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Tubers and Yams Crops – Local Solutions to Global Food Issues

Root and tuber crops, often overlooked on a global scale, are the unsung heroes of agriculture, playing a vital role in meeting the dietary needs of impoverished communities worldwide. Let’s delve into the intricate tapestry of these tubers, exploring their nutritional significance, medicinal applications, and the challenges they face in a rapidly modernizing world.

Table of Contents

Diversity Blooms Globally

sweet potato (yam) on white background
Sweet potato

Around the world, root and tuber crops contribute significantly to plant genetic resources, showcasing a rich biodiversity that extends beyond borders. However, this diversity faces a global threat as traditional knowledge rapidly erodes, especially among younger generations disinterested in learning from their elders.

The Nutritional Powerhouse

Root and tuber crops, with their high caloric value and carbohydrate content, serve as a nutritional powerhouse on a global scale. These low-maintenance crops exhibit resilience in the face of extreme weather conditions, contributing significantly to worldwide food security.

Medicinal and Industrial Applications

Certain tuberous species go beyond culinary use, offering global medicinal and industrial applications. The dual-purpose significance of plants like Tacca leontopetaloides and Dioscorea glabra emphasizes the intertwined relationship between nature and the livelihoods of communities worldwide.

Wild Edible Tuber Species

Globally, wild edible tuber species hold a significant place in the dietary habits of small farm families and communities, especially during periods of food scarcity. The versatility of tubers in providing sustenance, even in challenging conditions, emphasizes their importance as a reliable food source worldwide.

Preserving Tradition in the Face of Modernization

The traditional knowledge of tubers faces a grave threat from modernization on a global scale. As younger generations shift focus, important ethnobotanical information is at risk of being lost without proper documentation. Over 56 tuberous plants distributed in 35 genera are commonly used, with families like Dioscoreaceae taking the lead worldwide.

Ethnobotanical Insights

Exploring ethnobotanical information reveals that Dioscoreaceae, Zingiberaceae, Araceae, and Convulvulaceae are prominent families in tuber usage globally. Shrubs constitute 39% of the utilized sources for medicines, followed by climbers (32%), herbs (25%), and creepers (4%). The most common preparation methods include paste, juice, and powder forms.

Indigenous Tubers

Communities worldwide consume a variety of tubers, including Alu (Potato), Saru (Taro / Colocasia), Olua (Elephant foot), Mati Alu / Khamba Alu (Yam), Kandamula (Sweet Potato), Katha Kanda (Cassava), Palua (Arrowroot), and more. In 2020, global yam production reached 75 million metric tons, emphasizing the global significance of these crops.

Detoxification of Wild Tubers

Yams
Yam

Indigenous people possess a wealth of knowledge about the detoxification of wild tubers before consumption globally. Dioscorea bulbifera, Dioscorea hispida, and Urginea indica are among the tubers subjected to detoxification processes. The most commonly used tuber, Ipomoea batatas (Sweet Potato), undergoes specific detoxification to eliminate dioscorine, a water-soluble toxicant.

Indigenous Detoxification Practices

The detoxification process involves leaching out toxins by boiling, peeling, slicing, and steeping in running water, preferably salted. This meticulous process takes about three days, ensuring the removal of dioscorine. Indigenous communities also employ alternative methods like steeping in hot water, burying in black cotton soil, or using tamarind pods and desert dates as detoxifiers.

Use Value of Important Plants

Certain tuber species, such as Dioscorea oppositifolia, hold high use value globally. The seeds of these plants, sometimes containing toxic components, undergo a detoxification process involving steeping for three to four days. The slices of tubers are dried, detoxified, and pounded into a powder, used to prepare porridge or unleavened bread.

Tubers as Guardians of Tradition and Nutrition

The rich diversity of tubers globally not only sustains communities but also weaves a cultural tapestry that is under threat. As we witness the erosion of traditional knowledge, urgent steps must be taken to document and preserve the invaluable information embedded in the practices of indigenous communities worldwide. Tubers, with their nutritional and cultural significance, stand as guardians of tradition, nutrition, and resilience on a global scale.

