PHYSIOLOGICAL AND MOLECULAR CHARACTERIZATION FOR HIGH TEMPERATURE TOLERANCE IN GARDEN PEA
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Date
2023
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Division of Vegetable Science ICAR-Indian Agricultural Research InstituteNew Delhi – 110 012
Abstract
The garden pea is a cool-season legume crop commonly grown in temperate,
subtropical, and mild tropical climates. The optimum temperature ranges from 15-
23℃, and growth stops above 30℃. The maximum day temperature exceeds 38℃
during the first week of April in North India, which affects the major morphological,
physiological and biochemical processes of garden peas. Therefore, to extend its
growing season and increase its profitability, there is a dire need to breed for heat
tolerance in garden pea varieties. The present study, “Physiological and molecular
characterization for high-temperature tolerance in Garden pea” characterized 86
garden pea genotypes for 11 qualitative and 11 quantitative yield- related traits
followed by the screening at high temperatures in a growth chamber in phytotron
(controlled) and field condition (uncontrolled). In controlled screening in the growth
chamber, 34 and 7 genotypes were identified as tolerant during the seedling and
reproductive stages, respectively. Independent field screening during heat stress
season (Jan-April) identified 15 tolerant genotypes that survived and set pods at
39/16.4℃ and 15 moderately tolerant genotypes that survived with no pod set at
39/16.4℃. The identified fifteen tolerant genotypes were also classified as tolerant
during seedling stage screening in the growth chamber except for two genotypes,
while all the genotypes were classified as tolerant during reproductive stage screening
in a growth chamber. Hence this study proposes that screening in controlled conditions
could be used as a preliminary screening method in heat tolerant screening, which
could efficiently reduce the space and time involved in field screening. Field
screening also observed that only 19 genotypes flowered at 37/15.4℃, and only nine
were found to have >60% pollen viability at this temperature. Genotypes with >60%
pollen viability were also noted to have at least one pod set per plant. The
morphological characterization of 86 garden pea genotypes showed that yield per
plant and pod per plant were the most affected traits in heat stress season among
quantitative and yield-related traits, with 93.22% and 82.24% reduction, respectively.
The identified 15 tolerant, 15 moderately tolerant and 15 sensitive genotypes were
further characterized using nine physiological and biochemical traits to understand
their basis in heat tolerance. It was found that the average RWC and GI was found to
be 27.58% and 26.01% lower in heat stress condition, and the reduction was highest
in sensitive genotypes than in tolerant genotypes. The average canopy temperature in
heat stress conditions was 56.32% higher than in the normal season, and sensitive
genotypes showed 6.32 % higher canopy temperature than tolerant genotypes.
Similarly, MSI was found to be decreased by 44.51%, and the rate of reduction was
high in sensitive genotypes. The MDA was found to be increased by 4.71 times
during heat stress conditions than normal conditions and tolerant genotypes showed
lower accumulation of MDA. Similarly, H2O2 contents were also raised during heat
stress conditions, and the highest increase was found in sensitive genotypes
(262.92%). The antioxidant enzymes like superoxide dismutase showed increased
activity of 69.61%, and catalase showed 8.89 times higher activity in heat stress
season in tolerant genotypes. However, total sugar content was found to be decreased
by 5.67% in tolerant genotypes and 11.75% in sensitive genotypes. Estimating the
correlation coefficient showed that physiological and biochemical traits were very
important in determining the yield parameters of plants under heat-stress conditions.
Thus, the key physiological and biochemical traits like relative water content,
greenness index, membrane stability index, malondialdehyde, hydrogen peroxide,
superoxide dismutase and catalase could be used as an identification index for heat
tolerance. It was also found that there was considerable morphological and molecular
diversity among the studied garden pea genotypes. Of the 38 polymorphic SSR
markers used, 55.26% showed intermediate polymorphism, while 34.21% showed
high polymorphism. The markers 16213, psaa219, and psmpb16 recorded the highest
number of alleles per loci (10 alleles), and the marker psmpaa67 had a major allele
frequency of 0.95. The highest PIC of 0.81 was observed in the marker psmpsad141.
The garden pea genotypes were grouped into four populations by structure analysis,
and molecular variance among the population and within individuals was found to be
significant. The population groups with higher allelic divergence could be used as
parents for exploiting maximum heterosis. The identified tolerant genotypes viz. EC-
598646, EC-598638, 2019/PMPM-4, GP-61, GP-902, GP-912-II, EC-598649, GP-48,
EC-677211, EC-598654, GP-1104, EC-677214, GP-57, GP-915-II and EC-598602
could be greatly helpful in the development of heat tolerant garden pea varieties.