Effects of temperature on growth and photosynthesis in the seedling stage of the sheath blight-resistant rice genotype 32R

Huynh Van Kiet,Akihiro Nose

doi:10.1080/1343943x.2015.1128108

Abstract

The 32R rice genotype is resistant to sheath blight disease (ShB), with a high-yield potential. We examined effects of temperature on the plant responses of 32R in comparison with those of the ShB-susceptible rice genotype (29S) and Nipponbare (Nb, a Japonica standard cultivar). The seedlings at the 4th leaf stage of rice genotypes were exposed to 14/14, 19/14, 25/20, 31/26, 37/32 and 37/37 °C (day/night) for 5, 10 and 15 days. The dry weight, leaf area, photosynthesis, contents of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) and chlorophyll contents were examined. The dry weight showed lower in 32R than in 29S and Nb at a low temperature, and total dry weight correlated strongly with root dry weight and leaf area. The relative growth rate (RGR) correlated strongly with the net assimilation rate (NAR). Rubisco, chlorophyll contents and the photosynthetic rates were limited at a low temperature and showed lower in 32R than in 29S and Nb. The strong correlations between Rubisco and the rates of maximum photosynthesis and initial slope were found in 32R, but not found in 29S and Nb. In addition, RGR and NAR of 32R correlated positively with Rubisco. These suggest that 32R contains traits of cold-sensitive genotypes that are related to limiting Rubisco at a low temperature, thus diminishing photosynthesis and limiting plant growth. Differences of growth among 32R, 29S and Nb were discussed in the relation of genotypes.

Highlights

The 32R rice genotype is resistant to sheath blight disease (ShB), with a high-yield potential
Our previous studies indicated that the activity and gene expression of various key enzymes in the glycolytic, pentose phosphate and phenylpropanoid pathways increased after R. solani infection in the ShB-resistant rice genotype (32R) compared to the ShB-susceptible rice genotype (29S) (Mutuku & Nose, 2010, 2012)
Studies reported that net assimilation rate (NAR) plays a more important role in determining the variation in relative growth rate (RGR) (Loveys et al, 2002; Nagai & Makino, 2009), Villar et al (2005) reported that the leaf area ratio (LAR) plays a more important role in determining the variation in RGR under contrasting temperatures

Summary

Introduction

The 32R rice genotype is resistant to sheath blight disease (ShB), with a high-yield potential. RGR and NAR of 32R correlated positively with Rubisco These suggest that 32R contains traits of cold-sensitive genotypes that are related to limiting Rubisco at a low temperature, diminishing photosynthesis and limiting plant growth. Effects of climate change, especially contrasting temperatures, on the rates of growth and photosynthesis of plant remain dispute. A new rice variety with ShB resistance, high yield and cold resistance is expected to overcome the above conditions, in which the 32R is a useful candidate for developing a new variety for temperate areas under climate change. This study aimed to examine the rates of growth and photosynthesis of 32R under contrasting temperatures, which provides evidences for breeding a new cultivar with high yield and ShB resistance using QTL pyramiding. We addressed the questions: (i) what is the difference between the ShB-resistant and susceptible rice genotypes in terms of their responses to the rates of growth and photosynthetic? (ii) Are there any relationships between the temperature responses of individual leaf and whole-plants?

Objectives

Methods

Results