3.2 QTL Mapping of Fungal and Insect Surveys
Three QTL intervals containing a total of 26 markers were significantly associated with the abundance of fungal pathogens (Table 2, Figure 4a,b). An overlapping QTL on Chr04 (Figure 4a) was associated with bothMelampsora sp. (marker position = 3.50687, p-value = 0.001) andS. musiva leaf spot disease severity (marker position = 15.4912824, p-value = 0.026). The marker with the highest LOD score explained 54.1% of the variance in the disease severity ofMelampsora sp. within the Chr04 QTL interval, whereas the top marker within the overlapping interval only explained 3.31% of the variance in the disease severity of S. musiva . The positive allele contributing to an increase in fungal infection for both species was derived from P. trichocarpa . Binary presence of the canker symptoms caused by S. musiva (Figure 4b) was found to be associated with a QTL located on Chr16 (marker position = 60.81429, p-value = 0.022). The positive allele contributing to increase in presence of S. musiva canker was from P. trichocarpa .
Three QTL intervals containing a total of 40 markers were significantly associated with insect abundance (Table 2, Figure 4c,d). A QTL on Chr05 (marker position = 21.83874, p-value = 0.001) was associated with binary presence of M. vagabunda branch galls (Figure 4c). The positive allele contributing to an increase in presence of M. vagabundawas from P. trichocarpa . Two QTLs, one located on Chr10 (marker position = 57.69914343, p-value = 0.015) and one located on Chr13 (marker position = 84.43857329, p-value = 0.045) were associated with the number of leaf-folding galls from Phyllocolpa sp. (Figure 4d). The marker with the highest LOD score explained 9.65% of the variance in oviposition gall count while 8.82% of the variance was explained by the top marker located on Chr13. For both markers, the positive allele contributing to an increase in the number of female oviposition galls was from P. deltoides . There were no QTL intervals that passed the permutation threshold for the binary presence of P. populitransversus petiole galls (Figure 4c).