Effect of Mixed-Salt Salinity on Growth and Ion Relations of a Barnyardgrass Species

ABSTRACT

Recent investigations of the plant genome have revealed a large degree of similarity among cereal crops (specifically within the family Triticeae) and other related grass species. Recognition of the close genetic relationship among the grasses indicates that more exotic species, such as weedy grasses, may be exploited by plant breeders to enhance biotic/abiotic stress tolerance in cereal crops. Echinochloa crus-galli (L.) ^{1 1} Mention of company names or products is for the benefit of the reader and does not imply endorsement, guarantee, or preferential treatment by the USDA or its agents. Beauv. (barnyardgrass), a wide-spread, persistent C₄ weed species of agricultural importance, is reported to tolerate high levels of salinity. Growth and ion relations were studied in barnyardgrass using mixed-salt salinity (with final electrical conductivities (ECi) of 3 (control), 7, 11, and 19 dS m^?1 in the irrigation water) to determine whether the mechanism(s) for its salt tolerance are similar to those previously reported for other cereal crops. Such a finding would indicate that barnyardgrass may possess valuable genetic traits. Ion accumulation and ion selectivity ratios in the various treatments were determined from oven-dried shoot tissue. Significant (P < 0.01) linear regressions were obtained between either fresh weight or plant height and ECi. The point of 50% reduction (C₅₀) in fresh weight was predicted to occur at about 13.9 dS m^?1; the C₅₀ value for plant height was at about 22.9 dS m^?1. Statistical analysis of calculated Gapon constants for potassium (K)/sodium (Na) indicated that ion selectivity was not affected until after 11 dS m^?1. Calcium (Ca)/Na selectivity was not significantly affected by salinity. We concluded that, similar to some cereal crops, barnyardgrass maintains growth under saline conditions by maintaining high K/Na ratios, possibly because of better membrane integrity due to high Ca selectivity.     

Differential Growth Response to Salt Stress Among Selected Ornamentals

Evaluation of salt tolerance in herbaceous perennials was performed with mature potted plants under greenhouse conditions. Six herbaceous perennial species were evaluated for their tolerance to aqueous solutions of various sodium chloride (NaCl) concentrations over a 21 day period by measuring growth, water transpiration, and leaf nutrient content. Potential exists for utilization of these species in somewhat challenging saline environments along roadsides and in urban landscapes. Species evaluated in a mature growth stage included Achemilla mollis, Nepeta x faassenii, Sedum acre, Thymus praecox, Phlox subulata and Solidago cutleri. On the basis of relative growth rate and water transpiration responses to NaCl (0–400 mM) treatments, groundcovers were grouped into three tolerance categories: highly sensitive to salt treatment (S. acre), those with intermediate sensitivity (A. mollis, N. x faassenii, T. praecox, and P. subulata), and those exhibiting tolerance (S. cutleri). Sodium content in leaf foliage of S. cutleri was about ten-fold lower than other groundcover species in the 200 mM NaCl treatment, consistent with greater tolerance to NaCl treatments in terms of transpiration, biomass accumulation, and retention of green foliage. Comparison of foliar nutrient levels among groundcover species and treatments suggested strong differential response to NaCl treatment, indicating that changes in nutrient levels over time may be a reasonable way to predict NaCl tolerance in groundcovers.     

Tolerance of Two Hydroponically Grown Salix Genotypes to Excess Zinc

Woody cuttings from two Salix genotypes (genotype I—clone LUC-31, Salix alba and genotype II- clone STOTT, Salix viminalis) were grown hydroponically for 14 days at increasing concentrations of Zn: control, 50, 100 or 150 μ M Zn. Genotype tolerance to excess zinc (Zn) was evaluated using a root elongation test. The changes in growth, Zn, iron (Fe), copper (Cu) and manganese (Mn) concentrations as well as photosynthetic performance were used as additional evaluation criteria. Photosynthetic pigments concentrations in Zn-exposed cuttings of genotype II decreased as compared with genotype I, which corresponded well with the higher leaf Zn accumulation, decreased Fe concentrations as well as lowered photosynthetic rate. Based on the indicators used, genotype I (Salix alba) was classified as more tolerant to excess Zn than genotype II (Salix viminalis).     

