Phaseolus coccineus (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Phaseolus coccineus L.

Protologue: Sp. Pl. ed. 1: 724 (1753).

Family: Leguminosae

Chromosome number: 2n= 22

• Phaseolus multiflorus Lam. (1789).

• Runner bean (En)
• haricot d'Espagne (Fr).

The runner bean was domesticated in Mexico and perhaps in Guatemala. It is cultivated in highland areas of Africa and South America and in many temperate areas.

Runner beans are used as a green slicing bean and as a pulse. Many recent cultivars have substantial reduction in the fibrous vascular strands of the pod sutures, the stringless runner beans. Preparation is predominantly by boiling. Runner beans are often grown as ornamentals in areas too warm for satisfactory pod and seed production.

Production is almost exclusively for local consumption. Commercial production of pods is carried out in Great Britain and Argentina and of butter beans (white-seeded cultivars) in South Africa. Accurate global production figures are not available.

The green pods are good sources of vitamins as well as protein and dietary fibre. Dried seeds contain per 100 g edible portion: water 12.5 g, protein 20.3 g, fat 1.8 g, carbohydrates 62.0 g, fibre 4.8 g, ash 3.4 g. The energetic value averages 1420 kJ per 100 g. Seed weight is up to 100 g/100 seeds.

• A climbing (vining), tuberous perennial or a bushy (dwarf), annual herb. Stems up to 4 m length.
• Leaves trifoliolate, leaflets up to 15 cm long.
• Inflorescence axillary or terminal, long, producing many, few-flowered nodes. Petals scarlet, pink or white; keel spirally twisted to accommodate the style.
• Fruits linear, straight or slightly curved with a prominent beak, up to 40 cm long, fleshy, usually green. Seeds ovoid, variable in size, pink to purple dark mottled or sometimes black, white, cream or brown.
• Germination hypogeal, 10-14 days after sowing.
• Seedling with first pair of leaves opposite and simple.

Flowering 40-60 days after sowing, flowers open at sunrise and fade at sunset. Pollination is effected by insects. Pod set is favoured by warm, moist conditions, it is adversely affected in hot dry environments.

Cropping of green pods starts at 3 months after sowing and can be easily sustained for 2-3 months. Mature seed can be harvested 4-5 months after sowing. Dry weather at harvest is essential for production of good quality butter beans. Dwarf cultivars produce smaller earlier crops than do the climbing. The productive life span of runner beans is commonly terminated by frost, which kills the above ground parts but not necessarily the tuberous roots, or by excessively cool conditions and short daylength. The main differences from the similarP. polyanthusGreenm. are extrorse stigma and hypogeal seed germination.

Runner bean achieves greatest success in the (sub)tropics at high elevations (1500-2000 m), where ambient temperatures are without extremes of hot or cold. Its climatic optimum is best described as temperate. At high temperatures, under low relative humidities, pod set is totally inhibited. Waterlogging is detrimental but it is more tolerant of cold wet conditions than other Phaseolus species.

Propagation is by seed. High quality pods are grown on trellises, poles or other support because they should not touch the soil. Labour and material demands are high and may inhibit cultivation on any but a small scale. Crops can be produced on climbing genotypes without support if leading shoots are pinched out to induce a bushy growth form. Bushy cultivars are generally more satisfactory for seed than for pod production. Planting densities are 50 000-75 000 plants/ha for climbers and double this for bush types, requiring 75 kg and 150 kg/ha sowing seed respectively. The plant is shallow rooting and not very drought tolerant. Supplementary irrigation is beneficial. Cultivation should be shallow to avoid root damage. In general diseases and pests are similar to those in common bean. Bacterial halo blight, Pseudomonas phaseolicola, and common blight, Xanthomonas phaseoli are tolerated better. Green pod harvesting ideally is carried out when maximum length is achieved prior to the phase of rapid seed development. Dry seed crops can be pulled or cut when most pods are dry and are then allowed to dry out for a few days. Completely dry pods can be threshed. The practice of plucking leaves for a green vegetable is not established but it can be regarded as a potential food resource. Green pod yields of 10 t/ha and seed yields of 1.5 t/ha are possible.

Germplasm resources within runner bean are limited. For the improvement of runner bean the combined genetic resources of P. vulgaris and P. polyanthus are available. Breeding efforts have been directed to improvement of culinary quality (stringlessness) and pest and disease resistance. Selection for improved cooking quality is promising since seed proteins of runner bean are more polymorphic than of common bean. For dry seed production improvement of the shoot canopy architecture and shorter pods are appropriate selection objectives. It is questionable whether dwarf cultivars produce sufficient leaf area for achievement of high yields.

Compared with common bean, runner bean is underexploited. It has obvious potential as a vegetable and a pulse crop in highland tropical areas with a suitable rainfall regime. Increasing interest in vegetarian diets and the substitution of plant for animal protein might lead to increased interest in seed production. A promising species, also for South-East Asia.

• Duke, J.A., 1981. Handbook of Legumes of World Economic Importance. Plenum Press, New York and London. p. 189-191.
• Westphal, E., 1974. Pulses in Ethiopia, their taxonomy and agricultural significance. Pudoc, Wageningen. p. 135-140.

• J. Smartt