&V- Contents Page Prefacio iii Introduction I The Importance of Planting Material in Root and Tuber Crop Production 3 J. E. Bryan, CIP, Lima, Peru Chapter 1. Crop Descriptions: Importance, Growth, Production Systems, and uses 7 Potato Production 9 R. H. Booth and D. Horton, CIP, Lima, Peru Cassava Production 17 James H. Cock, CIAT, Cali, Colombia Sweet Potato, Yam, and Cocoyam Production 23 F. E. Caveness, S. K. Hahn, and M. N. Alvarez, IITA, Ibadan, Nigeria Chapter 2. Status Quo of Seed Production 33 Current Practices in the Production of Seed Potato 35 J. E. Bryan, CIP, Lima, Peru Current Practices in the Production of Cassava Planting Material 41 Dietrich E. Leihner, CIAT, Cali, Colombia Chapter 3. Physiological and Sanitary Problems in Seed Production 47 Physiological Problems in the Production of Seed Potato 49 R. H. Booth and S. G. Wiersema, CIP, Lima, Peru VI Physiological Problems in the Production of Cassava Planting 57 Material Dietrich E. Leihner, CIAT, Cali, Colombia Sanitary Problems in the Production of Cassava Planting Material 73 J. C. Lozano, A. Belhotti, and 0. Vargas, CIAT, Cali, Colombia Chapter 4. Special Techniques for Producing High-quality Seed 87 Virus Elimination in Potato and Cassava 89 L. Schilde-Rentschler, CIP, Lima, Peru W. M. Roca, CIAT, Cali, Colombia Virus Elimination in Sweet Potato, Yam, and Cocoyam 97 S. Y. Ng, IITA, Ibadan, Nigeria Chapter 5. Rapid Propagation Techniques 103 Rapid Propagation Techniques for Potato 105 J. E. Bryan, CIP, Lima, Peru Rapid Propagation Techniques for Cassava 109 James H. Cock, CIAT, Cali, Colombia Rapid Propagation Techniques for Sweet Potato, Yam, and Cocoyam 115 S. Y. Ng, IITA, lbadan, Nigeria Rapid Propagation of Yam by the Minisett Technique 119 0. 0. Okoli, NRCRI, 'JmUahia, Nigeria Chapter 6. Seed Storage 121 Seed Potato Storage 123 R. H. Booth, CIP, Lima, Peru Storage and Regeneration of Cassava Planting Material 131 Dietrich E. Leihner, CIAT, Cali, Colombia Chapter 7. Case Study: Production Programs for Seed Potato 139 Seed Potato Production in Brazil 141 Elcio Hirano, EMBRAPA, Planaltina, Brazil Seed Potato Production in Chile 147 Jos6 Santos Rojas, INIA, Osorno, Chile Seed Potato Production in Ecuador 165 Diego Estrella, INIAP, Quito, Ecuador VII Seed Potato Production in Mexico 169 Manuel J. Villareal Gonzdlez, INIA, Toluca, Mexico Seed Potato Production in Vietnam 175 Nguyen Van Uyen, Research Center for Experimental Biology, Ho Chi Minh, City, Vietnam Chapter 8. Case Studies: Production Programs for Cassava 179 Planting Material Production of Cassava Planting Material in Cuba 181 Adolfo Rodriguez Nadals, CEMSA, Villa Clara, Cuba Production of Cassava Planting Material in India 187 G. M. Nair, M. Prabhakar, N. G. Nair, and S. P. Gosh CTCRI, Trivandrum, India Production of Cassava Planting Material in Mexico 193 Victor W. Gonzilez Lauck, INIA, Huimanguillo, Mexico Production of Cassava Planting Material in Nigeria 197 J. E. Okeke, and 0. 0. Okoli, NRCRI, Umudike, Nigeria N. 0. Utoh, NSS, Southeastern Zone, Nigeria Production of Cassava Planting Material in Zaire 205 S. J. Pandey, PRONAM, Kinshasa, Zaire Chapter 9. Case Study: Seed Production Program for Sweet Potato, Yam, and Cocoyam 217 Seed Production in Sweet Potato, Yam, and Cocoyam at IITA 219 M. N. Alvarez and S. K. Hahn, IITA, Ibadan, Nigeria Conclusions and Recommendations 225 Index 231 INTRODUCTION The Importance of Planting Material in Root and Tuber Crop Production J. E. Bryan, CIP, Lima, Peru Most crop specialists agree that the use of good quality seed is the quickest way to increase crop production and productivity. (The term 'seed' is used tu denote true botanical seed, tubers, roots, or other plant parts. Since root and tuber crops are almost exclusively multiplied by vegetative propagation, this is the meaning of seed commonly used in this publication.) Without good seeJ, the impact ofother inputs on yield, such as fertilizer and soil preparation, will not be as significant or as economical. In addition, good seed can be adapted to small as well as large farms, and it is responsive even under less favorable climatic conditions. Many farmers, especially in developing countries, are not yet using good quality seed, despite its obvious advantages. One of the major reasons for this is that farmers are slow to change from the ancient practice of setting aside part of their crop, more or less non-selectively, as seed for the next, to the more recent idea of saving planting material only from the more vigorous and healthy plants. However, in order to produce good qualicy planting material in small-scale and subsistence agriculture, it is very important that this latter idea becomes ingrained into farmers' practices. The switch to improved seed means a drastic change for the individual farmer, with many new risks and new ways of thinking. The change is equally significant at the national level. The adoption of improved seeds implies initiating and maintaining complex, sizable, and costly long-range activities, including infrastructures for financing and training both at the scientific and farmer level. Trained manpower at the farmer level is the most critical. 