ARS | Publication request: Genetic Improvement of Switchgrass As a Biomass Energy Crop

Submitted to: Meeting Abstract
Publication Type: Abstract
Publication Acceptance Date: June 23, 2006
Publication Date: July 10, 2006
Citation: Vogel, K.P. 2006. Genetic improvement of switchgrass as a biomass energy crip. Abstracts Third Annual World Congress on Industrial Biotechnology and Bioprocessing. July 11-14, 2006, Toronto, Canada. p. 62.

Technical Abstract: Switchgrass, Panicum virgatum, has been identified as a primary herbaceous biomass energy crop for use in temperate areas. To date, switchgrass has been primarily used as a warm-season pasture grass in the Great Plains and Midwest, USA. Previously developed cultivars or varieties have been released for use by grazing animals or for specific conservation purposes. To date, no switchgrass hybrids or cultivars have been developed specifically for use as a biomass energy crop. The reproductive and physiological characteristics of a species determine the breeding procedures that can be used to breed improved cultivars of the species and the range of adaptation of those cultivars. Switchgrasses are photoperiod sensitive and their photoperiod requirement is based on the latitude where they evolved. Switchgrass cultivars are most productive and persistent when used in the USDA Plant Hardiness Zone of their origin or adjacent northern Hardiness Zone. As a result, cultivars need to be developed for specific geographic regions. Switchgrass has a basic chromosome number of x=9 and has two primary ploidy levels, tetraploid (2n=4x=36) or octaploid (2n=8x=72) which have nuclear DNA contents of 3.1 and 6.1 pg 2C-1, respectively. Switchgrass is a cross pollinated species which is enforced by a gametophytic self-compatibility system that is similar to the S-Z incompatibility system that exists in other grasses. Percentages of self-compatibility as measured by seed set from bagged panicles is typically less than 1%. A post-fertilization incompatibility system also exists that inhibits intermatings among octaploid and tetraploid plants. In nature, pollen is dispersed by wind. Normal bivalent chromosome pairing occurs in tetraploid and octaploid switchgrass plants. Switchgrass has two cytoplasm types, `L¿ and `U¿ based on chloroplast DNA (cpDNA) polymorphisms that are associated with the lowland and upland ecotypes, respectively. Because of these genetic characteristics, the primary conventional breeding procedures that have been used are population improvement breeding systems. The most efficient population improvement breeding systems for switchgrass are modifications or Restricted Recurrent Phenotypic Selection (RRPS) and Between and Within Half-sib Family Selection (B&WFS). Breeding work is conducted separately for populations of each ploidy level. Genetic research has demonstrated that genetic variation exists in switchgrass populations for improving biomass yield and modifying switchgrass composition to enhance ethanol yields using these conventional breeding systems. Recent research indicates that it should be feasible to further improve biomass yields by developing hybrid cultivars. There also is potential to improve switchgrass breeding efficiency using molecular biology technologies.