Vicia faba

Vicia faba, commonly known as the broad bean, fava bean, or faba bean, is a species of vetch, a flowering plant in the pea and bean family Fabaceae. It is widely cultivated as a crop for human consumption, and also as a cover crop. Varieties with smaller, harder seeds that are fed to horses or other animals are called field bean, tic bean or tick bean. This legume is commonly consumed in many national and regional cuisines.
Some people suffer from favism, a hemolytic response to the consumption of broad beans, a condition linked to a metabolic disorder known as G6PDD. Otherwise the beans, with the outer seed coat removed, can be eaten raw or cooked. With young seed pods, the outer seed coat can be eaten, and in very young pods, the entire seed pod can be eaten.

Description

Vicia faba is a stiffly erect, annual plant tall, with two to four stems that are square in cross-section. The leaves are long, pinnate with 2–7 leaflets, and glaucous. Unlike most other vetches, the leaves do not have tendrils for climbing over other vegetation.
The flowers are long with five petals; the standard petals are white, the wing petals are white with a black spot and the keel petals are white. Crimson-flowered broad beans also exist, which were recently saved from extinction. The flowers have a strong sweet scent which is attractive to bees and other pollinators.
The fruit is a broad, leathery pod that is green, but matures to a dark blackish-brown, with a densely downy surface; the wild species has pods that are long and 1 cm diameter, but many modern cultivars developed for food use have pods long and 2–3 cm thick. Each bean pod contains 3–8 seeds. They are round to oval and have a 5–10 mm diameter in the wild plant, but are usually flattened and up to 20–25 mm long, 15 mm broad and 5–10 mm thick in food cultivars. V. faba has a diploid chromosome number of 12. Five pairs are acrocentric chromosomes and one pair is metacentric.

Genome

The diploid genome of Vicia faba contains 13 GB of DNA, mostly obtained through amplification of retrotransposons and satellite repeats. The genome is one of the largest diploid field crops and contains a predicted 34,221 protein-coding genes.

Cultivation

Broad beans have a long tradition of cultivation in Old World agriculture, being among the most ancient plants in cultivation and also among the easiest to grow. While their wild ancestor has not been identified and their origin is unknown, charred legumes of a possible wild-type progenitor have been identified at the Natufian site of the el-Wad Terrace. Carbonised domestic faba bean remains were discovered at three adjacent Neolithic sites in Israel's Lower Galilee. Based on the radiocarbon dating of these remains, scientists now believe that the domestication of the crop may have begun as early as 8,250 BCE.
Broad beans are still often grown as a cover crop to prevent erosion because they can overwinter and, as a legume, they fix nitrogen in the soil. The broad bean has high plant hardiness; it can withstand harsh and cold climates. Unlike most legumes, the broad bean can be grown in soils with high salinity, as well as in clay soil. However, it prefers rich loams.
In much of the English-speaking world, the name "broad bean" is used for the large-seeded cultivars grown for human food, while "horse bean" and "field bean" refer to cultivars with smaller, harder seeds that are more like the wild species and used for animal feed, though their stronger flavour is preferred in some human food recipes, such as falafel. The name "broad bean" is the most common name in Commonwealth countries like the UK, Canada, Australia and New Zealand, while the term "fava bean" is used in the United States.

Pests and diseases

Many diseases appear at a higher rate in higher humidity. Therefore, cultivars being bred for higher density should be evaluated for disease problems. This can be mitigated by west–east rows for more sun drying effect.
Disease tolerance is an important part of breeding V. faba.
If transplanted instead of direct seeded there is a lower risk of some diseases including Botrytis fabae.

Parasites

In mainland Europe and North Africa, the plant parasite Orobanche crenata can cause severe impacts on fields of broad beans, devastating their yields.

Fungal diseases

''Botrytis fabae''

Vicia faba is attacked by Botrytis fabae, the chocolate spot fungus, which can have a severe impact on yield. It is one of the worst diseases in
broad beans, as it results in foliar damage, reduced photosynthesis, and reduced bean productivity. The fungus switches from non-aggressive growth to aggressive pathogenicity under the combination of increased temperature and humidity, which is worsened by low soil potassium and phosphorus content and by the higher humidity caused by higher seeding rates. The non-aggressive phase is marked by small red-brown leaf lesions, and sometimes the same on stems and pods. Treatment is less effective than prevention. Early planting avoids the problematic combination of high temperature and humidity in late spring into early summer. Decreasing seeding rate or thinning after emergence is also effective. Foliar fungicide is effective. If broad beans flower during the height of summer temperatures there is an increased risk of this disease. If transplanted instead of direct seeded there is a lower risk of Botrytis fabae outbreaks.

