Dosage effect of the short arm of chromosome 1 of rye on root morphology and anatomy in bread wheat

Abstract

The spontaneous translocation of the short arm of chromosome 1 of rye (1RS) in bread wheat is associated with higher root biomass and grain yield. Recent studies have confirmed the presence of QTL for different root morphological traits on the 1RS arm in bread wheat. This study was conducted to address two questions in wheat root genetics. First, does the presence of the 1RS arm in bread wheat affect its root anatomy? Second, how does root morphology and anatomy of bread wheat respond to different dosages of 1RS? Near-isogenic plants with a different number (0 to 4 dosages) of 1RS translocations were studied for root morphology and anatomy. The F(1) hybrid, with single doses of the 1RS and 1AS arms, showed heterosis for root and shoot biomass. In other genotypes, with 0, 2, or 4 doses of 1RS, root biomass was incremental with the increase in the dosage of 1RS in bread wheat. This study also provided evidence of the presence of gene(s) influencing root xylem vessel number, size, and distribution in bread wheat. It was found that root vasculature follows a specific developmental pattern along the length of the tap root and 1RS dosage tends to affect the transitions differentially in different positions. This study indicated that the inherent differences in root morphology and anatomy of different 1RS lines may be advantageous compared to normal bread wheat to survive under stress conditions.

Fig. 1.

Roots of different wheat genotypes with different number of 1RS translocations in spring bread wheat ‘Pavon 76’ background harvested 45 d after germination (grown in pots). Pavon 76 (R0)=0 dose of 1RS, Pavon 1RS.1AL×Pavon 76 (RA1)=1 dose of 1RS, Pavon 1RS.1AL (RA2)=2 doses of 1RS on 1AL, Pavon 1RS.1DL (RD2)=2 doses of 1RS on 1DL, and Pavon 1RS.1AL- Pavon 1RS.1DL (RAD4) = 4 doses of 1RS on 1AL and 1DL. (This figure is available in colour at JXB online.)

Fig. 2.

Stained transverse sections of different regions (A–E top, F–J middle, K–0 tip) of roots of wheat genotypes. (A, F, K) Pavon 76 (R₀); (B, G, L) F₁ of Pavon 1RS.1AL×Pavon 76 (RA₁); (C, H, M) Pavon 1RS.1AL (RA₂); (D, I, N) Pavon 1RS.1DL (RD₂); (E, J, O) Pavon 1RS.1AL-Pavon 1RS.1DL (RAD₄); (F) is labelled with C, cortex; CMX, central metaxylem vessel; E, endodermis; PX, protoxylem; Scale bar, 100 μm.

Fig. 3.

(A, B, C) Examples of patterns seen in the number of CMX vessels in the top region of tap root of the RAD₄ genotype (four doses of 1RS chromosome arm). (B) is labelled with arrowheads, inner xylem vessels; C, cortex; CMX, central metaxylem vessel; E, endodermis; PX, protoxylem; Scale bar, 100 μm.

Fig. 4.

Graphical representation of mean performances of anatomical traits: (A) stele diameter; (B) metaxylem vessel diameter; (C) number of central metaxylem vessels; (D) total metaxylem vessel area; (E) number of xylem poles (protoxylem); and (F) root diameter measured from top region of the roots of each wheat genotype with different number of 1RS translocation arms in the genetic background of spring bread wheat ‘Pavon 76’. The same small letters within a graph are not significantly different. X-axis, bread wheat genotypes namely Pavon 76 (R0)=0 dose of 1RS, Pavon 1RS.1AL×Pavon 76 (RA1)=1 dose of 1RS, Pavon 1RS.1AL (RA2)=2 doses of 1RS on 1AL, Pavon 1RS.1DL (RD2)=2 doses of 1RS on 1DL, and Pavon 1RS.1AL- Pavon 1RS.1DL (RAD4)=4 doses of 1RS on 1AL and 1DL; Y axis, scale for root trait.

Fig. 5.

Graphical representation of mean performances of (A) total metaxylem vessel diameter; and (B) average metaxylem diameter measured in root tips of the roots of different wheat genotypes with different number of 1RS translocation arms in the genetic background of spring bread wheat ‘Pavon 76’. The same small letters within a graph are not significantly different. X- axis, bread wheat genotypes, namely Pavon 76 (R0)=0 dose of 1RS, Pavon 1RS.1AL×Pavon 76 (RA1)=1 dose of 1RS, Pavon 1RS.1AL (RA2)=2 doses of 1RS on 1AL, Pavon 1RS.1DL (RD2)=2 doses of 1RS on 1DL, and Pavon 1RS.1AL - Pavon 1RS.1DL (RAD4)=4 doses of 1RS on 1AL and 1DL; Y -axis, scale for root trait.