Edible canna, belonging to genus canna (Cannceae), is cultivated largely in South America, Vietnam, Thailand and China (Puncha-arnon et al., 2007).
Edible canna originated in Peru, South America. Today, edible canna is widely grown in tropical and subtropical countries around the world. South America is a diverse center of canna, but Asia, Australia and Africa are the largest growers and users (Hermann et al., 1997) . There are two types of edible canna which include ‘green’ and ‘purple’ (Kay, 1987).
This crop is typically cultivated in subtropical highland, at an altitude of 1,000-2,500m, mainly in China and Vietnam, with the variable rhizome production (150,000-2,584,000 tonnes of rhizomes per year) (Piyachomkwan et al., 2002).
2.1.2. Scientific Classification of Edible Canna Edible canna (Canna edulis Ker-Gawl) Class: Liliopsida
Order: Zingiberales Family: Cannaceae Gennus: Canna L.
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About genus of edible canna: Edible canna has two types which includes diploid (2n = 18) and triploid (2n = 27) with a number of chromosomes is 9 (Kubitzki, 1998). According to Imai (2008) and Hermann et al. (1997), the edible canna cultivated in Vietnam and other Southeast Asia countries is a triploid species and it is closest to Columbian triploid based on the result of DNA analysis.
2.1.3. Some Characteristics of Edible Canna
Edible canna is cultivated in a small scale in subtropical and tropical regions of the world without intensive improvement. It is probably one of the first plants to have been domesticated in the Andean region. It has been suggested that the wild type was domesticated in mountainous areas from Columbia to Ecuador and rapidly transmitted through the Andean region into the west coast and northern Chili (Imai, 2008).
Edible canna can grows up to 3m at the late growth stage. Edible canna has a flower cluster (compound inflorescence) above the terminal leaf. As for floral differentiation, Roth and Lindorf (2013) described that the genus canna is neutral to day length. The leaves are large and thick with a layer of water storage cells (hypodermal cells) beneath the adaxial and abaxial epidermal cells. These cells are thought to be adapted to savanna conditions (Gade, 1966) and in fact, edible canna is relatively drought tolerant caused by hypodermal cells to shrink under a low soil-water level (10% water holding capacity) (Brück et al., 2001).
Edible canna is grown in all mountainous provinces and also in some low- lying areas. According to official estimates, some 20,000ha of canna are cropped in northern Vietnam. In the northern Vietnam, canna is cropped principally in the highlands (300-1,200m). Canna's season requirement is very strict, beginning at the onset of rains and lasting for 10-12 months. Propagation is by apical rhizome sections that are either immediately replanted or stored for 2-3 months to allow for staggered harvesting (Hermann et al., 1997).
10 The botanical characteristics of edible canna
Edible canna is a standing plant, 1.2 to 1.5m high, purple. Body underground bulge bulb, contains more starch. The bulb lies just below the ground. Leaves oblong, 50-60cm long, 25-30cm wide with large midribs.
Duration growth of edible canna is from 10-12 months: the first month (when the tree is growing) is the period of seedlings; the next 5 months are the full tillers of leafy foliage; the last 4 to 5 months is the bulb period, accumulation of starch. After 12 months, when the bulbs are germinated, the starch contents in the main bulbs will decrease.
The Stem: The stem of the edible canna is erect with height about 300cm or more at flowering stage and branched underground. The single leaves are attached to the stem with a short petiole. Edible canna has a flower cluster (compound inflorescence) above the terminal leaf.
The leaf: Leaves of edible canna include leaf blade and petiole with leaf margin at the base, leaf of canna longitudinal line, top surface of leaves are green or green-purple, green or purple underparts. Leaves are about 35-60cm long and 22-25cm wide. Around the edge of the leaf is bordered by a thin line of purple red or white in color; leaf blade has a large midrib, parallel tendon, green or red-purple; the petiole leaves are about 8-15cm long.
