Low light induced physiological changes determining yielding abilities in Brassica juncea (L.)

Physiological traits were studied in selected Brassica juncea genotypes and released varieties during two winter seasons (2017-19) under the low light stress to identify the shade insensitive genotypes /varieties. The experiment was laid in randomized block design with two treatments comprising shading with nets which cuts 25-30% of sunlight for 30 days and control/ no shading with nets or open sunlight. Observations were recorded at two stages after removal of low light stress imposed by nets i.e. 10 (S1) and 30 (S2) days. Our comprehensive studies revealed that chlorophyll b synthesis improved unlike other photosynthetic pigments which were significantly reduced after 10 days (S1) and relatively greater decline was observed after 30 days (S2). The photochemical efficiency of PSII (Fv/Fm) was reduced in response to shade. The effects of shade was profound on leaf traits like leaf area, specific leaf area, specific leaf weight, leaf water retention and relative water content which declined with low light stress while relative saturation deficit, water saturation deficit increased at both the stages (S1 and S2). The studied traits exhibited positive correlation with seed yield. Promising cultivars showed minimal reduction in physiological traits in response to low light stress.