Xanthosoma sagittifolium

Common names for X. sagittifolium include tannia, new cocoyam, '''arrowleaf elephant's ear, American taro, , ''', Cultivars with purple stems or leaves are also variously called blue taro, purplestem taro, purplestem tannia, and purple elephant's ear. == Ecology ==

Diseases Root rot is the most important disease in tannia. The oomycete Pythium myriotylum is probably the main causal agent of the root rot disease. Other organisms that could be involved are Phytopthora ssp., Fusarium ssp., Penicillium ssp., Botrydioplodia ssp., Erwinia ssp. and Pseudomonas ssp. Symptoms are stunted growth, wilting, chlorotic and withered leaves and a poor root system. The disease leads to low yields or even complete crop failure. The disease spreads through soil and planting material. The pathogens can persist for a long time in the soil, often forcing farmers to give up planting tannia in infected fields for at least five years. Wetland, floodings and poorly drained soils are associated with the appearance of root rot disease. As long as the field is not yet infected, the best method to control the disease is to use disease-free planting material. Further cultural control methods are general strengthening of plant health, drainage, crop rotation and planting on ridges. There are cultivars that are less susceptible to root rot, but none of them are resistant. Various fungicides are effective in case of infection. Taro leaf blight, caused by Phytophthora colocasiae, is not a problem in tannia. Some varieties of tannia even seem to be resistant against it. By contrast, in taro (Colocasia esculenta), a related and similar-looking crop plant, this is a major disease problem. == Cultivation ==

Climate requirements Although its exact native range is uncertain, the plant is now widely cultivated in the American tropics. This cultivation is not only for ornamental purposes but also, both privately and commercially, for its edible parts. Xanthosoma sagittifolium is an adaptable plant that grows optimally in warm and humid conditions and temperatures above 25 degrees Celsius. At lower temperatures and in arid climates, the development of the plant is hindered. For proper development, the plant needs rainfall evenly distributed throughout the year. It is noteworthy that tannia is one of the most shade-tolerant plants, which allows successful cultivation in traditional Agroforestry systems and facilitates intercropping with perennial crops such as bananas, cocoas or oil palms. The optimal soil conditions for the plant to thrive are well-drained, loamy soils with a pH between 5.5 and 6.5. During this time, it produces a large stem called a corm, which is surrounded by smaller edible cormels about the size of potatoes. Harvesting these edible aroids typically occurs when the leaves start to turn yellow. During the growth cycle, a plant typically produces approximately 40-50 leaves, which are usually harvested within a 40-50 day period. Mature cormels can be harvested continuously over an extended period of time, often exceeding 500 days, while the primary mother plant remains in the ground to produce a new crop. Harvesting is commonly carried out manually or with semi-mechanized equipment. After harvesting, the corms are cured to slow down the rate of physiological and pathological decay of the tuber, which would result in loss of quality. Further losses may occur due to the short shelf life of the tubers. Also storage at ambient temperatures poses a challenge. == Nutrition ==

Tannia is an important source of starch in many African countries such as Ethiopia. Its tubers contain approximately 85% carbohydrates in dry matter. Furthermore, the protein content amounts to 10% – a benefit for the resource-poor farmers by whom Tannia is mainly consumed. The plant is also rich in vitamin A and vitamin C and a good source of potassium, calcium and other minerals. However, the presence of calcium oxalate must be considered, a compound known to irritate mucous membranes, resulting in crystalline deposits commonly referred to as crystal sand. Consumption of these corms can lead to a scratchy sensation in the mouth and throat. To mitigate this effect, the corms need to be boiled before consumption, as this process allows the substances to dissolve in the cooking water, making the corms safe to eat. == Uses ==

Culinary Tannia is a versatile crop with both its corm and leaves suitable for human consumption. The corms can be categorized into smaller secondary corms and main corms. Secondary corms are primarily used in various culinary applications, in similar ways as potatoes. They can be boiled, fried, roasted, steamed, baked, or ground into flour. The leaves of the tannia plant find common culinary use as a leafy green, similar to spinach. In contrast, primary corms are typically designated for animal feed rather than human consumption because of the higher amount of oxalates. A big problem of tannia is the low storability because of the high moisture content of the corms and cormels. Processing the tubers into flour could increase the storability of the crop and could increase the added value. Local farmers then would be able to sell their crop for a higher price, which could then help the local community. Chicken feed Studies have shown that it is possible to replace up to 45% of the maize grain in chicken feed with tannia corm meal (TCM). This could be useful for farmers since chicken feed which consists of maize grains is very expensive - especially in poorer countries. At the beginning of their growing phase, chickens fed with TCM consume significantly more because TCM reduces the nutrient uptake and weight gain. Later in the growing stage, this effect diminishes and in the end, there is no difference in the weight of chickens fed with TCM in comparison to chickens fed entirely with maize grains. Other uses Tannia is used by some populations as a medicine against tarantula, scorpion and snake bites. and bowel cancer. Another study has shown that tannia can stop the cell cycle and force apoptosis in a cancer cell. Cocoa trees can grow in direct sunlight, but in some climates, the intense light in the afternoon can damage the leaves. Tannia has many leaves which makes it a good candidate for a cover crop that can protect the cocoa plant from direct sunlight. Another advantage of Tannia is that it can grow in many different climates and therefore would be suitable for many different countries. Tannia could also be used to make food preservatives (lactic acid), energy bars, chips and crisps, additives in beverages, sauce thickeners, purees, and sauces. There is also a possibility of using tannia to make ethanol for biofuel because of the high starch content and the high yield. ==References==