N (1.06 or 2.64%) were also examined but few significant interactions were found. Some interactions may have been obscured by the relatively large amount of random variability. Leaf sucrose decreased with increasing temperature but tended to increase with increasing leaf N. Glucose was absent in leaves of high-N plants but increased with decreasing temperature in low-N plants. In the top and middle one-third of the stem, fructose remained more or less constant in low N plants as temperature increased but decreased significantly with increasing temperatures in high-N plants. Percent forcing was little affected by treatment.
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