Selecting Rice Genotypes Tolerant to Zinc Deficiency and Sodicity: Differences in Concentration of Major Cations and Sodium/Potassium Ratio in Leaves

Zinc (Zn) deficiency is a major nutritional problem for rice under sodic conditions. Seedlings (35-d old) of 30 rice genotypes were transplanted in pots at pH₂ 9.8 [diethylene triamine penta acetic acid (DTPA) Zn 1.8 ppm] to identify genotypes tolerant to both sodicity and Zn deficiency. Ten genotypes (group A) showed potential to tolerate both the stresses. Sixteen genotypes (group B) were sensitive to Zn deficiency. However, some of the seedlings of group B genotypes were normal (without Zn deficiency symptoms). Four genotypes (group C) were sensitive to sodicity. Leaves and their leaf sheaths were analyzed at 33 d after transplanting for Ca, Mg, K, and Na. Group A genotypes (CSR-88IR15, CSR-89IR14, IR4630-22-2-5-1-2, and Trichi) had significantly less Na concentrations in their leaves and the leaf sheaths compared to group B genotypes (CSR10, CSR23, CSR-88IR1, 89H1-931098, and IR47538-3B-9-3B-1). The concentration of Na was invariably higher in the leaf sheath than its leaf in both the groups, but reverse was true for Ca, Mg, and K. Zinc deficient plants had relatively higher concentrations of Ca and Mg in their leaves and the leaf sheaths than group A. Concentration of K was somewhat better in group A than group B genotypes. Higher Na/K ratio in group B genotypes compared to group A may be attributed to increased concentrations of Na rather than decreases in K concentrations. Further studies are needed to understand the processes associated with differential uptake of Na and K by Zn deficient plants of group B genotypes resulting in higher Na/K ratio compared to group A genotypes.     

Mechanisms of Aluminum Tolerance in Phosphoenolpyruvate Carboxylase Transgenic Rice

Transgenic rice, in which C4-phosphoenolpyruvate carboxylase (PEPC) is overexpressed, was grown in hydroponic culture to evaluate its tolerance for high aluminum (Al) content in relation to organic acid synthesis and exudation into the rhizosphere. With regard to root growth in short-term experiments, PEPC-transgenic rice was more tolerant of Al than the wild type. At increased Al levels in the root medium, root tips of the transgenic rice accumulated less Al than those of the wild type. Aluminum-induced oxalate exudation from roots occurred at increased rates in the transgenic line. Overexpression of C4-PEPC drastically increased PEPC activity in leaves of the transgenic rice, causing higher organic acid concentrations in leaves and roots. The increased organic acid concentrations seemed to cause higher exudation rates of oxalate from roots, leading to a detoxification of Al in the root apoplast and rhizosphere.     

IDENTIFICATION OF GROUNDNUT (ARACHIS HYPOGAEA L.) CULTIVARS TOLERANT OF SOIL SALINITY

Field screening of 83 groundnut cultivars was undertaken for two seasons to assess their tolerance of salinity based on plant mortality and yield attributes. During the dry season, soil salinity of 4 dS m^?1 at sowing and 6–7 dS m^?1 21–98 days after sowing (DAS) caused high mortality without seed formation in any cultivars, however, at salinity 4.5 dS m^?1 during sowing and 3.5–3.0 dS m^?1 15–80 DAS during wet season, 61 cultivars produced seed. The cultivars ‘VRI 3’, ‘UF 70–103’, ‘TKG 19A’, ‘S 206’, ‘Tirupati 4’, ‘M 522’, ‘Punjab 1’, ‘BG 3’, ‘Somnath’ and ‘ICGV 86590’, with high plant stand during both the seasons and over 75 g m^?2 seed yield during wet season, were identified salinity tolerant. However, 15 cultivars with more than 50 g m^?2 seed yield were moderately tolerant and 28 cultivars with less than 25 g m^?2 seed yield were sensitive to salinity.     

Low pH and aluminum tolerance of Bradyrhizobium strains isolated from acid soils in Indonesia

Sixty-seven strains of Bradyrhizobium isolated from soybean plants growing on acid soils in West Java and Sumatra, Indonesia, were examined for the effect of the pH and aluminum concentration on their growth in nutrient media, compared with 61 strains of Bradyrhizobium from soils in Japan. The results in this study indicated that the indigenous population of Bradyrhizobium in the soils of Indonesia showed a large difference in acid- and Al-tolerance from that of Japan. Eighty-five and 48% of the isolates from Japanese soils and Indonesian soils, respectively, were unable to grow in YEM broth at pH below 4.5. The acid-tolerance was correlated with AI-tolerance of the isolates on YEM agar plates at pH 4.4. Seventy-five percent of the isolates that grew in YEM broth at pH 4.5 were also resistant to 400 µM Al on the YEM plates. Acetylene reduction assay of the root nodules revealed that 3 of the acid- and Al-tolerant isolates from Indonesian soils showed a significantly high nitrogen fixation activity.     

