Critical temperature requirement for the germination and establishment of mungbean (Vigna radiata L.) in temperate environments

Abstract

Mungbean (Vigna radiata (L.) R.Wilczek.) is an important annual legume cultivated in subtropical regions for its high-protein grains. However, it is susceptible to low temperatures (<20°C) during germination and establishment, which results in substantial yield loss. Early growth stages are crucial for successful cultivation in cooler climates to enable an optimal sowing window and effective establishment. This study aimed to identify cold-tolerant mungbean genotypes adapted to low-temperature germination (<20°C), particularly in southern Australia during November-December. The effects of temperature (14, 17 and 20°C) and soil water availability (40 and 80% of field capacity) on the germination and emergence of mungbean genotype were investigated through three experiments. In Experiment 1, thirty-two genotypes were evaluated for germination at constant temperatures of 14, 17 and 20°C using germination paper towels in a controlled environment. Additionally, in Experiment 2 and 3 in controlled environment experiments using soil-filled pots were conducted to determine the effect of temperature under constant (14, 17, and 20°C) and a range of diurnal temperature regimes (10-18°C, 13-21°C, and 16-24°C), ensuring that the average temperature for each treatment remained at 14, 17, and 20°C respectively. These temperatures were tested in factorial combination with soil water status (40 and 80% of field capacity) on the germination and emergence of commercial varieties Jade-AU and Celera II-AU. Germination occurred at all tested temperatures, with the highest germination percentage observed at 20°C on paper towels. Genotypes Putland, Jade-AU, Bari Mung-3, Bari Mung-4, Satin II, and Bina Mung-8 showed no significant differences in germination rates among the 14, 17, and 20°C temperature treatments, with average germination percentages exceeding 80% in the paper-towel evaluation. The median germination rate observed was highly variable (2-16 days) across genotypes in response to temperature treatment. The estimated base temperature of Celera II-AU and Jade-AU was 8.6 and 9.8°C, respectively. Seedling emergence was faster and higher for Celera II-AU than Jade-AU across the diurnal and constant temperatures. The germination was observed at both diurnal and constant temperature treatments of 20, 17, and 14°C. However, no emergence was observed at a constant temperature of 14°C for varieties Jade-AU and Celera II-AU. These findings suggest that mungbean can be successfully sown in early spring of southern Australia if soil temperature is at least 17°C. This research provides valuable insights for future breeding programs, germination studies, and sowing date recommendations in temperate environments.

Keywords: cold tolerance; constant temperature; diurnal temperature; germination; germination rate; low soil temperature; temperate.

Figure 1

Germination stand and paper setup within growth cabinet at Horsham, Victoria (Experiment 1).

Figure 2

The interaction effect of temperature (14, 17 and 20°C) and mungbean genotypes at 21 DAS on (A) germination percentage, (B) germination rate (GT₅₀), and (C) root length under controlled growth conditions (Experiment 1). During experiment 1, the average temperatures were 14 ± 0.2, 17 ± 0.1 and 20 ± 0.1°C for the constant temperature treatments of 14, 17 and 20°C, respectively. Points represent REML (Asreml-R) estimated means and error bars represent the 95% confidence interval for each genotype at each temperature treatment. The confidence interval between genotypes differs because the reference genotypes were evaluated across all five independent experimental runs (n = 20), whereas individual test genotypes were evaluated within a single run (n = 4). A Likelihood Ratio Test (LRT) confirmed no significant main effect of run (p > 0.05), allowing for the valid estimation of BLUEs across the integrated experimental structure. Genotypes with highest germination percentage (A) are denoted by letter “a” and genotypes with different letters are significantly different from “a” at 14°C, according to Wald test at a p ≤ 0.05. Genotypes with the lowest GT50 (B) are denoted by letter “a” and genotypes with different letters are significantly different from “a” at 14°C, according to the Wald test at a p ≤ 0.05. The genotypes with significantly higher and lower root length (C) at 20°C are indicated by different letters, according to Wald test at a p ≤ 0.05. Asterisks indicate significant differences between 14°C and 17°C temperature treatments for each genotype, according to the Wald test at a p ≤ 0.05. Treatment effects were tested using a REML (A–C) differences were considered significant according to the Wald test (p ≤ 0.05).

