THE TAPIOCA PLANT AND METHODS FOR EVOLVING IMPROVED STRAINS FOR CULTIVATION* BY T. K. KOSHY, M.A., PH.D., F.L.S. (Botany Department, University of Travaneore) Received March 7, 1947 (Communicated by Kajyasevapravina Dr. K. L. Moudgill) CONTENTS PAGE I. INTRODUCTION ........ .. 32 II. THE TAPIOCA PLANT ........ .. 34 Anatomy of Stem ........ .. 37 Anatomy of tubers ........ 39 HI. VARIETIES UNDER CULTIVATION IN TRAVANCORE 40 Classification ........ 42 IV. CULTIVATIONOF TAPIOCA .... 43 V. GENETICAL WORK ON TAPIOCA .. 44 1. Intervarietal hybridisation .. 44 2. Interspecific hybridisation .. 46 3. Back-crossing ...... 49 4. Evolution of polyploid forms .. .. 50 5. Evolution of triploids .... .. 53 6. Evolution of pure strains of Tapioca .. 54 VI. CHEMICAL COMPOSITION OF TUBERS .. .. 56 VII. SUMMARY ........ .. 57 Literature cited ...... .. 58 Explanation of Text-figures and Plates .. 59 I. INTRODUCTION TAPIOCA or the Cassava plant (Manihot utilissima, Pohl.) belongs to the milkweed family (Euphorbiace~e). It is a native of Brazil, South America. In the botanical literature of the last century the plant is described as Janipha manihot, Kth. or Jatropha manihot, Linn. It was introduced in this country more than a century ago. Drury in his " Useful Plants of India" published in 1858 has recorded that tapioca was then under extensive cultivation in Travancore. The Travancore State Manual has * A Monogram on the work done in the Department of Research, University of Travancore, during 1940-47. 32 The Tapioca Plant & Methods for Evolving Improved Strains 33 stated ' that the popularity of this crop plant is specially due to the exer- tions of His Highness Sri Visakham Thirunal Maharaja' (1837-1885). Burkill (1904) states that early Portuguese settlers introduced tapioca to Goa as well as to Africa. Macmillan (1925)records that Tapioca was introduced into Ceylon and India by the Portuguese in the 17th century. The success of Tapioca as a major crop has in large measure been due to the particularly favourable climatic and soil conditions of Travaneore. It is also likely that the growth habit and high yield of this plant ensured its popularity with the ryot. It is a hardy plant thriving even in the most barren soil. Little or no care is necessary for it after planting and the yield per acre is so high as to give for the ryot a good return for his labours. In pre-war days a pound of fresh tapioca tubers did not cost more than two pies. It was thus within easy reach of the poor and became practically the poor man's food in Travancore. Tapioca cultivation in consequence steadily increased so that to-day it is second only to paddy as a major crop in this State. Owing however, to the primitive methods of cultivation employed by the ryot and the poor quality of the varieties used for cultivation, the average yield here does not exceed two tons of tubers per acre at present. In Java, West Indies and other countries of the Far East where improved strains of tapioca are used for cultivation, the average recorded yield for this crop ranges from 10-15 tons per acre. It should therefore be possible substantially to increase the yield of this crop by enabling the ryot to have better varieties of tapioca and by introducing improved methods of cultivation. During the war when rice imports from Burma were cut off, tapioca has been a boon to Travancore. It saved the country from famine and its food value has received greater attention since then. Tapioca has also assumed importance in recent years as its starch is in great demand as a suitable sizing material in textile industry. There is no doubt, there- fore, that the cultivation of this crop will receive greater attention in future. The following account of the applications of modern genetical methods for evolving improved strains of tapioca undertaken at the Tapioca Research Farm* in the Department of Research, University of Travancore, is therefore presented with a view to stimulating interest in this crop plant. * This Farm is maintained from the Pattabhirama Iyer Endowment Funds donatod at the rate of Rs. 1,OOO per mensem by Sachivottama Sir C. P, Ramaswamy Iyr Dowaq Vi~. Chancellor. 