Structural-functional dissection and characterization of yield-contributing traits originating from a group 7 chromosome of the wheatgrass species Thinopyrum ponticum after transfer into durum wheat

Abstract

For the first time, using chromosome engineering of durum wheat, the underlying genetic determinants of a yield-improving segment from Thinopyrum ponticum (7AgL) were dissected. Three durum wheat-Th. ponticum near-isogenic recombinant lines (NIRLs), with distal portions of their 7AL arm (fractional lengths 0.77, 0.72, and 0.60) replaced by alien chromatin, were field-tested for two seasons under rainfed conditions. Yield traits and other agronomic characteristics of the main shoot and whole plant were measured. Loci for seed number per ear and per spikelet were detected in the proximal 7AgL segment (0.60-0.72). Loci determining considerable increases of flag leaf width and area, productive tiller number per plant, biomass per plant, and grain yield per plant were located in the distally adjacent 0.72-0.77 7AgL segment, while in the most distal portion (0.77-1.00) genetic effects on spikelet number per ear were identified. Contrary to previous reports, trials with the bread wheat T4 translocation line, carrying on 7DL a sizeable 7AgL segment of which those present in the durum wheat-Th. ponticum NIRLs represent fractions, gave no yield advantage. The hypothesis that ABA might be a factor contributing to the 7AgL effects was tested by analysing endogenous ABA contents of the NIRLs and their responses to exogenous ABA application. The 7AgL yield-related loci were shown to be ABA-independent. This study highlights the value of wheat-alien recombinant lines for dissecting the genetic and physiological basis of complex traits present in wild germplasm, and provides a basis for their targeted exploitation in wheat breeding.

Keywords: Alien gene transfer; Triticum aestivum; Triticum durum; biomass; chromosome engineering; flag leaf; grain yield; seed number; segregation distortion; tiller number; yield QTL..

Fig. 1.

Yield-contributing traits recorded on the whole plant of homozygous durum wheat NIRLs (HOM+) and of their 7AgL non-carrier controls (HOM–) in 2009 and/or 2010: (A) 2009 + 2010; (B) 2009 versus 2010; (C) 2010 only. GY, grain yield per plant; SN, seed number per plant; TKW, thousand-kernel weight; GYE, grain yield per ear; SNE, seed number per ear; TTN, total productive tiller number; B, biomass per plant; HI, harvest index; letters correspond to ranking of groups after Tukey HSD test, capitals P <0.01, lower case P <0.05; *, ** and *** indicate significant differences after Tukey HSD test at P <0.05, P <0.01. and P <0.001, respectively; the absence of any mark indicates non-significance. R5, R5-2–10; R112, R112-4; R23, R23-1; 09, 2009; 10, 2010.

Fig. 2.

Yield-contributing traits recorded on the main shoot in 2009 and 2010 of homozygous durum wheat NIRLs (HOM+) and of their 7AgL non-carrier controls (HOM-): (A) 2009 + 2010; (B) 2009 versus 2010. FLW, flag leaf width; FLL, flag leaf length; FLA, flag leaf area; EL1, ear length; GYE1, grain yield per ear; SNE1, seed number per main shoot ear; SPS1, seeds per spikelet; SPNE1, spikelet number per ear; letters correspond to ranking of groups after Tukey HSD test: capitals, P <0.01, lower case, P <0.05; * and *** indicate significant differences at P <0.05 and P <0.001, respectively; the absence of any mark indicates non-significance. R5, R5-2–10; R112, R112-4; R23, R23-1; 09, 2009; 10, 2010.

Fig. 3.

Discriminant analysis (DA) plot for homozygous durum wheat NIRLs (HOM+) and of their 7AgL non-carrier controls (HOM–) for traits recorded in (A) 2009 and 2010, and (B) 2010 only: dark blue, R5-2–10 HOM+; light blue, R5-2–10 HOM–; red, R112-4 HOM+; yellow, R112-4 HOM–; dark green, R23-1 HOM+; light green, R23-1 HOM–.

Fig. 4.

ABA and yield-contributing traits: effect of ABA treatment on yield-contributing traits of the main shoot of 7AgL-carrier (HOM+) and non-carrier (HOM–) genotypes of (A) durum wheat NIRLs and (B) bread wheat T4 line; (C) endogenous ABA content in spikes at the boot stage and relative water content (RWC) of the corresponding flag leaf. FLW, flag leaf width; FL-1W, flag leaf-1 width; FL-1L, flag leaf-1 length, FLA, flag leaf area; FL-1A, flag leaf-1 area; EL1, ear length; SPNE1, spikelet number per ear; DW, dry weight.

Fig. 5.

Cytogenetic maps of the 7A-7Ag recombinant chromosomes representing the durum wheat–Th. ponticum NIRLs used in the present study (adapted from Ceoloni et al., 2005, 2014), with assignment to defined 7AgL regions of markers (SSR, simple sequence repeats or microsatellites; STS, sequence tagged sites; EST, expressed sequence tags), known genes (Lr19, Sr25, Yp, Sd, see text), and putative loci for yield-contributing traits (SPS1, seed number per spikelet; SNE1, seed number per ear; FLW, flag leaf width; FLA, flag leaf area; TTH, tiller number at heading; TTN, total productive tiller number; SN, seed number per plant; GY, grain yield per plant; B, biomass per plant; SPNE1, spikelet number per ear). White background, 7A, grey background, 7AgL. FL, fractional arm length of the distance from the centromere, from 0=centromere to 1=telomere.