Michael C. Shannon

Evaluation of salt tolerance in rice genotypes by multiple agronomic parameters

AbstractThe lack of an effective evaluation method for salt tolerance in the screening process is one of the reasons for limited success in conventional salt tolerance breeding. This study was designed to identify useful agronomic parameters for evaluation of salt tolerance and to evaluate genotypes by multiple agronomic parameters for salt tolerance at different growth stages. Twelve genotypes were grown in a greenhouse in sand and irrigated with nutrient solutions of control and treatments amended with NaCl and CaCl2 (5:1 molar concentration) at 4.4 and 8.2 dS m-1 electrical conductivity. Wide genotypic differences in relative salt tolerance based on seedling growth were identified. The duration of reproductive growth between panicle initiation and anthesis was either reduced or increased by salinity, but the response was not strictly correlated with relative salt tolerance in seed yield among genotypes. Wide genotypic differences in relative salt tolerance based on spikelet and tiller numbers were identified. Few genotypic differences were identified for fertility and kernel weight. Spikelet and tiller numbers contributed most of the variation to seed yield among parameters investigated. When genotypes were ranked for salt tolerance based on the means of multiple parameters, dramatic changes of salt tolerance at early and seed maturity stages were observed in two genotypes, GZ5291-7-1-2 and GZ178. IR63731-1-1-4-3-2 was identified with a favourable combination of salt tolerance at early seedling and seed maturity stages. Cluster group ranking of genotypes based on multiple agronomic characters can be applied in salt tolerance breeding to evaluate salt tolerance and may have great advantage over conventional methods.

Salt-induced Na+H+ antiport in root plasma membrane of a glycophytic and halophytic species of tomato☆

Abstract Plasma membrane and tonoplast vesicles were isolated from roots of both the glycophytic cultivated tomato, Lycopersicon esculentum (Mill, cv. Heinz 1350) and its halophytic wild relative, Lycopersicon cheesmanii (Hook, C.H. Mull, ecotype 1401) grown under control and saline conditions. MgATP-dependent proton transport was measured by determining the rate of quench of quinacrine fluorescence. Rates of quench and rates of ATP hydrolysis were higher for both the plasma membrane and tonoplast from both species when grown under saline conditions. When ATPase activity was measured, the degree of stimulation of ATP hydrolysis in the presence of KCl, NaCl, and choline chloride was similar for the plasma membrane from control and salt grown plants. However, NaCl gave lower rates of proton transport than did KCl or choline chloride for the plasma membrane of both L. esculentum and L. cheesmanii grown under saline conditions. This may be interpreted as evidence of Na + H + antiport. A pH gradient (acid interior) was formed in vesicles by adding MgATP. After the establishment of a proton gradient, the effect of cations on proton efflux was estimated by adding EDTA to chelate the Mg2+. Fluorescence recovery rate was used as an indication of the rate of proton efflux. The addition of Na+ enhanced fluorescence recovery compared to K+ in plasma membranes from both species grown under saline conditions. Addition of K+ and valinomycin to the assay media did not affect Na + H + exchange, nor did addition of amiloride. No evidence was found for a Na + H + antiport mechanism in the tonoplast of either L. esculentum or L. cheesmanii regardless of growth conditions.

Selection for salt tolerance in Lesquerella fendleri (Gray) S. Wats.

