We'd like to understand how you use our websites in order to improve them. Register your interest. In Burkina Faso, cowpea serves as both a food and cash crop generating significant income for stakeholders. However, cowpea production is seriously hampered by several constraints among which is the parasitic weed Alectra vogelii. Cowpea genotypes were screened under artificial screen house and natural field A. For the screen house experiment the data were collected on parameters such as days to cowpea flowering and maturity, days to Alectra shoots emergence, the severity of Alectra attack.
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It is closely associated with cultivation, is occasional It is closely associated with cultivation, is occasionally found associated with weeds of fallows but rarely in natural vegetation.
Copious seed production and a long-lived seed-bank allow the rapid build up of infestations when susceptible crop cultivars are planted.
Tiny seeds are easily spread by wind, surface water flow or in crop seed. An assessment of its global invasive potential is given by Mohamed et al. Engler split the species into A. However, in his taxonomic revision of the genus, Melchior considered these all to be characteristic of A. All previous and subsequent major floras for West Africa Hutchinson and Dalziel, and south-eastern Africa Philcox, have maintained the name as A.
Although these accounts include the genus in the family Scrophulariaceae, a sequence analysis of three plastid genes suggested that it should be placed in the Orobanchaceae along with other closely related parasitic genera Olmstead et al. No morphological or anatomical evidence for this reclassification has however been advanced. As flowering specimens are very leafy and with a similar habit to many free-living plants, people who are not familiar with root hemi-parasites are unlikely to recognize that A.
Below ground, bright orange stems are attached to host roots by a spherical haustorium up to 2 cm in diameter. This is composed of a mass of host and parasite tissue and the orange adventitious roots of the parasite.
Plants grow to cm tall, often as a single stem but sometimes branching from near soil level. The stems and leaves, which can be 1. Leaf shape, particularly the nature and extent of toothing along the edge of the lamina, varies considerably. In parts of West Africa, leaf margins are almost entire, in central and southern Africa they may have two to five widely spaced teeth along each edge while in Kenya plants with five or six sharp teeth, each up to 3 mm long, have been collected.
Flowers appear singly on a short stem in the axils of upper leaves or bracts. Up to 10 flowers may open on one day. The flower buds are enclosed in a densely hairy calyx whose five lobes each have a triangular tip with an obtuse apex.
The tubular corolla is formed of five petals fused towards the base, so that the flower is bell-shaped when open.
The corolla is 0. The petals are pale yellow and may or may not have three deep red veins. Both types of flowers can be found in a group of plants. The anthers and filaments are glabrous. The flowers wither and remain covering the developing globose seed capsule which swells to approximately 5 mm in diameter at maturity. The dust-like seeds have a complex structure. An outer cell layer of the testa is modified into a cone or a 'trumpet-like' structure about 1 mm long within which the 'kernel' of the seed, measuring about 0.
The surface of the seed coat is covered in indentations. In the Nigerian savannahs it can be found in cowpea crops which are also attacked by Striga gesnerioides , and it has been reported as the major parasite of the crop in the northern Guinea savannah Lagoke, Elsewhere in West Africa, infestations tend to be more localized, as in southern Mali. The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status.
Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report. The species is assumed to have an origin in West Africa and to have spread with human migrations and along trade routes with cowpea cultivation but no records exist on its first appearance in particular areas. It is often present at low densities in stands of traditional cowpea land-races but builds up rapidly to become a problem when a susceptible exotic cultivar is introduced as occurred in Botswana from the late s.
There is no indication that the species is spreading although greater attention from development workers in communities where cowpea is produced for household food security has highlighted the distribution and importance of the species in the past years.
Although A. This should be prevented by undertaking seed multiplication on uninfested fields and careful inspection of the crop. The main danger in Africa would be to introduce biotypes with differential host specificity from one area to another. The accidental introduction of the related Striga asiatica , a noxious parasitic weed of maize and other cereals, into the USA in the s Parker and Riches, demonstrates that long-distance spread of the tiny seeds of these root parasites is possible.
Reports of the species in association with non-crop legumes and occasionally non-legumes always involve weeds on fallow or cropped arable land. It has not been reported as a component of natural vegetation. Cowpea is the major crop host of A.
Bambara, groundnuts, common bean, soyabean, mung bean, and tepary are also common hosts and there have been occasional reports of infestation of chickpea and runner bean. Pigeon pea is the only widely grown grain legume which is not parasitized. Host range tests Riches et al. Samples from eastern Botswana and northern areas of Northern Province, South Africa attack mung bean in addition to cowpea and groundnut.
