Good agricultural practices for seed potato production in Rwanda Published by: International Potato Center (CIP) Registered offices: Avenida La Molina 1895, La Molina, Apartado Postal 1558, Lima, Peru E cip@cgiar.org I cipotato.org Correct citation: CIP (2022). Good agricultural practices for seed potato production in Rwanda • Visual Aid. International Potato Center (CIP), Lima, Peru. Acknowledgements: This manual was developed through a collaboration between the International Potato Center (CIP), Rwanda Agriculture and Animal Resources Development Board (RAB) and Agriterra. This manual is published as derivative work of the manual ‘Good Agricultural Practices for Ware Potato Production in Cameroon – Trainer guide’ published by the German Federal Ministry for Economic Cooperation and Development (BMZ) and available at https://hdl.handle.net/10568/108468 under Creative Commons Attribution 4.0 International license (CC BY 4.0). We acknowledge the contribution of representatives from Imbaraga Farmers Organisation, Delphy, SPF-Ikigega, Rwandan Potato Stakeholders Platform, INES-Ruhengeri, UR-CAVM, Horizon-Sopyrwa, Musanze District, Holland Greentech, Hollanda Fair Foods, HoReCo Rwanda, Potato Unions in Musanze, Nyabihu and Rubavu Districts and CODEPO Potato Farmers Cooperatives supported by Agriterra in Rwanda. Funding was provided by Agriterra and the Bill and Melinda Gates Foundation through Excellence in Agronomy 2030 (Incubation Phase). Place and date of publication: Kigali / March 2022 1 The seed potato value chain in Rwanda 1 The seed potato value chain in Rwanda The use of quality seed potatoes is one of the most important yield-determining factors in potato production. Seed potato production in Rwanda comprises different stages: (1) production of in-vitro plants in a tissue culture laboratory, (2) production of minitubers or stem cuttings in screenhouses, (3) production of the third and fourth generation under field conditions (pre-basic and basic seeds), (4) further multiplication in the field to generate certified seeds. Why are quality seed potatoes Seed production is a very technical and intensive operation. A seed potato grower needed in potato production? in Rwanda must be officially registered and fulfil several criteria. What needs to be done to Quality seeds need to be clearly separated from ware potatoes through branding, separate quality seed potatoes labelling, and creating a separate seed value chain. from ware potatoes? Trust between seed producers and buyers is very important for developing a local What are the benefits of local seed business enterprise. multiplication? The use of quality seeds is one of the most important requirements for high potato yields. 2 Seed tuber characteristics Sprout Vegetative Tuber development growth initiation Tuber bulking Maturation 2 Seed tuber characteristics The life cycle of seed tubers can be divided into four successive phases: dormancy, single sprout, multiple sprouts and senility. Dormancy is the stage immediately after harvest when no sprouts develop. After dormancy, a single sprout with apical dominance starts to develop from the tuber. The apical sprout can be taken off to favour the development of more lateral sprouts. This should be done not more than once. In the third phase, multiple lateral sprouts develop from the seed tuber. During senility, whitish, long and tiny sprouts are formed. These tubers are too old to be planted. What is the ideal size of seed tubers? The right time for planting is when the seed tubers have 3 to 6 short 1-2 cm, strong and coloured sprouts. What are the four stages of the life cycle of a seed tuber? It is important to understand dormancy periods of different varieties to plan planting and harvesting times to ensure seed is ready for timely planting. What is the benefit of taking off the apical sprout? A well sprouted tuber ready for planting has 3 to 6 strong, coloured and short sprouts. 3 Seed quality and certification 3 Seed quality and certification Seed multipliers should build their reputation through continuously producing quality seed to gain trust with the customers. Seed potatoes are of high quality if they are free of pests and diseases, and have a uniform, small to medium size (28-55 mm). Seed multipliers should follow good agricultural practices for seed production to keep their seed potatoes free from any pest or disease. Potato diseases are easily transmitted by contact with infected plants, tubers, farming tools and materials, and operators crossing the field. Tools and shoes/trousers of operators should be changed or disinfected between visits to different fields. How can seed producers gain trust Seed certification in Rwanda is a quality assurance system whereby inspectors from RICA visit the seed producer for official control and inspection during production and with the customers? post-harvest management. What are the charactaeristics of For seed certification, seed inspectors visit the multiplier 4 times during the season, at high-quality seed potatoes? 