Leaf Trichome Morphology of Durio Kutejensis Landraces from Kalimantan

The leaf trichome morphology of 19 Durio kutejensis (lai) landraces was studied. The observation of cr ssand paradermal sections of D. kutejensis leaves showed that all landraces have glabrous lea ves on the adaxial surface, while their abaxial surfaces are covered by six trichome types, one gla ndu r (oneor two-celled stalks with a spheroid m ulticellular glandular head) and five non-glandular (complex peltate, simp le peltate, cushioned stellate, flat stellate, and four-armed stellate trichome with a central cushion). All landraces wer e rarely covered by glandular trichomes. The non-gl a dular trichomes are varied in type, density, number of layers, diameter , and shape and margin color of the complex peltate among landraces. One landrace comprises three non-glandular trichome types, while the other landraces consist of four or five non-glandular trichome types. The shapes and margin color of comp lex peltate trichomes of D. kutejensis are the specific characteristics which distinguish this species from the other Durio species, however these characteristics cannot be u sed to differentiate one D. kutejensis landraces from the other. Therefore, other characteristics need to be explored in order to distinguish one D. kutejensis landraces from the other.


Introduction
Durio kutejensis (Hassk.) Becc. is a member of the family Malvaceae. This species was first described by Beccari in Malesia in 1889. This species is a perennial tree which can be as high as 24-30 m tall and 40-60 cm in stem diameter. Stipules are present but drop early. Leaves with elliptic to oblong, chartaceous, or coriaceous blades are alternately arranged. It has a green leaf blade that is glabrous or very glossy on the adaxial surface, but its leaves are covered with a few layers of trichomes on the abaxial surface [1][2][3][4].
D. kutejensis is considered as a cultivated plant that has an economic value as an edible fruit tree [4][5][6]. This species has five local names: Lai, Pampakin, Pampaken, Ruas, and Pekawai [1,3,4,6]. Borneo, as the native area of D. kutejensis, provides a wide variety of morphological characteristics. Local people in North Kalimantan, East Kalimantan, and South Kalimantan classify this species into different landraces based on their fruit characteristics [5]; however, due to the seasonal fruiting times, the fruit is not always available throughout the year.
Trichomes in plants are the appendages of epidermal cells that are diverse in form, structure, and function [7][8][9]. They have a few functions, such as protecting the plant from herbivores, heat, and sunlight, and also for controlling leaf temperature and water loss [10]. A previous study of the leaf trichome morphology on Durio has already performed in Malaysia. It showed the trichome feature among Durio species and varieties [11], however, there was no report for leaf trichomes among D. kutejensis landraces. The main purpose of this study is to observe the variation of morphological characteristics of leaf trichome types on the leaf surfaces of D. kutejensis landraces.

Materials and Methods
Plant material was collected from December 2011 to September 2013, taken from areas which cover South Kalimantan, East Kalimantan, North Kalimantan, Central Kalimantan, and West Kalimantan ( Figure 1; Table 1).
Fresh and dried leaves from 19 D. kutejensis landraces were observed (Table 1), based on the method applied on the previous leaf trichome observation [11,12]. From each landrace, a small leaf piece of 1 cm 2 was cut from the middle of the leaf (abaxial and adaxial surfaces), then was made cross-and paradermal sections. The abaxial and adaxial surfaces then were scraped and the peelings were pasted onto a glass slide [11,12]. Five slices of leaf were mounted onto a glass slide. All slides were directly observed under a fluorescence microscope and documented using a photomicroscope. The number of trichomes was calculated; there were as many as 25 observations for each D. kutejensis landrace using 100x and 400x magnifications.

Results and Discussion
D. kutejensis leaves have different colors between the adaxial and abaxial surfaces. The color of the adaxial leaf surface is usually green, while abaxial leaves are golden to reddish brown. Adaxial leaf surfaces of all D. kutejensis landraces are glabrous, while abaxial leaf surfaces are significantly covered with six trichome types, one glandular and five non-glandular. The glandular trichome type is a one-to two-celled stalk with a spheroid multicellular glandular head ( Figure 2a). It covers all D. kutejensis leaves with rare density (  Table 2).
The complex peltate trichomes has an undulating margin, two to five lobes, long fimbriates, one to two fissures (Figure 2b), and a golden basic color. All landraces were covered with densely complex peltate trichomes on the abaxial leaf surface. A few variations were found in the shape and margin color of complex peltate trichome among D. kutejensis landraces. All landraces have two until five lobes.
The margin color of the trichomes has three variations, reddish brown, brown, and dark brown. Reddish brown margins were found on 14 landraces, while brown margins were found on Gincu and Belimbing landraces. Batuah, Durian, and Kesumba landraces have dark brown margins (Table 2).
The simple peltate trichome has strongly lobed, long fimbriates with no splits (Figure 2c). The densely simple peltate trichome covers the abaxial leaf of all D. kutejensis landraces ( Table 2). The trichome type forms five layers on 10 landraces, and nine landraces comprise three to four layers. The most varied diameters of simple peltate trichomes were found on Besar (174.45-500.35 µm) ( Table 3).
The cushioned stellate trichome forms more than five rays with a central cushion ( Figure 2d). Generally, this type has an intermediate to dense density, but Belimbing and Pampaken have a rare density ( Table 2).

