Molecular phylogenetic analysis, genetic mapping, and improvement of switchgrass (Panicum virgatum L.) for bioenergy and bioremediation to excess phosphorums in the soil
Missaoui, Ali M.
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Research was conducted to explore the genomic organization of switchgrass (Panicum virgatum L.) and its potential for bioenergy and bioremediation to excess P in the soil. The utility of nrDNA ITS1-5.8S-ITS2 region and chloroplast trnL(UAA) intron in determining relatives of switchgrass in the genus Panicum were evaluated using 42 Panicum taxa. The ITS sequences exhibited higher divergence than trnL(UAA) and provide potential in resolving the classification of this genus. Alignment of trnL(UAA) sequences from 34 switchgrass accessions revealed a 49 nucleotide-deletion (.350-399) specific to lowland accessions, which can be used for the classification of upland and lowland germplasm. The extent of genetic diversity in 21 upland and lowland switchgrass genotypes was investigated using 85 RFLP probes. Jaccard and Dice distances showed a high genetic diversity between and within ecotypes. The segregation and linkage of 224 single dose restriction fragments (SDRF) generated from 99 RFLP probes in 85 progenies of two tetraploid (2n = 4x = 36) parents (Alamo x Summer) indicated that switchgrass is an autotetraploid with high degree of preferential pairing. The recombinational length of switchgrass genome is 4617 cM. Greenhouse and field investigation of the genetic variation and heritability of P uptake in 30 genotypes under fertilizer rates of 450 mg P and 200 mg N Kg -1 soil showed that switchgrass accumulates high levels of P (0.76 % in the greenhouse and 0.36% in the field). P uptake was correlated more with biomass production (r= 0.65 to 0.90) and less with P concentration (r= 0.10 to 0.42). Expected gain from selection for P concentration is low (1 to 2%). A substantial progress can be achieved through selection for higher biomass. Effectiveness of the honeycomb selection design in identifying superior genotypes for biomass production in switchgrass was evaluated at 1.2 m inter-plant spacing. In four field experiments, yield of half-sib lines derived from polycrossing 15 genotypes selected for high yield was on average higher than the yield of half-sib lines derived from 15 genotypes selected for low yield from Alamo and Kanlow nurseries. This suggests that identifying superior genotypes at 1.2 m spacing using the honeycomb method is possible.