Effects of soil acidity and water stress on corn and soybean performance under a no-till system

Background and Aims

Field studies have demonstrated that aluminum (Al) toxicity is low in no-till systems during cropping seasons that have adequate and well-distributed rainfall. This study evaluated the performance of corn (Zea mays L.) and soybean (Glycine max L. Merrill) on an acid loamy soil under a long-term no-till system, in response to surface liming and as affected by genotypic tolerance to Al and water stress.

Methods

A field trial examined the effect of surface application of lime (0, 4, 8, and 12 Mg ha^?1) on no-till corn and soybean nutrition and yield. Trials were also carried out in undisturbed soil columns taken from the unlimed and limed plots. Two hybrids/cultivars of corn and soybean, one sensitive and the other moderately sensitive to Al were grown at two soil moisture levels with and without water stress (50 % and 80 % water filled pore space).

Results

Alleviating soil acidity by liming improved nutrition and increased grain yields of corn and soybean. The benefits of liming on root length density, nutrient uptake and shoot biomass production of corn and soybean were more pronounced in Al-sensitive genotypes under water stress.

Conclusions

The results suggest that plants exposed to drought stress under no-till systems are more affected by Al toxicity.     

Population structure and association mapping of yield contributing agronomic traits in foxtail millet

Key message

Association analyses accounting for population structure and relative kinship identified eight SSR markers ( p < 0.01) showing significant association ( R ²  = 18 %) with nine agronomic traits in foxtail millet.

Abstract

Association mapping is an efficient tool for identifying genes regulating complex traits. Although association mapping using genomic simple sequence repeat (SSR) markers has been successfully demonstrated in many agronomically important crops, very few reports are available on marker-trait association analysis in foxtail millet. In the present study, 184 foxtail millet accessions from diverse geographical locations were genotyped using 50 SSR markers representing the nine chromosomes of foxtail millet. The genetic diversity within these accessions was examined using a genetic distance-based and a general model-based clustering method. The model-based analysis using 50 SSR markers identified an underlying population structure comprising five sub-populations which corresponded well with distance-based groupings. The phenotyping of plants was carried out in the field for three consecutive years for 20 yield contributing agronomic traits. The linkage disequilibrium analysis considering population structure and relative kinship identified eight SSR markers (p < 0.01) on different chromosomes showing significant association (R ² = 18 %) with nine agronomic traits. Four of these markers were associated with multiple traits. The integration of genetic and physical map information of eight SSR markers with their functional annotation revealed strong association of two markers encoding for phospholipid acyltransferase and ubiquitin carboxyl-terminal hydrolase located on the same chromosome (5) with flag leaf width and grain yield, respectively. Our findings on association mapping is the first report on Indian foxtail millet germplasm and this could be effectively applied in foxtail millet breeding to further uncover marker-trait associations with a large number of markers.     

Stable carbon and nitrogen isotope ratios of Eucalyptus and Acacia species along a seasonal rainfall gradient in Western Australia

Key message

Eucalyptus and Acacia species were surprisingly similar with respect to variations in δ ¹³ C, δ ¹⁵ N. Both genera respond with speciation and associated changes in leaf structure to drought.

