Genotype x environment interactions for root depth of wheat

Numerous studies in have reported on genotype x environment (G x E) interactions for yield and components of yield, but none to our knowledge have attempted to use this approach for root traits. G x E interactions for root depth were assessed for 24 wheat genotypes over six field environments with contrasting soil physical characteristics in the low rainfall zone (ca. 320 mm) of Western Australia. Genotype accounted for only 12% of total variance compared with 40% for G x E interaction. Three environment and six genotype groups were identified, which accounted for 72% of the G x E sums of squares. Of this, AX1, AX2 and AX3 accounted for 30, 24 and 18% of the G x E-SS, respectively. We consider axes AX1 and AX2 to be representative of soil physical characteristics of either a sudden or gradual increase in soil strength with depth, respectively, which constrained root growth. AX3 was linked with other soil parameters related to root growth, possibly boron sensitivity. The three environment groups were defined according to their soil physical characteristics broadly grouped into low (E2), medium (E1) or high (E3) soil strength. The majority of the genotype groups aligned along the diagonal from negative for AX1 and AX2 in the lower left to positive for AX1 and AX2 in the upper right. Genotype groups containing Halberd (G3) and Machete (G5) were better adapted to soil physical constraint and vice-versa for Cranbrook (G2) and C18 (G6) groups. The Janz group (G4) was mapped most negative for both axes, indicating an adaptive preference for friable soils. The Spear group (G1) exhibited a preferential adaptation to soil conditions in which a hardpan was encountered, or in which physical constraint increased early or suddenly. These results indicate that different root traits combinations are required for different target soil environments, as G x E for root depth was significant.