''Erysiphe'' spp.

species such as Erysiphe baeumleri are not uncommon on Vicia species. Resistant cultivars and overhead irrigation are preventative. Sulfur fungicides are recommended in severe outbreaks.

''Fusarium solani''

This soil borne pathogen is mitigated by lower temperature, aeration, drainage, and sufficient nutrition. Symptoms include stunting, yellowing, necrotic basal leaves, and brown or red or black streak-shaped root lesions that grow together and may show above the soil as the disease progresses.

''Uromyces viciae-fabae'' var. ''viciae-fabae''

is a fungal pathogen commonly affecting broad bean plants at maturity, causing small orange dots with yellow halos on the leaves, which may merge to form an orange lawn on both leaf surfaces.

''Sclerotinia'' stem rot

Both Sclerotinia sclerotiorum and S. trifoliorum are pathogens of interest. Lithourgidis et al. have done extensive work over the years, including in 2007 for S. t., 2005 for S. s., and 1989 regarding procedures for field testing with ''S. s.''

Bacterial diseases

''Xanthomonas campestris'' and ''X. axonopodis''

Xanthomonas campestris and X. axonopodis can be inoculated by seed contamination and by overwintering in crop residue. Increased incidence with higher temperatures, rainfall, and humidity. Produces deliquescent, necrotic lesions, sometimes with a wider yellow lesion around them, and in advanced disease the plant will look burned. Can be prevented or treated by use of uninfected seed, resistant cultivars, seed treatments, and copper bactericides.

''Pseudomonas syringae''

Pseudomonas syringae overwinters on residue. Uninfected seed, rotation, and removal of residue are preventative.

Viral diseases

Faba bean necrotic yellows virus which it shares with other Vicia. Timchenko et al. 2006 find Clink is not obviously necessary but highly conserved nonetheless, suggesting it is maintained by necessity for infection of other Vicia.

Insect pests

''Aphis fabae''

Broad bean plants are highly susceptible to early summer infestations of the black bean aphid, which can cover large sections of growing plants with infestations, typically starting at the tip of the plant. Severe infestations can significantly reduce yields, and can also cause discolouration of pods and reduction in their saleable values.
Aphis fabae is a major pest. May infest transplants. Reflective plastic mulch may be preventative. May be mechanically removed by high pressure water once plant is established. V. fabae is tolerant to low and medium degrees of infestation, so insecticide application is only required under high infestation.

Toxicity

Beans generally contain phytohaemagglutinin, a lectin that occurs naturally in plants, animals, and humans. Most of the relatively low toxin concentrations found in V. faba can be destroyed by boiling the beans for 10 minutes.
Broad beans are rich in levodopa, and should thus be avoided by those taking irreversible monoamine oxidase inhibitors to prevent a pressor response.

Genetic predisposition

Sufferers of favism must avoid broad beans, as they contain the alkaloid glycoside vicine which may initiate a hemolytic crisis. A low-content vicine-convicine faba bean line was identified in the 1980s and the trait has been introduced into several modern cultivars. Low vicine-convicine faba beans are safe for consumption by G6PD-deficient individuals. As of 2019, a molecular marker may be used for marker-assisted breeding to reduce levels of vicine-convicine in broad beans.

Uses

Culinary

Raw mature broad beans are 11% water, 58% carbohydrates, 26% protein, and 2% fat. A 100-gram reference amount supplies of food energy and numerous essential nutrients in high content. Folate, and dietary minerals, such as manganese, phosphorus, magnesium, and iron, have considerable content. B vitamins have moderate to rich content. Broad beans present the highest protein-to-carbohydrate ratio among other popular pulse crops, such as chickpea, pea and lentil. Moreover, their consumption is recommended along with cereals as both foods are complementary in supplying all essential amino acids.
Broad beans are generally eaten while still young and tender, enabling harvesting to begin as early as the middle of spring for plants started under glass or overwintered in a protected location, but even the main crop sown in early spring will be ready from mid to late summer. Horse beans, left to mature fully, are usually harvested in the late autumn, and are then eaten as a pulse. The immature pods are also cooked and eaten, and the young leaves of the plant can also be eaten, either raw or cooked as a pot herb.
Preparing broad beans involves first removing the beans from their pods, then steaming or boiling the beans, either whole or after parboiling them to loosen their exterior coating, which is then removed. The beans can be fried, causing the skin to split open, and then salted and/or spiced to produce a savory, crunchy snack.