Abstract

Stable carbon and nitrogen isotope ratios (δ¹³C and δ¹⁵N) in leaves of eucalypts (Corymbia and Eucalyptus) and Acacia (and some additional Fabaceae) species were investigated together with specific leaf area (SLA), leaf nitrogen (N) and leaf phosphorous (P) concentration along a north–south transect through Western Australia covering winter- and summer-dominated rainfall between 100 and 1,200 mm annually. We investigated 62 eucalypts and 78 woody Fabaceae species, mainly of the genus Acacia. Leaf δ¹³C values of Eucalyptus and Acacia species generally increased linearly with latitude from ?29.5 ± 1.3 ‰ in the summer-dominated rainfall zone (15°S–18°S) to about ?25.7 ± 1.1 ‰ in the winter-dominated rainfall zone (29°S–31°S). δ¹⁵N increased initially with southern latitudes (0.5 ± 1.6 ‰ at 15°S; 5.8 ± 3.3 ‰ at 24–29°S) but decreased again further South (4.6 ± 3.5 ‰ at 31°S). The variation in δ¹³C and δ¹⁵N was probably due to speciation of Eucalyptus and Acacia into very local populations. There were no species that were distributed over the whole sampling area. The variation in leaf traits was larger between species than within species. Average nitrogen concentrations were 11.9 ± 1.05 mg g^?1 in Eucalyptus, and were 18.7 ± 4.1 mg g^?1 in Acacia. Even though the average nitrogen concentration was higher in Acacia than Eucalyptus, δ¹⁵N gave no clear indication for N₂ fixation in Acacia. In a multiple regression, latitude (as a surrogate for rainfall seasonality), mean rainfall, leaf nitrogen concentration, specific leaf area and nitrogen fixation were significant and explained 69 % of the variation of δ¹³C, but only 36 % of the variation of δ¹⁵N. Higher nitrogen and phosphorus concentration could give Acacia an advantage over Eucalyptus in arid regions of undefined rainfall seasonality.     

Response of Populus tremula to heterogeneous B distributions in soil

Background

Poplars accumulate inordinate amounts of B in their leaves and are candidate plants for the remediation of B contaminated soil. We aimed to determine the effect of heterogeneous B distribution in soil by comparing the growth and B accumulation of young Populus tremula trees growing in soil with heterogeneous and homogeneous B distributions.

Methods

The first of two experiments focused on the tolerance and B accumulation of P. tremula under heterogeneous soil B distributions, while the second was designed to study fine root growth under such conditions in detail.

Results

Growth and B accumulation of P. tremula were unaffected by the spatial distribution of B. Root and shoot growth were both reduced simultaneously when leaf B concentrations increased above 800 mg kg^?1. In the heterogeneous soil B treatments, root growth was more reduced in spiked soil portions with B concentrations >20 mg kg^?1. Fine root length growth was stronger inhibited by B stress than secondary growth.

Conclusions

The root growth responses of P. tremula to B are primarily a systemic effect induced by shoot B toxicity and local toxicity effects on roots become dominant only at rather high soil B concentrations. Local heterogeneity in soil B should have little influence on the phytoremediation of contaminated sites.     

Heterologous expression of Arabidopsis C-repeat binding factor 3 (AtCBF3) and cold-regulated 15A (AtCOR15A) enhanced chilling tolerance in transgenic eggplant (Solanum melongena L.)

Key message

Our study shows that the expression of AtCBF3 and AtCOR15A improved the chilling tolerance in transgenic eggplant.

Abstract

In an attempt to improve chilling tolerance of eggplant (Solanum melongena L) plants, Arabidopsis C-repeat binding factor 3 (AtCBF3) and cold-regulated 15A (AtCOR15A) genes both driven by an Arabidopsis RESPONSIVE TO DESSICATION 29A promoter (AtRD29A) were transferred into the plants of eggplant cultivar Sanyueqie. Two independent homozygous transgenic lines were tested for their cold tolerance. The leaves of the transgenic plants in both lines withered much slower and slighter than the wild-type plants after exposure to cold stress treatment at 2 ± 1 °C. The gene expression of AtCBF3 and AtCOR15A was significantly increased as well as the proline content and the levels of catalase and peroxidase activities, while the relative electrical conductivity and the malondialdehyde content were remarkably decreased in the transgenic plants compared with the wild type at 4 ± 0.5 °C. The results showed that the expression of the exogenous AtCBF3 and AtCOR15A could promote the cold adaptation process to protect eggplant plants from chilling stress.     

QTL mapping for salt tolerance and domestication-related traits in Vigna marina subsp. oblonga,a halophytic species

Key message

QTL mapping in F ₂ population [ V. luteola × V. marina subsp. oblonga ] revealed that the salt tolerance in V. marina subsp. oblonga is controlled by a single major QTL.