Conservation and Promotion of Tuber Crops

In the face of extreme climatic conditions and dwindling paddy production, indigenous communities are turning to innovative agricultural practices, particularly intercropping and crop rotation, to secure supplementary food sources. The shift towards cultivating tuber crops has emerged as a strategic response to climate variability and the economic challenges posed by low-profitability paddy cultivation.

Climate Variability and Its Impact

Indigenous communities are grappling with the consequences of climate change, which has a significant role in the growth and production of paddy. The erratic weather patterns and extreme climatic conditions have led to a decrease in paddy production, compelling indigenous farmers to explore alternative crops that are more resilient and economically viable.

Shifting Landscape: From Paddy to Tubers

Driven by the need for sustainable agricultural practices, many farmers are shifting their focus from paddy cultivation to tuber crops. The cultivation of tuber crops, such as sweet potatoes, yams, and cassava, serves a dual purpose—meeting the staple food needs of the community and contributing to economic sustainability through cash crops.

Intercropping and Crop Rotation

Indigenous communities have adopted a multifaceted approach to farming, incorporating intercropping and crop rotation into their agricultural practices. Tuber crops are often intercropped with other crops like brinjal, amaranthus (Saag), and maize, creating a diversified and resilient farming system. Additionally, crop rotation with vegetables such as pumpkins, chili, watermelons, and corn has proven to be a successful strategy.

Profitability and Soil Productivity Boost

Farmers are reporting increased profitability and enhanced soil productivity as a result of intercropping and crop rotation. The synergy between different crops in the same field not only maximizes the use of resources but also minimizes the risk associated with mono-cropping. This sustainable approach is proving to be a win-win for both farmers and the environment.

Motivating Change and Ensuring Food Security

Recognizing the potential of tuber crops in addressing food and nutritional security while diminishing rural poverty, the state government plays a pivotal role. There is a pressing need for the government to prioritize and promote the cultivation and proper storage of tuber crops. Motivational programs led by government agencies like Krishi Vigyan Kendra (KVK) and associated NGOs can significantly influence and guide indigenous communities toward adopting these practices.

Tuber Crops for a Sustainable Future

Geographical location and climatic factors play crucial roles in shaping agricultural practices. The promotion of intercropping and crop rotation, especially through government initiatives, can minimize rural poverty by creating diversified income sources for indigenous communities. Tuber crops, with their adaptability to challenging conditions, hold the promise of ensuring food security and economic sustainability for these communities.

In conclusion, the conservation and promotion of tuber crops signify a transformative shift towards sustainable agriculture. It is not just about adapting to changing climates but also about creating a resilient and profitable farming ecosystem. As the state government takes the lead in motivating and supporting these changes, tuber crops are poised to become the cornerstone of a brighter and more sustainable future for indigenous communities.

Yams: Rooted in Diversity, Sustaining Communities

Yams, the edible tubers derived from various species in the Dioscorea genus, hold a unique position in the culinary and agricultural landscapes. As a staple food in many temperate and tropical regions, particularly in West Africa, South America, the Caribbean, Asia, and Oceania, yams contribute not only to dietary diversity but also play a crucial role in sustainable agriculture.

A Diverse Family of Tubers

Plowed land and potato tubers in box. Agriculture
Plowed land and potato tubers in box

Yam, a common name for select plant species in the Dioscorea genus, encompasses a wide range of edible tubers. However, caution is warranted, as certain species like D. communis can be toxic. There are approximately 870 known yam species, with a few cultivated for their edible tubers. These tubers, often referred to simply as “yams,” come in diverse forms due to numerous cultivars and related species.

Global Significance and Climate Resilience

Yams are resilient crops that can thrive in diverse climates, including degraded soils. They occupy a vital position as the second-largest source of carbohydrates globally, following cereals. Their adaptability to abnormal weather conditions makes them a reliable food source, especially for indigenous communities facing food scarcity during certain periods of the year.

Global Domestication and Indigenous Consumption

Yams have a rich history of independent domestication on three continents—Africa (D. rotundata), Asia (D. alata), and the Americas (D. trifida). Indigenous communities, particularly in Africa, have been consuming tubers and yams collected from forests for generations. While cultivation by indigenous communities is rare, the consumption of these crops remains integral, especially during food-scarce months.

