Parasitism of grain legumes by Alectra species (Scrophulariaceae)

Abstract

SummaryIn glasshouse pot experiments in the United Kingdom, the host preference of nine seed samples of Alectra vogelii from Eastern, Western and Southern Africa and of two samples of A. picta from Cameroon and Ethiopia, to cultivars of cowpea, groundnut, bambara and mung bean, was assessed. A susceptible cowpea cultivar, Blackeye, and four cultivars of groundnut were attacked by all samples of both parasitic species regardless of whether the host of origin was cowpea, groundnut or bambara.Five “strains” of A. vogelii were distinguished using two criteria: their ability to parasitise bambara and/or mung bean and their ability to parasitise cowpea B301 and bambara TVU 870. The latter proved in an associated experiment to be resistant to collections of the parasite from some locations. Strain 1, including populations from Mali, Nigeria and Cameroon, attacked all groundnuts, cowpea cultivar Blackeye, but not cowpea line B301, mung bean or bambara. Strain 2, from Botswana, differed in attacking B301 and mung bean. Three other strains were identified which attacked susceptible lines of all four legume species. Strain 3 from Kenya failed to attack either cowpea B301 or bambara TVU 870, strain 4 from Malawi attacked cowpea B301, but not bambara TVU 870, while strain 5 from Northern Transvaal, South Africa, attacked bambara TVU 870, but not cowpea B301. Cowpea B359 was resistant to A. vogelii samples from all locations and also to A. picta, which has a similar host preference to strain 1 populations of A. vogelii from West Africa. Two out of 13 groundnut lines tested showed low susceptibility to A. vogelii from Cameroon suggesting there is scope for selecting resistance in this crop also.

Screening techniques and sources of resistance against parasitic weeds in grain legumes

“…A. vogelii populations from West Africa and Cameroon attack cowpea and groundnut. Those from Eastern Botswana and northern areas of Northern Province of South Africa also attack mung bean, while populations from eastern areas of Northern Province, Kenya, Malawi and Zimbabwe parasitize bambara in addition to the crops that are susceptible elsewhere (Riches et al, 1992). Beyond West Africa, Chad and northern Cameroon, populations of S. gesnerioides occurring in natural vegetation are unable to attack cowpea and extreme host specificity has been demonstrated by a number of authors.…”

“…A further narrowing of the host ranges of both A. vogelii and S. gesnerioides is seen among populations which attack cowpea but are only able to attack some cultivars but not others that are susceptible elsewhere (Parker & Polniaszek, 1990;Riches et al, 1992). In the case of S. gesnerioides five strains have been identified in West and Central Africa, classified on the basis of their ability to develop on seven differential cowpea lines (Lane et al, 1994(Lane et al, , 1997.…”

“…The landrace B301, collected from Botswana, has been used as a "differential" line to distinguish between parasite populations. Although B301 is resistant in the field in Kenya and to A. vogelii from West Africa, pot trials have indicated that it is susceptible to strains of the parasite from Malawi, Botswana and some areas of South Africa (Riches et al, 1992). Unfortunately lines selected as resistant in Nigeria, where there have been considerable efforts to develop cowpeas with dual resistance to both A. vogelii and S. gesnerioides will not necessarily be resistant in East and Southern Africa (Riches, 2001).…”

“…An initial attempt to combine A. vogelii resistance from the late-maturing B359 with early maturity from the improved line TVX3836 proved successful in breeding work in Botswana although the progenies were not taken through to the stage of a resistant variety suitable for release to farmers (Riches, 1989). B359 has been shown in pot trials to be resistant to collections of A. vogelii from a number of countries in East, Southern and West Africa including Botswana, Cameroon, Mali, Malawi, Nigeria and South Africa (Riches et al, 1992). Mainjeni (1999) demonstrated the superiority of B359 as a source of resistance for southern Africa.…”

Phenotypic variation in cowpea (Vigna unguiculata [L.] Walp.) germplasm collection from Botswana

“…Some local cultivars which mature extra early, dual purpose and triple purpose were identified (Botswana Cowpea Project, 1982/83;DAR, 1985/86). Sources of resistance to Alectra vogelli have been found among local germplasm (Fite, 2010), other local materials such as B301 and B359 have been explored in other international institutions (Singh and Emechebe, 1990;Lane et al, 1996;Riches et al, 1992).…”