Abstract

The habitats of beach cowpea (Vigna marina) are sandy beaches in tropical and subtropical regions. As a species that grows closest to the sea, it has potential to be a gene source for breeding salt-tolerant crops. We reported here for the first time, quantitative trait loci (QTLs) mapping for salt tolerance in V. marina. A genetic linkage map was constructed from an F₂ population of 120 plants derived from an interspecific cross between V. luteola and V. marina subsp. oblonga. The map comprised 150 SSR markers. The markers were clustered into 11 linkage groups spanning 777.6 cM in length with a mean distance between the adjacent markers of 5.59 cM. The F_2:3 population was evaluated for salt tolerance under hydroponic conditions at the seedling and developmental stages. Segregation analysis indicated that salt tolerance in V. marina is controlled by a few genes. Multiple interval mapping consistently identified one major QTL which can explain about 50 % of phenotypic variance. The flanking markers may facilitate transfer of the salt tolerance allele from V. marina subsp. oblonga into related Vigna crops. The QTL for domestication-related traits from V. marina are also discussed.     

Standing fine root mass and production in four Chinese subtropical forests along a succession and species diversity gradient

Background and aims

The influences of succession and species diversity on fine root production are not well known in forests. This study aimed to investigate: (i) whether fine root biomass and production increased with successional stage and increasing tree species diversity; (ii) how forest type affected seasonal variation and regrowth of fine roots.

Methods

Sequential coring and ingrowth core methods were used to measure fine root production in four Chinese subtropical forests differing in successional stages and species diversity.

Results

Fine root biomass increased from 262 g·m^?2 to 626 g·m^?2 with increasing successional stage and species diversity. A similar trend was also found for fine root production, which increased from 86 to 114 g·m^?2 yr ^?1 for Cunninghamia lanceolata plantation to 211–240 g·m^?2 yr ^?1 for Choerospondias axillaries forest when estimated with sequential coring data. Fine root production calculated using the ingrowth core data ranged from 186 g·m^?2 yr ^?1 for C. lanceolata plantation to 513 g·m^?2 yr ^?1 for Lithocarpus glaber – Cyclobalanopsis glauca forest.

Conclusions

Fine root biomass and production increased along a successional gradient and increasing tree species diversity in subtropical forests. Fine roots in forests with higher species diversity exhibited higher seasonal variation and regrowth rate.     

Maintaining elevated Fe2+ concentration in solution culture for the development of a rapid and repeatable screening technique for iron toxicity tolerance in rice (Oryza sativa L.)

Background and aims

Iron toxicity decreases rice (Oryza sativa) grain yield especially in acid soils after flooding. Our aim was to establish a high-throughput screening technique using nutrient solution culture for identifying Fe-toxicity-tolerant genotypes.

Methods

Varying levels of Fe, pH, and chelators in Yoshida nutrient solution culture were tested to maintain sufficient Fe²⁺ concentration over time to optimize the severity of Fe toxicity stress for distinguishing between a tolerant (Azucena) and sensitive (IR64) genotype. The optimized solution was tested on 20 diverse genotypes in the greenhouse, with measurement of leaf bronzing scores and plant growth characteristics at the seedling stage. The same 20 genotypes were grown to maturity in a field with natural Fe toxicity stress, with measurement of seedling-stage leaf bronzing scores and grain yield to determine their inter-relationship.

Results

Optimized nutrient solution conditions were 300 mg L^?1 Fe supplied as Fe²⁺ at pH 4.0 with a 1:2 molar ratio of Fe:EDTA, which maintained sufficient Fe²⁺ stress over 5 days. The highest correlation of nutrient solution phenotypic data with field grain yield was found with leaf bronzing scores at 4 weeks, with a Pearson r of 0.628 for simple association and a Spearman corrected r of 0.610 for rank association (P?<?0.01) using 20 diverse rice genotypes with proven Fe toxicity tolerance reaction. The Leaf bronzing scores at 4 weeks in nutrient culture solution were also found highly correlated with LBS under natural field stress after 8 weeks that had highest correlation with grain yield under stress.