34 T.K. Koshy II. THE TAPIOCA PLANT Tapioca, known as 'maracheeni' or 'kappacheeni" in Malayalam is a crop plant cultivated in all dry soils in Travancore. Within a week after planting, two or three buds sprout from the nodes of the seed canes and grow up as erect branches. These stems branch repeatedly in threes and run into several such grades in an apparently trichotomous mode of branching (Fig. 1). While this type of branching with a spreadings shoot Fie. 1. The Tapioca Plant The Tapioca Plant & Melhods for Evolving Improved Strains 35 system is characteristic of all flowering varieties, it is significant that non- flowering varieties seldom branch, growing as erect, tall plants, reaching a height of 6-8 feet. The colour of the stern varies with varieties. It may be green, grey, pink, dark-brown or purple. Leaves stipulate, long petioled, palmate, divided nearly to their base into 5-7 lanceolate, entire lobes dark green above and glaucous beneath. Midrib prominent below and usually of the same colour as the petiole. Petiole long, inserted obliquely on the stem and arranged in a 2/5 spiral. Stipules thin, dissected, pointed, greenish white, occasionally with a reddish base falling off just after the leaf has fully spread. On an average about 15 leaves will be present on the terminal region of the branch. Leaves become mature and fall within about six weeks, leaving prominent nodal protuberances on the stem. These nodal swellings are surmounted by circular leaf-scars with-an obliquely transverse knife-edge like extension on each side formed by the stipular scars. The stem thus presents a rugged exterior with these close-set and spirally arranged swellings. Cork formation commences early on the stem developing a scaly skin which can be easily peeled off. Roots grow from the cut-end of the seed cane within a few clays after planting. They are long, slender and white, spreading in the soil more or less horizontally about 3-5 inches below the surface. As the plant grows FIr 2. Young Plant growing from a cutting 36 T.K. Koshy older, some of these roots become tuberous while the majority of them continue to be thin and function as absorbing organs. Both absorbing and tuberous roots are spreading in habit so that hardly any root lies deeper than 8-10 inches in the soil. As the tuberous roots begin to store starch in them they gradually increase in thickness, developing when mature, a skin as in the stem, a rind and the starchy inner portion with a central strand of conducting tissue. In most varieties growth of the tubers is completed in about eight months. The plants flower in about six months. The flowers are borne in terminal panicles. The first panicles usually appear at the junction of branches of the second grade (Fig. 3). Flowers unisexual, protogynous. FEQ. 3. Flowers and Fruit of Tapioca Male flowers smaller than the female and usually in terminal clusters. Perianth cup-shaped, with five imbrecate lobes enclosing a 10-lobed glandular disc. Stamens 10, springing from the base of the perianth and curving out through the lobes of the disc. In the open flower the anthers are arranged in two levels; five small with shorter filaments curved inwards and five large with spreading filaments. The small stamens are opposite the perianth lobes while the large ones alternate these lobes. Anthers dorsifixed and dehisce by longitudinal slits. Pollen grains are large, spherical and few in each sac. In the centre of the disc a pistillode is represented by a small conical projection. The female flowers are deve- loped earlier than the male flowers of the panicle and are fewer in number. The perianth of the female flower is deeply 5-lobed and with purple border. Pistil has a basal ring. Ovary trilocular, spherical with a capitate 3-lobed The Tapioca Plant & Methods [or Evolving Improved Strains 37 stigma. Ovule one in each loculus, pendulous, anatropous with ventral raphe and micropyle directed upwards and outwards. At the tip of the outer integument a soft tissue, the caruncle, is formed which caps the ovule. There is also an obturator mechanism which is a peg-like process formed from the placenta. This grows towards the ovule, curves round the caruncle and enters the nucellus through the micropyle (Fig. 3, B. 5). It is composed of thin-walled, elongated cells with rich contents. The pollen-tube in its passage to the embryosac directs its course through the obturator. This interesting mechanism thus serves as a short-cut to the micropyle besides being a nutritive tissue for the pollen tube as suggested by Strasburger (1921). After fertilisation the obturator dis- appears. Fruit globular, about one inch in diameter with six thin, narrow wings. Capsule hard, splitting into three cocci each with a seed. Seeds elliptical, black, grey or mottled, shining, resembling a castor seed. The seed-coat is thick, hard and polished. Inside the seed-coat there is the endosperm which is massive enclosing the embryo. The two leaf-like cotyledons of the embryo are pressed against each other by the endosperm. The radicle of the primary axis is directed towards the micropyle. During germination the radicle pushes itself out through the micropyle and develops branch roots at its tip. The hypocotyl is curved and by its further elongation the cotyledons are pulled out of the seed (Fig. 4). They then expand, become green and behave like foliage leaves. Anatomy of the Stem (a) Macroscopical.mThe stem is light, breaks easily and has a thin skin which gets easily peeled off exposing a green soft tissue inside.