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).