Conclusion

This culture solution-based standardized screening technique can be used in plant breeding programs as a high-throughput technique to identify genotypes tolerant to Fe toxicity.     

Precipitation variability does not affect soil respiration and nitrogen dynamics in the understorey of a Mediterranean oak woodland

Background and aims

Future climate scenarios for the Mediterranean imply increasing precipitation variability. This study presents a large-scale water manipulation experiment simulating changes in precipitation variability, aiming at a better understanding of the effects of rainfall patterns on soil C and N cycling and understorey productivity in a Mediterranean oak woodland.

Methods

We used rain-out shelters to achieve (1) a normal dry period (7 days), and (2) a dry period increased three-fold (21 days), without altering total annual precipitation inputs.

Results

The temporal patterns of soil respiration (R _s) and soil inorganic N were not affected by treatment. However, water infiltration and N leaching increased with large infrequent watering events. R _s and soil NH₄ ⁺-N correlated with soil temperature, with soil NO₃ ^?-N being influenced by leaching.

Conclusions

The lack of significant treatment effects on either R _s or soil inorganic N can be explained by (1) minor differences in plant productivity between the treatments, suggesting equal plant N demand, and (2) the absence of moisture dependence of R _s and soil NH₄ ⁺-N. Increased N leaching with large infrequent precipitation events may have longer-term consequences for ecosystem functioning. Our results contribute to an improved understanding of possible climate change effects on key ecosystem processes in Mediterranean ecosystems.     

Genetic dissection of temperature-dependent sorghum growth during juvenile development

Key message

Promising genome regions for improving cold tolerance of sorghum were identified on chromosomes SBI-01, SBI-03, SBI-07, and SBI-10. Chlorophyll fluorescence had no major effect on growth rates at low temperatures.

Abstract

Developing fast growing sorghum seedlings is an important breeding goal for temperate climates since low springtime temperatures are resulting in a prolonged juvenile development. The adaptation of sorghum to tropical and subtropical highlands gives hint for certain genetic variation. The goals of the present study were to detect marker-trait associations for leaf and dry matter growth rate and for chlorophyll fluorescence and content (SPAD) in relation to temperature. A diversity set comprising 194 genotypes was tested in eight controlled environments with temperatures ranging from 9.4 to 20.8 °C. Significant marker-trait associations (p < 0.05) were identified for each individual temperature regime and on the parameters of regression analyses describing the responses of growth or chlorophyll related traits to temperatures. The diversity set was fingerprinted with 171 diversity array technology (DArT) and 31 simple-sequence repeat (SSR) markers. SSRs were used to analyze the population structure while association studies were performed on DArT markers. Promising marker-trait associations for growth rates in relation to temperature were detected on chromosomes SBI-01, SBI-03, SBI-07, and SBI-10. Many promising loci were also significantly associated to the results obtained in individual low-temperature environments. Marker-trait associations for chlorophyll content and fluorescence did occasionally co-locate to those for growth during juvenile development but there was no evidence supporting our hypothesis that seedling growth at low temperatures is largely influenced by SPAD or fluorescence.     

Expression of hsp70, hsp100 and ubiquitin in Aloe barbadensis Miller under direct heat stress and under temperature acclimation conditions

Key message

The study determined the tolerance of Aloe vera to high temperature, focusing on the expression of hsp70 , hsp100 and ubiquitin genes. These were highly expressed in plants acclimated at 35 °C prior to a heat shock of 45 °C.

