Photosynthetic traits and antioxidative enzymes under low light stress in Indian mustard (Brasica juncea L.) genotypes
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Date
2018
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Punjab Agricultural University, Ludhiana
Abstract
The present investigation was carried out to assess the effect of low light stress on photosynthetic
traits and antioxidative enzymes in Brassica juncea genotypes. Shading was done with nets from
mid Dec. 2015 – mid Jan. 2016 which cuts 25-30% natural sunlight. Flower and fruit initiation
took more number of days while flowering and fruiting duration declined with shading. PHR-1
took maximum days for flowering and siliqua initiation, PBR-357 for flowering completion, PHR2
for flowering duration, PBR-210 for siliquing completion and duration. Reproductive phase was
shortened by 5.6 days whereas days to maturity were comparable under control and shaded
treatments. At two stages of investigations (10 and 30 days after removal of nets) LAI and PAR
significantly declined by 40, 12.6% and 43.4, 19.7% respectively however extinction coefficient
(k) increased by 30.7% and 33% at two respective stages. Plant water status declined in terms of
RWC by 1.9%, LWR by 16.6% along with SLW (16.6%), SLA (14.5%) and leaf traits to
appreciable extent with shading removal after 10 days. Similar trend was recorded for these traits
30 days after removal of nets however, WSD increased from 9.3% to 34.2% at two stages with
shading. Decline in SPAD values were comparable at two dates whereas Chl a, total Chl, Chl a/b
and carotenoids were higher under control and declined under shading. Interestingly Chl b
enhanced with shading at two stages. Antioxidative enzymes and MDA content increased whereas
sugars and protein content decreased with shading at two stages of assay. Low light stress induced
by shading had a profound effect on growth parameters, yield components and seed yield in
studied genotypes with a mean reduction of 5.4% for plant height, 2.7% for length of main raceme
and 1.2% for primary branches in PBR-210 whereas 0.5% for secondary branches in PBR-357.
Differential response was registered with shading for nitrogen content, crude proteins,
glucosinolates and oil content along with N-uptake. Declining trend with shading over control was
witnessed in fatty acids profiling however oleic, linoleic and erucic acids did not vary much in
PHR-2. PBR-422 suffered lesser reduction in seed yield followed by RLM-619 accompanied by
lesser decline in the morpho-physiological traits and increased antioxidative enzymes.
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