15 days after planting, at flowering, before harvest, and during storage. What is the procedure for seed certification? High quality seed potatoes are free of pests and diseases and have a uniform, small to medium size of 28-55 mm. 4 Seed stock replacement Season 1 Season 2 Season 3 Sold New Replant Sold Sold New Replant New Season 1 Season 2 Season 3 4 Seed stock replacement Sold New Replant Sold Seed degeneration Sold is an accumulation of pests and/or diseases and physiological disorders in the seed tubers over successive cycles of field New multiplication, causing a reduction in seed quality and yields. Replant To avoid seed degeneration, seed producers must renew their stock of New starter (basic) seeds regularly. Producers of certified seed in Rwanda should not replant seed tubers multiplied from the same stock of basic seeds more than once. Hence, producers of certified seed should multiply a stock of basic seeds for maximally two seasons. New basic seeds and seeds replanted from a past basic seed stock should be planted in different fields. What is seed degeneration? For how many seasons (maximally) Basic seeds should be obtained from registered producers (Rwanda should a certified seed producer Agriculture and Animal Resources Development Board (RAB), Horyzon Sopyrwa, the Institute of Applied Science (INES), or private small-scale multiply seeds from the same basic producers of minitubers and basic seeds). seed stock? Where can basic (starter) seeds be obtained? Local multipliers of certified seed should multiply a new stock of basic seeds for maximally two seasons. 5 Record keeping 5 Record keeping All expenditures and income related to the seed production should be entered in record books. Record keeping is important for a seed producer to monitor expenses and analyse the profitability of seed production. Types of expenditures generally consist of: starter seeds, organic inputs and mineral fertilizer, sacks to package harvest produce, fungicides, insecticides, and labor. Why is record keeping important? What are the types of expenditures in seed production? What is the difference between gross income and net income? Record keeping will allow the seed producer to monitor costs and evaluate whether his/her business is profitable. 6 Land selection and crop rotation 6 Land selection and crop rotation The risk of pests and diseases is lower in fields at higher positions in the landscape. New stocks of starter seed should therefore be grown at the highest position in the landscape, while a later generation can be grown in fields at a lower position. Adequate distance (at least 20 m) between fields with seed and ware potatoes should be maintained, or barrier crops such as Napier grass, maize or other crops that are not sister crops of potato should be planted between seed and ware potato fields. Soil should be deep, well drained and loose for proper development of tubers. To reduce the risk of pests and diseases, select a site where potato or its sister Why is it important to consider the crops (eggplant, pepper, tomato, tobacco) have not been grown for at least the position in the landscape during field last 4 seasons. selection for seed multiplication? Plan a 5-seasons rotation scheme, alternating potato with crops such as maize, Is it advisable to plant seed potatoes wheat, beans, carrots, cabbage, and other legumes. Avoid planting maize before where you have harvested potatoes potato in fields with a history of infestation by nematodes or low soil fertility. or crops of the same family during Continuously remove all volunteer plants sprouted from left-over tubers during the previous season? Why? the rotation. What are the crops of the same family as potato grown in your area? Seed producers should wait at least 4 to 5 seasons before planting again seed potatoes in the same field. 7 Land preparation 30 - 40 cm 7 Land preparation Ploughing can be done using a hoe, animal-drawn plough, motocultivator or tractor-drawn plough. Prepare land until the ground becomes soft, free from clods and dug to a depth of at least 30 cm. Proper seed bed preparation will help to improve the condition of the soil, control weeds and manage diseases. In case of risk of erosion or poor drainage, ridging should be carried out. Where ploughing is done mechanically, avoid the so-called “plough-pan” by varying year after year the ploughing depth. Up to what depth (at least) do you Tools used for land preparation (including tractor accessories) must be need to plough the soil during land cleaned and sanitized before moving from one field to the other. preparation and why? Why is proper land preparation important in seed production? What is the risk of mechanical land preparation in potato production? How can it be avoided? The use of motocultivators or tractors can reduce the burden of land preparation. 30 - 40 cm 8 Application of manure, compost and mineral fertilisers 8 Application of manure, compost and mineral fertilisers Try to get a site-specific fertilizer recommendation based on soil characteristics of the field. In the absence of a site-specific fertilizer recommendation, it is recommended to apply 3 kg NPK 17-17-17 per are (300 kg per hectare), divided in two applications, half at planting and half at first weeding and hilling (1.5 kg per are at planting and 1.5 kg per are at top-dressing). In addition to mineral fertilizer, apply up to 2 handfuls of well-decomposed manure or compost for each seed tuber at planting (200-300 kg of manure or compost per are or 20-30 tonnes per hectare). At planting, apply the manure or compost first, then add the fertilizers, and cover Why is it important to get a with 5-10 cm of soil. Then place the seed potato. site-specific fertilizer recommendation? After emergence, apply fertilizers in a hole at 10-15 cm of the plant base. What are the mineral fertilisers Fertilization with high amounts of N depresses tuber growth and yield and should that are recommended for potato be avoided. in your area? At which dose? What is the risk of applying too much N fertilizer? Planting seed potatoes on a poor soil without manure and mineral fertilisers is a waste of time and resources. 