Role in Global Food Supply

Yams hold a prominent place in the world’s food supply, serving not only as a direct source of nutrition but also contributing to processed products for human consumption. The edible starch stored in the underground parts of yam plants, such as roots, stem rhizomes, corm, and tubers, is a valuable resource.

Culinary Diversity and Income Generation

In different regions of India, yams take on diverse culinary roles. In central parts, finely sliced and deep-fried yams are a delicacy. Southern India sees yams as popular accompaniments to rice dishes and curries. The purple yam, D. alata, known as the violet yam, is also cherished. Locally known as “taradi,” yams like D. belophylla and Dioscorea deltoidea are major income sources for indigenous communities.

Global Distribution and Challenges

While yams can be invasive plants and are considered “noxious weeds” outside cultivated areas, 95% of these crops are grown in Africa. The plants can grow up to 15 meters in length and 7.6 to 15.2 centimeters in height, with the tuber potentially reaching depths of 1.5 meters. Despite their challenging exterior, the edible tuber’s softer interior, ranging in color from white or yellow to purple or pink, makes them a versatile ingredient.

Cultivation Techniques and Challenges

Cultivating yams involves planting whole seed tubers or tuber portions into mounds or ridges at the onset of the rainy season. The crop yield is influenced by various factors, including planting methods, mound sizes, spacing, provision of stakes, yam species, and desired tuber sizes. Small-scale farmers often intercrop yams with cereals and vegetables, utilizing up to 30% of their harvest for planting the next year.

Environmental Requirements and Pest Management

Yams thrive in a humid tropical environment, requiring over 1,500 mm of annual rainfall distributed uniformly throughout the growing season. They face challenges from insect pests, fungal and viral diseases, and nematodes. Yam growth and dormant phases align with the wet and dry seasons, respectively. Despite these challenges, yam cultivation remains profitable, driven by high consumer demand in specific African subregions.

In conclusion, yams stand as versatile crops deeply rooted in cultural practices and essential for global food security. Their ability to thrive in diverse climates, coupled with their nutritional significance, positions yams as a key player in sustainable agriculture, contributing to the well-being of communities worldwide.

Diversity of Cultivated Yam Species

Yams, a diverse group of tuberous plants belonging to the Dioscorea genus, have been integral to the culinary and agricultural heritage of various regions. This article delves into the major cultivated yam species, highlighting their significance, characteristics, and global distribution.

D. rotundata and D. cayennensis: The African Staples

D. rotundata, the white yam, and D. cayennensis, the yellow yam, stand as the primary cultivated yams native to Africa. Initially considered distinct species, most taxonomists now treat them as the same. With over 200 varieties cultivated, these yams play a pivotal role in African cuisine. The white yam boasts a cylindrical shape, smooth brown skin, and firm white flesh. In contrast, the yellow yam, with its carotenoid-induced yellow flesh, displays a slightly firmer skin. The Kokoro variety is especially crucial for producing dried yam chips.

Culinary Note: In Africa, these yams often find their way into the traditional dish of “pounded yam,” locally known as Iyan, after 7 to 12 months of growth.

D. alata: The Purple Yam with Global Reach

D. alata, or the purple yam, holds a unique position with its global distribution, cultivated in Southeast Asia, the Pacific islands, Africa, and the West Indies. Recognized by various names like greater yam, ube, and water yam, it differs from the Okinawan purple “yam,” which is a sweet potato. With a cylindrical tuber shape and white, watery flesh, the purple yam has historical significance, having been carried by Austronesian cultures during migrations.

Culinary Note: The popularity of water yam is noteworthy, especially in Africa, where it ranks second only to white yam.

D. polystachya: The Chinese Yam

D. polystachya, or the Chinese yam, hails from China and exhibits adaptability to cooler conditions. Smaller than its African counterparts, this yam has vines of around 3 meters. Introduced to Europe in the 19th century, it is still cultivated in France for the Asian food market. Harvested after approximately 6 months, Chinese yam tubers find uses in various dishes, including noodles and traditional medicines.

Culinary Note: Some Chinese yams are eaten immediately after harvesting, while others become ingredients for diverse culinary creations.

