Morphological Characteristics of Batuah Red-Fleshed Durian (Durio graveolens), an Endemic Exotic Plant from East Kalimantan, Indonesia

Kalimantan is the largest island in Indonesia, with high level of biodiversity in the world. Kalimantan, especially East Kalimantan, is a place of mega biodiversity with humid tropical forest climate conditions (Debnath, et al., 2014; Ercisli & Sagbas, 2017). The humid tropical climate is a climate with humidity above 90%, high rainfall (more than 1500 mm/year), annual temperature above 18oC, and the difference between the rainy season and the dry season is not very clear (Poepenoe, 1974). One of the rich diversity that exists is the presence of various types of tropical fruits, most of which are endemic to East Kalimantan. Indonesia is one of the eight centers of plant genetic diversity in the world, especially for tropical fruits such as durian (Biodiversity International, 2007; Brown, 1997). At present, it is recorded that of around 27 species of Durio worldwide, 18 of them are grown in Kalimantan, 11 are in Malaya, and seven are in Sumatra (Milow, et al., 2014). The great diversity of species and sources of germplasm Durio spp. in Indonesia is very important as basic capital for breeders (Poerwanto, 2003; Ryugo, 1988; Chakravarty, et al., 2016). The high number of Durio species that grow in Kalimantan illustrates that this area is the most important distribution centre for durian relatives. In addition to being rich in durian diversity, Indonesia is also rich in the diversity of sources of germplasm from Durio spp. In Indonesia, there are quite a lot of durian cultivars that differ from one another in taste, aroma, and color of the flesh. Even durian seeds can be found without seeds. From plant breeding, it is expected that superior seeds will be obtained both in quality and fruit production. This rich diversity of species and germplasm has not been utilized optimally. Therefore, plant breeding in durian relatives (Durio spp.) in Indonesia needs to produce superior cultivars/seeds (The Indonesian Ministry of Agriculture, 2011). This can be done by collecting data and information about the rich diversity of species and sources of germplasm Durio spp. in Indonesia (Belgis, et al., 2015). The next step is select the types of sources of germplasm that have more value. With the availability of diversity in germplasm types or sources, the desired superior cultivars/seeds will be assembled. To be able to determine the type of plants to be planted, it must be known the characteristics of these plant types, especially ARTICLE HISTORY


INTRODUCTION
Kalimantan is the largest island in Indonesia, with high level of biodiversity in the world. Kalimantan, especially East Kalimantan, is a place of mega biodiversity with humid tropical forest climate conditions (Debnath, et al., 2014;Ercisli & Sagbas, 2017). The humid tropical climate is a climate with humidity above 90%, high rainfall (more than 1500 mm/year), annual temperature above 18 o C, and the difference between the rainy season and the dry season is not very clear (Poepenoe, 1974). One of the rich diversity that exists is the presence of various types of tropical fruits, most of which are endemic to East Kalimantan. Indonesia is one of the eight centers of plant genetic diversity in the world, especially for tropical fruits such as durian (Biodiversity International, 2007;Brown, 1997). At present, it is recorded that of around 27 species of Durio worldwide, 18 of them are grown in Kalimantan, 11 are in Malaya, and seven are in Sumatra (Milow, et al., 2014). The great diversity of species and sources of germplasm Durio spp. in Indonesia is very important as basic capital for breeders (Poerwanto, 2003;Ryugo, 1988;Chakravarty, et al., 2016).
The high number of Durio species that grow in Kalimantan illustrates that this area is the most important distribution centre for durian relatives. In addition to being rich in durian diversity, Indonesia is also rich in the diversity of sources of germplasm from Durio spp. In Indonesia, there are quite a lot of durian cultivars that differ from one another in taste, aroma, and color of the flesh. Even durian seeds can be found without seeds. From plant breeding, it is expected that superior seeds will be obtained both in quality and fruit production. This rich diversity of species and germplasm has not been utilized optimally. Therefore, plant breeding in durian relatives (Durio spp.) in Indonesia needs to produce superior cultivars/seeds (The Indonesian Ministry of Agriculture, 2011). This can be done by collecting data and information about the rich diversity of species and sources of germplasm Durio spp. in Indonesia (Belgis, et al., 2015). The next step is select the types of sources of germplasm that have more value. With the availability of diversity in germplasm types or sources, the desired superior cultivars/seeds will be assembled. To be able to determine the type of plants to be planted, it must be known the characteristics of these plant types, especially in relation to climate, soil, and growth velocity factors (Marschner, 1995;Bernier, et al., 2018;Sundari, 2015). Plants with the cross-pollination mechanism as well as the genus Durio spp. derived from natural crosses in nature is very difficult to obtain with potentially superior character (Chakravarty, et al., 2016). Therefore it is important to do a morphological identification activities and documentation of potential superior commodities in East Kalimantan.
Kutai Kertanegara Regency has many kinds of durian trees that have been traditionally and conventionally planted for a long time, and this has caused many interesting nature modifications of the Durio spp. plant character to be studied and do scientifically identified. Durio graveolens is one of durian species found in East Kalimantan. It has a unique size and good taste. This study aims to find, identify, and initially characterize of Batuah D. graveolens in Kutai Kertanegara district, East Kalimantan, Indonesia, as potentially superior endemic fruit plants