9 Planting techniques Ø: 30 mm Ø: 40 mm Ø: 50 mm Ø: 30 mm Ø: 40 mm Ø: 50 mm 9 Planting techniques Four to six weeks before planting, the main sprout should be taken off to promote the development of more lateral sprouts. Ensure the seed tubers are well sprouted with strong, green and short (1-2cm) sprouts and avoid old tubers with long sprouts. Plant seed tubers of the same size category in one area. Prepare furrows or rows of holes at a spacing of 70-75 cm. Within rows, use a plant spacing of 20 cm when seed tubers are small (around 30 mm), 25 cm when seed tubers are medium sized (around 40 mm), and 30 cm when they are large (around 50 m). What should you do before the start of the season to increase the number Place seed tubers at a depth of 5 to 10 cm in holes or furrows with sprouts facing of seed tubers harvested per plant? upwards before they are covered. What is the optimal plant spacing for On a sloping terrain, furrows or seed holes should run across the slope. seed potato production? How would you arrange plant rows on a sloping terrain? Seed potatoes damaged by pests or diseases should never be used for planting. 10 Weeding and hilling 1st hilling 2nd hilling 30 - 35 cm wide 20 - 25 cm wide 10 - 15 cm 10 - 15 cm 30 cm BEFORE AFTER BEFORE AFTER 10 Weeding and hilling 1st hilling 2nd hilling 30 - 35 cm wide 20 - 25 cm wide 10 - 15 cm 10 - 15 cm 30 cm Weeding reduces competition for light, nutrients and water, and prevents weeds from harboring pests and diseases. First weeding should be done right after plant emergence, when the plants BEFORE AFTER BEFORE AFTER are about 10-15 cm tall. Hilling is mounding earth around the stems of potato plants when they are young. Good hilling leads to a higher number of tubers and protects the tubers from pests and diseases. Why must a potato field remain clean, Two hilling are required for potatoes planted on flat land. Do the first hilling without weeds, until the harvest? at first weeding after plant emergence. Why is it important to hill up Do the second hilling 2-3 weeks later. A third hilling is not recommended for potatoes? seed production as it may result in tubers that are too large. When should potatoes be hilled up? The height of the ridge after 2 hilling should be at least 30-45 cm with an arc of about 90 cm. Proper hilling is very important for increasing the number of tubers, and protecting the seed tubers from pests and diseases. 11 Roguing 1 3 2 4 1 3 11 Roguing 2 4 Roguing (also known as negative selection) consists of regularly inspecting the potato field and removing any abnormal plants. Plants to be rogued are either diseased (e.g., bacterial wilt), off-type plants (resulting from variety mix up), or volunteer plants sprouted from left-over tubers. A seed lot may be rejected for seed certification if roguing is not performed consistently. Start with roguing when plants have reached 20-25 cm of height and continue roguing once a week until the foliage of potato plants closes the rows. Field inspection works well when done early morning, while walking away from the sun for better identification of abnormal plants. Which kind of plants need to Remove diseased plants by uprooting the entire plant along with the soil in which it was be rogued? planted. Plants with soil should be placed in a basket or bag and taken out of the field and How often should roguing buried or burnt into a deep pit. Lime or kitchen ash can be applied in the hole where the be carried out? plant was removed to kill the disease. What should be done with diseased plants? For seed producers, roguing is crucial as their seed lot may be rejected during the certification process if abnormal plants are not eliminated. 12 Control of late blight 12 Control of late blight Late blight damages the leaves, stems and tubers. Infected leaves or stems have grey/brown/black spots as if they were burned. Symptoms also include white fluffy strands at the underside of the leaves. Late blight spreads through wind, water, soil and infected tubers and plant material. Wet conditions are favorable for late blight. Plant clean seeds of less susceptible varieties to avoid late blight in the field. Collect and burn potato foliage after harvest to sanitize the field. A wider plant spacing reduces humidity in the field which can help to reduce late blight. Use contact fungicides (e.g. Mancozeb) to prevent infection and systemic fungicides What are the key symptoms of late (e.g. Ridomil) to treat infection: blight in the field? And what are - Spray a contact fungicide right after plant emergence when the plants are around the key conditions for its outbreak? 