Nadeem Hussain

The rapid increase in population growth under changing climatic conditions causes drought stress, threatening world food security. The identification of physiological and biochemical traits acting as yield-limiting factors in diverse germplasm is pre-requisite for genetic improvement under water-deficit conditions. The major aim of the present study was the identification of drought-tolerant wheat cultivars with a novel source of drought tolerance from local wheat germplasm. The study was conducted to screen 40 local wheat cultivars against drought stress at different growth stages. Barani-83, Blue Silver, Pak-81, and Pasban-90 containing shoot and root fresh weight >60% of control and shoot and root dry weight >80% and 70% of control, respectively, P (% of control >80 in shoot and >88 in root), K⁺ (>85% of control), and quantum yield of PSII > 90% of control under polyethylene glycol (PEG)-induced drought stress at seedling stage can be considered as tolerant, while more reduction in these parameters make FSD-08, Lasani-08, Punjab-96, and Sahar-06 as drought-sensitive cultivars. FSD-08 and Lasani-08 could not maintain growth and yield due to protoplasmic dehydration, decreased turgidity, cell enlargement, and cell division due to drought treatment at adult growth stage. Stability of leaf chlorophyll content (ABS), maximum quantum yield (Fv/Fm) associated with increase in Vj, absorption (ABS/RC), and dissipation per reaction center (DIo/RC) while a decrease in electron transport per reaction center (ETo/RC). During the present study, differential modifications in morpho-physiological, biochemical, and photosynthetic attributes that alleviate the damaging effects of drought stress in locally grown wheat cultivars were analyzed. Selected tolerant cultivars could be explored in various breeding programs to produce new wheat genotypes with adaptive traits to withstand water stress.

Global food production is threatened due to increasing salinity and can be stabilized by improving salt tolerance of crops. In the current study, salt tolerance potential of 40 local wheat cultivars against 150 mM NaCl stress was explored. Salt treatment at seedling stage caused less reduction in biomass, K⁺ and P while more decline of Na⁺ in tolerant cultivars due to reduced translocation and enhanced exclusion of Na⁺ from leaves. Principal component analysis based selected S-24, LU-26S, Pasban-90 (salt tolerant) and MH-97, Kohistan-97, Inqilab-91 and Iqbal-2000 (salt sensitive) cultivars were evaluated at adult stage applying 150 mM salinity. Osmotic adjustment by accumulation of soluble sugars and proline and accelerated antioxidant enzymes activities caused efficient scavenging of reactive oxygen species making S-24 and LU-26S tolerant while in MH-97 and Kohistan-97, high MDA represent greater membrane damage due to oxidative stress making them salt sensitive. Chlorophyll a fluorescence transients confirmed better efficiency of photosystem II in S-24 and LU-26S based on energy fluxes (ABS/RC, TRo/RC, ETo/RC and DIo/RC), performance index (PI_ABS) and maximum quantum yield (Fv/Fm). These findings can be correlated using molecular techniques to identify genes for salt exclusion, osmotic adjustment and photosynthetic activity for use in molecular breeding programs.

Salt tolerant wheat cultivars may be used as genetic resource for wheat breeding to ensure yield stability in future. The study was aimed to select salt tolerant cultivar(s) to identify novel source of salt tolerance in local wheat germplasm. Initially, 40 local wheat cultivars were screened at 150 mM NaCl stress at seedling stage. Selected salt-tolerant (three; S-24, LU-26S and Pasban-90) and salt-sensitive (four; MH-97, Kohistan-97, Inqilab-91 and Iqbal-2000) wheat cultivars were further evaluated using growth, yield, biochemical and physiological attributes. Growth and yield of selected cultivars were reduced under salt stress due to decline in plant water status, limited uptake of macronutrients (N, P and K), reduced K⁺/Na⁺ratio, photosynthetic pigments and quantum yield of PSII. Wheat plants tried to acclimate salt stress by osmotic adjustment (accumulation of total soluble sugars, proline and free amino acids). Degree of salinity tolerance in cvs. S-24 and LU-26S found to be associated with maintenance of K⁺/Na⁺ratio, osmo-protectant and photosynthetic activity and can be used as donor for salt tolerance in wheat breeding program at least in Pakistan. These cultivars can be further characterized using molecular techniques to identify QTLs/genes for salt exclusion, osmo-protectant and photosynthetic activity for molecular breeding.