Seed and Germination Study of a New Guinea Endemic Plant Species Grevillea papuana Diels

ABSTRACT Grevillea papuana is a culturally important endemic plant species of New Guinea highland. Although G. papuana conservation and propagation attempts were already conducted, this species seed and germination characters information were still very limited. This study aimed to provide information regarding G. papuana seed and germination biology. Seed characteristic and germination trials were conducted in this study. Data analysis was conducted descriptively, while germination parameters were also calculated. G. papuana has a light, elliptic, and winged seed. The species germination was low and ununiform with phanerocotylar epigeal foliaceous (PEF) seedling functional type.

propagation research of the species was also reported by Priyono et al. (2002) and Kuswantoro and Solihah (2016).
Despite all these researches, research on G. papuana seed and germination characteristics is still needed to be done as to the best of our knowledge, little report on G. papuana seed characteristic is present, while no record regarding this species seeding functional type was reported. This condition is unfortunate as seed and germination characteristics can provide information regarding plant species adaptation strategies that is valuable for the plant conservation effort (Kuswantoro & Oktavia 2019;Handayani 2019). Due to its importance, germination biology and seedling functional type of several plant species such as Euchresta horsfieldii, Pinanga arinasae, Areca vestiaria, Artabotrys hexapetalus, and some Annonaceae species were already studied in Bali and Bogor Botanic Garden (Lestari & Asih 2015;Handayani 2017;Kuswantoro & Oktavia 2019;Handayani 2019). Thus, this study aimed to describe seed morphology, germination type, and seedling functional type of G. papuana. We hope that this study will contribute to the plant species conservation effort by enhancing our understanding of its seed and germination biology.
The study was carried out in November 2019-March 2020 at Bali Botanic Garden Seed Bank Laboratory. Seeds were harvested from the only G. papuana plant cultivated in the garden. Of all thirty-six seeds collected during the harvesting period, twenty-five seeds were randomly selected for morphometric and weight measurement. Seed measurement parameters used in this study are the seed length (SL) and seed wide (SW), which defined as the measurement of the seed length and wide, as well as total seed length (TL) and total seed wide (TW), which defined as the measurement of the total seed area, including the seed wing. Measurement of G. papuana seed conducted in this study is illustrated in Figure 1. All thirty-six G. papuana seeds were then sown in a clear, closed plastic container with straw paper as the germination media. Before the sowing process, the seeds, container, and straw papers were sterilized by dipping them into boiling water for about one and a half minutes. The seeds were then incubated at room temperature within the seed bank laboratory. The germination observation was carried out every day and terminated after 120 days after sowing.
Descriptive data analysis was conducted to describe G. papuana seed morphology, germination process, and seedling functional type. Moreover, calculation of the seed final germination percentage (FGP), the first day of germination (FDG), last day of germination (LDG), and time spread germination (TSG) values are also conducted. The calculation of germination parameters value is following Kader (2005) as follows: FDG = First day when germination occurred LDG = Last day when germination occurred TSG = time between first and last day of germination Meanwhile, the seed germination type is defined following Tjitrosoepomo (2009), while the seedling functional type is defined according to Ibarra-Manríquez et al. (2001) and Pérez-Harguindeguy et al. (2016).
Grevillea papuana seeds are light, elliptic, and winged. G. papuana seed elliptic shape is based on its morphometric measurement result, which indicated that the seed averages total length value is about 1.87 times of the seed average total wide value (Table 1.). Meanwhile, the average seed weight value of G. papuana measured in this study which lighter than the seed weight of six Grevillea species studied by Auld and Denham (1999) highlight the seed lightness. G. papuana light seed is probably due to its small embryo and endosperm, reported by Priyono et al. (2002). Grevillea papuana seed is surrounded by a thin wing (Figure 2). This discovery corresponds with Priyono et al. (2002), who also reports wing in G. papuana seed. As G. papuana native range is in New Guinea highland, the species light and winged seed are in correspondence with Makinson (2000), who stated that a light, flat and winged seed is a strong trend in tropical and South Western Australia Grevillea species. The presence of wing in G. papuana seeds suggests that the seed is wind-dispersed. Our suggestion that G. papuana seeds are wind-dispersed is also based on our observation during this study seed collection period, which found that G. papuana mature seed pods were open to allow wind mediated dispersal (Figure 2). The result showed that G. papuana FGP value is 25%. Meanwhile, its FDG, LDG, and TSG values were 20, 117, and 97 days respectively ( indicates the time difference between fast and slow germination seed within the seed population (Kader 2005). Several factors might cause G. papuana low FGP value acquired from this study. The presence of hard seed coat induced dormancy can be considered as one of the factors as Briggs et al. (2005) recorded that three types of seed coat induced dormancy potentially occurred in three Grevillea species. As seed anatomical study was not conducted in this study, we can not suggest that a hard seed coat is present in G. papuana. However, Priyono et al. (2002) reported that a hard seed coat does present in G. papuana seed. The presence of hard seed coats probably caused the low germination of G. papuana seed as research by , , Baker et al. (2005), Guo et al. (2012), and Ma et al. (2015) stated that seed coat removal was able to increase Grevillea spp. germination rate.
Although a study by von Richter et al. (2001) suggested that fire-related cues were not required to produce a high germination rate in G. kennedyana. Studies by , Kenny (2000), Briggs and Morris (2008), and Guo et al. (2012), reported that fire-related cues such as smoke, temperature, and heat could improve the germination rate of some Grevillea species. Heat and smoke may also alleviate seed coat-induced dormancy in G. juniperina (Briggs et al. 2016). Thus, as there seems to be a various factor contributing to Grevillea low germination rate, further research needs to be conducted to understand the factor that contributes to the low FGP value of G. papuana.
Grevillea papuana FDG value acquired from this study is lower than G. papuana FDG value previously reported by Priyono et al. (2002) and Kuswantoro and Solihah (2016). G. papuana FDG value acquired from this study is comparable with the FDG value of another New Guinea highland plant species, Pittosporum spicessens, which was 19-21 days (Satyanti et al. 2015). Following the Annonaceae germination standard mentioned in Handayani (2019), based on its FDG value acquired from this study, G. papuana was grouped into fast germinated plant species. However, this study also reported a high TSG value in G. papuana germination, indicating low germination uniformity in its seed population. The low germination uniformity indicated low seed population quality, as Egli et al. (2010) suggested that germination uniformity is related to the seed population vigor.
Observation of G. papuana germination in this study revealed that the species seed germination is epigeal. At the same time, the species seedling functional type is Phanerocotylar Epigeal Foliaceus (PEF). According to Tjitrosoepomo (2009), epigeal germination is a type of germination in which, during the germination period, the cotyledon is elevated from the germination media. Phanerocotylar is defined by Ibarra-Manriquez et al. (2001) and Rifai (2004) as a condition in which the cotyledon is exposed during the germination period. Meanwhile, Ibarra-Manriquez et al. (2001) and Pérez-Harguindeguy et al. (2016) defined foliaceus as a condition in which the cotyledon shape and primary function are reassembling the shape and function of a leaf as a photosynthesis organ. The illustration of the G. papuana germination process observed during this study is presented in