10 cm tall. What are the most effective - Spray a systemic fungicide 40-45 days after planting only if there is a lot of rain and measures to control late blight in a lot of late blight in the area. the field? - For subsequent sprays, use contact fungicides at 2-weeks interval, except when What is the difference between a disease symptoms are visible in the field. In that case, use a systemic fungicide. contact and a systemic fungicide? Once disease symptoms have disappeared, return to spraying with a contact fungicide. When using fungicides, always use the dosage that is recommended by the manufacturer. Late blight is the most damaging foliage potato disease. Keeping a Contact fungicides (such as Mancozeb) should be applied at least 6 hours before it rains to avoid the fungicides to be washed away. Systemic fungicides (such as Ridomil) field free of late blight is crucial should be applied at least 3 hours before it rains. The leaves need to be dry before for producing high-quality seeds. spraying (no dew on the leaves). 13 Control of bacterial wilt Contamination 13 Control of bacterial wilt Bacterial wilt causes partial to complete wilting of a plant even if there is enough water in the soil. When an infected tuber is cut in half, black or brown rings can be seen. The disease can spread via infected seed, water, roots, soil, farming tools, livestock and Contamination people. It also affects other crops from the same family such as chili, tomato, tobacco, and eggplant, as well as several weed species. There is no commercial chemical for controlling bacterial wilt. Plant clean seeds of less susceptible varieties in fields free from bacterial wilt. What are the symptoms of bacterial Rotate potato crops with other crops not belonging to the potato family, such as wilt on the plant and the tubers? legumes and cereals. How can you detect bacterial wilt Uproot and destroy wilting plants together with soil around roots. in the field? Do not use compost with plant material from potato or crops from the same family. What are the most effective measures to control bacterial wilt? Clean and/or disinfect farm tools with fire or Jik before and after use. Wash/disinfect hands, shoes and pants between visits to different fields. Put a stake on all the hills where wilted plants were eliminated. Harvest the two neighboring plants separately, and sell or consume the tubers as ware potatoes. There is no commercial chemical to control bacterial wilt. It is difficult to eradicate the disease once present in the soil. 14 Control of soft rot (or blackleg) 14 Control of soft rot (or blackleg) Soft rot, also known as blackleg, alters tuber tissue into liquid or soft rot and causes black lesions at the base of the stem. Infected tubers rot either in field or in storage and produce a bad smell. Manage this disease by applying the same control measures recommended for bacterial wilt (clean seeds, rotation, uprooting of diseased plants and disinfecting farm tools). What is potato soft rot (blackleg) and what are the symptoms? How would you differentiate soft rot (blackleg) from bacterial wilt? What are the most effective measures to control soft rot (blackleg)? There is no commercial chemical to control soft rot (blackleg). It is difficult to eradicate the disease once present in the soil. 15 Control of viral diseases 15 Control of viral diseases Any plant infected with viruses must be eliminated immediately to avoid spread to other plants and transmission to further seed generations. Viral diseases are difficult to recognize in the field. With mild infections, plants can show no signs of disease at all. Moderate to severe infections cause changes in the shape of plants (leaf curling, yellowing of the leaves, bubbling leaves, short and stunted plants). Viral infections lead to smaller potato tubers. Selecting small tubers as seeds for the next season can reduce yields in the next season as these tubers are likely infected! Control the disease by planting clean seeds of less susceptible varieties. How are potato viruses spread? Uproot and destroy infected plants. If in doubt about whether a plant is infected or not, it is better to remove it from the field. What are the most effective measures to control viral diseases? Clean and/or disinfect farm tools with fire or Jik before and after use. Keep the field and surrounding area free of weeds. Why is it important to control insects such as aphids and whiteflies in a Insects such as aphids or whiteflies can spread viral diseases. Insecticides may be used seed multiplication field? to control these insects, but cautiously to avoid harm to the environment and human health. There is no need to know the names of viruses. What is important is to be able to differentiate a normal (healthy looking) plant from a diseased one. 16 Control of potato tuber moth 16 Control of potato tuber moth Potato tuber moths (also called potato tuber worms) infest the crop in the field and move with tubers to the store. Moth larvae create tunnels in the tubers and form mines in leaves and stems. Avoid planting in too light and loose soil as it facilitates exposure of the tubers. Perform high hilling to protect the tubers. Inspect the tubers carefully before and during storage and remove each tuber showing openings/galleries and/or excreta. Use natural repellent plants such as Lantana or Eucalyptus that cause moths to fly away. What is potato tuber moth (PTM)? The field may be sprayed with appropriate insecticides at 2–3 week intervals, What are the symptoms of PTM on but cautiously to avoid harm to the environment and human health. tubers in storage? What are the most effective measures to control PTM in storage? Good hilling is very important for avoiding infestation of tubers with PTM in the field. 