Identification of QTLs associated with seedling root traits and their correlation with plant height in wheat

Abstract

Genetic relationships between plant height and root morphology were investigated in a diverse set of wheat germplasm [199 double-haploid progeny derived from a cross between Avalon and Cadenza (Triticum aestivum L.), Rht near-isogenic lines (NILs), and accessions from the Watkins Collection] to investigate whether Rht genes controlling shoot height also control seedling root growth. A germination paper screen was developed to measure seedling root length (distinguishing seminal axes from seminal lateral roots), surface area, volume, and dry weight, and these were compared with shoot dry weight and the root to shoot ratio. Field experiments were conducted to measure mature plant height (PH) and grain characteristics for the mapping population. Forty-three quantitative trait loci (QTLs) for PH, root and seed traits were identified. Some QTLs for roots and either height or seed characteristics were coincident: chromosome 2D had co-locating root and PH QTLs; chromosomes 4D had co-locating root, PH, and seed QTLs; chromosome 5A and 6A had co-locating root and seed QTLs; and other non-co-locating root and PH QTLs were found on chromosomes 3A and 3B. Rht NILs illustrated that some known dwarfing genes reduce both PH and root proliferation. However, analysis of 25 short and 23 tall lines from the Watkins wheat germplasm collection indicated that PH and root proliferation are not simply related.

Fig. 1.

Histograms of frequency distribution of root traits, SDW, R/S, PH, and TGW for the Avalon×Cadenza doubled-haploid population used in this study. Data are means of 36 plants for root traits, SDW, and R/S, of 12 independent measurements of PH (4 years, three replicate plots per year), and three samples (single year, three replicate plots) for TGW.

Fig. 2.

QTL mapping for root (blue), plant height (red), shoot (SDW and R/S; black), and TGW (purple) in molecular linkage maps. QTLs for all traits are indicated by bars and caps, which are 1- and 2-LOD likelihood intervals. Data are means of 36 plants for root traits, SDW, and R/S, of 12 independent measurements of PH (4 years, three replicate plots per year), and three samples (single year, three replicate plots) for TGW.

Fig. 3.

Effect of Rht alleles on seminal axes (shaded bar), seminal lateral roots (white bar), and total root traits (shaded + white). Data are the means of three replicates, each replicate consisting of four plants. Error bars are standard errors of these means. Significant differences from the Mercia control are indicated with an asterisk (*P < 0.05) in the appropriate bar or above the stacked bar for the total value.

Fig. 4.

Plant height (PH) as a function of selected root traits for 25 short and 23 tall lines from the Watkins collection of wheat cultivars. Data points are the means of three replicates, each replicate consisting of four plants.