Promiscuous arbuscular mycorrhizal symbiosis of yam (Dioscorea spp.), a key staple crop in West Africa

Abstract

Yam (Dioscorea spp.) is a tuberous staple food crop of major importance in the sub-Saharan savannas of West Africa. Optimal yields commonly are obtained only in the first year following slash-and-burn in the shifting cultivation systems. It appears that the yield decline in subsequent years is not merely caused by soil nutrient depletion but might be due to a loss of the beneficial soil microflora, including arbuscular mycorrhizal fungi (AMF), associated with tropical "tree-aspect" savannas and dry forests that are the natural habitats of the wild relatives of yam. Our objective was to study the AMF communities of natural savannas and adjacent yam fields in the Southern Guinea savanna of Benin. AMF were identified by morphotyping spores in the soil from the field sites and in AMF trap cultures with Sorghum bicolor and yam (Dioscorea rotundata and Dioscorea cayenensis) as bait plants. AMF species richness was higher in the savanna than in the yam-field soils (18-25 vs. 11-16 spp.), but similar for both ecosystems (29-36 spp.) according to the observations in trap cultures. Inoculation of trap cultures with soil sampled during the dry season led to high AMF root colonization, spore production, and species richness (overall 45 spp.) whereas inoculation with wet-season soil was inefficient (two spp. only). The use of D. cayenensis and D. rotundata as baits yielded 28 and 29 AMF species, respectively, and S. bicolor 37 species. AMF root colonization, however, was higher in yam than in sorghum (70-95 vs. 11-20%). After 8 months of trap culturing, the mycorrhizal yam had a higher tuber biomass than the nonmycorrhizal controls. The AMF actually colonizing D. rotundata roots in the field were also studied using a novel field sampling procedure for molecular analyses. Multiple phylotaxa were detected that corresponded with the spore morphotypes observed. It is, therefore, likely that the legacy of indigenous AMF from the natural savanna plays a crucial role for yam productivity, particularly in the low-input traditional farming systems prevailing in West Africa.

Diversity and species composition of arbuscular mycorrhizal fungi in Clerodendrum species

“…In fact, Glomus is the most widely distributed AMF species and it is considered as cosmopolitan in many ecosystems (Sýkorová et al 2007). Tchabi et al (2009) reported that G. etunicatum which is one of the dominant species in this study tend to be a dominant species in soil samples from the yam field sites.…”

Global Patterns of Cropland Use Intensity

“…However, as these census data were used to develop global inventories of harvested crop area [20] and cropland extent [21] applied as major input for MIRCA2000, these statistics cannot be used for validation purposes in a strict sense, but show nevertheless the consistency between input data used to develop MIRCA2000 and results derived from the dataset. Furthermore there is also evidence from the literature that shifting cultivation or slash-and-burn farming is practiced in many subtropical or tropical regions that have low cropping intensity and large fallow extent in MIRCA2000 [12][13][14][27][28][29][30][31]. Therefore the general pattern of cropping intensity presented in this study is reasonable, but there is a need to verify it by using independent information, e.g.…”

Changes in an Arbuscular Mycorrhizal Fungi Community Along an Environmental Gradient

“…Host preference was several times reported from different environments [37][38][39]. On the other hand, trap culture studies with single host plant species revealed that the large majority of AM fungi, present in the soils, could be propagated on single plant species [40,41]. In this respect, it is also notable that, even for specific plant species, differences between intraradical and extraradical AMF communities might exist, although most AMF species prefer to explore the soils and thus, preferentially live and sporulate in the rhizospheric soil environment.…”