D. bulbifera: The Air Potato with Invasive Traits

D. bulbifera, known as the air potato, spans both Africa and Asia. It is a large vine producing both tubers and bulbils at the base of its leaves. The bulbils, resembling potatoes in size, are a vital food product. Although not commercially favored due to flavor preferences, it remains popular in home gardens. Introduced to Florida in 1905, the air potato has become an invasive species, posing challenges to native vegetation.

Culinary Note: Varieties of air potatoes may require detoxification before consumption, highlighting their versatility and adaptability.

D. esculenta: The Lesser Yam

D. esculenta, the lesser yam, originating from Southeast Asia, is among the earliest cultivated yam species. Despite being the third-most cultivated in Southeast Asia, it sees limited cultivation globally. With vines seldom exceeding 3 meters, its small tubers are baked, boiled, or fried, resembling potatoes in culinary versatility.

Culinary Note: Mechanical cultivation is feasible due to the smaller size of lesser yam tubers, suggesting potential future popularity.

D. trifida: The Cush-Cush Yam

D. trifida, the cush-cush yam, native to the Guyana region of South America, distinguishes itself as the most important cultivated New World yam. Thriving in tropical rainforest conditions, its growth cycle is less tied to seasonal changes, offering potential for increased production.

Culinary Note: Known for its good flavor and ease of cultivation, the cush-cush yam holds promise for broader cultivation.

Wild Taxa and Lesser-Known Yam Varieties

Several wild taxa and lesser-known yam varieties contribute to the rich tapestry of yam diversity globally. D. hirtiflora subsp. pedicellata in Tropical Africa, known as lusala or lwidi, plays a vital role in the diets and incomes of rural households in Southern Zambia. Another notable variety, D. japonica, the East Asian mountain yam, native to Japan, Korea, China, Taiwan, and Assam, is used for food, with related varieties like jinenjo finding use in soba noodles.

In conclusion, the cultivation and diversity of yam species reflect not only their culinary importance but also their adaptability to various climates and conditions. From African staples to globally distributed varieties, yams continue to be a source of sustenance and cultural significance.

Harvesting: A Labor of Love and Precision

In West Africa, the art of harvesting yams is a testament to the intimate connection between farmers and the land. Typically done by hand using sticks, spades, or diggers, this process is labor-intensive and physically demanding. Wooden tools, favored for their gentleness on the delicate tubers, require frequent replacement.

Harvesting involves a range of movements—standing, bending, squatting, and sometimes sitting on the ground, depending on factors like mound size and tuber depth. Care is paramount to prevent damage, as injured tubers do not store well and spoil rapidly. Some farmers incorporate staking and mixed cropping, adding complexity to the harvesting task.

In forested areas, where yams share space with other tree roots, freeing the tubers from entwined roots becomes an additional challenge. Manual plucking of aerial tubers or bulbils from the vine further adds to the meticulousness required in harvesting. While mechanization could potentially improve yields and reduce costs, the current crop production practices and species used present significant hurdles, particularly for small-scale rural farmers. Successful mechanization would necessitate substantial changes in traditional cultivation practices.

Storage: Preserving Freshness in Nature’s Pantry

Many potato tubers lie on the loose soil after the harvesting process.
Many potato tubers lie on the loose soil after the harvesting process.

Roots and tubers, living organisms even in storage, continue to respire, leading to starch oxidation. Yam, considered among the least perishable, requires careful attention during storage. Successful storage involves several key practices:

  1. Initial Selection: Choose sound and healthy yams for storage.
  2. Curing: Properly cure yams, ideally combined with fungicide treatment.
  3. Ventilation: Ensure adequate ventilation to remove heat generated by tuber respiration.
  4. Regular Inspection: Regularly inspect stored yams, removing any rotting tubers and sprouts.
  5. Protection: Shield yams from direct sunlight and rain.

While lower temperatures reduce respiration rates, temperatures below 12 °C can cause chilling damage, breaking down internal tissues and increasing susceptibility to decay. The optimal storage temperature for yams is between 14 and 16 °C, with controlled humidity and climatic conditions, following a curing process. In many yam-growing countries, high-technology storage systems are often impractical due to economic constraints.

Certain yam cultivars store better than others. Those adapted to arid climates exhibit longer dormancy periods, preserving their quality. Varieties like yellow yam and cush-cush yam have shorter dormancy periods than water yam, white yam, or lesser yam. Storage losses in Africa are high, primarily due to bacteria, insects, nematodes, and mammals, posing persistent challenges to preserving this vital food source.