4 Global Workshop on Root and Tuber Crops Propagation. Breeding programs and varietal selection are of little value without the necessary infrastructure to maintain and multiply a new variety to the quantity and quality necessary to make a significant impact on pro­ ductivity. Governments wishing to motivate farmers to use improved seed, improved varieties, or modern techniques are faced with the need not only to provide educational and credit facilities but also to ensure that the required seed and related inputs are available to the farmers at the correct time. Good planting material naturally implies freedom from diseases, insects, and other pests, but it also implies physiological quality. This is extremely important when working with vegetatively propagated crops such as potatoes, cassava, yams, and sweet potatoes. In the case of potatoes, there is a 65-year history of reducing diseases and insects in planting materials. However, the importance of physiological quality in planting materials is less well known. Root and tuber crops, being propagated vegetatively, are inherently more susceptible to the maintenance, increase, and dissemination of both systemic and nonsystemic diseases than are the sexually reproduced crops using true seed as planting material. The systemic diseases-viruses, viroids, and mycoplasma pathogens, as well as several bacteria-are the most devastating in terms of yield loss for the root and tuber crops. Recent progress using thermotherapy and meristem techniques have enabled scientists to remove many of these systemic diseases from planting materials. Increased use of rapid multiplication techniques is enabling scientists to produce large amounts of 'pathogen-free' material. Because most rapid multiplication techniques in root and tuber crops involve the use of aerial portions of the plant, contact with soil and tuber/root portions is broken and most nonsystemic pathogens and pests can be eliminated. However, when replanted in contaminated soils, the plants become reinfected, as is also the case with systemic diseases, but usually reinfection with these is at a slower rate if appropriate precautions are taken. Crop losses are difficult to define in monetary terms. Individual diseases vary tremendously in their effect on yield reducton. With 100% infection, potato virus X (PVX).normally reduces yield less than 10%. However, the yield of certain susceptible cultivars has been reduced in excess of 25%. Mild strains of potato virus Y(PVY) only reduce yield 25-30%, but severe PVY and potato leaf roll virus (PLRV) can reduce total yield in excess of 60%. This loss varies with plant density, seed tuber size, fertility, and other ic Importance o/l'lanting,,ateriaI. 5 agronomic practices, as well as with variety. The bacteria Pseudomonas solanacearuncan cause 100% crop loss at harvest or prior to purchase by the consumer. Similar losses are reported in the root crops. Crop losses are caused in several ways. The first and most important is by yield reduction, in which fewer and smaller roots or tubers are produced. As these losses occur below the ground, they are not noticeable until harvest. This is particularly true for the virus diseases and nematodes. The second type of loss is through rotted, damaged, misshapen, or off-color roots or tubers. These types of losses are often caused by bacterial or fungal pathogens, as well as by insects, viroids, and mycoplasma. Again, these losses are most obvious at harvest. The third type of loss occurs on the portion of the plant above the ground. The cumulative effect of mild insect infestations, lack of chlorophyll caused by viruses, and mild leaf spots caused by certain fungi are often underrated because they are nut serious by themselves. The last and most obvious type of loss is caused by pathogens killing the plant or causing severe leaf' or stem damage. Fungi, bacteria, insects, and certain viruses do the most damage. Most of the above types of losses can be attributed to infected planting materials. But the effect of planting material quality is not limited to yield losses. It also affects the storage properties of the product and its eating quality. It is therefore appropriate for agricultural programs to devote a significant share of their resources to this important aspect of crop production. CHAPTER 1. CROP DESCRIPTIONS: IMPORTANCE, GROWTH, PRODUCTION SYSTEMS, AND USES Potato Production R. H. Booth and D. Horton, CIP,Lima, Peru Importance On a worldwide basis, potato is the most important root crop with 4n annual production of about 258 million tons compared with 146 million tons of sweet potato, 121 million tons of cassava, 22 million tons ofyams, and around 6 million tons of cocoyams (Table 1). Similarly, potatoes are grown in more countries of the world than any other root and tuber crop.