Populations sampled from Kenya, Malawi and eastern areas of Northern Province, South Africa, parasitize bambara as well as crops which are susceptible elsewhere. No association has been observed between morphological variation, largely in leaf shape, and host preference. Many other legumes are hosts including species such as lab lab and velvet bean which are often introduced as fodder or green manure crops in infested areas.
Genetics The chromosome number 2n is 38 Parker and Riches, The extent of genetic variation within or between populations is not known. Reproductive Biology Controlled experiments have shown that A.
However, field observations demonstrate that the anthers will only release pollen when stimulated to do so by foraging insects Riches, ; Parker and Riches, Pollen-feeding flies in the genera Cosmia , Ischiodon , and Rhyncomya and various bees including Amegilla and Lasioglossum species release a cloud of powdery pollen as they forage over the anthers onto the adjacent large stigma to effect self-pollination.
As bees carry loads of pollen as they forage throughout a flowering stand of the parasite, it is likely that cross-pollination also results from insect activity. The relative importance of self- or cross- pollination has not been studied. Parker and Riches have reported that seeds may remain viable in the soil for up to 12 years. Each A. Physiology and Phenology A. The seed has no after-ripening requirement. Prolonged periods of imbibition of the seed in water, in the absence of a stimulant, does not induce a 'wet dormancy' characteristic of many parasites in the related genus Striga Botha, Four substances that stimulate A.
A stimulant termed alectrol, isolated from cowpea root exudates Muller et al. Synthetic analogues of strigol, including GR7 and GR24, are effective stimulators of the germination of A. The radicle of A. Growth towards the root is a chemotropic response to a concentration gradient of host root exudate Visser, The parasite grows within the host until contact is made with xylem vessels and phloem sieve tube elements of the host stele. About 12 days after germination, the parasite has penetrated the host and the parasite stem begins to elongate following the differentiation of the first leaves.
The parasite stimulates a proliferation of host lateral roots in the region around penetration and formation of the haustorium. Shoots emerge above ground about 4 weeks after the parasite radicle has penetrated a cowpea root and first flowers are produced some 2 weeks later. Environmental Requirements As A. By and large these are found in semi-arid areas with a short growing season of 4 to 6 months, below m altitude.
The parasite is most commonly found in areas of mono-modal rainfall with a long dry season as in Botswana or the Guinea savannah of West Africa, but it is also a pest in bimodal rainfall areas as in north-west and coastal Tanzania. Although crops are not produced during the cold dry season in the range of the parasite, frost at the end of the growing season will kill host plants surviving in crop residue on residual moisture and will prevent further seed production by A.
Host crops are largely associated with free-draining sands and sandy-loams. Some herbivorous insects and fungal diseases have been reported from A. Larvae of the moth Stenoptiloides taprobanes feed on the flowers preventing seed production on predated flowers Parker and Riches, From East Africa, Greathead and Milner have reported both Ophiomyia strigalis attacking roots and Platyptilia sp. However, only a small proportion of plants are attacked so the overall effect on seed production is probably not significant.
The reticulated surface of the minute seeds trap pockets of air when they float on water, making the seed buoyant and easily dispersed at least for short distances in rainwater run-off. The trumpet-like structure of the outer seed coat makes the seeds aerodynamically suited to being wind-blown even in the lightest breeze, and windy conditions are common in the dry season in regions where A.
Man is a dispersal agent through the harvesting of legume seed pods from infested stands. Seeds of the parasite may contaminate grain legume seeds during threshing and be transported to markets or neighbouring farms during local sales.
Before parasite emergence, aboveground affected cowpea plants may appear wilted. Delayed flowering, a reduced number of flowers and pods all contribute to yield loss. The extent of yield loss depends on the susceptibility of the cultivar with greatest losses reported for introduced lines rather than landrace types Parker and Riches, Most information on the economic impact of A. Late sown crops of soyabean may be completely destroyed by the parasite in northern Nigeria Lagoke, In Tanzania, A.
Introduced cowpeas are often very susceptible. Cowpea is an inexpensive, high quality source of protein of major importance to the nutrition of poor rural households in sub-humid and semi-arid areas of sub-Saharan Africa Singh et al. Studies from these areas show a high incidence of poverty and associated problems such as malnutrition among under-5s e.
The presence of so-called 'beards' or hairs on the stamen filaments of A. The leaves of A. However, in Cameroon and West Africa, leaves of the two species are similar. Both species are known from the same areas of Cameroon and Malawi and in Malawi both have been observed growing in the same row of groundnuts. The host range is almost entirely on weeds or natural vegetation, especially the Compositae Parker,
List of symptoms / signs
Alectra vogelii Benth.