Untangling the Influence of Heat Stress on Crop Phenology, Seed Set, Seed Weight, and Germination in Field Pea (Pisum sativum L.)

Abstract

The apparent climatic extremes affect the growth and developmental process of cool-season grain legumes, especially the high-temperature stress. The present study aimed to investigate the impacts of high-temperature stress on crop phenology, seed set, and seed quality parameters, which are still uncertain in tropical environments. Therefore, a panel of 150 field pea genotypes, grouped as early (n = 88) and late (n = 62) maturing, were exposed to high-temperature environments following staggered sowing [normal sowing time or non-heat stress environment (NHSE); moderately late sowing (15 days after normal sowing) or heat stress environment-I (HSE-I); and very-late sowing (30 days after normal sowing) or HSE-II]. The average maximum temperature during flowering was about 22.5 ± 0.17°C for NHSE and increased to 25.9 ± 0.11°C and 30.6 ± 0.19°C in HSE-I and HSE-II, respectively. The average maximum temperature during the reproductive period (RP) (flowering to maturity) was in the order HSE-II (33.3 ± 0.03°C) > HSE-I (30.5 ± 0.10°C) > NHSE (27.3 ± 0.10°C). The high-temperature stress reduced the seed yield (24-60%) and seed germination (4-8%) with a prominent effect on long-duration genotypes. The maximum reduction in seed germination (>15%) was observed in HSE-II for genotypes with >115 days maturity duration, which was primarily attributed to higher ambient maximum temperature during the RP. Under HSEs, the reduction in the RP in early- and late-maturing genotypes was 13-23 and 18-33%, suggesting forced maturity for long-duration genotypes under late-sown conditions. The cumulative growing degree days at different crop stages had significant associations (p < 0.001) with seed germination in both early- and late-maturing genotypes; and the results further demonstrate that an extended vegetative period could enhance the 100-seed weight and seed germination. Reduction in seed set (7-14%) and 100-seed weight (6-16%) was observed under HSEs, particularly in HSE-II. The positive associations of 100-seed weight were observed with seed germination and germination rate in the late-maturing genotypes, whereas in early-maturing genotypes, a negative association was observed for 100-seed weight and germination rate. The GGE biplot analysis identified IPFD 11-5, Pant P-72, P-1544-1, and HUDP 11 as superior genotypes, as they possess an ability to produce more viable seeds under heat stress conditions. Such genotypes will be useful in developing field pea varieties for quality seed production under the high-temperature environments.

Keywords: GGE biplots; growing degree days; heat stress; seed germination; seed loss; seed set.

FIGURE 1

Average daily weather conditions of the experimental site during the period of study.

FIGURE 2

Exposure of field pea genotypes to maximum temperature(T_MAX) during 50% flowering (°C) and average ambient temperature during reproductive period (°C) under timely sown and late-sown conditions. The error bars represent ± standard error of means. NHSE, normal sowing time; HSE-I, 15 days after NHSE; HSE-II, 30 days after NHSE. Different lowercase letters (a–c) represent significant different within the row values (p < 0.05). Different uppercase letters (A, B) represent significant difference within the column values (early and late genotypes) (p < 0.05).

FIGURE 3

Days to 50% flowering (A), days to maturity (B), reproductive period (C), percent seed set (D), 100-seed weight (E), seed germination (F,G), and germination rate (H) of early, late, and overall field pea genotypes under timely sown and late-sown conditions. The error bars represent mean ± standard error of means. Different lowercase letters (a–c) represent significant difference (p < 0.05) within the row values (between environments). Different uppercase letters (A,B) represent significant difference (p < 0.05) within the column values (between early and late genotypes).

FIGURE 4

Scatter plot of field pea genotypes on PCA coordinates under NHSE (A), HSE-I (B), and HSE-II (C) environments. Black dots represent early-maturing genotypes, while red asterisk represents late-maturing genotypes. RP, reproductive period; GDDR, growing degree days at reproductive period; GDDF, growing degree days of full crop season; DTM, days to maturity; TMAX(RP), maximum temperature at reproductive period; HSW, 100-seed weight; TMAX(F), maximum temperature at flowering; DTF, days to 50% flowering; GDDV, growing degree days at vegetative period; GMT, germination rate; SS, seed set; GP, germination percent; PCA, principal component analysis.

FIGURE 5

GGE biplots developed by plotting the first and second principal components derived from the germination value of early-maturing genotypes of field pea evaluated in three environments (NHSE, HSE-I, and HSE-II). (A) “Mean versus Stability” view of genotypes. (B) Discriminating ability and representativeness of three environments, (C) which won where/what of field pea genotypes under different environments.

FIGURE 6

GGE biplots developed by plotting the first and second principal components derived from the germination value of late-maturing genotypes of field pea evaluated in three environments (NHSE, HSE-I, and HSE-II). (A) “Mean versus Stability” view of genotypes. (B) Discriminating ability and representativeness of three environments, (C) which won where/what of field pea genotypes under different environments.

FIGURE 7

GGE biplots developed by plotting the first and second principal components derived from the germination value of all the genotypes of field pea evaluated in three environments (NHSE, HSE-I, and HSE-II). (A) “Mean versus Stability” view of genotypes. (B) Discriminating ability and representativeness of three environments, (C) which won where/what of field pea genotypes under different environments.