Arbuscular mycorrhizal fungi for enhanced nutrient and moisture utilization in sweet potato production
Mukhongo, Ruth Wilhem
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Sweet potato (Ipomoea batatas (L) Lam) yields are low in Uganda recording 4.5 t ha-1, which is about 10% of attainable yield (45 t ha-1) in Africa (CIP, 2006). The low yields are attributed to infertile soils especially a deficiency in phosphorus (P) in tropical soils. Arbuscular Mycorrhizal Fungi (AMF) enhance P mobilization for plant uptake. However, most soils have a low AMF abundance and require inoculation. Therefore, specific objectives of the study were to determine i) the composition and spore abundance of AMF in sweet potato producing regions in Uganda for local inoclum production; ii) the efficacy of native AMF and phosphorus on growth and yield of sweet potato; iii) the effect of native AMF on P uptake and growth of sweet potato under moisture stress, and iv) the effect of combining commercial AMF with nitrogen and potassium fertilizers for increased sweet potato productivity. Assessment of the composition and spore abundance of AMF in sweet potato zones revealed a similarity in the AMF communities with Glomus and Acaulospora species accounting for 38 and 20%, respectively of the enumerated spores. Native Acaulospora sp.2 was competitively effective as the commercial species Glomus etunicatum, G. mosseae, and G. claroideum in root colonization intensity, apparent P recovery efficiency (APRE), and biomass. Glomus etunicatum combined with 45 kg P ha-1 resulted in the highest root colonization intensity, APRE, and biomass at varying soil moisture levels followed by Acaulospora sp.2. However, increasing moisture stress increased root colonization while reducing moisture stress increased nutrient uptake, and biomass/yield. Multiple species inoculants highly increased root colonization, nutrient uptake and biomass as compared to single species. Multiple species inoculant (G. etunicatum, G. mosseae, G. claroideum, and G. intraradices) combined with 90 kg N ha-1 and 100 kg K ha-1 gave tuber yield (24.3 t ha-1) that was statistically (p<0.05) similar to the yield of 45 kg P ha-1 combined with 90 kg N ha-1 and 100 kg K ha-1 (23.7 t ha-1). Therefore, native superior AMF species should be isolated and identified for efficacy testing and multiplication for commercialization which will reduce the cost of bioinoculants in Uganda and her neighbors.