Figure 2. Indumentum Types on Abaxial Surfaces of D. kutejensis Leaf Landraces. a) A one-or two-celled Stalks with a Spheroid Multicellular Glandular Head, b) Complex Peltate Trichome, c) Simple Peltate Trichome, d) Cushioned Stellate Trichome, e) Flat Stellate Trichome, and f) Four-armed Stellate Trichome with a Central Cushion
The number of layers of cushioned stellate trichomes on Belimbing is consisted of two layers, while the other landraces has three to five layers. The smallest diameter of this type was found on the Belimbing landrace (97.27-146.44 µm), and the largest diameter was on Wild landraces (560.88-870.21 µm) ( Table 3).
The flat stellate trichomes have five rays without a central cushion (Figure 2d). Most landraces have rare to dense density of flat stellate trichomes (Table 2). Lai-1 has the thinnest layers (two layers) of the flat stellate trichomes, while six landraces have the thickest layers (five layers). For flat stellate trichomes, the most varied diameters were found on the Wild landrace (742.90-1101.40 µm) ( Table 3).
The four-armed stellate trichome with a central cushion has four rays with a central cushion (Figure 2f). This type was found in three landraces with various (rare to intermediate) density (Table 2). The number of fourarmed stellate trichomes with a central cushion layer are varied (one to four layers), and the Sahang landrace has one layer and the most varied diameters of four-armed stellate trichomes with a central cushion (132.21-395.64 µm) ( Table 3).
In this research, some additional notes were recorded, including the density of glandular trichomes and nonglandular trichomes, as well as in complex peltate trichome shape, the margin color of complex peltate trichomes, and the diameter of complex peltate trichome characteristics. Some new specific characteristics were also recorded, comprises the simple peltate trichome The non-glandular trichome arrangement of D. kutejensis landraces is similar to previous descriptions for D. kutejensis [3] and Neesia [4]. In Malvaceae, dense trichomes on abaxial leaf surfaces were also found in many species, i.e., D.  [11], Kostermansia malayana [14], Neesia altissima, N. malayana [12], Coelostegia griffithii, and C. chartacea [13].
The density of glandular trichomes in this study was a rare density however the previous study [11] mentioned that the density of glandular trichomes was an intermediate one. The complex peltate trichome comprises two to five lobes with a golden basic color, and the margin color is varied from reddish brown, brown, and dark brown. Meanwhile, the previous study mentioned that the complex peltate trichome has four to five lobes that were dark brown and golden in color. The layer number of the complex peltate trichome was not reported in the previous study. The range of complex peltate trichome diameters was wider, 237.12-1309.58 µm ( The cushioned stellate trichome is varied from rare to dense density. A previous study has reported that D. kutejensis only has a dense density of the cushioned stellate trichome [11]. The layer number and the diameter of cushioned stellate trichomes are the new characteristics which were discovered in this study. They could be used to differentiate among Belimbing with other landraces.
The study is also revealed the variation of the flat stellate trichome density, which was not reported in the previous study [11]. The layer number and diameter of the flat stellate trichome were the only characteristics that could be used to distinguish the Belimbing landrace from others.
The four-armed stellate trichome with a central cushion is also varied in its density, layer number, and diameter, which was the additional information for D. kutejensis. The layer number of four-armed stellate trichomes with a central cushion can be used to distinguish Sahang from other landraces.
Belimbing was a very specific landrace. It was easily differentiated from other landraces based on several trichome characteristics, including the smallest trichome type (four types), diameter (97.27-146.44 µm), and two layers of cushioned stellate trichomes. The rare to dense stellate trichomes in this study are differed from those reported by Salma [11], who stated that D. kutejensis only has a dense stellate trichomes. However, the stellate trichomes were able to be distinguished between Neesia altissima, N.glabra, N. malayana, N. pilatiflora, and N. synandra [12].
The leaves datas from several locations were randomly collected and examined, but the trichome characters were similar in many aspects, i.e., type, density, shape and margin color of complex peltate trichomes, number of layers, and diameter among landraces. These characteristics could not be used to differentiate one D. kutejensis landraces from the other because the differentiation of density, number of layers, and diameter of leaf trichomes among D. kutejensis landraces were the adaptive features to reduce the leaves temperature or to prevent damage when water is not available in their habitat [9].

Conclusions
Six trichome types were found on 19 landraces of D. kutejensis, comprise one glandular trichome (one-or two-celled stalks with a spheroid multicellular glandular head) and five non-glandular trichomes (complex peltate, simple peltate, cushioned stellate, flat stellate, and four-armed stellate trichomes with a central cushion) on the abaxial leaf surface. Trichome characteristics of D. kutejensis were more varied than the other Durio species in the shapes and margin color of complex peltate trichomes, but these characteristics cannot be used to distinguish one D. kutejensis landraces from the other.