Potato and Tuber Crops

Botany and Taxonomy

• Sweet potato is a hexaploid species with 90 somatic chromosomes.
• It is a perennial herb with trailing vines and with a cluster of few medium sized tubers.
• For cultivation purpose, it is treated as an annual with duration of 90 to 120 days.
• Though plants produce viable seeds, highly heterozygous nature of the crop results in a heterogeneous population.
• Hence stem cuttings are used for propagation purpose.
• Sweet potato has an extensive fibrous root system both at stem cuttings and at nodes touching soil.
• Some roots act as storage organs for storing reserve food.
• Storage roots may be fusiform, spindle or globular in shape and surface is smooth.
• Skin has white, red or light copper colour.
• Flesh may be white or creamy with different combinations of orange and red.
• Leaves are simple, alternate and exstipulate.
• They vary in size and shape occasionally in same plant. Shape varies from ovate to cordate, hastate or. deeply lobed and may change on ageing.
• Leaf shape is an important character for identifying clones.All clones do not flower and in flowering ones, duration and initiation of flowering vary.
• Flowers are axillary and borne solitary or in simple cymes. Flowers are bisexual. Corolla is attractive and funnel shaped formed by fusion of five petals. Anthesis starts before dawn and closes by 9-11 a.m. Pollination is entomophilous.
• Fruit is a capsule with false septa.
• Seed coat is hard and impervious to water. Hence, scarification is required for promoting germination.

Botanical Name	Ipomea batatus L.
Family	Convulvulaceae
Chromosome No.	2n = 6X = 90
Progenitor	Ipomea trifida

• Ipomoea trifida is progenitor of sweet potato .
• It is herbaceous perennial but cultivated as annual.
• Branching stem with milky juice.
• Leaves are more or less heart shaped with green to purple colour.
• Tubers vary in size, shape and colour.
• Inflorescence is a cyme,
• Corolla is funnel shaped with 5 lobes.
• Fruit is capsule with up to 4 seeds but usually 1 or 2 develop.
• Angular seeds black in colour with hard seed coat.
• Delayed germination needs scarification.

Growth and development

• Better growth with low night temperatures
• High temperature and high soil moisture leads to excessive growth during starch accumulation period at the cost of root development.
• 20 to 300C is better for tuber formation.
• Long days (16 hr.) stimulate vine length.
• Short days (9 hr) promote tuberisation.

Flowering

• It is a short day plant.
• Long nights and high temperature favour flowering.
• 11 hrs day is ideal for flowering.
• It is a self incompatible plant.