Salt tolerance of grain crops in relation to ionic balance ability to absorb microelements

A greenhouse experiment was conducted to investigate the effect of exchangeable Na on the growth and absorption of metal elements in barley, rye, and maize. The plants were cultivated in soils whose exchangeable sodium percentages (ESP) were 6.6 (saline soil: Saline), 17.4 (saline-sodic soil: Sodic 1), and 39.6 (sodic soil: Sodic 2), which were prepared from Tottori sand dune soil (Control). The dry weight (DW) and concentrations of metal elements Ca, Mg, Mn, Zn, and Cu) in shoots were analyzed. The shoot DW was smaller with higher ESP, but in barley the difference between all the treatments was no longer observed with time. In Sodic soils, the growth of barley was vigorous, whereas rye growth was poor, and maize plants died by 5 weeks after planting. The Na concentration in shoots of all the species was higher with higher ESP. The K concentration in shoots was low at the early growth stage, but in barley it was higher in the Saline and both Sodic soils than in the Control at the subsequent stages. The concentrations of Ca and Mg in shoots of barley and maize in the Saline and both Sodic soils were higher than those in the Control, but in rye the concentrations were lowest in Sodic 2. The concentrations of Mn, Zn, and Cu in barley shoots in the Saline and bothSodic soils tended to be higher than those in the Control, whereas in rye they were lower than in the Control in both Sodic soils. Barley showed a higher ability to absorb low available microelements than rye and maize. These results indicate that barley is tolerant to sodicity as well as salinity, maize is tolerant to salinity, but is very sensitive to sodicity, and rye is moderately sensitive to both stresses. We suggest that the tolerance of grain crops to ESP involves a tolerance to a high Na concentration in shoots, the ability to keep suitable concentrations of essential cations in the presence of a high concentration of Na in shoots and the ability to absorb low available microelements.     

Consistent responses of yield and resistance of wheat cultivars to the root-lesion nematode,Pratylenchus thornei,in the Australian northern subtropical region,but not in the temperate southern region

To understand the yield response of cereal cultivars to Pratylenchus thornei, eight experiments were conducted within the subtropical northern, and temperate southern grain-producing regions of Australia. Wheat cultivars (Triticum aestivum) ranging from susceptible to moderately resistant to P. thornei were grown in Year 1 to establish a range of population densities. In Year 2 before sowing, P. thornei was quantified in each plot and six cereal cultivars were each grown on a similar range of population densities (average minimum to maximum of 3.4–60.6 P. thornei/g soil); P. thornei was quantified again at harvest. In the four experiments in the northern region there was a significant, negative logarithmic response of yield of the three most intolerant/susceptible cultivars as P. thornei population densities increased (yield decreased 172–479 kg/ha per unit increase in log_e-transformed P. thornei/g soil). The responsiveness of yield to increasing P. thornei population densities diminished as the tolerance and resistance of the cultivars improved. In the southern region, there was no relationship between yield and P. thornei in three experiments and minor, positive increases in one experiment (1.6 kg/ha per unit increase in P. thornei/g soil). Across both regions, the change in P. thornei population densities from sowing to harvest was logarithmic and positive, and generally greatest in the northern region. The contrast of responses of cereal cultivars between the regions, despite similar population densities of P. thornei, is indicative of the influence of the environment particularly on tolerance, therefore management with a regional focus is essential.     

不同基因型玉米萌芽期的抗旱性研究

对4个玉米杂交种辽单24、丹413、沈丹16、沈农87进行了萌芽期的抗旱性研究。结果表明水分胁迫降低了杂交种的发芽势和发芽率,阻碍了胚根和胚芽的生长,也降低了叶片的蒸腾速率和光合速率。但不同杂交种在抗旱性上存在明显差异,在水分胁迫下,抗旱性强的杂交种仍然保持较高的发芽势和发芽率。水分胁迫下,玉米种子的吸水速率减小,但吸水速率与抗旱性间相关性不明显。各品种在20%PEG水分胁迫处理下的萌动吸水伤害率间差异明显,可以作为一个抗旱鉴定指标。研究表明,利用室内高渗溶液萌发法通过对玉米萌芽期抗旱性高度相关的性状的测定得出的萌芽期抗旱性鉴定结果与田间直接鉴定的结果基本相符,说明室内高渗溶液萌发法是鉴定玉米萌芽期抗旱性的一种快速、简便、准确的方法。