Characterization and screening of Native Arbuscular Mycorrhizal Fungi Isolates from Maize (Zea Mays L.) Agro Ecosystems in South Kivu, Democratic Republic of Congo

Abstract

Maize (Zea mays) is a staple food playing a crucial role in food security and income generation for many farmers but its productions is constrained by low soils fertility and poor crops husbandry in DRC. Phosphorus (P) is a critical macronutrient required for maize production and yet most deficient in the agricultural soils of South Kivu which are inherently low in P content coupled by high fixation capacity. Maize is a highly mycorrhizal plant but little is known about its mycorrhization in its cropping system in different agroecologies in South Kivu. The objectives of this study were to characterize the occurrence and diversity of native AMF and natural mycorrhizal infectivity potential of soils from maize cropping systems of South Kivu, DR Congo, and to screen and evaluate the influence of AMF isolates on maize growth, P and Zn nutrients uptake, and root colonization in dominant acidic soils of South Kivu namely Ferralsol and Nitisol, under controlled conditions. Soil samples were collected from maize rhizosphere in 12 villages spread across four territories representative of the 3 AEZs in South Kivu. A trap culture was initiated and AMF spores were extracted from field and trap culture soils and species identified using the morphotypes criteria. AMF diversity, frequency of occurrence and species richness were examined. Roots colonization was assessed after bio infectivity assay for soils mycorrhizal potential determination. Soil monospecies inoculums were produced and after screening, five native AMF strains named AMF1 (Gigaspora gigantea). AMF2 (Gigaspora sp.), AMF3 (Gigaspora margarita), AMF4 (Rhizophagus intraradices) and AMF5 (Acaulospora. reducta) were selected as probable good AMF biofertilizers. A greenhouse experiment was conducted using single specie inoculation and these inoculums, applied in a Ferralsol and a Nitisol, were compared to the inorganic P application, the commercial biofertilizer Rhizatech and the control. Plant height, chlorophyll content, shoot biomass, shoot P and Zn content, hyphal P contribution and root colonization were observed. Data were subjected to analysis of variance and means separated by the Fisher‘s least significant difference. A total of 45 strains of AMF distributed in 11 genera were obtained with the majority being from Gigasporaceae, Acaulosporaceae and Glomeraceae. Acaulospopra excavata, Acaulospopra bireticulata, Dentiscutata erythropa, Funneliformis mosseae and Scutellospora pellucida were ubiquitous in all the agroecologies. Species distribution was mostly influenced by the soil pH and exchangeable Al. At least 22% of the soils had a mycorrhizal infectivity potential as good as the Rhizatech. The soil AMF inoculum produced had low spore densities (0 - 2.85 spores g-1) compared to the density of Rhizatech (4 spores g-1). In the Ferralsol, there was no difference for the P content (p= 0.195), xiii but for the Zn content, AMF2 was the highest followed by AMF1. The roots were colonized equally (p = 0.252) in all the treatments. In the Nitisol, AMF4 equalized with the Pi application for the shoot biomass, followed by AMF1. The highest root colonization was observed in AMF4 (31%) and Rhizatech (28%). This is the first report on the study of native AMF species in South Kivu and there is probably a species that was found for the first time. The high number of ubiquitous species indicates adaptation to a wide range of physicochemical environments and could also reduce the cost of production of inoculants. Other methods of AMF inoculum production like the mass production using in-vitro techniques or the stimulation of naturally occurring AMF species in the fields should be tested. Furthermore, there is a need to screen for efficient AMF strains that could improve nutrients acquisition and maximize plants benefits from the symbiosis. Further studies assessing the performance of these selected efficient AMF Gipaspora gigantea, Gigaspora sp., Rhizophagus intraradices and Acaulospora reducta with high spores densities are recommended.