Compendium of Potato Diseases - (PDF, 101 mb) - USAID

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more in the tropics. It requires cool nights and well drained soil with adequate moisture and does not produce well in low altitude, warm, tropical environments. Certain types of South American potato have considerable tolerance to warm temperatures and to temperatures a few degrees below freezing; clones tolerant to both extremes are being sought. The potato is a native of the Andean highlands of South America, where it has served as a staple of the diet of Andeans for centuries or millennia. Widely diverse types have been selected. Dehydrated tubers have been preserved since antiquity as chuho, a product of various types obtained by freezing tubers, pressing liquid from them after thawing, and then freezingand drying them. Today tubers are boiled and dried for preservation. The potato was introduced into Spain sometime before 1573, when it was first mentioned as a food source. Its use in England was first reported in herbals in 1596. From northern Europe it was first reported in herbals in 1596. From northern Europe it was returned to North America in 1719 and grown in the colonies. Cultivated Types Cultivated potatoes, consisting of a number of species or species hybrids, belong to the Solanaceae, section Tuberarium, which contains approximately 150 tuber-bearing species. In the Andean highlands, the distinction between cultivated and wild varieties has little relevance to indigenous populations, The most common potato is the tetraploid (2n :=4x = 48 chromosomes), Solanum tu/'erosum I..which may he divided into the completely cross-fertile subgroups Tuberosum and Andigena or into subspecies tuerosut and adigena.Survival of these in the wild occurs only in excep'ional cases. Their survivai and extensive dispersal have resulted from human selection. Andigena is the most widely grown in South America. It has deep eyes, is often pigmented. and produces tubers in days of short length. The Tuberosum type grown in northern Europe and North America tends to need a long day for effective tuberization. These two types are not completely distinct, and obtaining the Tuberosum type by selection from Andigena is possible. Another classification also places certain diploids and triploids within S. tuherostim. Diploid cultivated potatoes (2n = 2x = 24) belong to two main groups, S. stenotomln, with a period of tuber dormancy, and S. phure/a, without a welldefined dormant period. S. stenotonmn is regarded as the ancestral type, giving rise to Andigena types through chromosome doubling. Cultivated triploids (2n = 3x = 36) in group S. X chaucha are possibly naturally occurring hybrids from crosses between Andigena and Stenotomum or Phureja. Another triploid species, S. X.juzepczukii, is highly frost tolerant and may have originated from natural hybridization between the wild species S. acaule (a tetraploid) and the diploid S. stenotomtm. A pentaploid, S. X curtilobun (2n = 5x = 60), believed to have originated from natural hybridization of S. acaule and S. and, gena, is grown in the high Andes because of its frost tolerance. It is bitter tasting but useful for making chuio. The hexaploid S. demisstm (2n = 6x = 72) has been used as a source for cultivars resistant to late blight, Perpetuation ofthe many geneticdifferences is attributable to asexual propagation through tubers. Variability existing within the potato groups is believed to have originated through: I) hybridization between diverse types, 2) chromosome doubling, 3) mutations in germ plasm, and 4) nitatiori in vegetative tissue and perpetuation as chimaeras. Vegetatively propagated clone lines, assumed to be genetically stable, as are presently accepted cultivars, are capable of further variation and change through somatic mutation, The potato may be propagated from true seed, which is 2 common in genetic studies and in potato breeding programs. In certain parts of Ecuador and Colombia true seed is planted for commercial crop production. The Peoples Republic of China grows over 10,000 ha from true seed to avc,id virus spread and long distance transport of seed tubers. At the International Potato Center, transplants from true seed produce homogeneous families that yield an average of more than I kg per plant. These practices permit full use of tubers as food and avoid diseases carried through seed tubers. Commercial production of most potatoes is primarily through vegetative propagation by means of lateral buds formed on the tuber, a modified stem. Through such vegetative propagation, many diseases are transmitted from generation to generation. Although disease affects each of the types listed above, much of potato pathology has been done wth S. tuero.stim ssp. tuherostm in northern Europe and North America. Increased importance of the crop in the tropics and subtropics has occasioned unprecedented work during the past half century on tropical diseases and evaluation of wild and cultivated genotypes as sources of disease resistance. The Pjant The potato, S. tuberosun ssp. tuherosutn and ssp. andigena, is an annual, herbaceous dicotyledonous plant with potential perennial capacity because of reproduction through tubers. Flowers Flowers are five-parted of various colors with single style and stigma and two-loculed ovary. Pollen is typically windborne. Self-fertilization is natural; cross-fertilization is relatively rare, and when it occurs, insects are probably involved. Diploids are self-incompatible with very few exceptions. Fruits Fruits are round to oval (1-3 cm or more in diameter), green, yellowish green or brown, and red to violet when ripe. Fruits are two-celled, with up to 200-300seeds. Because of several sterility factors, seeds may be absent even though fruits are formed. Vegetative Structures Plants from true seed are typically seedling plants with primary tap root, hypocotyl, cotyledons, and epicotyl, from which a stem and foliage develop. In contrast, the commerical potato plant contains one or more lateral branches, each arising from a bud on the "seed tuher," and the roots are adventitious (Fig. I). The "seed" in commerical production is an asexual propagative organ and not comparable to the sexually derived true seed. Stems These are usually green, but can be red to purple, angular, and nonwoody. Late in the season the lower portions may be relatively woody, however. Leaves are pinnately compound, although early leaves of seedlings and the first leaves of plants grown from tubers may be simple. Leaf types differ widely among the many species and cultivars. Stomata are more numerous on the lower leaf surfaces, and hairs of various types are present on aboveground parts. Secondary branches are common, arising from axillary leaf buds. Leaves on the underground stem are small and scalelike, and stolons arise from these axillary buds. Stolons and tubers are modified adventitious stems. Roots and stolons develop from the underground stem between the seed tuber and the soil surface. Thus, the vegetative propagative unit (theseed tuber ora portion of it, theseed piece) should be planted sufficiently deep to permit adequate root and stolon formation.