Abstract

Aloe barbadensis Miller (Aloe vera), a CAM plant, was introduced into Chile in the semiarid IV and III Regions, which has summer diurnal temperature fluctuations of 25 to 40 °C and annual precipitation of 40 mm (dry years) to 170 mm (rainy years). The aim of this study was to investigate how Aloe vera responds to water and heat stress, focusing on the expression of heat shock genes (hsp70, hsp100) and ubiquitin, which not studied before in Aloe vera. The LT₅₀ of Aloe vera was determined as 53.2 °C. To study gene expression by semi-quantitative RT-PCR, primers were designed against conserved regions of these genes. Sequencing the cDNA fragments for hsp70 and ubiquitin showed a high identity, over 95 %, with the genes from cereals. The protein sequence of hsp70 deduced from the sequence of the cDNA encloses partial domains for binding ATP and the substrate. The protein sequence of ubiquitin deduced from the cDNA encloses a domain for interaction with the enzymes E2, UCH and CUE. The expression increased with temperature and water deficit. Hsp70 expression at 40–45 °C increased 50 % over the controls, while the expression increased by 150 % over the controls under a water deficit of 50 % FC. The expression of all three genes was also studied under 2 h of acclimation at 35 or 40 °C prior to a heat shock at 45 °C. Under these conditions, the plants showed greater expression of all genes than when they were subjected to direct heat stress.     

Nitrogen application enhanced the expression of developmental plasticity of root systems triggered by mild drought stress in rice

Background

The promoted root growth under developmental plasticity triggered specifically by mild drought stress (MDS) is known to contribute to maintained water uptake and dry matter production (DMP).

Aims

To examine whether the expression of developmental plasticity of root systems and its contribution to DMP would be affected by the levels of nitrogen (N) application.

Methods

Two genotypes (CSSL50 derived from Nipponbare/Kasalath cross and Nipponbare) were grown under soil moisture gradients with a line source sprinkler system. Three N fertilizer treatments were used; 25 (low), 75 (standard) and 150 kg N ha^?1 (high) in 2009 and 60 (low), 120 (standard) and 180 kg N ha^?1 (high) in 2011.

Results

Across varying N level treatments, there were no significant differences in any of the traits examined between the two genotypes under well-watered and severe drought stress conditions. In contrast, under MDS conditions (15–25 % w/w of soil moisture content (SMC) in 2009 and 17–25 % w/w of SMC in 2011), CSSL50 showed greater DMP than Nipponbare. The difference, however, varied with N level treatments since CSSL50’s greater root system development under MDS, was more pronounced at standard and high N levels than at low N level than it was for Nipponbare.

Conclusions

N application enhanced the expression of plasticity in root system development at standard and high N levels as compared with low N level under MDS conditions, which contributed to the maintenance of DMP.     

Relating water use to morphology and environment of Nothofagus from the world’s most southern forests

Key message

This study is the first to quantify tree water use below 50°S. Tree morphology differs markedly among the two investigated species, reflecting adjustment to different environmental cues.

Abstract

A pronounced environmental gradient dictates the dominance of Nothofagus in the foothills on the eastern side of the Andes Mountains in Patagonia, Argentina. Below 50° southern latitude, open forests of Nothofagus antarctica (ñire) dominate the landscape towards the Patagonian steppe where annual rainfall is low. With increasing rates of annual rainfall, corresponding with an increase in elevation, closed forests of N. pumilio (lenga) replace those of ñire. During a short-term study we assessed differences in stand structure and examined environmental, structural and functional traits related to tree water use of ñire and lenga. Sap velocity reached similar maximum rates (95–100 L m^?2 sapwood h^?1), but whole-tree water use (Q) was significantly lower in ñire (8–13 L day^?1 tree^?1) compared to lenga (20–90 L day^?1 tree^?1) resulting in lower stand transpiration (ñire: 0.51 mm day^?1; lenga: 3.42 mm day^?1) despite similar tree densities. Related to this, wind speed had a particularly significant impact on Q of ñire, but not lenga. The ratio of leaf area to sapwood area (A _L/A _S) clearly identified ñire to be more structurally proficient at conserving water. While stem diameter (DBH) and crown area (A _C) were well related in both species, only lenga exhibited relationships between variables related to tree allometry and physiology (A _C/Q, DBH/Q). Our results provide the first ecophysiological characterization of the two Nothofagus species that define important and widespread ecosystems in southern Patagonia (not only below 50°S), and provide useful data to scale water use of both species from tree to stand.     

