Genetic Diversity ofStriga hermonthicaPopulations in Ethiopia: Evaluating the Role of Geography and Host Specificity in Shaping Population Structure

Abstract

Striga hermonthica, a root hemiparasitic Orobanchaceae, severely constrains grain production in subSaharan Africa. Host specificity and geography may play important roles in shaping the population structure of S. hermonthica, with the Rift Valley potentially presenting a significant barrier to dispersal. Genetic diversity was assessed in 12 S. hermonthica populations from locations in Ethiopia. Of these, seven populations were parasitic on sorghum, two each on tef and maize, and one on finger millet. Genetic variation was detected using four amplified fragment length polymorphism (AFLP) primer combinations. After correcting for repeatability, 385 fragments were detected across all primer combinations. The percentage of polymorphic loci was relatively high, ranging from 53.2% to 76.4%. Expected heterozygosity ranged from 0.168 to 0.279. Genetic differentiation between populations was relatively high, and all populations were significantly different from each other. F ST values ranged from 0.032 to 0.293 and averaged 0.146. Genetic differences between populations could not be attributed to host specificity. Instead, geography was the main determinant of population structure. There was a correlation between geographic and genetic distance. A significant portion of the genetic variance could be apportioned on either side of the Rift Valley (5%; P ¼ 0:001). Also, a significant geographic barrier was identified in the southern portion of the sampled region.

Assessment of Reaction Patterns of Hybrids to Striga hermonthica (Del.) Benth. under Artificial Infestation in Kenya and Nigeria

“…Some diversity assessment studies using allozymes and random amplified polymorphic DNA demonstrated that geographic distance played a major role in determining the genetic differentiation in S. hermonthica populations collected from different countries in the various regions of Africa (Bharathalakshmi et al, 1990; Kuiper et al, 1996; Koyama, 2000). Similar evidence was presented in another study that examined the genetic diversity among S. hermonthica collections from different regions in Ethiopia using amplified fragment length polymorphism (Welsh and Mohamed, 2011). The occurrence of such variable populations of S. hermonthica may elicit significant changes in reaction patterns of host genotypes from one region to another (Haussmann et al, 2001).…”

Host differentiation and variability of Orobanche crenata populations from legume species in Morocco as revealed by cross‐infestation and molecular analysis

“…First, geographic location appears to play the greatest role in determining genetic differences between the two O. crenata accessions (with only 19% of the divergence occurring among the two faba bean or lentil grown O. crenata accessions). In the case of O. aegyptiaca , O. cumana and Striga hermonthica , genetic distance observed among populations is proportional to the geographical distance between the populations . However, conflicting results showed that there is no clear tendency in distribution of the genetic variability when considering geographical distance in O. crenata populations in Egypt, Spain or Israel as well as for O. hederea and O. ramosa in France …”

The red queen in the corn: agricultural weeds as models of rapid adaptive evolution

“…For example, witchweed (Striga hermonthica), a parasitic weed of cereal crops, has been shown to withstand a wide range of environmental conditions and can parasitize different hosts (Dawoud and Sauerborn, 1994;Ali et al, 2009). Based on AFLP (amplified fragment length polymorphism) markers, this genetically diverse outcrossing weed does not show genetic differentiation correlated with host specificity, but rather, it is correlated with geography (Welsh and Mohamed, 2011), suggesting that the weed is a generalist that can easily invade new crop hosts. Similarly, no genetic differentiation based on AFLP has been found between populations of broomrape (Orobanche foetida) infesting wild legumes and a population parasitizing cultivated vetch, suggesting a generalist ability to undergo host shifts onto cultivated species (Vaz Patto et al, 2008).…”