Fig. 1.A, Lower portion of young potato plant showing: a, stem; b, stolons; c, roots; and d, seed tuber. B, Bud on stolon tip (bar represents 100 ,m). C, Starch grains within cells of a potato tuber (bar represents 10pm), showing characteristic refraction patterns within the grain. Tubers The tuber (Fig. 2) is formed at the tip of the stolon (rhizome) as a lateral proliferation of storage tissue resulting from rapid cell division and enlargement. Enlargement approximates a 64-fold cell volme increase. 'Re stolon usually breaks offclose to the tuber during harvest or dies with the plant on maturity and is evident either as a short stub o r sm all scar .,E In stens, stolons, and tubers, vascular tissue initiallv forms as bikollateral bundles with groups of thin-walled phloem cells outside of'the xylem (outer phloem) and toward the center and inside the xyleml(inner phloem). As th' stolon enlarges to form the tuber. parenchyna developing within the bundles tends to split the separa it iroups. and the vascular ring becomes spread olt. New groups of phloem including sieve tubes, companion cells, and conducting parenchyma elements are formed as the tuber enlarges. Carbohydrates are stored within storage parenchyima ce',s of pith and cortex in the form of starch granules with characteristic markings. Tuber constitucnts vary with cultivar and growing conditions. E:stimated amounts of constituents may also reflect differences in methods ofchemical analysis. Ranges in the whole fresh tuber are: water, 63-87i: carbohydrates, 13-30("i (including a fiber content ofN. 17-3.48Ci ): protein, 0.7-4.61"; fat, 0.02-0.96(' ; and ash, 0.44-1.91". Additional constituents include sugars, notnstarchy polysaccharides, enzymes, ascorbic acid and other vitamins, phenolic substances, and nucleic acids, The tuber surface permits or excludes entrance of pathogens, regulates rate ofgas exchange or water loss, and protects against mechanical damage. The surface is not fixed and static but will maintain and regenerate itself through wound healing reactions which influence disease incidence and severity, preservation in storage, and seed germinability and performance, Tle epidermis exists for only a short time on tile youngest tubers of approximately I cm or less in diameter. Stomata are scattered ir the epidermis and permit gas exchange. A shortlived penuerm is derived from tile epidermis and is soon replaced by a more permanent periderm or cork layer arising from meristenatic cambium cells below the epidermis. This periderm in mature tubers is composed of 6-10 layers of bricklike, thin-wvalled cells, one on top of tie otiher, without intercellular spaces and with suberized cell walls. Periderm STEM ED J 0 \,\ . ". " APEX BUDEND NEEL E, ROSE END STOLO , R ID, ' A C A L U D ORSK-N ' OR'eye CORTEX' LATERAL UD VASCULAR RING LAOR EYE VASCULAR ITORASE BO OFEY ARENCHYA ! its Trts Fig. 2. The potato tuber and its parts. characteristics vary considerably with cultivar (Fig. 3). Wound healing (Fig. 3) develops under cut, bruised, or torn surfaces. Suberin forms within 3-5 days in walls of living cells under the wound. A cork cambium layer developing under the suberized cells gives rise to a wound periderm. The promptness with which wound healing develops is Jependent upon environment (temperature, humidity, and aeration) and the physiology of the tuber. Cut tuber surfaces exposed to dr. ing air may seem to have a tough, resistant covering. Drying kills living surface cells and interferes with normal wound-healing activity. Dried surfaces do not exclude pathogens nor prevent dehydration and should not be confused with wound healing. Rates of' wound healing, including both suberization and periderm development, increase approximately threefold between 5 and 10' C and again threefold between 10 and 200 C. Oxygen supply less than that of the atmosphere and carbon dioxide greater than that of tile atomosphere progressively inhibit wound healing. Wound healing is most rapid between 80 and 100%rh: however, the presence of free water on the surface that excludes oxygen is detrimental. Wound healing is more rapid in stored, recently harvested tubers, and as the tubers age, ability to heal wounds gradually diminishes. Also, periderm development in the cortical areas is more rapid than in the medullary region. Irradiation by sunlight or by ionizinggamma 3
Page 1 and 2: , ,. ,o . ; , . o , . r. , -' .L ,
Page 3 and 4: Compendium of Potato Diseases W. J.