MATERIALS AND METHODS
Observations were carried out on productive crops, having produced more than three times, and productive. Identification was done by used survey method and in-depth interview to the owner of plants and farmers, as well as related stakeholders to explore the potential of D. graveolens fruit crops, and then made the characterization of durian plants. The experiment was conducted in Kutai Kertanegara, East Kalimantan, Indonesia, Agronomy Laboratory, Faculty of Agriculture, Universitas Mulawarman, Samarinda, East Kalimantan Province, Indonesia, from January to September 2019. Research was conducted used International Plant Genetic Resources Institute (IPGRI) morphological characteristics.

Statistical Data Analysis
This research was conducted by using a descriptive method of exploration. Sampling methods with purposive sampling, by tracing the primary data and secondary data from the informer, either directly from the key person(s) and library data.

The Origin of D. graveolens
Kalimantan Island is one of the centres of diversity of durian plants (Durio spp.). Generally, durian trees in Kalimantan are grow wildly in primary or mixed forests, and residents in gardens have planted only a small portion. Type D. zibethinus Murray (durian) can be found around Indonesia and another country nearby. This type of durian habitat is in primary and secondary forests and can grow on various types of soil. This type of durian is widely cultivated by people in Kalimantan, including in East Kalimantan (Uji, 2005), although it has not used optimal cultivation technology.
The potential to find new various types of durian in Kalimantan is very large. Kurniadinata et. al (2019) success identifying six new potential superior plants varieties from natural cross breading of durian and lai plants which are endemic plants in Kalimantan. D. graveolens is a relative of durian, which is also an endemic plant in Kalimantan. This species has different fruit morphological characters from durian plants, especially for the flesh colour. Its tree is almost the same as D. zibethinus, but the leaves are wider than other durians. Trunk surface is rough, growth straight, with irregular crown shape and branching density medium to dense. The colour of its skin fruit is an orange yellow to orange, and the spines are dense, short, and sharp. The flesh of is drier than the other types of durian, with red, dark colour and strong aroma. The existence of various genera of Durio spp. in the forests of Kalimantan makes it possible for plants with distinctive character, especially D. graveolens in East Kalimantan.

Morphological Characteristics of D. graveolens
Observations were made in the production phase of D. graveolens plants that grow in Kutai Kertanegara, East Kalimantan. Based on observations of the morphological characteristics, there is diversity in the morphological characteristics of trees, leaves, flowers, fruits, and seeds. This species has an irregular crown shape with a tree height of approximately 10-15 meters (Figure 1). The stems are rough and grow straight, grey stems with a diameter of approximately 50 cm.

Figure 2. The appearance of D. graveolans fruit
The fruit colour is orange yellow to orange with bright intensity (Figure 2). Its fruit length is 10-13 cm with a diameter of 9-10 cm. The fruit consists of 5 segments, with aryl thickness in a medium to thick scale. It has red flesh with a slight sweet taste and soft texture. D. graveolens from East Kalimantan also has dark red flesh colour, with flesh thickness are medium with soft texture (Figure 3). Flesh is non-juicy with fair creaminess and has a strong aroma/odour. The unique odour of this D. graveolens is different compared to D. zibenthinus odour.

Figure 3. The segment and fleshes of D. graveolens
Each segment only has one flesh with seed and the seed length around 4.5-5 cm, with ellipsoid shape and dark brown colour. Some fruits only have 3 or 4 arils and seed each fruit because of some seed and aril, not growth in the rest of the segment (Figure 4).  Table 1. Based on plant and fruit morphology characteristics, D. graveolens fruit from East Kalimantan has unique flesh color, different taste, and also different aroma if compared with D. zibethinus. The flesh color becomes the most unique character compare to other Durio spp plants, and it will become one of the advantages of this durian. Aside from being an exotic commodity, it is also a source of genetic diversity from Kalimantan, Indonesia, to develop another superior durian. Therefore, D. graveolens has a high potential economic value to be improved as superior commodities from East Kalimantan Province, Indonesia.

CONCLUSION
Batuah Durio graveolens fruit is a unique plant that differs from the other species of Durio spp. It has a red, dark color flesh, unique and strong aroma with soft texture aril. Therefore, Batuah Durio graveolens has a high potential economic value to be improved as Superior Commodities from East Kalimantan Province, Indonesia.