Roots and rhizomes: Edible canna has fibrous roots which are typical to monocotyledons. The root system is comprised of thick adventitious roots and thinner primary and secondary lateral roots. The adventitious roots generate in pairs simultaneously near the nodes of rhizomes. The ‘horizontal roots’ running shallow underground and the ‘vertical roots’ growing deep in the soil are clearly distinguished. The roots generated from the basal and apical side of the nodes of the rhizomes tend to develop into ‘vertical roots’ and ‘horizontal roots’, respectively. The ‘vertical roots’, especially those near the rhizome, have superior tissue structure and physical characteristics compared with the
‘horizontal roots’.
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Figure 2. Adventitious roots which generate in pairs (right) from the rhizome and a part of root (left) (Imai, 2008)
Flower: The flower length of edible canna is about 7 to 9cm, with 3 calyxes, 3 lanceolate petals, 3 staminodia and 1 anther. Staminodia are coloured bright red or orange, with the anther pale yellow and 1cm in length, shedding many pollen grains when it ruptures. There is one pistil with a broad, flat yellow style and stigma connected with an inferior ovary at the bottom.
The ovary wall is dotted, pale green, with 3 loculi containing many ovules and axile placentation. Single flowers bear a membranous bract, waxed on the surface. In the case of two flowers, the first flower (with longer pedicel is bractless), and the second flower (with short pedicel) has two bracts. Flowering within a raceme will begin from the basal one and continuing acropetal. When two flowers are present together, the first flower will also open first. The flower is highly sterile, and as the result, no fertile seed can be obtained (Lai and Tsai, 1989).
2.1.4. The Nutritional Value and Pharmaceutical Activities of Edible Canna
As a statement of Zhang and Wang (2013), the dry rhizome of edible canna contained the starches of 70 to 80% and it found to be more digestible than other kinds of starches. In addition, the phytochemical analysis of edible canna revealed that it contained many different nutritional components such as: crude
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protein: 6.34 ± 0.21g/100g, crude lipid: 4.31 ± 0.11g/100g, crude fiber: 5.78 ± 0.08 g/100g, and calorific value: 1611.54 kJ100g-1DM (Al-Snafi, 2015; Mohan and Kalidass, 2010). With a high amount of fiber in the by-product of edible canna, it was considered as a good source for the production of soluble dietary fiber of obesity, diabetes, cardiovascular patients (Zhang and Wang, 2013).
Moreover, in Vietnam, edible canna is used in traditional Vietnamese medicine: leaf was used to clear ulcers and rheumatism and as a diuretic.
Rhizome was used as a diuretic and demulcent, and treatment of heart-related disease and acute hepatitis. Canna edulis rhizome extracts have been viewed to be a source of natural antioxidants as it contains a high amount of polyphenolic compounds (Mishra et al., 2011). In another study, DPPH radical scavenging activity has been determined with IC50 of 658àg/ml fresh weight basis, and maximum NO scavenging activity and hydroxyl radical inhibition activity were observed in bioactive diethyl ether: ethyl acetate (1:1) fraction (Mishra et al., 2012). Lignin isolated from Canna edulis Ker residue exhibited strong inhibition on α-D-glucosidate than acarbose with IC50 of 5.3±0.3 àM, which provides evidence that edible canna can be used for treactivitiesatment of type 2 diabetes (Xie et al., 2017).
2.1.5. Economic Benefits of Edible Canna
Edible canna is an easy-to-cultivate crop and high yield. It is mostly cropped in Backan province, Vietnam. The growing areas in this province were estimated to be 1.040 ha with production over 71.000 tons, edible canna starch noodle production over 20.000 tons. 1 kg of edible canna starch noodle traded from 3 US$ (normal quality) to 5 US$ (best quality). Therefore, edible canna is of commercial value and can provide an applicable cash income to small and poor villagers (Tanaka, 1998). Although edible canna is considered as an agriculture food crop to reduce poverty and ensure food security, it also is facing many difficulties and challenges, especially the management of product quality and branding.