Parameter Value
Final germination percentage (FGP) 25%  Figure 3. During this study, G. papuana cotyledon is observed as a pair of thin, leaf-like organs with green color. The thin and green cotyledon suggests that its primary function is as a photosynthetic organ. Satyanti et al. (2009) also supported this statement, suggested that phanerocotylar cotyledon is a photosynthetic cotyledon. These conditions supported our suggestion that G. papuana exhibit PEF seedling functional type. Ibarra-Manriquez et al. (2001) report that PEF is the dominant seedling functional type in non-animal mediated seed dispersal plant species. The statement corresponded with this study result, which indicated that G. papuana has a wind-dispersed seed. G. leucopteris is another Grevillea species with a wind-dispersed seed (Lamont 1982). Ibarra-Manriquez et al. (2001) and Ressel et al. (2004) also stated that PEF is the dominant seedling functional type in pioneer species. PEF seedling functional type observed in this study suggests that G. papuana might also be a pioneer species. A study by Purwanto (2003) supports this suggestion, as they report G. papuana as one of the species that dominated secondary forest in Baliem Valley, Jayawijaya. This study finding further highlighted the seed biology study potency to provide information regarding plant species adaptation strategies, which important for the plant species conservation effort. In conclusion, this study record G. papuana light, elliptic and winged seed exhibited low and ununiform germination with epigeal germination type and Phanerocotylar Epigeal Foliaceus (PEF) seedling functional type.

AUTHORS CONTRIBUTION
F.K. contributes to seed collection, conducting trials, data collection and analysis, and manuscript writing.