Potato & tuber crops morphology

For study purpose only

1. POTATO The potato is a tuber — a short, thick, underground stem with stored starches and sugars — of the potato plant. It was given its botanical name,  Solanum tuberosum ,  in 1596 by the Swiss botanist Gaspard Bauhin S. tuberosum  is an erect, juicy herb with numerous fleshy, robust, angular, branched stems up to 1.2 m tall and subterranean tubiform stolons . Root system usually 40-50 cm deep, without obstructions up to 1 m. Tubers developing at the tip of the stolons , globose to ellipsoid, very variable in size, weight and colour; tuber skin with scars of scale leaves ('eyebrows'), axillary buds ('eyes', usually several eye buds per eyebrow), numerous lenticels, almost impermeable to chemicals, gases and liquids, providing good protection against microorganisms and water loss; number of eyes very variable, normally about 10-15 on a tuber of 50 g.

2. Inflorescence : The complete flower, including bud, pedicel and peduncle Internode: The portion of the stem between the nodes or branches of the stem; Leafstalk: The petiole, midrib, central vein, or supporting stalk of a leaf; Node: The slightly enlarged part of a stem where buds are formed and where leaves, branches and eyes originate; Petiole: The stalk connecting a leaf or leaflets to a stem; Senescence: To die prematurely as a result of stress from environmental conditions or disease, or to die as a result of maturity (old age). Senescence may be a gradual process or sudden occurrence; Stolon: The underground stem of a plant, the end of which may form a tuber; Tuber: The short fleshy underground stem bearing buds or eyes; Variety: Seed potatoes that: are distinguished by common morphological, physiological, cytological, chemical or other common characteristics, and retain their distinguishing characteristics when reproduced; Wings : Protruding ridges running along the stem .

3. Apical: Usually refers to terminal leaflets or the eye, bud, or rose end of tubers Axil : The upper angle between a branch or leaf and the stem from which it grows ; Axillary bud: Located at the juncture of the stem and leaflet which may give rise to secondary branches; Bud: Sprout or shoot consisting of rudimentary foliage or floral leaves; Cultivar: A variety of potatoes; Eyebrow: The ridge over the eye of a potato; Foliage: Masses of leaves and stems that make up a plant; Haulm: Plant stems or stalks; the vines of potato plants;

4. A typical potato leaf is composed of two to four pairs of primary leaflets arranged on the mid-rib with a terminal leaflet on the end Leaves Leaves alternate, petiolate , odd pinnately compound, with or without numerous interstitial leaflets, in outline 10-30 cm x 5-15 cm; lateral leaflets opposite or alternate, usually 3-4 pairs, very unequal in size, largest ones stalked, ovate to ovate-elliptical, 2-10 cm x 1-6 cm, smallest ones subsessile , ovate to suborbicular , 1-15 mm in diameter; terminal leaflet usually largest; all leaflets thinly to densely pubescent, dark green, pinnatinerved .

5. Between the primary leaflets are smaller ones, called secondary leaflets, which are often placed irregularly along the mid-rib. Tiny inconspicuous rudimentary or tertiary leaflets can also be evident along the mid-rib. The leaf is attached to the plant by a petiole.

6. Open Leaf Structure Closed Leaf Structure

7. Depending on the variety, the leaf may: be long or short; be rigid, drooping or spreading; be flat or with side leaflets arched or drooping; or have a distinct petiole angle between leaf and stem which occasionally can be used as a distinguishing feature. Arrangement and number of leaflets whether primary, secondary or rudimentary, can also vary according to variety. Leaflets may: be light, dark or grey-green in color ; be hairy, smooth or wrinkled; be waxy, dull or glossy; be large or small; be broad or narrow; be flat or somewhat folded; or have equal or unequal lobes.

8. Stems Identification criteria for stems include: Amount and location of pigment; Thickness; Hardness; Branching or non-branching habit; Stem emergence; Internode length (between leaves); Node size (swollen nodes are typical of a few varieties); Wing structure either wavy or straight. Wings are protruding ridges running along the stem. Their characteristic of being wavy or straight are often very useful in confirming variety identification (see Figure 3-4). In most potato variety descriptions, mention is only made to wing structure when it is wavy. In all other cases it is straight or nearly so. Incidentally, most varieties have hollow internodes. Stems up to 1.5 cm in diameter, usually hollow, winged; wings sometimes decurrent and undulate- crenulate .

9. Potato Stems Showing Types of Wings Stem A demonstrates a straight, double wing. Stem B demonstrates a waved, double wing. Finally , Stem C demonstrates a slightly waved, double wing. Particularly , stem B has a dentate wing while stem C is more undulate.

10. Inflorescence The term  inflorescence  includes the complete pedicel (stalk which holds individual flowers), bud and peduncle (stalk that holds flower clusters)  Potato Inflorescence Potato flowers may be: White, Purple, and Faint blue.

11. Potato Flower Cross Sectional View Inflorescence a many-flowered cymose panicle, sometimes with small bracteoles; peduncle 5-15 cm long, branching above; pedicel up to 3.5 cm long, articulate at or above the middle; flowers white or white suffused with pink or violet, typically with a greenish-yellow central star

12. Tubers The end of the tuber which joins the stolon is called the stem end; the other end where the eyes are clustered is known as the  bud end Tuber Shape

13. Lenticels are breathing pores that appear as tiny slits on the tuber surface. They are the gateway for the gas exchange (primarily to take in oxygen and exchange carbon dioxide) in the tuber necessary for growth and development. Potato tubers have 28 to 274 lenticels per tuber. Lenticel numbers will vary by cultivar and tuber size. As tubers rapidly grow, the rupturing of the periderm often forms more lenticels.

