Nj Mendham

Potassium and sodium relations in salinised barley tissues as a basis of differential salt tolerance

A large-scale glasshouse trial, including nearly 70 barley cultivars (5300 plants in total), was conducted over 2 consecutive years to investigate plant physiological responses to salinity. In a parallel set of experiments, plant salt tolerance was assessed by non-invasive microelectrode measurements of net K+ flux from roots of 3-day-old seedlings of each cultivar after 1 h treatment in 80 mm NaCl as described in our previous publication (Chen et al. 2005). K+ flux from the root in response to NaCl treatment was highly (P < 0.001) inversely correlated with relative grain yield, shoot biomass, plant height, net CO2 assimilation, survival rate and thousand-seed weight measured in glasshouse experiments after 4-5 months of salinity treatment. No significant correlation with relative germination rate or tillering was found. In general, 62 out of 69 cultivars followed an inverse relationship between K+ efflux and salt tolerance. In a few cultivars, however, high salt tolerance (measured as grain yield at harvest) was observed for plants showing only modest ability to retain K+ in the root cells. Tissue elemental analysis showed that these plants had a much better ability to prevent Na+ accumulation in plant leaves and, thus, to maintain a higher K+/Na+ ratio. Taken together, our results show that a plants ability to maintain high K+/Na+ ratio (either retention of K+ or preventing Na+ from accumulating in leaves) is a key feature for salt tolerance in barley.

Growth and physiological responses of six barley genotypes to waterlogging and subsequent recovery

In this study, the growth response of 6 barley genotypes of different origin (3 from China, 2 from Australia, 1 from Japan) to waterlogging and subsequent recovery was evaluated in 2 different soil types, an artificial potting mix and a Vertosol. A range of physiological measurements was assessed, to develop a method to aid selection for waterlogging tolerance. Plants at the 3 or 4 expanded leaf stages were subjected to waterlogging for 3 weeks followed by 2 weeks of recovery. Both shoot and root growth was negatively affected by waterlogging. As waterlogging stress developed, chlorophyll content, CO2 assimilation rate, and maximal quantum efficiency of photosystem II (Fv/Fm) decreased significantly. The adverse effect of waterlogging was most severe for genotype Naso Nijo, intermediate for ZP, Gairdner, DYSYH, and Franklin, and least for TX9425 in both trials. Studies of the root anatomy suggested that such a contrasting behaviour may be partially due to a significant difference in the pattern of aerenchyma formation in barley roots. The adverse effects in stressed plants were alleviated after 2 weeks of drainage for all genotypes. In general, TX9425 continued to grow better than other varieties, whereas recovery of Naso Nijo was extremely slow. It is suggested that screening a small number of lines for waterlogging tolerance could be facilitated by selecting genotypes with least pronounced reduction of photosynthetic rate or total chlorophyll content, and for a larger number of lines, chlorophyll fluorescence is the most appropriate tool. Additional keywords: chlorophyll content, photosynthesis, chlorophyll fluorescence, aerenchyma.

Comparative mapping of quantitative trait loci associated with waterlogging tolerance in barley (Hordeum vulgare L.)

BackgroundResistance to soil waterlogging stress is an important plant breeding objective in high rainfall or poorly drained areas across many countries in the world. The present study was conducted to identify quantitative trait loci (QTLs) associated with waterlogging tolerance (e.g. leaf chlorosis, plant survival and biomass reduction) in barley and compare the QTLs identified across two seasons and in two different populations using a composite map constructed with SSRs, RFLP and Diversity Array Technology (DArT) markers.ResultsTwenty QTLs for waterlogging tolerance related traits were found in the two barley double haploid (DH) populations. Several of these QTLs were validated through replication of experiments across seasons or by co-location across populations. Some of these QTLs affected multiple waterlogging tolerance related traits, for example, QTL Qwt4-1 contributed not only to reducing barley leaf chlorosis, but also increasing plant biomass under waterlogging stress, whereas other QTLs controlled both leaf chlorosis and plant survival.ConclusionImproving waterlogging tolerance in barley is still at an early stage compared with other traits. QTLs identified in this study have made it possible to use marker assisted selection (MAS) in combination with traditional field selection to significantly enhance barley breeding for waterlogging tolerance. There may be some degree of homoeologous relationship between QTLs controlling barley waterlogging tolerance and that in other crops as discussed in this study.

