**8. Multiplication and supply of healthy planting materials**

Traditional farmers multiply sweet potato vines by growing them on residual moisture in rice fields after rice harvest or under fruit trees [42, 43]. The danger is that this traditional method of vines multiplication could transmit pests and diseases from one crop to the next. Therefore, improved methods using healthy mother plants are needed to produce healthy, disease-free vines for planting. Vines are multiplied in primary and secondary nursery as shown below.

#### **8.1 Primary nursery**

Primary nursery is prepared 3 months prior to planting in the main field. An area of 100 square metres (m2 ) is required for primary nursery. About 100–125 kg of medium-size roots are needed to produce vine cuttings enough to plant in the secondary nursery. Seed roots taken only from healthy, disease-free mother plants are planted at 20-cm spacing on ridges formed 60 cm apart. The nursery is irrigated as required. About 15 days after planting (DAP), 1.5 kg urea per 100 m2 is top-dressed to boost the growth of vines. At about 40–45 DAP, vines are harvested and cut into 20–30 cm long cuttings for multiplication in secondary nursery [44].

#### **8.2 Secondary multiplication**

A secondary nursery area of 500 m2 is required to produce vines for planting one hectare of main field. The nursery area is ploughed, harrowed, and levelled before forming the beds or ridges. About 500 kg of organic manure or compost is incorporated into the soil during first ploughing. Vine cuttings taken from primary nursery are planted at 60 cm x 20 cm spacing on raised beds or ridges. To enhance vegetative growth, 5 kg urea is applied in two splits at 15 and 30 DAP. The nursery is irrigated as required. Vines are harvested at 45 DAP and cut into 20–40 cm long cuttings for planting in the main field [44].

#### **8.3 Preparing and hardening of vine cuttings**

Only the middle and top parts of the vines are used for getting vine cuttings. The length of cuttings ranges from 20 to 40 cm. The 20–40 cm long cuttings produce high yields [45]. Vine cuttings from the top produce higher root yields than those from mid-stems [46].

Cut vines can be planted soon after cutting, or they can be hardened by keeping them in a shady place for 1–3 days. During this hardening time, roots will begin to grow on the nodes, and the cuttings will become tougher and more resistant to the transplanting shock. Vine cuttings stored for 3 days established well and produced higher marketable root yield than fresh cuttings [47]. When stored for longer than 3 days, vine cuttings start drying, and planting of such dried cuttings results in poor crop establishment and low yields.
