Research

Projects: Sorghum breeding program for biofuel production | Photosynthesis | Photoprotection | Plant architecture | Cold tolerance

Sorghum breeding program for biofuel production
Biofuels have been suggested as a potential major contributor to the energy security of the United States, to the economic growth of Iowa and to the reduction of greenhouse gasses emission that contribute to climate change. The Energy Independence and Security Act (2007) established that 36 billion gallons of biofuels per year had to be produced by 2022. In 2007, 6.45 billion gallons of ethanol were produced from maize, and even though maize-based ethanol is predicted to continuously grow, it cannot supply the total demand and it has important detrimental implications for food and feed supplies. Therefore, other sources need to be developed to efficiently produce ethanol in large scale, such as lignocellulosic feedstock and/or sucrose producing crops (i.e sweet sorghums).

In 2008, Dr. Salas Fernandez initiated the sorghum breeding program for biofuel production at Iowa State University. The main goal of the program is to conduct research that leads to and supports the development of sorghum germplasm for biofuel production adapted to Iowa. The breeding program is centrally located in Ames, IA, with winter nursery activities in Puerto Rico and three testing locations in Iowa were experimental hybrids are evaluated every year using an experimental forage chopper purchased and adapted by the Department of Agronomy and Agricultural engineers at ISU. (link to video)

Theoretical ethanol yields for corn grain are estimated to be approximately 540 gallons/acre considering yields of 200 bushels/acre. Sorghum ethanol yields vary depending on the type of sorghum cultivated. Sweet sorghums can produce 900 gallons/acre, if we consider a standard composition, yields of 16 Tn of dry matter per hectare and a 90% conversion efficiency. Our yield trials provided information to demonstrate that biomass sorghum can produce, in theory, up to 870 gallons/acre as a lignocellulosic feedstock, considering our highest yields of 27 Tn dry matter/ha, a standard composition and a 90% conversion efficiency (link to farm reports). Therefore, sorghum could become the preferred bioenergy crop, considering its high yield potential for ethanol production and the additional benefit of low input use, since it requires less nitrogen and water than corn. Sorghum could be planted in unexploited marginal areas but it could also become a primary crop in rich soil areas of Iowa due to lower production costs.

Photosynthesis
Carbon assimilation through photosynthesis is the basis of crop productivity. However, increases in crop yield achieved in the last 50 years have not been attributed to changes in photosynthetic capacity. The complex genetic architecture of C assimilation and the lack of correlation between grain yield and photosynthesis were the most important arguments to postpone significant investments in this scientific area. The advancement of "omics" technology, high-throughput phenotyping methods and biofuels has significantly changed the paradigm. Considering there is a direct association between photosynthetic efficiency and biomass yield, the discovery and exploitation of the genetic architecture controlling C assimilation could have a significant impact on biomass yield for biofuel production. Dr. Salas Fernandez and her team are investigating genes/alleles associated with higher leaf photosynthetic capacity under field conditions. Two projects were recently funded in this area, one focusing on carotenoids and their role as important pigments in photosynthetic complexes (Sorghum Checkoff program) and a second project investigating genome-wide allelic variation associatied with higher photosynthetic capacity and growth (USDA-DOE Plant Feedstock Genomics for Bioenergy).

 licor

Photoprotection
Any environmental stress such as cold, drought, heat, etc. that could limit the amount of CO2 that can be fixed through photosynthesis, triggers a set of mechanisms to dissipate the excess energy collectively called photoprotection.

Photosynthesis and photoprotection are closely interconnected mechanisms since absorbed light will either be used for C assimilation or dissipated to avoid cell damage. Both physiological mechanisms will affect biomass production but unfavorable environmental conditions will reduce the plant photosynthetic capacity and therefore under those conditions, photoprotection will affect plant performance and productivity even more. In sorghum, yield losses attributed to unfavorable environmental conditions can be as high as 80% of its potential yield. Climate change will represent an extra burden on crop production since global temperatures are predicted to rise and food, feed, fiber and fuel will have to be produced under more extreme environmental conditions. Therefore the contribution of a novel abiotic stress mechanism such as photoprotection can be significant.

The discovery and exploitation of natural genetic variation controlling photoprotective mechanisms under cold and drought conditions are currently under investigation by our group in a project funded by NSF (CAREER Plant Genome Research Program).

Plant architecture
Several hormones are involved in the biochemical and physiological responses that determine plant architecture characteristics highly correlated with biomass yield such as plant height, leaf angle, stem diameter, tillering, number of florets, etc. Brassinosteroids, gibberellins and auxins have the strongest impact without severe undesirable pleiotropic effects. Identifying genes involved in biosynthetic and signaling pathways of these groups of hormones and the effects of alternative alleles will reveal the allelic combination to obtain a particular plant type. Sorghum germplasm offers a vast genetic diversity to dissect plant architecture traits and identify genes/alleles controlling specific characteristics. Once markers closely linked to functional polymorphisms are identified, they can be exploited in breeding programs to develop specific plant types for different production systems more efficiently and in shorter periods of time.

With the need to produce more food, feed and fuel in the same or smaller area (due to erosion), and considering the predicted consequences of climate change in the coming years, manipulating genes to create desirable plant types in a shorter period of time and more efficiently will be essential in breeding programs. Sustainable production of biofuel will also require using fewer inputs, in more marginal lands, and therefore producing a specific sorghum plant for that production system will be very valuable as well.

 plant diversity
seeds germinating

Cold tolerance
Sorghum can be cultivated in many countries and regions in the world but it is best adapted to tropical and subtropical areas due to its African origin. Therefore, low soil temperature during early season is one of the major limitations for sorghum production in temperate climates. Tolerance to low temperatures at germination is not only desirable to ensure a good stand but it would also facilitate early planting, which could translate into longer growing seasons and, therefore, higher yields. Tolerance to cold temperatures at germination is also essential to expand sorghum cultivation to more extreme latitudes and it is a required trait for no-till or minimum-tillage practices in temperate climates.

Sorghum cold tolerance at germination has been characterized as a highly heritable trait, with significant general combining ability. QTL have been identified and could be incorporated into a marker-assisted breeding program after validation. However, a limited number of sorghum lines have been classified as cold tolerant at germination and these lines have undesirable agronomic characteristics that have hindered their use in sorghum breeding programs. Considering that it is important to find additional sources of variation for the trait, we are characterizing an unexploited set of sorghum accessions under controlled and field conditions to determine their potential to contribute cold tolerant characteristics to our breeding program.