The impact of timing and duration of grass control on growth of a young Eucalyptus globulus Labill. plantation

Interference by an introduced grass, Holcus lanatus L. (Yorkshire fog grass) in a young E. globulus (Tasmanian blue gum) plantation was investigated. The objectives were to determine (1) the ‘critical period’ of competition, and (2) how the timing and duration of competition was related to the interaction between tree growth and resource availability. This was investigated during the first two years of establishment. Weed interference was severe with height and diameter growth of weedy trees being 52% and 40% of weed-free trees, respectively, at age two years. Most growth losses occurred during the first year. The critical period of weed interference was from planting to age 18 m and effective weed control was required for this period to maximise tree growth potential. The application of nitrogen to weedy trees promoted a significant growth response suggesting that competition for nitrogen was occurring. There was no significant response to level of irrigation. The use of critical period analysis is discussed.

Aluminium tolerance in barley (Hordeum vulgare L.): Physiological mechanisms, genetics and screening methods

Aluminium (Al) toxicity is one of the major limiting factors for barley production on acid soils. It inhibits root cell division and elongation, thus reducing water and nutrient uptake, consequently resulting in poor plant growth and yield. Plants tolerate Al either through external resistance mechanisms, by which Al is excluded from plant tissues or internal tolerance mechanisms, conferring the ability of plants to tolerate Al ion in the plant symplasm where Al that has permeated the plasmalemma is sequestered or converted into an innocuous form. Barley is considered to be most sensitive to Al toxicity among cereal species. Al tolerance in barley has been assessed by several methods, such as nutrient solution culture, soil bioassay and field screening. Genetic and molecular mapping research has shown that Al tolerance in barley is controlled by a single locus which is located on chromosome 4H. Molecular markers linked with Al tolerance loci have been identified and validated in a range of diverse populations. This paper reviews the (1) screening methods for evaluating Al tolerance, (2) genetics and (3) mechanisms underlying Al tolerance in barley.

Identification of quantitative trait loci contributing to Fusarium wilt resistance on an AFLP linkage map of flax ( Linum usitatissimum )

Abstract An AFLP genetic linkage map of flax (Linum usitatissimum) was used to identify two quantitative trait loci (QTLs) on independent linkage groups with a major effect on resistance to Fusarium wilt, a serious disease caused by the soil pathogen Fusarium oxysporum (lini). The linkage map was constructed using a mapping population from doubled-haploid (DH) lines. The DH lines were derived from the haploid component of F2 haploid-diploid twin seed originating from a cross between a polyembryonic, low-linolenic-acid genotype (CRZY8/RA91) and the Australian cultivar ‘Glenelg’. The AFLP technique was employed to generate 213 marker loci covering approximately 1400 cM of the flax genome (n=15) with an average spacing of 10 cM and comprising 18 linkage groups. Sixty AFLP markers (28%) deviated significantly (P<0.05) from the expected segregation ratio. The map incorporated RFLP markers tightly linked to flax rust (Melamspora lini) resistance genes and markers detected by disease resistance gene-like sequences. The study illustrates the potential of the AFLP technique as a robust and rapid method to generate moderately saturated linkage maps, thereby allowing the molecular analysis of traits, such as resistance to Fusarium wilt, that show oligogenic patterns of inheritance.

