Low genetic variability of Striga gesnerioides populations parasitic on cowpea might be explained by a recent origin

Abstract

Dube M‐P & Belzile FJ (2010). Low genetic variability of Striga gesnerioides populations parasitic on cowpea might be explained by a recent origin. Weed Research50, 493–502. Summary Striga gesnerioides is an obligate root hemiparasitic plant that causes considerable yield losses to cowpea, an important crop legume of Sub‐Saharan Africa. The use of resistant cultivars is the easiest and most effective method to control the parasite. Several cowpea cultivars exhibiting resistance have been identified during the last decades. However, most resistant cultivars show a differential response when grown in different countries across West Africa, suggesting that there are different races of S. gesnerioides. In this study, we investigated the genetic variability within and between 43 populations of five of the previously recognised races of the parasite present in West Africa. Amplified fragment length polymorphism (AFLP) markers were used on up to 10 individuals from each population. These markers showed almost no genetic variability within populations. The variability between the populations was also extremely low and did not allow discrimination of the five races. There was a certain geographical structure, but no ‘racial’ clustering could be seen. Even AFLP markers previously reported to be race‐specific on another set of Striga populations proved unable to discriminate between races in this collection of populations. Possible causes of the low level of genetic variability include the hypothesis that this strain has only quite recently arisen. Such a low level of variability and the absence of specific markers for the virulence will have consequences on the evolution of the parasite and on the development of adequate control methods.

Genetic diversity of Orobanche cumana populations from Spain assessed using SSR markers

“…in West Africa or Indigofera hirsuta L. in Florida. The low genetic diversity was explained on the basis of a common origin of the populations from a limited number of founder plants (Westwood & Fagg, ; Botanga & Timko, ; Dube & Belzile, ). In the case of the O. minor study, the authors also found two clearly different groups of populations, which suggested that they developed from two separate introduction events, as is probably the case for the Cuenca and the Guadalquivir Valley gene pools of O. cumana reported in the present study.…”

“…This indicated that virulent populations do not share a common origin and strongly suggests that they might be the result of independent mutational events. Studies on S. gesnerioides populations collected on cowpea also showed lack of correspondence between genetic diversity and virulence groups in populations showing low genetic variability between and within populations (Dube & Belzile, ). Similarly, Semblat et al .…”

Parasitic Weeds: A World Challenge

“…However, thanks to the extreme host specificity of this species, and its autogamy, it has been possible to find crop varieties each differing in a single dominant gene, with complete immunity to one or more of its races (Li et al 2009;Singh et al 2006). One of the most valuable sources of resistance to be identified (from cowpea landrace line B301 with coincidental resistance to A. vogelii in Botswana) has proved effective against almost all the six or seven recognized races but not to a local race in Benin, which is thought to have evolved relatively recently (Dube and Belzile 2010). This and some other sources identified in West Africa have been used in breeding programs to produce varieties resistant to the local races of the parasite and with other desirable characters (Singh et al 2006).…”

Management of Infection by Parasitic Weeds: A Review

“…To date, at least 7 races (A–G) have emerged along with seven resistant genes ( Or1 – Or7 ). The same type of “arms race” could be observed in both species of witchweeds, S. asiatica [ 126 ] and S. gesnerioides [ 127 ].…”