Temperature and Irradiance Effects on Vegetative Growth of Two Species of Leucocoryne

J. AMER. SOC. HORT. SCI. 128(6):815–820. 2003. Temperature and Irradiance Effects on Vegetative Growth of Two Species of Leucocoryne J.L. Catley The Horticultural and Food Research Institute of New Zealand Ltd., Private Bag 11030, Palmerston North, New Zealand ADDITIONAL INDEX WORDS. bulb, cutflower, leaf emergence, Leucocoryne coquimbensis, Leucocoryne ixioides, dropper ABSTRACT. The influences of temperature and irradiance on vegetative growth of two species of Leucocoryne(Leucocoryne coquimbensisF. PhilandL. ixioides (Hook.)Lindl.)were examined in controlled environment growth rooms. The growing environments had day/night temperatures of 10/5, 15/10, or 20/15 °C, providing mean temperatures of 7.5, 12.5, or 17.5 °C, and photosynthetic photon fluxes (PPF) of 497 or 710 µmol·m–2·s–1. Leaf emergence data were recorded up to three times a week, and measurements of vegetative growth were made in the rooms twice weekly. Destructive harvests were carried out at intervals up to four weeks apart. Leaves of L. ixioides emerged first in all mean temperatures. As mean temperature decreased from 17.5 to 7.5 °C, the differences in first emergence dates became more apparent between species. Appearance of the second leaf of both species occurred in less than half the number of days the first leaf took to emerge. The time taken for further leaves to develop increased as temperature decreased, particularly for L. ixioides and at mean temperatures below 12.5 °C. Although leaves of L. ixioides emerged first, days to emergence of further leaves increased to lag behind production of L. coquimbensis leaves, particularly when mean temperatures dropped below 12.5 °C. Temperature also significantly affected growth of other plant parts. As mean temperature increased, maximum leaf, root and main bulb dry weights increased for both species, along with secondary bulb dry weights of L. coquimbensis. As irradiance increased, maximum leaf dry weights decreased and maximum bulb dry weights increased of both species, and maximum dropper dry weights of L. coquimbensis increased. Leucocoryne coquimbensis appears to have the greatest capacity to multiply vegetatively and this is enhanced by high mean temperatures. These results suggest that mean temperatures higher than those used in this study are required for sustained leaf emergence, particularly for L. ixioides although this species has the capacity to emerge at low temperatures. High mean temperatures are also likely to promote vegetative mass of all plant parts of both species, whereas higher irradiance levels than used in this study would enhance main bulb growth. Leucocoryne is a geophytic genus from Chile comprised of driest part of the year. Ohkawa et al. (1997) and van Leeuwen 11 (Hoffman, 1989) or 12 species (Zoellner, 1972). Taxa clas- (1992) have shown that L. coquimbensis requires a minimum of sification has varied for this genus from Amaryllidaceae (Bryan, 4.5 months dry storage at an optimum temperature of 20 °C to 1989) to Liliaceae (Willis, 1973), but Dahlgren et al., (1985) break dormancy. Hoffman (1989) lists the conservation status of seem to provide the most thorough analysis of its taxa, placing these two species as vulnerable. it in the Alliaceae family. The genus Nothoscordum, is the clos- In New Zealand, Leucocoryneis grown in plastic structures that est relative of Leucocoryne (Crosa, 1988). Other related Chilean provide rain protection, and where it flowers in spring. However, genera include Ipheion, Tristagma, Zoellnerallium, Pabellonia, there is little knowledge of the effects of temperature and light and Triteleia (Hoffman, 1989). on bulb development, vegetative growth and flowering. Previous Two species of Leucocoryne, L. coquimbensis and L. ixioides, studies on Leucocoryneby Kim et al. (1998a and 1998b), Ohkawa have potential as cutflower crops. Leucocoryne coquimbensis is et al. (1998), Ohkawa et al. (1997) and van Leeuwen (1992) have endemic to the coast of central Chile from Coquimbo (hence its examined either flower bud development, bulb weight, storage name) to Aconcagua (latitude 30 to 33°S) (Hoffman, 1989; Run- temperatures or durations, and their effects on flowering. Elgar del, 1981; Zoellner, 1972). Leucocoryne ixioides is found over a et al. (2003) have studied vase life and Lancaster et al. (2000) narrower latitude band (latitudes 32 to 34°S) with some overlap have identified an undesirable aroma produced by some species with L. coquimbensis. The habitats of L. ixioides are farther south of Leucocoryne. Therefore, until now there has been no attempt and farther inland, in the slightly more elevated central provinces to define the effects of the environment on vegetative and floral of the Cordillera de la Costa (Hoffman, 1989; Zoellner, 1972). growth, or to describe the sequence of plant development. As Temperature