The dominance of salt water across the surface of the earth has lead to the widespread occurrence of salt-affected soils. Salt-tolerant plants (halophytes) have evolved to grow on these soils, with halophytes and less tolerant plants showing a wide range of adaptations. However, most of our crops are salt-sensitive. Consequently, salinity is an ever-present threat to agriculture, especially in areas where secondary salinisation has developed through irrigation or deforestation. Attempts to improve the salt tolerance of crops have met with very limited success, due to the complexity of the trait, both genetically and physiologically. Tolerance shows all the characteristics of a multigenic trait, with quantitative trait loci (QTLs) identified in barley, citrus, rice and tomato. Attempts to produce salt-tolerant crops have involved both the domestication of halophytes and the manipulation of existing crop species through conventional breeding programmes, the use of in vitro selection, pooling physiological traits, interspecific hybridisation, the use of marker-aided selection and the development of transgenic plants. After 10 years of research, the value of using transgenic plants to alter salt tolerance has yet to be tested in the field. The use of physiological traits in breeding programmes and the domestication of halophytes currently offer viable alternatives to the development of tolerance through the use of transgenic technologies.

Why does salinity pose such a difficult problem for plant breeders

Scarcity of water for irrigation is an alarming issue limiting crop production worldwide and is becoming increasingly severe with the passage of time in Pakistan. Rice production in Pakistan is thus, being adversely hampered by the shortage of water. The study was therefore, contemplated to determine t he effect of drought stress on some physiological and agronomic parameters of three rice cultivars naming Basmati-Super, Shaheen-Basmati and Basmati-385. The field experiment was laid out in split plot design with randomized complete block arrangement, kee ping cultivars in main and water stress stages viz; panicle initiation, anthesis and grain filling along with control in sub -plots. Cultivar ShaheenBasmati exhibited comparatively more tolerance to drought stress at all the three growth stages under study with less reduction in various physiological and agronomic traits. Similarly, less increase in transpiration rate and sterile tillers per hill were observed in Shaheen-Basmati under drought stress at all the three stages. Growth stage panicle initiation was the most sensitive one exhibiting more adverse effects on all the physiological and agronomic parameters under study., PAR, photosynthetic rate, RWC and stomatal conductance showed strong and positive correlation with WUE whereas; transpiration rate expressed negative correlation with WUE. Similarly, all the physiological and yield components under study except transpiration rate and number of sterile grains per panicle had a strong and positive correlation with paddy yield.

/pdf/impact-of-water-deficit-stress-on-various-physiological-and-4sktg3fo9c.pdf

IMPACT OF WATER DEFICIT STRESS ON VARIOUS PHYSIOLOGICAL AND AGRONOMIC TRAITS OF THREEBASMATI RICE (Oryza sativa L.) CULTIVARS

Relative water content (RWC) in the leaf of different rice cultivars dropped significantly in relation to reduced soil water content (SWC), especially in PT1 and IR20. In contrast, the proline content in the leaf-blade and leaf-sheath increased when plants were subjected to 7% SWC. The RWC was positively related to chlorophyll degradation. Chlorophyll a, chlorophyll b, total chlorophyll, total carotenoids, maximum quantum yield of PSII, stomatal conductance and water use efficiency in rice grown under water-deficit conditions declined significantly in comparison to the control group, leading to a reduction in net-photosynthetic rate. In addition, when exposed to water-deficit, panicle length and fertile grains in KDML105 and NSG19 were stabilized, leading to greater productivity than in PT1 and IR20. These data were utilized as effective criteria for the classification of water-deficit tolerance. From the results, KDML105 and NSG19 were identified as water deficit-tolerant, and PT1 and IR20 as water deficit-susceptible.