17 Control of nematodes 17 Control of nematodes Two types of nematodes are known in potato production: root-knot nematodes (most widely spread) and potato cyst nematodes. Potato plants infested with nematodes may show stunting, yellowing of leaves and a tendency to wilt under moisture stress. Nematodes also cause blemishes on tubers making them unmarketable. Control of nematodes is primarily preventive because they are difficult to eradicate once they are present in the field. Plant clean seeds of less susceptible varieties in fields that are free from nematodes. Once nematodes are present in the field, wait 5 years before planting potato in the What is potato nematode? field again while avoiding crops from the same family (such as tomato, eggplant, chili). What are the symptoms of nematodes on tubers? What are the most effective measures to control nematodes? Nematodes are hard to eradicate once introduced in the soil. Preventive measures are always the most effective approach. 18 Dehaulming 18 Dehaulming Dehaulming is the act of removing or destroying potato shoots ahead of the complete maturity of the plant. Dehaulming stops tuber growth and hardens the skin of the tubers which protects them from damage and infection by diseases during harvest, transport, and storage. This is especially important in seed production. Towards the end of flowering (at around 80 days after planting), enter the field once a week and randomly dig up a few tubers. When about 75% of the tubers have reached the target size of 28-55 mm (about the size of a chicken sized egg), dehaulming should be carried out immediately. Check each variety separately as the best time of dehaulming will differ among varieties. Why is it important to dehaulm a There are three methods of dehaulming: (1) pulling out the potato plants while stepping seed potato crop before harvest? around their base, (2) cutting the stems with a sickle or machete, and (3) killing the How should a seed producer identify foliage with herbicides. The second method is not desirable as it has the risk of transmitting diseases to the tubers through infected tools. the right moment for dehaulming? What are the different methods that can be used for dehaulming and what are their advantages/disadvantages? Dehaulming ensures the skin of the tubers harden which is very important for the quality of seed potatoes. 19 Harvesting, sorting and grading 19 Harvesting, sorting and grading Harvest should be done when the tuber skin is sufficiently hardened, about 2 to 3 weeks after dehaulming. To determine the right time for harvest, take a tuber and rub it between the thumb and index finger. If the skin is firm and cannot be removed by light rubbing, it is the right time for harvest. Harvesting should be done in dry weather and not when it is raining. Always handle the tubers gently, during digging up, packing and transport, to avoid wounding the tubers. Never throw or drop tubers from a height of more than 30 cm. Harvesting can be done by hand or using a hoe. Harvesting by hand takes longer and is more labour-intensive, but produces good quality and undamaged tubers. What is the right time for harvesting seed potatoes? After digging up the tubers, leave them on the ground for a while (max 2 hours) to How can it be determined? allow soil to dry out and fall off. What is the difference After harvest, sanitize the field by gathering and destroying residues and rotten between sorting and grading? tubers. What should be done with Tubers from diseased plants must be harvested and collected last and never used tubers from diseased plants? as seeds. They should be packed separately from other tubers. Healthy looking tubers should be graded, while still in the field and before packing, separating seed sizes: 28-35 mm (small size), 36-45 mm (medium size) and 46-55 mm (large size). Seed tubers should be handled To pack the seed tubers, do not use old bags previously used for packing tubers to gently during harvest. Any bruise avoid transmission of diseases. or wound on the seed tubers can greatly reduce the quality of the entire seed lot. 20 Seed storage 20 Seed storage Diffused Light Storage (DLS) is the recommended system for storing large quantities of seed tubers. A DLS is made from locally available materials, with potatoes stored in diffused (indirect) light with good ventilation. In a DLS, you should have enough light to read a newspaper, not more, not less. DLS induces short, strong and coloured sprouts, which is ideal for potato production. A DLS is usually made of wooden planks set at least 1 inch apart to allow light and air to enter, and one or more translucent iron roofing sheets. What is the recommended storage An aphid proof net should be used to line the inner walls to prevent insects from system for seed tubers produced by entering the store. local multipliers? Arrange tubers in thin layers (2-3 tubers) so that each tuber receives enough light What are the materials needed to and for easy inspection. build a Diffused Light Store? Keep different varieties, generations and seed lots in different shelves or trays. What should be done to reduce the spread of pests and diseases inside Properly label each lot, indicating variety name, generation and harvest date. the store? Regularly inspect the store and remove rotten tubers. Four to six weeks before planting, the main sprout should be taken off to promote the development of more lateral sprouts. Storing seed potatoes in a well- managed DLS will ensure seed potatoes produce short, strong, coloured sprouts and remain free from pests and diseases.