Location: Grain Quality and Structure Research2012 Annual Report
1a. Objectives (from AD-416):
1) Determine if differences in mycorrhizal dependence exist in selected US elite sorghum hybrids and African sorghum lines, and determine how this is reflected in their response to low input management (low levels of N and P); 2) Integrate these findings into measures of the growth and production of sorghum crops, grain quality, and evaluation of end-use quality.
1b. Approach (from AD-416):
Our approach will be to 1) evaluate mycorrhizal dependency of modified sorghum cultivars in controlled greenhouse studies; 2) determine consequence of reductions in dependency on the symbiosis by assessing: drought tolerance, grain quality (C:N:P) and quantity, biomass production, and root morphology (e.g. root length production) of selected cultivars; 3) assess drought tolerance, tissue quality, and biomass production of selected cultivars grown with and without the fungal symbiont, under high- and low-input fertilization; 4) conduct biochemical characterization of sorghum starch and protein; and 5) evaluate end-use grain quality from each cultivar.
3. Progress Report:
The rapid decline of soil fertility of cultivated lands in the sub-Saharan savannas of Africa is considered to be the main cause of the increasingly severe constraints of food production. The soils in this tropical area are highly fragile, and crop yields are limited by characteristically low levels of phosphorus and nitrogen. Under these conditions, the multiple benefits of the arbuscular mycorrhizal (AM) symbiosis are likely to play a pivotal role for maintaining soil fertility and enhancing plant nutrient uptake, plant health, grain quality, and stabilization of soil structure. Specific goals of this research were to 1) evaluate mycorrhizal dependency of modified sorghum cultivars in controlled greenhouse studies; 2) determine consequence of reductions in dependency on the symbiosis by assessing: biomass production, tissue and grain quality of selected cultivars grown with and without the fungal symbiont, under high- and low-input fertilization. Genotypes developed by the sorghum breeding and genetics program at Kansas State University were screened to evaluate the mycorrhizal dependency of sorghum cultivars that have been modified for increased yield capacity. Cultivars were grown in one of 4 treatments: 1) non-amended native prairie (low-nutrient, high soil quality) 2) native prairie soil with fertilization (N and P), 3) native prairie with fungicide (suppress AM fungal activity), or 4) native soil with both fungicide and fertilization amendments. Plants were harvested at grain production, and growth and production of sorghum cultivars, and grain quality was determined. Significant progress has been made on understanding the influence of cultivar selection on arbuscular mycorrhizal (AM) dependence of sorghum crops. This two year greenhouse study assessed the role of AM symbiosis on sorghum biomass production and grain quantity and quality. Modern (modified) and African sorghum cultivars were grown in native low-nutrient prairie soil and treated with low- and high-fertilization (N and P). Half of the sorghum plants were treated with fungicide to suppress the AM symbiosis. 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 starch quality. 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.