2. CULTURAL DESCRIPTION OFDIOSCOREA BATATAS

MORPHOLOGY

Like all Dioscorea species,D. batatas is a perennial. In many botanical textbooks they are classified as monocotyledons, but Ayensu (1972) doubts this. According to him, dicotyledonous embryos have also been observed (Ayensu, 1972). Its twining shoots can grow to a length of 8 to 10 meters. During the growing season from May to October, the tendrils become woody almost to the ends of their shoots. The leaves ofD. batatas are heart-shaped (up to 8 cm long and 6 cm wide). The leaf position on one and the same plant can be alternate or opposite. The many small white flowers (dioecious) have the pleasant scent of cinnamon. They form small, loose racemes, each individual flower of which is only 2 to 3 mm in size. The seed capsules of the female plants resemble beechnuts (Fig. 34, p.114). The seeds are generally not very fertile (the germination rate is about 2%). Male and female plants produce bulbils, small above-ground tubers that form in the leaf axils on the tendril and with which they can reproduce vegetatively. The roots form starchy, bulbous thickenings in a wide variety of shapes. There are various statements on the size and weight of the tubers; for example, Chittenden (1956) states that they can reach a depth of over one meter. A root tuber grows to a length of 100 cm within two years and can reach a good 10 cm in diameter. At this stage, the root tuber can weigh up to 2 kilograms. As it is a perennial plant, older specimens can weigh many times more.

FIGURE 3: MORPHOLOGY OF DIOSCOREA BATATAS

(Source: Lemure& van Houtte, 1855)

Figure 4: DIOSCOREA BATATAS/LICHTYAM: TENDRILS WITH FOLIAGE LEAVES AND BULBILS PHOTOS: M. BUSL

Figure 5: INFLORESCENCE OF MALE D. BATATAS (4-6 CM LONG)- SMELLS OF CINNAMON AND VANILLA

Figure 6: DIOSCOREA BATATAS: THE INFLORESCENCE OF THE FEMALE PLANT IS ABOUT TWICE AS LARGE AS THE MALE (6-12 CM LONG, LOCATION ÜBERLINGEN-BONNDORF 2012)

(Source: Gilg& Schumann 1900)

FIGURE 7: MORPHOLOGY OF DIOSCOREA BATATAS: INFLORESCENCE

SITE FACTORS

D. batatas requires deep, well-drained soils for optimal growth. Compacted subsoils and waterlogged sites are unsuitable. The species thrives in a pH range of 5-7 (Franke 1994). SinceD. batatas commonly occurs in alluvial landscapes, it typically grows in silty clay soils characteristic of these environments (Beyerl 2001).

Soil structure is critical for tuber development, as the tubers penetrate the soil directly rather than forming from thin roots. Dense, waterlogged soils promote tuber rot. To ensure adequate soil loosening and aeration, tillage requirements increase proportionally with fine soil content (Franke 1994).

CLIMATIC CONDITIONS

D. batatas can survive in a number of different habitats and climatic conditions; in the wild, it usually grows in bright clearings along the edges of tropical floodplain forests (Yayskievych 1999). It therefore has a relatively high demand for warmth. Optimal temperatures are between 20°C and 30°C. The leaves are very sensitive to frost; they can freeze at 1°C. However, the root tubers can also be left in the soil over winter (Thompson, 1878) if the frost does not penetrate too deeply into the soil during this time. Sufficient humidity and a continuous supply of water are necessary for good growth. Franke (1994) writes of annual precipitation between 1,100 and 10,000 mm. In the first five months after planting, the soil must therefore be well and regularly moistened. Periods of drought should not exceed 4-5 months. The cultivation period is between 8-12 months. Yields are higher under alternately moist conditions than in constantly moist areas (Franke 1994).

REPRODUCTION

D. batatas generally repr