Water deficit stress in the reproductive stage of four indica rice (oryza sativa l.) genotypes

Medicago sativa L. cv. Longzhong is a nutritious forage plant in dryland regions of the Loess Plateau with strong drought tolerance and broad adaptability. To understand the adaptation mechanism of alfalfa (M. sativa L. cv. Longzhong) to drought stress, growth, and physiological parameters including levels of chlorophyll content, osmotic adjustment, reactive oxygen species (ROS), and antioxidant enzymes and antioxidants were measured under simulated levels of drought (− 0.40, − 0.80, − 1.20, − 1.60, and − 2.00 MPa). The changes in M. sativa L. cv. Longzhong were compared with those of plants of M. sativa L. cv. Longdong control (Variety I) suited to moderate rainfall areas and M. sativa L. cv. Gannong No. 3 (Variety II) suited to irrigated areas. The results showed that root–shoot ratio, the chlorophyll (a + b) and osmolytes contents, the degree of lipid peroxidation and ROS production, and the levels of antioxidative enzymes and antioxidants increased significantly with increasing drought stress, whereas plant height, aboveground biomass, chlorophyll a/b ratio, leaf water potential (Ψ1), and relative water content (RWC) decreased in response to drought. The Longzhong variety responded early to beginning drought stress (between 0 and − 0.4 MPa) compared with the controls. Under drought stress (between − 0.4 and − 2.0 MPa), the Longzhong variety had significantly higher belowground biomass, root–shoot ratio, Ψ1, RWC, catalase (CAT) activity and reduced glutathione content than those of Varieties I and II, but hydrogen peroxide and hydroxyl free radical (OH·) contents were significantly lower. Step regression analysis showed that OH·, CAT, malondialdehyde, superoxide anion-free radical (O
 2
 ·−
 ), and superoxide dismutase of Longzhong had the most marked response to drought stress. In conclusion, the stronger drought tolerance of the Longzhong variety might be due to its higher water-holding capacity, root–shoot ratio, and ability to coordinate enzymatic and non-enzymatic antioxidant systems, which coordinate the peroxidation and oxidative systems.

Physiological and biochemical changes in different drought-tolerant alfalfa ( Medicago sativa L.) varieties under PEG-induced drought stress

Abiotic Stresses: Challenges for Plant Breeding in the Coming Decades.- Breeding for Stress-Tolerance or Resource-Use Efficiency?.- The Physiology of the Abiotic Stresses.- Breeding for Nitrogen Use Efficiency.- Breeding for Phosphorous Use Efficiency.- Breeding for Water Use Efficiency.- Breeding for Salinity Tolerance.- Breeding for Aluminum Tolerance.- Breeding Heat-Stress Tolerance.- Breeding Perennial Species for Abiotic Stresses.

Plant breeding for abiotic stress tolerance

The aim of this study was to investigate the biochemical, physiological and morphological responses of rice cultivars to iso-osmotic water deficit and salt stress. Seedlings of three rice cultivars were photoautotrophically grown in MS media and subsequently exposed to -0.23 (control), -0.42 or -0.94 MPa iso-osmotic mannitol (water-deficit stress) or NaCl (salt stress). Chlorophyll a (Chla), chlorophyll b (Chlb), total carotenoids (Cx+c), maximum quantum yield of PSII (Fv/Fm) and photon yield of PSII (ΦPSII) in the osmotically-stressed seedlings were significantly reduced when compared to those of the control group (without mannitol or NaCl), leading to net-photosynthetic rate (Pn) and growth reduction with positive correlation. In addition, physiological changes and growth parameters of salt stressed seedlings were more sharply reduced than those of water-deficit stressed seedlings, especially in PT1 salt susceptible. On the other hand, the proline contents in the root and leaf tissues of osmotically-stressed seedlings increased significantly, especially in response to iso-osmotic salt stress. The chlorophyll pigments in isoosmotically-stressed leaves were significantly degraded, related to low water oxidation, low Pn and growth reduction. Those multivariate parameters were subjected to classify the salt tolerance, HJ and salt susceptible, PT1 and RD6 as well as the water deficit tolerance, HJ and RD6 and water deficit susceptible, PT1 using Hierarchical cluster analysis.

Effect of mannitol- and salt-induced iso-osmotic stress on proline accumulation, photosynthetic abilities and growth characters of rice cultivars (oryza sativa l. spp. indica)

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Effect of mannitol- and salt-induced iso-osmotic stress on proline accumulation, photosynthetic abilities and growth characters of rice cultivars (oryza sativa l. spp. indica)