patterns in central Chile are primarily a function of Leucocoryne has potential as a cutflower crop, such knowledge topography (Rundel, 1981). Coastal areas of central Chile show will benefit flower growers as it will aid scheduling decisions and a gradual reduction in rainfall over the latitudes where L. coqui- potentially improve flower quality. The objectives of this study mbensis is found, changing from a Mediterranean climate in the were to determine the influence of temperature and irradiance on south to a desert climate in the north (Dallman, 1998; Rundel, plant growth and development of two species of Leucocoryneunder 1981). Precipitation levels increase inland due to orographic lift- controlled environment conditions. The results of the vegetative ing of air masses. In both areas winter frontal rains are the main stages of plant growth are reported in this paper and those of the source of precipitation with virtually all moisture falling over the floral stages in a previous paper (Catley, 2003). period from April to September (Rundel, 1981). These rains trigger growth, followed by flowering in late spring and early summer Materials and Methods (Bryan, 1989). A dormant period occurs during the hottest and PLANT MATERIAL.Bulbs of seedling populations of Leucocoryne Received for publication 28 May 2003. Accepted for publication 1 July 2003. coquimbensis and L. ixioides were obtained from a commercial J. AMER. SOC. HORT. SCI. 128(6):815–820. 2003. 815 045-Dev 815 9/27/03, 11:13:35 AM grower. Before receipt, the bulbs were stored dry at 20 to 25 °C of count data. Leaf data were analyzed using the GLM procedure for §28 weeks. Bulbs were prepared for planting immediately in SAS with count variables being square-root transformed before on arrival by removing all secondary bulbs from the main bulb. analysis (SAS Institute, 1993). Each bulb (defined as the main bulb in this study) weighed between 1.0 and 2.5 g. Main bulbs were sorted according to Results weight, then four main bulbs of similar weights (±0.1 g) were planted in 1.25 L pots, containing a 1 peat : 1 pumice : 1 gravel LEAF APPEARANCE: TIMING AND PATTERN. Temperature sig- (by volume) growing medium. The medium was amended with nificantly affected the days from planting to leaf emergence 3 g·L–1 3-month Osmocote (14N–6.1P–11.6K), 6 g·L–1 9-month for both Leucocoryne species (P = 0.021), particularly as mean Osmocote (18N–2.6P–10K), 3.3 g·L–1 Sierra Micromax (Grace temperature dropped below 12.5 °C (Fig. 1). As mean tempera- Sierra, Heerlen, The Netherlands), 8 g·L–1 dolomite lime and 3.3 ture decreased, the number of days to emergence of the first leaf g·L–1 superphosphate (Ravensdown Fertilizer Co-op, Napier, New increased, particularly for L. coquimbensis. There was also a Zealand). During growth, a modified half-strength Hoagland·s significant species difference (P < 0.001). In the regime with the A nutrient solution was applied to excess twice daily (Brooking, highest mean temperature (17.5 °C), L. ixioides emerged faster 1976). Each treatment consisted of 36 pots, and each treatment (48 d) than L. coquimbensis (51 d). With a mean temperature was allocated to 1.5 trolleys. Trolley positions were reallocated reduction from 17.5 °C to 12.5 °C, L. ixioides took longest to within each room twice weekly to minimize positional effects. emerge (50 d), whereas L. coquimbensis took 57 d. In the regime A completely randomized design was used for each irradiance with the lowest mean temperature of 7.5 °C, L. ixioides took and temperature combination. 58 d to emerge in comparison to 67 d for L. coquimbensis. The ENVIRONMENTAL CONDITIONS. The pots were placed on trolleys in three controlled environment growth rooms at the New Zealand Controlled Environment Laboratory belonging to HortResearch in Palmerston North, in a range of growing regimes with day/night temperatures of 10/5, 15/10, or 20/15 °C, providing mean growing temperatures of 7.5, 12.5, or 17.5 °C respectively. Daily lighting in each room consisted of a 12-h light period of 710 µmol·m–2·s–1 photosynthetic photon flux (PPF) at pot level. Vapor pressure deficits of 0.4/0.3 kPa (day/night) were maintained in these rooms. The changeover between day and night for temperature and vapor pressure deficit took 2 h, with the 12-h light period starting midway through this period. The light levels in the main lighting period were provided by four 1-kW high pressure discharge lamps (Sylvania ‘Metalarc·) and four 1-kW tungsten halogen lamps. An additional irradiance level was achieved by fitting half the trolleys with neutral density synthetic screening to obtain 497 µmol·m–2·s–1 at pot level. The two irradiance levels of 497 or 710 µmol·m–2·s–1 in each room provided daily photon receipts of 21.5 or 30.6 mol·m–2·d–1 respec- Fig. 1. Effects of temperature on days from planting to emergence of the first tively.

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