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- Author or Editor: M. C. Shannon x
Rapid screening techniques for selecting salt-tolerant plants are heretofore untried, untested, or unproven. Theoretically, we know it is possible to screen plants for this trait. Halophytes and salt-tolerant ecotypes exist in nature and variability in tolerance has been demonstrated in a number of agronomic species (48). However, the complexities of salt tolerance and the multitude of ways in which plants adjust and adapt to it have caused much confusion. The effect of salinity on a plant may depend on ontogeny (3, 11), humidity (21, 22, 34), temperature (21, 35), light (14, 35), irrigation management (8, 9), cultural practices (6, 11), soil fertility (10, 32), air pollution (20, 26), and the particular growth or yield parameter measured (3, 49). If all environmental conditions are optimal it is possible to grow some agricultural crops at seawater salinity concentrations. Barley, wheat, millet, and various other crops have been grown on sandy beach areas using seawater for irrigation (4, 5, 16, 24). The use of sand facilitates leaching and minimizes salinity accumulation. Additionally, coastal areas may be cool and humid, and, if fogs are common, have low light intensities. These factors create a favorable environment and decrease salinity damage. Recently, Epstein and colleagues used such an environment to screen a barley composite for salt tolerance (16). Several lines were selected which seemed to produce higher yields than the test cultivars. It is possible that such research will result in the selection of traits that will enhance salt tolerance in barley cultivars adapted to other environments.
Four clones of Eucalyptus camaldulensis Dehn. (4543, 4544, 4573, and 4590) and one clone of E. rudis Endl. (4501) were grown in greenhouse sand cultures irrigated with waters designed to simulate saline drainage waters present in the San Joaquin Valley of California, and compositions that would result from further concentration of the waters. The drainage waters are typically high in Na+, SO4 2-, Cl-, and Mg2+. Electrical conductivities of the solutions were 2, 12, and 28 dS·m-1. Ion uptake and distribution patterns in above-ground components were studied in members of these clones grown under treatment for 7 weeks. Results indicated the clones could be separated into two distinct groups by significant differences in leaf-ion relations. Group 1 clones 4543, 4544, and 4573 accumulated less Na+ and more Ca2+ and Cl- in leaves than group 2 clones, 4501 and 4590. Group 2 clones accumulated Na+ under low salinity, but apparently possessed some mechanism for restricting Na+ accumulation by the leaves that was activated as salinity increased. Leaf and stem Cl- concentrations tended to be lower in all clones grown at 28 dS·m-1 than at 2 dS·m-1, despite increases in Cl- concentration in the irrigation waters. Under saline conditions, K+ and P were preferentially accumulated in the youngest leaves in the upper portion of the canopy, whereas Na+, Ca2+, and Mg2+ were retained in the older leaves.
The salt tolerance of 3 muskmelon cultivars (Cucumis melo L. cv. Top Mark, PMR 45, and Hale's Best) was determined in plots artificially salinized with NaCl and CaCl2. Marketable yield, total dry weight, vine dry weight, and total fruit weight of all cultivars decreased with increasing salinity. ‘Top Mark’, the highest yielding cultivar at low salinity, yielded least at high salinity. ‘PMR 45’ was the least affected with increasing salinity. Na and Cl in the leaves and fruit and % soluble solids in the fruit all increased with increasing salinity levels.
Salt tolerance differences among 115 plant introductions of lettuce (Lactuca sativa L.) were screened in sand cultures under greenhouse conditions. Leaf and root fresh weights of plants grown for 4 to 5 weeks in salinized sand cultures were compared to a benchmark cultivar, ‘Buttercrunch’. Plant introductions showed a wider range of salt tolerance than standard cultivars of the United States and therefore have some potential in breeding programs designed to increase the salt tolerance of this crop.
The salt tolerances of a cultivated tomato (Lycopersicon esculentum L. cv. Heinz 1350) and three wild species [L. cheesmanii (Hook) C.H. Mull, L. peruvianum (L.), and L. pennellii (Cornell) D’Arcy] were determined in both sand and solution cultures. Curvilinear and two-piece linear methods were used to obtain response curves for fresh and dry weights of shoots. In solution cultures containing 0, 50, 100, and 150 mM added salt composed of 1:1 molar ratio of NaCl and CaCl2, ‘Heinz 1350’ was as salt-tolerant as any of the wild species. On the basis of relative decreases in vegetative dry weight, ecotype 1400 of L. cheesmanii was more sensitive to salt than ecotype 1401. After 4 weeks growth in sand cultures irrigated with nutrient solutions containing 0, 12.5, 25, 50, 75, and 100 mM added salts (5:1 molar ratios of NaCl and CaCl2), L. pennellii had higher relative salt tolerance than the other species. After 14 weeks, the cultivated species and L. pennellii were more sensitive at low salinity than the other two species. However, relative yield decreases with increasing salinity were not significantly different between the cultivated tomato and the 1401 ecotype of L. cheesmanii at higher salt concentrations. L. peruvianum and L. pennellii accumulated less leaf Cl- and more leaf Na+ than the other species. Significant differences in the partitioning of ions between mature and developing leaves were found for all species. The physiological mechanisms involved in tolerance at moderate salinities may differ from those required for survival at high salinity.
