The rapid decline of soil fertility of cultivated lands in developing countries such as sub-Saharan savannas of Africa is considered to be the main cause of increasingly severe constraints of food production. The soils in tropical areas are highly fragile, and characteristically low levels of phosphorus and nitrogen limit crop yield. Arbuscular mycorrhizal fungi (AMF) are the primary providers of P, N, and other trace minerals and increase soil stability in most natural ecosystems. Therefore, enhancing this symbiosis will likely play a pivotal role in maintaining soil fertility and enhancing plant nutrient uptake, plant health, grain quality, and stabilization of soil structure.
Our study assesses mycorrhizal responsiveness of three US modern sorghum hybrids and three African sorghum lines to assess the role of AM symbiosis on low-input management (reduced nutrient applications). Modern (modified) and African sorghum cultivars were grown in native low-nutrient prairie soil maintained under greenhouse conditions. We conducted a complete factorial of the following treatments: 1) not fertilized (controls); 2) fertilized (N and P): 3) not treated with fungicide to suppress the AM symbiosis; 4) treated with fungicide. We assessed AM root colonization, total vegetative production, grain biomass, and grain quality (protein, protein digestibility, starch properties).
Results/Conclusions
When grown in non-amended, low nutrient soil, all African cultivars had significantly greater vegetative and grain production and quality, compared to the modern cultivars. Vegetative biomass was 59.00% greater in the African lines vs modern cultivars and 58.97% greater in grain production, and significantly greater in protein digestibility. This may be attributed to a higher responsiveness to AM symbiosis, as the African cultivars had an average AM colonization of 50.17% compared to 21.83% for the modern cultivars. Fertilizer amendments reduced AM colonization of African cultivars to < 15% and modern cultivars to < 2%. Fertilization increased vegetative and grain production of the modern cultivars. However, fertilization reduced vegetative and reproductive biomass in the African cultivars. Modern and African cultivars were highly responsive to AM fungi in low nutrient soils, as the addition of fungicide substantially reduced production and none of the cultivars produced grain. Fungicide applications reduced AM colonization to < 4%. Fungicide applications were not phytotoxic, as fungicide-treated plants with fertilizer amendments produced biomass similar to that of the corresponding controls. Assessing mycorrhizal dependence of sorghum cultivars could be essential in ensuring sorghum production and grain quality while optimizing sustainability in low-input agricultural systems.