Pleiotropic effect
We hypothesized that loci impacting panicle traits might show strong pleiotropic relationships with other important characteristics of switchgrass growth and development. To test this idea we examined whether the QTL identified for panicle traits shared the same QTL with flowering (FL50), tiller count (TC), and biomass (BIO) in switchgrass. Our results (Figure 4 and Table 4) showed that two QTL (2K@77.89, 3N@62.06) for PL overlapped with QTL for BIO, one QTL (4K@26.26) overlaps with FL50, and one QTL on 9N@38.02 clusters with FL50, TC, and BIO. Out of the seven QTL for PBN, six QTL shared the same QTL with either FL50, TC or BIO, with five QTL (2N@66.12, 3K@38, 5N@84.04, 7N@54.06, 9N@26.03) exhibiting pleiotropy with FL50, two QTL (3K@38, 5N@84.04) with TC and one (2K@74.02) with BIO. One QTL of SBN (9N@38.02) clustered with QTL of TC and BIO. Among these pleiotropic QTL, some showed similar patterns of QTL x E, providing further support for a pleiotropy hypothesis. For example, the QTL 3N@62.06 for PL exhibited condition-specific effects (Figure 5) and the overlapping QTL for BIO showed a similar pattern (data not shown). The QTL 9N@38.02 for PL displayed the same pattern (i.e., no QTL x E, figure 5) as the overlapping QTL for FL50 and BIO, but not for TC, suggesting there may be different loci controlling PL and TC.