Flower stem height

It was recorded weekly with a Truper^® tape measure, accuracy of 0.01 cm, from their base to the meristematic apex.

Stem diameter, number of leaves, leaf area, and greenness index

In the middle part of each plant, the diameter of the stem was recorded with a Truper^® digital vernier with accuracy of 0.01 mm; the number of leaves was obtained by direct counting, the leaf area with a Li-Cor model Li-3000A leaf area integrator, and the greenness index in the leaves of the middle part with a Hansatech^® model CL-01 portable SPAD meter.

Visual appearance of flower stems and roots

For the visual appearance, images were constructed from photographs taken with a Nikon^® D3500 digital camera and processed with Adobe Photoshop^® CS6.

Number, length and fresh weight of flower buds, time to flowering and anthesis period

In each stem, the number of flower buds was counted directly; the length of each one was obtained with a Truper^® digital vernier with accuracy of 0.01 mm; the fresh weight was recorded with an Ohaus Adventurer^® model AR3130 digital balance with accuracy of 0.01 g; the time to flowering was obtained by counting the number of days elapsed from planting to the opening of the first flower bud, and the period of anthesis by counting the days that elapsed from flowering to senescence.

Dry biomass of roots, bulbs, stems, leaves, and flower buds

Three flower stems per treatment were selected to be fractionated into roots, bulbs, stems, leaves, and flower buds. Each one had its fresh biomass recorded, they were placed in paper bags, and dried at 80 °C for 24 h in a Reavel^® model REA-II-2240 oven; the dry biomass was obtained with the same balance.

Statistical analysis

Data were processed with descriptive statistics, one-factor analysis of variance, and mean comparison tests (Tukey, p≤ 0.05) with the SAS^® 9.0 software for Windows.

Flower stem height

In Asiatic Lilium cv. Litouwen, the application of PBZ decreased the height of the flower stems from day 28 (beginning of the vegetative phase) and it became more evident at flowering (84 to 91 d). In this phase, stems with 0 or 2.5 mg L^-1 were 61.5 cm tall, in those with 5 or 10 mg L^-1 it decreased to 55.6 cm, and for concentrations of 20, 40, 100, and 200 mg L^-1 of PBZ, the height of the flower stems was 43.4, 29.1, 18.4, and 14.1 cm, respectively (Figure 1).

Figure 1 Height of the flower stems of Asiatic Lilium cv. Litouwen grown with eight concentrations of paclobutrazol. Means with different letters, at each evaluation time, indicate significant differences (Tukey, p≤ 0.05). Each data represents the average of six experimental units (eighteen flower stems) ± standard error. 

Results such as those shown by ^{Francescangeli et al. (2007}); ^{Currey and López (2010}); ^{Latimer and Freeborn (2011}), mention that Lilium cv. Ercolano, Royal Respect, Nellie White, and Lilium lancifolium reduce between 23 and 59% the height of their flower stems, which is 63 cm, when applying 20 to 150 mg L^-1 of PBZ. In Lilium cv. Litouwen, its height decreased between 9.6 and 77.1% compared to the control (61 cm).

Stem diameter, number of leaves, leaf area, greenness index

Stem diameter was similar (6.92 ±0.13 mm) in treatments with 0, 2.5, 5, 10 or 20 mg L^-1 of PBZ, but increased by 51% in those with 100 or 200 mg L^-1. The number of leaves and leaf area decreased from 77 to 32.3 and from 658.55 to 227.93 cm² from 0 to 200 mg L^-1, while the greenness index increased from 25.21 to 75.77 USPAD with the same doses of PBZ (Table 1).

In Asiatic Lilium cv. Litouwen, the larger diameter of the stem due to the application of 40, 100 or 200 mg L^-1 of PBZ could be related to an increase in the cortex and medulla or to the greater number of vascular bundles, medulla cells and vessel elements, as mentioned by ^{Tsegaw et al. (2005}); ^{Torres-Pio et al. (2021}) for Solanum tuberosum and Lilium cv. Arcachon, respectively.

In treatments with 100 or 200 mg L^-1, the decrease in the number of leaves coincides with the reduction in leaf area, but contrasts with the greenness index. If the visual aspect, which can be seen in Figure 2, the number or length of flower buds (Table 2) are referred to, the previous answer would indicate that the photosynthetic efficiency per unit area increased in treatments with 100 or 200 mg L^-1 of PBZ, as occurs in plants that are subjected to some type of stress (^{Taiz and Zeiger, 2010}).

Figure 2 Visual appearance of Asiatic Lilium cv. Litouwen grown with eight concentrations of paclobutrazol. 

