A novel QTL associated with rice canopy temperature difference affects stomatal conductance and leaf photosynthesis

Abstract

Canopy temperature can be a good indicator of stomatal conductance. To understand the genetic basis of phenotypic differences in stomatal conductance between average and high-yielding rice (Oryza sativa L.) cultivars, we conducted a quantitative trait locus (QTL) analysis of canopy temperature. We developed reciprocal series of backcross inbred lines (BC₁F₆) derived from a cross between the average-yielding japonica cultivar 'Koshihikari' and the high-yielding indica cultivar 'Takanari'. A stable QTL, qCTd11 (QTL for canopy temperature difference on chromosome 11) on the short arm of chromosome 11, accounted for 10.4 and 19.8% of the total phenotypic variance in the two lines; the 'Takanari' allele decreased the canopy temperature difference value. A chromosome segment substitution line carrying the Takanari qCTd11 showed a greater reduction in canopy temperature than 'Koshihikari', and had higher stomatal conductance and photosynthetic rate. These results suggest that qCTd11 is not only involved in canopy temperature, but is also involved in both stomatal conductance and photosynthetic rate.

Keywords: canopy temperature difference; chromosome segment substitution lines; photosynthetic rate; quantitative trait loci; rice (Oryza sativa); stomatal conductance.

Fig. 1

Visible (A and B) and thermal (C) images of three rice varieties cultivated in a paddy field. The images were taken at 11:13 on 8 July 2014 (48 days after transplanting). The reference variety was ‘Koshihikari’. The purple areas in (B) were eliminated as background. The central column of each variety in (C) was analyzed to determine the canopy temperature.

Fig. 2

Changes in air temperature (Ta), vapor pressure deficit (VPD), photosynthetic photon flux density (PPFD), canopy temperature depression (CTD) in ‘Koshihikari’ and ‘Takanari’, and canopy temperature difference (CTd) between ‘Koshihikari’ and ‘Takanari’ in three experimental blocks of a rice field in 2014.

Fig. 3

Frequency distribution of canopy temperature differences (CTds) in two reciprocal populations crossed between ‘Koshihikari’ and ‘Takanari’. Black and white arrows indicate CTds in ‘Takanari’ and ‘Koshihikari’, respectively. The reference variety was ‘Koshihikari’ in BKT or ‘Takanari’ in BTK for the calculation of CTds as described in Materials and Methods. The weather conditions at the measurements were shown in Supplemental Fig. 2.

Fig. 4

Correlation between canopy temperature differences (CTds) and four basic agronomic traits. The reference variety was ‘Koshihikari’ in BKT or ‘Takanari’ in BTK for the calculation of CTds as described in Materials and Methods. Asterisks indicate significant differences in the correlation coefficient (*P < 0.05; Pearson’s product-moment correlation coefficient).

Fig. 5

Genotype of SL1, which was developed from a cross between ‘Koshihikari’ and ‘Takanari’.

Fig. 6

Canopy temperature differences (CTds) between ‘Koshihikari’ and SL1, or ‘Takanari’, in plants grown in a paddy field (A) and pots (B) in 2014. All plants were evaluated before heading. The weather conditions at the measurements were shown in Supplemental Table 1. Vertical bars in (A) and (B) represent the S.D.s of four replicates of experimental blocks and eight replicates of measurements, respectively. Different letters indicate significant differences (P < 0.05; Tukey’s honest significant difference test).

Fig. 7

Long-term and diurnal changes in canopy temperature differences (CTds) between ‘Koshihikari’ and SL1, or ‘Takanari’, in plants grown in pots from the maximum tillering stage to the stage just prior to heading (A), and from morning to afternoon at 53 days after transplanting (B), in 2015. The weather conditions at the measurements were shown in Supplemental Table 1. Vertical bars in (A) and (B) represent the S.D.s of 6–12 and eight or nine replicates of measurements, respectively. Different letters indicate significant differences (P < 0.05; Tukey’s honest significant difference test).

Fig. 8

Comparison of canopy temperature differences (CTds) between ‘Koshihikari’ and SL1, or ‘Takanari’ and leaf photosynthesis in ‘Koshihikari’ and SL1, or ‘Takanari’. CTds (A) were measured at 53 days after transplanting in 2015. Stomatal conductance (g_s) (B), leaf photosynthetic rate (P_n) (C), transpiration rate (T) (D), and soil-plant analysis development (SPAD) value (E) per leaf area in each topmost expanded leaf of the main culm of ‘Koshihikari’, SL1, and ‘Takanari’ grown in pots were determined on the same day as the CTd measurements. All plants were evaluated before heading. Values are means ± S.D. (A, n = 9; B–E, n = 3 or 4). Different letters indicate significant differences (P < 0.05; Tukey’s honest significant difference test).