Multivariate Analysis of Root Morphological Traits of T. repens × T. uniflorum Interspecific Hybrids and White Clover at Contrasting Soil P Concentrations

Previous studies found variation among T. repens x T. uniflorum interspecific hybrids for improved growth at low soil phosphorus (P) levels, compared with the parental species T. repens (white clover). A structured population was then developed using two F₁ hybrids (225-2 and 900-4) with different T. uniflorum parental accessions, each backcrossed to three cultivars of white clover to study the effect of parentage on hybrid P responses. In addition, the six BC₁ families, two T. uniflorum parental accessions, three white clover cultivars, and Lotus corniculatus (species control) were screened for root morphological traits, at two soil P levels (low and control). Three week old seedling roots were scanned, and analysed using WinRhizo™ software. The data were used to create clustered image maps and principal components to analyse the relationships between plant lines and traits. This showed that plant lines generally cluster by P level. Clustering of lines differed within P levels, but there were patterns based on genetic background. The three hybrid families with the 225-2 F₁ parent always cluster together, and at the control P level showed high values across size related traits. However, the families with the 900-4 F₁ parent were more different to each other, although two of these cluster together at both P levels. At low soil P the greatest differences were between T. uniflorum and the white clover cultivars, with the latter showing low values across size related traits. The greatest difference at control soil P was for the three 225-2 hybrids with T. uniflorum and Lotus. Overall, the use of multivariate analysis successfully illustrates differences among plant lines for root traits, and associations among traits. This could be refined by including root architectural traits, and extended to nodal roots of different ages to confirm traits of interest for functional roots and established plants.