Agroforestry plantations offer environmentally acceptable strategies for the reuse of saline drainage waters. Tree species suitable for use in such systems must be selected for survival and sustained growth under highly saline conditions. In this screening trial, four clones of Eucalyptus camaldulensis Dehn. (4543, 4544, 4573, and 4590) and one clone of E. rudis Endl. (4501) were grown in greenhouse sand cultures irrigated with sodium sulfate–dominated waters. Solution compositions were prepared to simulate saline drainage waters typically found in the San Joaquin Valley of California. Electrical conductivities of the solutions ranged from 2 to 28 dS·m–1. Treatments were replicated three times. All plants survived and were harvested after 7 weeks under saline treatment. Plant height was measured weekly and shoot biomass was determined at final harvest. The salinity levels that resulted in a 50% reduction in biomass production (C50) were 16.4 (4573), 17.1 (4543), 17.7 (4544), 29.0 (4590), and 30.0 dS·m–1 (4501). Over the range of salinities from 4 to 20 dS·m–1, clones 4501, 4590, and 4573 generally maintained higher relative growth rates (RGR) than did clones 4544 and 4543. However, at the highest salinity, RGRs of clones 4501, 4544, and 4573 were significantly greater than those of clones 4543 and 4590. Assessed on the basis of biomass production, clones 4501 (E. rudis) and 4590 (E. camaldulensis) showed exceptional potential for use in agroforestry systems where the saline drainage waters are sodium sulfate–dominated.
Cultivated and wild accessions of Cucumis melo L. were evaluated for salt tolerance to identify germplasm useful in breeding programs. Entries were tested for seed germination and seedling emergence in a -6.0 bar osmotic solution of NaCl + CaCl2 (2:1 molar ratio) under laboratory conditions. Seedling growth was measured in the greenhouse as fresh weight of plants grown in sand cultures irrigated with saline nutrient solutions of -0.3, -1.7, and -3.3 bars osmotic potential. Salinity decreased emergence and growth, but quantitative responses varied with differences in environmental conditions between experiments. A wide range of variation in response to salt stress was found for both emergence and vegetative growth. Several plant introductions had better emergence rates and growth than the cultivar ‘Top Mark’ under saline conditions. Salt tolerance exhibited by these introductions may be useful in breeding programs to improve muskmelon performance under saline conditions.
The response of lettuce (Lactuca sativa L.) to salinity was studied in greenhouse tests. Seven-day-old seedlings were grown in solution culture with salinity (NaCl + CaCl2, 2:1 molar ratio) ranging from 0.6 to 26 decisiemens per meter (dS m−1). Fresh weight (FW) declined as salinity increased; root weight was not affected as much as leaf weight. Regression analysis of 30-day-old seedlings showed that FW was significantly reduced at 4.6 dS m−1. FW decreased an additional 4.5% for each dS m−1 increase above 4.6 dS m−1. Results were similar 60 days after growth, and were comparable to previous field studies. A screening test for salt tolerance in lettuce was developed using sand culture. Considerable variability exists among 85 U.S. lettuce cultivars and breeding lines irrigated with 5.6 to 6.2 dS m−1 solution. ‘Climax’, ‘Climax 84’, ‘Shawnee’, ‘Tom Thumb’, ‘Fulton’, and ‘Wintergreen’ were the most tolerant cultivars tested. ‘Bibb’, ‘Ruby’, ‘Gustoverde’, ‘Prizehead’, and ‘Big Boston’ were significantly more sensitive to salinity.
Saline agricultural drainage water may be used as a resource to grow high value horticultural crops and reduce the volume of drainage for eventual disposal. To explore reuse options the effects of salinity and timing of application were tested on selected leafy vegetables grown in 24 sand culture plots in Riverside, Calif. The leafy winter vegetables included `Ruby Red Chard' Swiss chard [Beta vulgaris L. var. flavescens (Lam.) Lam.], `Space' spinach (Spinacia oleracea L.), `Vitamin Green' salad greens [Brassica rapa L. (Narinosa Group)], `Red Giant' mustard greens [Brassica juncea L. (Czerniak)], pac choi [Brassica rapa L. (Chinensis Group)], `Winterbor' kale [Brassica oleracea L. (Acephala Group)], tatsoi [Brassica rapa L. (Narinosa Group)], `Salad King' curly endive (Cichorium endivia L.), and `Red Preco No. 1' radicchio (Cichorium intybus L.). All vegetables were planted at the same time and irrigated initially with tap water and nutrients. At 3 and 7 weeks after seeding (application times), six salinity treatments were initiated by adding salts to the irrigation water to represent the chemical compositions of drainage waters found typically in the San Joaquin Valley, Calif. The six salinity treatments had electrical conductivities of 3 (control), 7, 11, 15, 19, or 23 dS·m-1. A randomized complete block design was used with (6 salinities × 2 application times × 2 replications). Within each plot a 1.5-m row of each of the nine vegetables was grown as split plots. Salinity reduced fresh weight (FW) yields of all species. Salt stress applied at 3 weeks after seeding reduced FWs for seven of the nine vegetables compared to salination at 7 weeks. Analyses of salt tolerance curves, maximum yields, and the point of 50% yield reduction (C50) were conducted. Greens produced the highest biomass at 874 g/plant, but was the most affected by application time. Swiss chard and radicchio were not significantly affected by timing of salinity application, and Swiss chard was the most salt tolerant overall. Greens, kale, pac choi, and to a lesser extent, tatsoi, have potential as winter-grown, leafy vegetables in drainage water reuse systems.