Genetic Variation for Biomass Yield and Identification of Genomic Regions Associated with Regrowth Vigor and Salinity Tolerance in Lowland Switchgrass (Panicum virgatum L.)
Nayak, S.  2019.  Ph.D. Dissertation.

Switchgrass (Panicum virgatum L.) is a warm ̶ season perennial grass and valued as a promising candidate species for biofuel feedstock production. The genetics underlying feedstock quality, stand stability under changing harvest management, and production of switchgrass on salt-affected land is not well understood. Three studies were conducted to address these areas: (i) Genetic variation for biomass yield and predicted genetic gain in lowland switchgrass ‘Kanlow’, (ii) Assessment of genetic variation and identification of quantitative trait loci (QTL) associated with regrowth vigor in lowland switchgrass, and (iii) Identification of genomic regions associated with salinity tolerance in lowland switchgrass. The results of the first study revealed significant genetic variation for biomass yield (p < 0.05) including feedstock quality traits hemi ̶ cellulose (p < 0.05), and lignin (p < 0.01) content among kanlow half ̶ sib families. With a narrow-sense heritability estimate of 0.10, a genetic gain of 16.5% is predicted for biomass yield in each cycle of selection by recombining parental clones of 10% of superior families. The second study utilized a nested association mapping (NAM) population to identify the genomic regions associated with regrowth vigor in switchgrass. The results showed notable variation among NAM families for regrowth vigor (P < 0.05). Ten QTL associated with regrowth vigor were detected, which accounted for phenotypic variation up to 4.7% with the additive genetic effects ranging from −0.13 to 0.26. In the third study, a subset of NAM population was used. A total of seven QTL associated with salt injury score (SIS) were identified, which accounted for phenotypic variation up to 6.5% with the additive genetic effects ranging from ̶ 0.07 to 0.63. The transcript sequences of the identified QTL have a very high similarity with the genes found in closely related species of switchgrass. These genes are known to play a variety of roles in the plant developmental processes and salinity tolerance mechanism, providing evidence that QTL could be useful in marker ̶ assisted selection after validating their functional effect. The results of these studies would help breeders to integrate classical and molecular breeding to expedite switchgrass improvement.