Development of transgenic imazapyr-tolerant cowpea (Vigna unguiculata)

Key message

Here we present the development of cowpea lines tolerant to a herbicide from imidazoline class (imazapyr). Plants presented tolerance to fourfold the commercial recommended dose for weed control.

Abstract

Cowpea is one of the most important and widely cultivated legumes in many parts of the world. Its cultivation is drastically affected by weeds, causing damages during growth and development of plants, competing for light, nutrients and water. Consequently, weed control is critical, especially using no-tillage farming systems. In tropical regions, no-till farming is much easier with the use of herbicides to control weeds. This study was conducted to evaluate the possibility of obtaining transgenic cowpea plants resistant to imidazolinone, which would facilitate weed control during the summer season. The biolistic process was used to insert a mutated acetohydroxyacid synthase coding gene (Atahas) which confers tolerance to imazapyr. The transgene integration was confirmed by Southern blot analysis. Out of ten lines tested for tolerance to 100 g ha^?1 imazapyr, eight presented some tolerance. One line (named 59) revealed high herbicide tolerance and developmental growth comparable to non-transgenic plants. This line was further tested for tolerance to higher herbicide concentrations and presented tolerance to 400 g ha^?1 imazapyr (fourfold the commercial recommended dose) with no visible symptoms. Line 59 will be the foundation for generating imidazolinone-tolerant cowpea varieties, which will facilitate cultivation of this crop in large areas.     

Increasing relevance of spring temperatures for Norway spruce trees in Davos,Switzerland, after the 1950s

Key message

Relevance of spring temperatures for tree-ring growth steadily increased since 1950s. Closely linked tree-ring growth and net CO ₂ exchange driven by spring temperatures.

Abstract

We investigated long-term (over 100 years) tree-ring width (TRW) variabilities as well as short-term (10 years) variations in net ecosystem productivity (NEP) in response to climate to assess the driving factors for stem growth of Norway spruce in a subalpine forest at Davos in Switzerland. A tree-ring width index (TRWi) chronology for the period from 1750 to 2006 was constructed and linked with climate data from 1876 to 2006, and with NEP available for the period from 1997 to 2006. Based on TRWi, we found that only two out of the 257 years exhibited extreme negative TRWi, compared to 29 years with extreme positive anomalies, observed mainly in recent decades. Annual temperature, annual precipitation, as well as autumn and winter temperature signals were well preserved in the TRWi chronology over the last 130 years. Spring temperatures became increasingly relevant for TRWi, explaining less than 1 % of the variation in TRWi for the period from 1876 to 2006, but 8 % for the period from 1950 to 2006 (p = 0.032), and even 47 % for 1997–2006 (p = 0.028). We also observed a strong positive relationship between annual TRWi and annual NEP (r = 0.661; p = 0.037), both strongly related to spring temperatures (r = 0.687 and r = 0.678 for TRWi and NEP, respectively; p = 0.028; p = 0.032). Moreover, we found strong links between monthly NEP of March and annual TRWi (r = 0.912; p = 0.0001), both related to March temperatures (r = 0.767, p = 0.010 and r = 0.724, p = 0.018, respectively). Thus, under future climate warming, we expect stem growth of these subalpine trees and also ecosystem carbon (C) sequestration to increase, as long as water does not become a limiting factor.     

Nostoc, Microcoleus and Leptolyngbya inoculums are detrimental to the growth of wheat (Triticum aestivum L.) under salt stress

Background and aims

This study investigated the effect of cyanobacterial inoculants on salt tolerance in wheat.