Figure 3

(A) Relationship between the final germination (%) and the time to median germination (GT₅₀) of mungbean genotypes under controlled growth cabinet at 14, 17 and 20°C. The solid line shows the fitted regression line. Asterisks (***) denote a significant correlation at p < 0.001 (Experiment 1). (B) Mungbean seed germination rates of Jade-AU and Celera II-AU genotypes at 14, 17, and 20°C (Experiment 1). The solid lines show the fitted regression line. The extrapolation of linear regression back to the temperature axis (x-intercept) gave estimates of base temperature (T_b) of 8.6 and 9.8°C for Jade-AU and Celera II-AU, respectively. The average temperatures observed during Experiment 1 were 14 ± 0.2, 17 ± 0.1 and 20 ± 0.1°C for the constant temperature treatments of 14, 17 and 20°C, respectively.

Figure 4

(A) The emergence percentage (%) was observed at two soil water treatment levels, 40 and 80% field capacity (FC), and three constant temperatures (14, 17 and 20°C) over a period of 21 DAS (Experiment 2). (B) The emergence percentage (%) of Celera II-AU and Jade-AU was recorded at three constant temperatures (14, 17 and 20°C) over a period of 21 DAS (Experiment 2). The observed temperatures (mean ± sd) of constant temperature treatments for 14, 17 and 20°C were 14 ± 0.2, 17 ± 0.3 and 20 ± 0.2°C, respectively, during the Experiment 2. Mean and standard error values of four independent biological replicates (n = 4, pool of five plants) from Experiment 2 are presented. The black error bar within the graph signifies the least significant difference (LSD) at a significance level of p ≤ 0.05 for comparison of (A) the temperature × soil water status × DAS interaction (LSD_0.05 = 5.4) and (B) temperature × variety × DAS interaction (LSD_0.05 = 5.4). Asterisks indicate the significant differences between 20°C and 17°C at each DAS according to LSD test (p ≤ 0.05). Hashtags indicate the significant differences between 17°C and 14°C at each DAS according to LSD test (p ≤ 0.05).

Figure 5

The effect of temperature and soil water status percent of field capacity (% FC) on mungbean genotypes (Celera II-AU and Jade-AU) under controlled conditions where, (A, B) = Constant temperature and (C–G) = Diurnal temperature. Mean and standard error values of four replicates (n = 4, pool of five plants) from Experiment 2 (A, B) and eight replicates (n = 8, pool of five plants) pooled from two independent experimental repetitions from Experiment 3 (C–G) are presented. During the Experiment 2, the observed temperatures (mean ± sd) of constant temperature treatments for 14, 17 and 20°C were 14 ± 0.2, 17 ± 0.3 and 20 ± 0.2°C respectively. While during Experiment 3, The observed mean temperatures (mean ± sd) for diurnal temperatures were 14 ± 3.6, 17 ± 3.6 and 20 ± 3.6°C for the temperature treatments of 14, 17 and 20°C respectively. The black error bar in the graph represents the least significant difference (LSD) at p ≤ 0.05 for comparisons of the interaction between the factors (temperature, genotype and soil water status) at each figure. Bars followed by different letters differ significantly according to Fisher’s least significant difference (LSD) test at a p ≤ 0.05. No significant repetition effect was observed in Experiment 3 (F = 0.10, p > 0.05).

Figure 6

Emergence of mungbean genotypes (Celera II-AU and Jade-AU) grown at two soil water content (40 and 80% of field capacity) and three temperatures over a period of 21 days (Experiment 3). During the experiment, the observed mean temperatures (mean ± sd) for diurnal temperatures were 14 ± 3.6, 17 ± 3.6 and 20 ± 3.6°C for the temperature treatments of 14, 17 and 20°C respectively. Mean and standard error values of eight replicates (n = 8, pool of five plants) pooled from two independent experimental repetitions from Experiment 3 are presented. The black error bar within the graph signifies the least significant difference (LSD) at a significance level of p ≤ 0.05 for comparison of the temperature × genotype × soil water status × DAS interaction (LSD_0.05 = 12.2). No significant repetition effect was observed (F = 0.10, p > 0.05). Asterisks indicate the significant differences between 20°C and 17°C at each DAS according to LSD test (p ≤ 0.05). Hashtags indicate the significant differences between 17°C and 14°C at each DAS according to LSD test (p ≤ 0.05).