Visual appearance of flower stems and bulbs

The flowering stems of Asiatic Lilium cv. Litouwen treated with 0, 2.5, 5 or 10 mg L^-1 of PBZ had similar visual appearance, intense green foliage, flower buds with good appearance and striking. The bulbs were turgid, with no damage or visible symptoms of disease, with similar root density, except in those treated with 10 mg L^-1, which had more numerous and longer roots.

From 20 mg L^-1 of PBZ, the flower stems were more compact, reduced in height, but with no effect on the number of flower buds, these changes gave them a striking visual appearance. The bulbs maintained their good appearance, with no signs of damage, but the root density increased (Figure 2).

In Lilium cv. Ercolano, Royal Respect, Nellie White, Arcachon, Armandale or Tresor, application of PBZ in concentrations ranging from 20 to 200 mg L^-1 reduces flower stem height, increases color intensity and root density compared to the control (0 mg L^-1 of PBZ) (^{Francescangeli et al., 2007}; ^{Currey and López, 2010}; ^{Torres-Pio et al., 2021}; ^{Rios et al., 2022}).

A similar response occurred in this research with Asiatic Lilium cv. Litouwen since with concentrations of 2.5, 5 or 10, no visual changes were perceived, but with 20, 40, 100 or 200 mg L^-1 of PBZ, the flower stems were more compact and reduced in size, which facilitates their handling as potted plants and expands the possibilities for their commercialization with a more diverse public. Regarding the physiology of the crop, the increase in root density could improve the absorption of water and essential elements for the hydration or nutrition of the leaves or flower buds.

Number, length and fresh weight of flower buds, time to flowering and anthesis period

Regardless of the treatments, the number of flower buds was 2.75 ±0.14, while their length decreased from 78.44 (with 0, 2.5, 5, 10 or 20 mg L^-1 of PBZ) to 42.58 or 43.08 mm with 100 or 200 mg L^-1. The fresh weight of flower buds, the days to flowering and the anthesis period increased by the application of 40, 100 or 200 mg L^-1 of paclobutrazol (Table 2).

Findings such as those presented by ^{Ranwala et al. (2002}); ^{Currey and Lopez (2010}); ^{Torres-Pio et al. (2021}) mention that, in Lilium cv. Ercolano, Nellie White or Arcachon, the application of PBZ in concentrations ranging from 30 to 200 mg L^-1 reduces stem height and keeps the number of flower buds (5.7 on average) and the days to flowering (72.5 in ‘Ercolano’; 111 in ‘Nellie White’) unchanged. In Asiatic Lilium cv. Litouwen there were only 2.75 buds per flower stem as temperatures inside the greenhouse fluctuated between 30 and 43 °C from 10:30 am. to 6:00 pm. during their cultivation, which led to absorption of the flower buds.

Research by ^{Runkle (2018}) mentions that the Asiatic Lilium crop performs well with daytime temperatures of 21 to 27 °C, but when these exceed 29.4 °C, flower bud abortion occurs (^{Evans and Beck, 2007}). The fresh weight coincided with that reported by ^{Torres-Pio et al. (2021}) for Lilium ‘Arcachon’. The time to flowering is delayed and the anthesis period is doubled by the application of 40, 100 or 200 mg L^-1 of PBZ.

Dry biomass of roots, bulbs, stems, leaves, and flower buds

The dry biomass of roots, bulbs or flower buds increased 2, 2.2 or 1.6 times by the application of PBZ at concentrations ≥ 20 mg L^-1. In contrast, in stems and leaves, dry biomass decreased three and two times with respect to the control, the values of which were 2.85 and 2.36 g, respectively (Table 3).

Dry root biomass could be related to the absorption of water and essential elements that are required for crop growth and flowering since a root system with abundant and long roots has a greater capacity for exploration compared to scarce and short roots (^{Taiz and Zeiger, 2010}). In this case, the dry root biomass of Asiatic Lilium cv. Litouwen increased by the application of 20 to 200 mg L^-1 of PBZ, which was able to improve the absorption of essential elements to increase the biomass of bulbs or flower buds.

This combination maintained the good appearance of the flower stems (Figure 2). On the other hand, the decrease in dry biomass in stems would imply a reduction in the vascular system, particularly phloem for the translocation of photoassimilates, while a lower dry biomass in the leaves would be associated with a reduction in the photosynthetically active area, which would negatively affect the visual appearance of the flowering stems. Nevertheless, this was not the case, suggesting an increase in translocation capacity or photosynthetic efficiency per unit area (^{Taiz and Zeiger, 2010}).