Physiological Screening of Some Sunflower Varieties Against Abiotic Stress

Abstract

Physiological screening of some sunflower cultivars (S.28111, SF0049, Hysun-33, Hysun-39) under abiotic stresses like salt, drought stress individually and in combination were performed. The stresses were applied on 30-days-old plants by gradual increment which lasted for two weeks. To evaluate the physiological performance; PSI and PSII efficiencies, relative water content, osmotic potential, stomatal conductance, chlorophyll contents, ion analysis and antioxidants activities were investigated. Photochemical activities were examined using chlorophyll ‘a’ fluorescence transient (JIP) test. Variations in PSII activities were related to nature of the treatment and sunflower cultivar. Combined stress was found to be fatal for photochemical activities in sunflower cultivars compared to individual stress. Maximum quantum yield of PSII, absorption flux of light per cross section of leaf, phenomological fluxes, plastoquinone pool size, performance indexes and driving force of absorption were computed and deduced from chlorophyll fluorescence analysis and were greatly reduced in combined stress. The photosynthetic apparatus of the sunflower cultivar S.28111 and SF0049 were found less affected under salt and drought stresses as compared to both Hysun cultivars. Observation reveals that individual and combined salt and drought stresses altered the maximum fluorescence (Fm), electron transport rate through PSII (Fm/Fo), photochemical quenching (qP), efficiency of photosystem II (ΦPSII), linear electron transport rate (rETR), non-photochemical quenching (NPQ), non-photochemical quenching co-efficient (qN), size and number of active reaction centre of photosynthetic machinery (Fv/Fo). Performance indexes that depends on the efficiency of energy transfer, yield and primary photochemistry were also decreased. The Hysun-33 and Hysun-39 showed a very low value of Fm and then essentially lowest fluorescence transient curve; this may result in structural changes as well as increase in energy dissipation and disturbance in electron transport. The temperature of leaf is an indicator of environmental stresses. In plants, leaf temperature can be measured by high-tech IR thermography. A comparable difference in stress tolerance was observed in sunflower cultivars under salt and drought stresses. It was simple technique based on IR thermal imaging performed for the screening sunflower cultivars and confirmed a greater consistency in ranking cultivars as observed through growth and physiological studies. Carotenoids and free proline contents in drought stress were elevated as compared to salt stress. In combined stress antioxidant enzymes activity reduced which results in decreased physiological performance of sunflower plants. Ascorbate peroxidase (APX), catalase (CAT) and superoxide dismutase (SOD) showed the highest activity in salt and drought stresses with less accumulation of H2O2 and electrolyte leakage. The antioxidant activities were greater in S.28111 and SF0049 as compared to both Hysun cultivars under stressful environments. Form the data it was observed that S.28111 and SF0049 had greater capacity to scavenge the reactive oxygen species and less Na+ and Cl- ions concentration, hence protect their photosynthetic apparatus under combined stress. The effects of combined stress on Hysun-39 were synergistic whereas in S.28111 cross tolerance in most of the physiological processes were found. Photochemistry of PSII, antioxidant activities and ion accumulation assessment for individual (salt/drought) and combined stress related studies to compare tolerance in crop cultivars may be much appropriate. However, among the cultivars, S.28111 and SF0049 were found to be more tolerant to drought, salt and combined stress as compared to both Hysun cultivars. The screened cultivars may be recommended for field trials. Later, it will be used by the farmers of salinized or desertified areas and would be helpful to fulfil the demand of edible oil of ever growing population of Pakistan