Methods

Unicyanobacterial crusts of Nostoc, Leptolyngbya and Microcoleus were established in sand pots. Salt stress was targeted at 6 and 13 dS m^?1, corresponding to the wheat salt tolerance and 50 % yield reduction thresholds, respectively. Germinated wheat seeds were planted and grown for 14 (0 and 6 dS m^?1) and 21 (13 dS m^?1) days by which time seedlings had five emergent leaves. The effects of cyanobacterial inoculation and salinity on wheat growth were quantified using chlorophyll fluorescence, inductively coupled plasma-optical emission spectrometry and biomass measurements.

Results

Chlorophyll fluorescence was negatively affected by soil salinity and no change was observed in inoculated wheat. Effective photochemical efficiency correlated with a large range of plant nutrient concentrations primarily in plant roots. Inoculation negatively affected wheat biomass and nutrient concentrations at all salinities, though the effects were fewer as salinity increased.

Conclusions

The most likely explanation of these results is the sorption of nutrients to cyanobacterial extracellular polymeric substances, making them unavailable for plant uptake. These results suggest that cyanobacterial inoculation may not be appropriate for establishing wheat in saline soils but that cyanobacteria could be very useful for stabilising soils.     

Mapping resistance genes for Oculimacula acuformis in Aegilops longissima

Key message

This study identified three QTL conferring resistance to Oculimacula acuformis in Aegilops longissima and their associated markers, which can be useful in marker-assisted selection breeding for eyespot resistance.

Abstract

Oculimacula acuformis is one of two species of soilborne fungi that cause eyespot of wheat, the other being Oculimacula yallundae. Both pathogens can coexist in the same field and produce elliptical lesions on stem bases of wheat that are indistinguishable. Pch1 and Pch2 are the only two eyespot resistance genes readily available to wheat breeders, but neither provides complete control. A new source of eyespot resistance was identified from Aegilops longissima (2n = 14, S^lS^l), a wild relative of wheat. Three QTL for resistance to O. acuformis were mapped in chromosomes 1S^l, 3S^l, and 5S^l using a recombinant inbred line population developed from the cross Ae. longissima accessions PI 542196 (R) × PI 330486 (S). The three QTL explained 66 % of phenotypic variation by β-glucuronidase score (GUS) and 84 % by visual rating. These QTL had LOD values of 10.6, 8.8, and 6.0 for GUS score, and 16.0, 10.0, and 13.0 for visual rating. QTL associated with resistance to O. acuformis have similar chromosomal locations as some for resistance to O. yallundae, except that a QTL for resistance to O. yallundae was found in chromosome 7S^l but not for O. acuformis. Thus, it appears that some genes at the same locus in Ae. longissima may control resistance to both eyespot pathogens. QTL effective against both pathogens will be most useful for breeding programs and have potential to improve the effectiveness and genetic diversity of eyespot resistance.     

The effect of heterogeneous soil bulk density on root growth of field-grown mangrove species

Background and aims

In Australia’s Mediterranean hyperdiverse vegetation, species that produce cluster roots to mobilise poorly-available nutrients (e.g. Banksia spp.) are an important functional and structural component. Cluster roots are only active during the wet season, indicating a strong dependence on suitable surface soil moisture conditions. Winter rainfall in this region is declining due to global climate change, with a delayed commencement of rains and a decline in precipitation. It is unknown how lower soil moisture levels will affect the root dynamics of these globally-significant plant communities.

Methods

We determined the root dynamics and root lifespan with minirhizotrons with or without irrigation to simulate reduced rainfall scenarios.

Results

We found a major effect of irrigation on the early production (0.24 m m^?2 d^?1 increase), occurrence (97% increase) of cluster roots and only slight effects on lifespan (~10 days less) of all root types. With irrigation, the resultant greater soil moisture levels increased the deployment of cluster roots. Apart from cluster roots, the dynamics of other roots did not decline at lower soil moisture levels, suggesting that this system shows some resilience to decreased rainfall.

Conclusions

Future research should focus on assessing if climate-altered cluster-root activity may be promoting compositional shifts in plant communities with additional restraining effects on root trait diversity.