Physiological and cytological response of salt-tolerant and non-tolerant barley to salinity during germination and early growth

Seven barley cultivars (Franklin, Gairdner, YU6472, Numar, CM72, ZND3 and YUQS) were evaluated for NaCl tolerance in relation to physiological and cytological responses during germination. Standard germination techniques were employed using blotting paper saturated with different NaCl solutions (0, –0.3, –0.6, –0.9, –1.2, –1.5 or –1.8 MPa) at 20°C. The results showed significant differences among varieties for germination percentage, frequency of abnormal seedlings, and Na+, K+ uptake. Of the 7 barley cultivars, CM72 was similar in salt tolerance to Numar, while YUQS and ZND3 were the most sensitive to high salinity. The tolerant cultivars showed much higher germination percentage under salinity stress than susceptible varieties. Both CM72 and Numar maintained more than 90% germination at –1.2 MPa osmotic potential while YUQS and ZND3 had only 57% germination at the same level of salinity. The tolerant varieties also showed shorter mean germination time at low osmotic potential. The start of the first mitosis was delayed, while both the frequencies of aberrant anaphases at the first cell divisions, and the numbers of abnormal seedlings were increased in higher salt concentrations. During the seedling stage, tolerant varieties showed significantly higher K+ concentrations, lower Na+ concentrations, lower Na+/K+ ratio and higher photosynthetic rate than susceptible varieties under salinity stress. Screening of barley cultivars or breeding lines could be best achieved by a combination of germination testing and measurement of photosynthetic rate and/or Na/K balance in young seedlings.

Host location and oviposition of lepidopteran herbivores in diversified broccoli cropping systems

1 Host location and oviposition are crucial steps in the life cycles of insect herbivores. A diversified cropping system may interfere with these processes, ultimately reducing pest colonization of crops and the need for chemical interventions.

Amelioration of detrimental effects of waterlogging by foliar nutrient sprays in barley

Six barley (Hordeum vulgare L.) cultivars contrasting in their waterlogging tolerance were subjected to waterlogging for 2 weeks under glasshouse conditions. The adverse effects of waterlogging were significantly alleviated by the foliar spray of nutrients (quarter- or full-strength Hoagland solution) in all cultivars. Beneficial effects of nutrient sprays included improved shoot and root growth and reduced leaf senescence. Chlorophyll content was increased, as was net CO2 assimilation, photochemical efficiency of PSII, and adventitious root production compared with waterlogged plants with no added foliar nutrients. Auxin was found accumulated at the shoot base in waterlogged plants, and the spray of foliar nutrients significantly increased this accumulation in waterlogged plants after 14 days of treatment. Foliar application of 1-NAA also promoted the production of adventitious roots. The highest concentration of auxin was measured in the stem region between 1.2 and 1.6 cm above the shoot-root junction. Foliar nutrient application also improved nitrogen and potassium content in both shoot and root, but calcium content was hardly affected. It is concluded that the improvement of waterlogged plant growth by foliar nutrient sprays could be related to both the improved plant nutrition and increased auxin accumulation in the shoot base, responsible for development of adventitious roots.

A reliable screening system for aluminium tolerance in barley cultivars

Aluminium (Al) toxicity in the soil is an important factor that limits the production of barley in areas with acid soil. Selection and breeding of barley cultivars tolerant to Al toxicity is one of the most useful approaches to increase productivity. A reliable screening system is very important for selecting Al-tolerant plants in a breeding program. Using a hydroponic culture technique in which all the treatments were isolated in order to minimise complex interaction between genotypes, experiments were conducted to distinguish between susceptible and tolerant cultivars. Three different methods were investigated. Two previously reported methods could not provide consistent results or detect the difference between tolerant and susceptible cultivars. A new method was developed as follows: pre-germinated seedlings (2 days at 22°C) were cultured for 3 days in nutrient solution (Al free) followed by 24 h growing in a solution with 50 or 100 µm Al, and then 48 h regrowth in Al free nutrient solution. Following this method, seminal root regrowth length (SRRL) and relative seminal root regrowth length (RSRRL) showed significant differences between tolerant and sensitive cultivars. The SRRL of the most tolerant cultivar, Dayton, was 4–8 times greater than of the sensitive cultivars and about twice as long as of the other tolerant cultivars, FM404 and Brindabella. All the sensitive cultivars showed significantly shorter SRRL or RSRRL. Both SRRL and RSRRL were found to be closely correlated with plant height, plant dry weight, and grain weight in a soil-based experiment. This method was also used to evaluate F2 populations from crosses between tolerant and susceptible cultivars. Both SRRL and RSRRL gave results consistent with the hypothesis that the tolerance was controlled by a single dominant gene.