Page 5 and 6: In memory ofimy respected colleague
Page 7 and 8: Acknowledgments Planning Committee
Page 9 and 10: Introduction 1 Potato Disease 1 The
Page 11: A potato disease is an interaction
Page 15 and 16: +q I B Fig 4. Natural openings in a
Page 17 and 18: Part I. Disease in the Absence of I
Page 19 and 20: more heavily in the vascular region
Page 21 and 22: the air temperature when tubers are
Page 23 and 24: iiO A B 'D C Fiq. 14 Second growth:
Page 25 and 26: identifying tissue bruised by black
Page 27 and 28: Internal Sprouting multiple sprouts
Page 29 and 30: conditions permits normal leaf deve
Page 31 and 32: Epidemiology Oxidant injury is pres
Page 33 and 34: sevritof stnting, chiorosis. loss o
Page 35 and 36: Selected Reference brown to bronze
Page 37 and 38: Part II. Disease in the Presence of
Page 39 and 40: should be planted on land with at l
Page 41 and 42: Control I) Use disease-free tubers
Page 43 and 44: FOI-SO M. D, and I. A. FRIEDMAN. )9
Page 45 and 46: Fungi Powdery Scab liberating powde
Page 47 and 48: Histopathology Sort of sporangia de
Page 49 and 50: any time but generally occurs late
Page 51 and 52: '40 ff .. . '1 f . ."L', . '1 .,. "
Page 53 and 54: A \, 2) Powdery mildew is rarely a
Page 55 and 56: R., Inst.. Kew. Surrey. ngland. 609
Page 57 and 58: TORRES, H.. E. R. FRENCH, and I.. W
Page 59 and 60: d AC D A 0 Fig 53 Gray mold. A, Bot
Page 61 and 62: strands of pigmented hyphae. Sclero
Page 63 and 64:
tuber malformation. Roots are also
Page 65 and 66:
1. Giant-hill plants, taller than n
Page 67 and 68:
13. Bacterial soft rot. Erwinia car
Page 69 and 70:
24. Wart. Synchytrium endobioticum
Page 71 and 72:
34. Pleospora herbarum (Stemphylium
Page 73 and 74:
44. Charcoal rot. Macrophomina phas
Page 75 and 76:
55. Leafroll virus. Current season
Page 77 and 78:
67. Mop-top virus. Primary tuber 68
Page 79 and 80:
77. Aster yellows mycoplasma sympto
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Symptoms Small, localized, light br
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obovoid, and 14-30 X 5-10 pm. Pycni
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invaders through the IFusarium lesi
Page 87 and 88:
necrosis extending into the tuber t
Page 89 and 90:
do not survive drying. Both species
Page 91 and 92:
cauisal. Tesis Magister Scientiae e
Page 93 and 94:
penetration, and subsequent disease
Page 95 and 96:
have been demonstrated, including t
Page 97 and 98:
In P..floridana,strains of PVY" and
Page 99 and 100:
infects certain comnie,-cial stocks
Page 101 and 102:
cytoplasm of infected potato cells
Page 103 and 104:
WETTER, C. 1971. Potato virus S. No
Page 105 and 106:
3) Resistance has not been identifi
Page 107 and 108:
nm), which do code for coat protein
Page 109 and 110:
Symptoms AMV may induce Other predo
Page 111 and 112:
Disease Cycle I)escriptions of Plan
Page 113 and 114:
Selected References KASSANIS, B. 19
Page 115 and 116:
Control 1)Avoid locations in wkhich
Page 117 and 118:
The "yellows" types of disease, cha
Page 119 and 120:
modifying cultural practices and by
Page 121 and 122:
immature females in the white or ye
Page 123 and 124:
l.aboratory, Control. and Quarantin
Page 125 and 126:
They attack many major crops in the
Page 127 and 128:
infested areas of North America sev
Page 129 and 130:
antennal tb l tuberce u antenna eye
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carbon tetrachloride, applied at th
Page 133 and 134:
Diagnostic Microbial Structures Scl
Page 135 and 136:
Surface and or interior Shades of g
Page 137 and 138:
Equivalent Names of Potato Diseases
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Common Name Causal Factor Other Nam
Page 141 and 142:
Common Name Causal Factor Other Nam
Page 143 and 144:
coalesce-union of similar structure
Page 145 and 146:
many days following removal of the
Page 147 and 148:
Index Abrasions, tuber surfaces. 14
Page 149:
Irost tolerance in. 9 aniligena. 68
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Compendium of Potato Diseases - (PDF, 101 mb) - USAID

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