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2.1.6. Summary of Studies about Edible Canna
Although edible canna rhizomes were considered as a source of commercial starch, the researches about it have not received much attention from the scientist (Tanaka, 2004). The research about edible canna are mainly focused on analyzing characteristics, molecular structure and conducted by many authors. According to Piyachomkwan et al. (2002), edible canna as an alternative starch source was evaluated on the basis of genetic characteristics, agronomic and starch properties. The finding of this research also revealed that starch yields of edible canna were lower than cassava. However, edible canna provides starches with very attractive properties and totally different from cassava and it was also considered as a new starch source to alternate cassava starch.
Thitipraphunkul et al. (2003) studied about the starch from different edible canna. The results indicated that the absolute amylose content ranged from 19 to 25% and the amylopectin of edible canna starches contained high amount of organic phosphorus, from 391 to 420 ppm.
However, Using starch from the fresh tuber of edible canna to produce ethanol was conducted by Huang et al. (2013). The findings revealed that edible canna contained reasonable P, K+, Ca2+, and Mg2+ content and a nitrogen source containing organic and inorganic nitrogen in the fresh tuber of edible canna was widely used to ameliorate nitrogen deficiencies in ethanol fermentation.
Starch of edible canna is mostly used for traditional food in the Southeast Asia regions (Wandee et al., 2015). The study of Wandee et al. (2015) about the quality of edible canna noodles showed the potential of using canna starch and its derivatives to improve the qualities of rice noodles.
Hermann (1996) denoted that canna noodles in Vietnam have excellent eating quality, much superior to extrusion noodles made experimentally from
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sweet potato and cassava starches which are widely available in Southeast Asia. The high amylose content (25% to 30%) of edible canna starches as compared with other root starches. Moreover, the findings of this study showed that canna processing in Vietnam can provide employment to many thousands of people in rural communities with as little as 500m2 of arable land per capita and improve income for local people in mountainous.
Furthermore, Tanaka (1998) showed the economic botanical notes of edible canna in the South of Vietnam. The results indicated that edible canna production had a vital role in the life of local people. The local people used it for traditional food and starch extracted from rhizomes of edible canna was used to produce noodle which was sold in the market.
2.1.7. Edible Canna Production in Backan Province
In Vietnam, edible canna is being planted in many regions such as Caobang, Backan, Tuyenquang, Hagiang, Quangninh, Sonla,…, and it is considered as economic crop of local people in the North of Vietnam. The average area planted by edible canna is around 30,000 ha per year and annual output is about 1.8 million tons of fresh bulbs (Son, 2013).
Edible canna is a plant suitable for local conditions and bring high economic efficiency for local people in Backan. In recent years, Backan province has focused on strategies to promote the edible canna production to increase income, economic development and poverty reduction. The strategy of Backan was shown in Decision No.2094, date issued 21/12/2016 about production, processing and consumption edible canna during 2015-2025 and toward to 2030 (BK, 2016).
The area and productivity of edible canna in Backan were presented in the Table 2.1.
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Table 2.1. Area and productivity of edible canna production in Backan province during 2016-2018
Source: Statistical data (BKSO, 2019; GSO, 2018)
Table 2.1 showed that edible canna cultivation in Backan province remains small size and disperse. During the period from 2016-2018, the area and productivity of edible canna were the highest in mountainous Nari district (with 500 ha and approximately 36.89 thous. tons in 2018). It was followed by Babe (with 366 ha and 24.70 thous.tons), Bachthong (4.83 thous. tons) and Chomoi (2.70 thous. tons) in 2018 (BKSO, 2019). In contrast, other districts such as Nganson, Pacnam, Chodon and Backan city, the area and productivity of edible canna are quite low.
It is clearly that there is an increasing trend in both productivity and yield of edible canna in Backan province in the period from 2014 to 2018. Edible canna production increased from 51.573 thousand tons in 2014 to 72.88 thousand tons in 2018, and the edible canna yield increased from 68.04 tons/ha (2014) to 70.04 tons/ha (2018) (BKSO, 2019; GSO, 2018).
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The growth of edible canna production and edible canna yield over the 5 years period was represented in Figure 3 as follows:
Figure 3. Edible canna production in Backan province, 2014-2018 Source: Statistic data (BKSO, 2019; GSO, 2018)