14. Fruit a subglobose berry, up to 2 cm in diameter, yellow-green, 2-carpellate, many-seeded, poisonous. Seed flat, subcircular to ovate, 1-3 mm in diameter, pale yellow-brownish.

15. Sweet Potato/ Ipomoea batatas / Convolvulaceae / 2n = 6X = 90/ Ipomea trifida

16. Arrowroot  / Maranta arundinacea / Marantaceae Arrowroot is an erect, perennial plant growing about 1.2 metres tall. It has a shallow root system, with rhizomes that penetrate more deeply into the soil. The plant produces a starch-rich root that is the main source of arrowroot and also has various medicinal applications. Often harvested from the wild, it is also widely cultivated in tropical regions for its root and is often grown as a ground cover and ornamental in tropical gardens and as a pot plant in cooler climates

17. Cassava/ Tapioca/ Manihot esculenta / Euphorbiaceae / 2n=36

18. Colocasia and Xanthosoma together are known as coco yam. In Colocasia , leaves are peltate and sterile appendage is at top of spadix . In Xanthosoma , leaves are sagitate and sterile appendage is absent. Colocasia ( Colocasia esculenta  L. Scott) / Araceae

19. Xanthosoma sagittifolium / 2n = 26/ Araceae The genus Xanthosoma belongs to tribe Colocasia . Tannia is a tall herbaceous plant growing to 1.5 to 2.7 m and has about 6 large outspreading hastate leaves in contrast to peltate leaves in taro. In tannia , mother corm is more or less cylindrical and surrounded by cormels which develop from lateral buds adjacent to leaf scars on the corm. Similar to taro, mother corms and cormels are used for planting. Since plants grow vigorously, tannia is widely spaced at 1 x I m.

20. Amorphophallus (Elephant foot yam )/ Amorphophallus paeoniifolius / 2n = 28/ Araceae

21. Dioscorea / Araceae Greater yam ( Dioscorea alata ) (Hindi : Ratula) (2n = 20, 30, 40-80 ) White yam ( D. rotundata ) Lesser Yam Dioscorea esculenta 2n = 40,60,90,100

22. Jerusalem artichoke ( Helianthus tuberosus

23. Horseradish  ( Armoracia rusticana, syn . Cochlearia armoracia )

24. Morphology Sweet potato is a perennial plant mainly grown as an annual. The roots are adventitious, mostly located within the top 25 cm of the soil. Some of the roots produce elongated starchy tubers that vary largely in shape, colour and texture depending on the variety. The flesh of the tubers can be white, yellow, orange and purple whereas their skin can be red, purple, brown or white. The stems are creeping slender vines, up to 4 m long. The leaves are green or purplish, cordate , palmately veined, borne on long petioles. Sweet potato flowers are white or pale violet, axillary, sympetalous , solitary or in cymes. The fruits are round, 1-4 seeded pods containing flattened seeds Sweet potato

25. Growth habit . The sweet potato is a herbaceous and perennial plant. However, it is grown as an annual plant by vegetative propagation using either storage roots or stem cuttings. Its growth habit is predominantly prostrate with a vine system that expands rapidly horizontally on the ground. The types of growth habit of sweetpotatoes are erect, semierect , spreading, and very spreading

26. Root system . The sweetpotato root system consists of fibrous roots that absorb nutrients and water, and anchor the plant, and storage roots that are lateral roots, which store photosynthetic products. The root system in plants obtained by vegetative propagation starts with adventitious roots that develop into primary fibrous roots, which are branched into lateral roots. As the plant matures, thick pencil roots that have some lignification are produced. Other roots that have no lignification, are fleshy and thicken a lot, are called storage roots. Plants grown from true seed form a typical root with a central axle with lateral branches. Later on, the central axle functions as a storage root

27. Tuber-root . It is also called storage root have a skin coloured from red to purple, from brown to white depending on the variety; as well as the pulp that varies from white to yellow, orange or purple. A tuberous root or storage root, is a modified lateral root, enlarged to function as a storage organ.

28. Stem . A sweetpotato stem is cylindrical and its length, like that of the internodes, depends on the growth habit of the cultivar and of the availability of water in the soil. The erect cultivars are approximately 1 m long, while the very spreading ones can reach more than 5 m long Leaves . The leaves are simple and spirally arranged alternately on the stem in a pattern known as 2/5 phyllotaxis (there are 5 leaves spirally arranged in 2 circles around the stem for any two leaves be located in the same vertical plane on the stem).

29. The leaf color can be green-yellowish, green or can have purple pigmentation in part or all the leaf blade. Some cultivars show purple young leaves and green mature leaves.

30. Flowers . Sweetpotato cultivars differ in their ability of flower. Under normal conditions in the field, some cultivars do not flower, others produce very few flowers, and others flower profusely. The inflorescence is generally a cyme

31. Fruits and seeds . The fruit is a capsule, more or less spherical with a terminal tip, and can be pubescent or glabrous . The capsule turns brown when mature.

32. Storage-root . The storage roots are the commercial part of the sweetpotato plant, and sometimes are mistakenly named "tubers". Most cultivars develop storage roots at the nodes of the mother stem cuttings that are underground. However, the very spreading cultivars produce storage roots at some of the nodes that come into contact with the soil. The parts of the storage roots are the proximal end that joins to the stem, through a root stalk, and where many adventitious buds are found from which the sprouts are originated; a central part which is more expanded; and the distal end that is opposite to the root stalk.

33.  Type of storage-root formation