A potential seedling-stage evaluation method for heat tolerance in Indian mustard (Brassica juncea L. Czern and Coss)

Abstract

Heat stress is one of the major limitations to crop productivity. In the present study, an efficient method of screening was adopted for identification of heat tolerant Indian Mustard genotypes by applying 4-day cycle of heat stress to seedlings. Thirty-four genotypes were screened based upon lipid peroxidation and survival percentage and classified them into five different classes according to membership function value (MFV) for response against high temperature. The maximum and minimum value of mean MFV were 0.89 (highly heat tolerant, TPM1) and 0.12 (highly heat sensitive, JM2), respectively. The coefficient of determination (R ²) between the mean MFV and the heat tolerance index (HTI) of MDA content, survival percentage was 0.914 and 0.808 suggesting that these parameters are reliable traits to evaluate the heat tolerance of Brassica juncea genotypes. The evaluation method was further validated using identified contrasting genotypes and assessment of heat stress associated biochemical parameters. Results showed efficient recovery of tolerant genotype as compared to sensitive genotype. Expression profiling of heat stress-related genes (HSP21 and HSFA7A) showed significant upregulation in the tolerant genotype (TPM1) (9.73- and 4.87-fold, respectively) as compared to the sensitive genotype (JM2) (4.18- and 1.73-fold, respectively) under heat stress condition. The results imply development of an efficient screening method which is useful for evaluation and breeding of thermo-tolerant B. juncea.

Keywords: Brassica juncea; Heat shock protein 21; Heat stress; ROS scavenging; Screening of germplasm.

Fig. 1

a Proportion of the 34 B. juncea genotypes with different heat tolerances. HHT: highly heat tolerant; HT: heat tolerant; MHT, moderately heat tolerant; HS: heat sensitive; HHS: Highly heat sensitive. The linear fit between mean MFV and the STI of survival percentage (b) and MDA content (c) of B. juncea genotypes

Fig. 2

NBT dye assay for qualitative super oxide radical detection in heat tolerant contrasting genotypes (tolerant—TPM1, Pusa Jaikisan and sensitive—RGN-73, JM2)

Fig. 3

Fold change in electrolyte leakage (a) and MDA content (b) after heat treatment and recovery in heat tolerant contrasting genotypes (tolerant—TPM1, PusaJaikisan and sensitive—RGN-73, JM2)

Fig. 4

Effect of heat stress on superoxide dismutase (SOD) (a) and catalase (CAT) (b) activity in two contrasting heat tolerant genotype. All values are means of triplicates ± SE. Bars bearing asterisks are significantly different (p ≤ 0.01)

Fig. 5

Effect of heat stress on the expression of HSP21 and HSFA7A. Tubulin was used as an internal control. The vertical column indicates the log-twofold expression level change. The x-axis represents the expression level of genes in control (untreated) sample. All values are means of triplicates ± SE. For each gene, bars bearing asterisks are significantly different (p ≤ 0.05)