In essence, the harvesting and storage of yams are delicate processes that bridge traditional wisdom with modern challenges, ensuring that the bounty of nature remains a source of sustenance for communities worldwide.

Nutrition Beyond the Surface

Raw yams, often underrated in nutrient density, unveil a trove of essential elements for a balanced diet. Boasting notable quantities of potassium, vitamin B6, manganese, thiamin, dietary fiber, and vitamin C, yams are nutritional powerhouses. With 118 calories per 100 grams, they stand out as a significant dietary contributor. Surprisingly, yams top the charts for potassium levels among the world’s major staple foods, offering a commendable 10% or more of the Daily Value.

Yams also carve a unique niche in the glycemic index landscape. With a lower index (54% of glucose per 150-gram serving) compared to potato products, they present a favorable option for those mindful of blood sugar levels.

Protein Profile and Dietary Nuances

Roots and tubers, including yams, generally exhibit lower protein content and quality compared to other staples. Yams and potatoes, with approximately 2% protein on a fresh-weight basis, play a pivotal role alongside cassava in protein intake. However, as a relatively low-protein food, yams lack essential amino acids, underscoring the importance of supplementing a yam-centric diet with protein-rich foods for optimal growth, especially in children.

Yams: Dietary Backbone for Communities

In the undivided KBK region, yams emerge as more than just a dietary element. Contributing over 200 calories per person per day to a staggering 300 million people between 2006 and 2010, yams become a vital source of sustenance and income. Cultivated in poor farms with limited resources, yams, rich in starch, offer versatility in preparation, availability year-round, and cultural significance. These attributes collectively elevate yams to a preferred food and a crucial food security crop.

Medicinal Marvels

Beyond culinary applications, yams find a place in traditional medicine. Tubers are employed in treating piles, amenorrhea, indigestion, anorexia, joint pain, and even elephantiasis, showcasing their multifaceted contributions to well-being.

Health Properties

The health benefits of yams extend beyond basic nutrition:

  1. Rich in Minerals: Offering high percentages of daily fiber, potassium, and manganese, yams support bone health, heart health, growth, and metabolism.
  2. Immune Booster: Copper and vitamin C in yams contribute to blood health, healthy iron absorption, red blood cell production, and overall immune system strength.
  3. Digestive Support: Resistant starches in elephant foot yams act like soluble fibers, promoting gut health and increasing digestive enzymes.
  4. Cholesterol Control: Special soluble fiber in yams assists in managing cholesterol levels by binding and removing it from the body.
  5. Anti-Cancer Properties: Antioxidants present in yams may help prevent cancer, providing an additional layer of protection.
  6. Anti-Inflammatory Benefits: Rich in anti-inflammatory antioxidants, yams may help alleviate chronic inflammation associated with various health conditions.
  7. Heart Health: By regulating sodium levels, yams contribute to heart health, reducing the risk of hypertension, heart attack, and stroke.
  8. Skin and Hair Care: Antioxidants aid in cell regeneration, fighting free radicals, and promoting skin health, while collagen and vitamin C contribute to healing and anti-aging.
  9. Weight Management: Glucomannan, a beneficial fiber in yam roots, may aid in weight loss by creating a gel in the stomach, promoting a feeling of fullness and reducing cravings.

In essence, yams offer not just sustenance but a myriad of health benefits, embodying nature’s gift to both the plate and well-being.

Ravi S. Behera
Ravi S. Behera
Mr. Ravi Shankar Behera, PGDAEM, National Institute of Agricultural Extension Management (MANAGE), Hyderabad is an independent freelance Consultant and Author based in Bhubaneswar. He is an Honorary Advisor to grassroots Voluntary Organizations on Food Security, Forest and Environment, Natural Resource Management, Climate Change and Social Development issues. Ravi has lived and worked in various states of India and was associated with international donors and NGOs over the last twenty three years including ActionAid, DanChurchAid, Embassy of Sweden/Sida, Aide et Action, Sightsavers, UNICEF, Agragamee, DAPTA and Practical Action. He has a keen interest in indigenous communities and food policy issues.
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