Abstract In a study conducted in 1997–1998 to determine the salt tolerance of Lesquerella fendleri (Gray) S. Wats., saline irrigation waters greater than 21 dS m−1 electrical conductivity were found to cause high plant mortality. Surviving plants were inter-mated under controlled conditions and seeds were collected from these plants. The following season, seeds of the selected salt tolerant full-sibs, designated WCL-SL1, were direct-seeded into 21 outdoor sand tanks, along with two other lines. One line was the original seed planted the previous year called ‘1986 bulk’, and the other was an unselected line, designated ‘line 54’. In an effort to determine whether salt tolerance is a heritable trait in lesquerella, this study compared the salinity response of WCL-SL1 with the two other lines. After seeding into the sand tanks, they were irrigated daily with complete nutrient solutions. Seven salinity treatments were imposed by stepwise additions of mixed salt salinity composed of Na+, SO42−, Cl−, Mg2+ and Ca2+. Final electrical conductivities (ECi) of the irrigation waters were 3, 7, 11, 15, 18, 21 and 24 dS m−1. Two weeks after salinization, significant treatment differences in both plant height and survival were observed among lines. The parental line ‘1986 bulk’ was most sensitive, WCL-SL1 line most tolerant, and ‘line 54’ intermediate. Shoot weights in all lines decreased as a function of increasing salinity and ranked mean differences within lines were consistent across all salinity levels. At 7, 15 and 18 dS m−1 salinity levels, the shoot weights of the WCL-SL1 line were significantly greater than the parental line. Total seed oil and lesquerolic acid contents increased significantly as irrigation water salinity increased from 3 to 18 dS m−1. Improved salt tolerance of line WCL-SL1 was not attributed to differences in mineral ion uptake and accumulation in leaf tissue. Our results indicate that a single cycle of selection with lesquerella in salinized sand cultures resulted in an improved lesquerella line that had higher absolute and relative salt tolerance based on seedling survival, plant height, shoot biomass production, and seed yield than the original line.

Salinity and Irrigation Method Affect Mineral Ion Relations of Soybean

Abstract Soybean [Glycine max(L.) Merrill] is moderately salt tolerant, but the method of irrigation used for crop production under saline conditions may influence the uptake and distribution of potentially toxic salts. This field study was conducted to determine the effects of application of saline waters by different methods, namely, drip and above‐canopy sprinkler irrigation, on the ion relations of soybean cultivar “Manokin”. Salinity was imposed by adding NaCl and CaCl2 (1:1 by weight) to nonsaline irrigation waters. Saline treatments with electrical conductivity (EC i ) of 4 dS m−1 were compared with nonsaline controls (EC i = 0.5 dS m−1). Ion concentrations in leaves, stems, roots, and when present, pods were determined at four stages of growth: vegetative, flowering, podding, and grain filling. Both Na+ and Cl− were excluded from the Manokin leaves and stems when plants were drip‐irrigated and the uptake of these ions occurred solely via the root pathway. However, when saline water was applied by sprinkling, the ions entered leaves by both foliar absorption and root uptake and their concentrations in the leaves were about 9‐fold higher than in those under saline drip irrigation. Regardless of treatment, leaf‐K was highest during the vegetative stage, then decreased with plant age as K+ was mobilized to meet nutrient demands of the developing reproductive structures.

Soil water and temperature regimes in drip and sprinkler irrigation, and implications to soybean emergence

Abstract Irrigation has long been used in agriculture as a primary means of water management. It is well known that water distributions in the soil differ depending on the methods of irrigation. However, it is less clear how soil thermal regimes would change over time and space when irrigation methods are different. A field study was conducted to investigate the interactive effect of soil water and temperature regimes in drip and sprinkler irrigation. The effect of different methods of irrigation on soil water and thermal environment was then used to interpret differences in soybean emergence and seedling growth under the two irrigation treatments. Time domain reflectometry wave-guides and thermocouples were installed in field plots to provide soil water content and temperature measurements. Soybean seeds were planted to assess the emergence and seedling development. Consistent with infiltration theory, soil water contents were higher directly under the drip tapes in drip irrigation, but were relatively more uniform across the whole soil surface in sprinkler irrigation. Although five times more water was used in the sprinkler than in the drip plot, the soil water content at the seed zone was similar. Soil temperature was significantly higher in the drip than in the sprinkler plot, which led to a higher emergence rate and enhanced seedling growth. Drip irrigation not only conserved water but also maintained the soil profile at a higher temperature more favorable for plant emergence and seedling development.