How nematodes reduce yield

[Introduction]: Pratylenchus thornei is a major pathogen of wheat crops in the northern grain region of Eastern Australia with an estimated annual yield loss of $38 million. Damaged crops show symptoms of water and nutrient stress that suggest water and nutrient uptake is significantly affected. In order to understand the mechanisms involved in reducing water uptake and consequently plant yield, detailed measurements of water extraction and leaf area were conducted on a range of wheat cultivars with differing levels of tolerance and resistance to P. thornei. This study is part of a larger project that aims to better understand the growth, development and mechanisms with which P. thornei reduces the yields of susceptible crops in the northern grains region. The hope is by fully understanding the mechanisms with which this microscopic pathogen can reduce yields, better management strategies can be developed to reduce its impact within intolerant crops and across the rotation

Survey for root-lesion and stunt nematodes in the northern Australian grain region

The presence of root-lesion nematodes (Pratylenchus thornei and P. neglectus) and stunt nematode (Merlinius brevidens) in some parts of the northern grain region has been known since the 1960's and yield loss in wheat caused by P. thornei has been demonstrated since the late 1970's. However, the distribution of P. thornei was considered restricted to the Darling Downs in Queensland and to a few localities in northern NSW. Following the diagnosis of P. thornei in a wheat crop in a newer cropping area around Goondiwindi in 1996 a more extensive survey of wheat fields was conducted. Soil samples (0-30cm) collected mainly from under wheat crops were processed manually and nematodes extracted by the Whitehead tray method and enumerated under a compound microscope. Out of 795 fields tested from 1996 to 2002, Pratylenchus thornei occurred in 67%, P. neglectus in 32% (both species occurred together in 26%) and no Pratylenchus spp. were detected in 27%. Merlinius brevidens occurred in 73% of fields. Edaphic factors controlling the incidence of these nematodes were tested on 833 samples collected in 1996-7. All three nematode species had a broad pH range, namely from 6.5 to 9.5 for both Pratylenchus spp. and from 6.0 to 9.5 for Merinlius brevidens. All species were detected in soil samples ranging from <20 to 80% clay and from 80% sand. However, within this range maximum incidence of P. thornei was in finer textured soils than for P. neglectus. Soil organic carbon had no clearcut effect on the incidence of the species. The incidence of P. neglectus appeared to increase with increasing concentration of DTPA-extractable zinc and bicarbonate–extractable phosphorus in the soil. Observations indicate that P. thornei was spreading in the region in run-off water and in soil on farm machinery and increasing under intense cropping to wheat

Enhancement of the Electron Spin Resonance of Single-Walled Carbon Nanotubes by Oxygen Removal

We have observed a nearly fourfold increase in the electron spin resonance (ESR) signal from an ensemble of single-walled carbon nanotubes (SWCNTs) due to oxygen desorption. By performing temperature-dependent ESR spectroscopy both before and after thermal annealing, we found that the ESR in SWCNTs can be reversibly altered via the molecular oxygen content in the samples. Independent of the presence of adsorbed oxygen, a Curie-law (spin susceptibility $\propto 1/T$) is seen from $\sim$4 K to 300 K, indicating that the probed spins are finite-level species. For both the pre-annealed and post-annealed sample conditions, the ESR linewidth decreased as the temperature was increased, a phenomenon we identify as motional narrowing. From the temperature dependence of the linewidth, we extracted an estimate of the intertube hopping frequency; for both sample conditions, we found this hopping frequency to be $\sim$100 GHz. Since the spin hopping frequency changes only slightly when oxygen is desorbed, we conclude that only the spin susceptibility, not spin transport, is affected by the presence of physisorbed molecular oxygen in SWCNT ensembles. Surprisingly, no linewidth change is observed when the amount of oxygen in the SWCNT sample is altered, contrary to other carbonaceous systems and certain 1D conducting polymers. We hypothesize that physisorbed molecular oxygen acts as an acceptor ($p$-type), compensating the donor-like ($n$-type) defects that are responsible for the ESR signal in bulk SWCNTs.Comment: 14 pages, 7 figure

Pneumoproteins and biomarkers of inflammation and coagulation do not predict rapid lung function decline in people living with HIV

Chronic obstructive pulmonary disease (COPD) is among the leading causes of death worldwide and HIV is an independent risk factor for the development of COPD. However, the etiology of this increased risk and means to identify persons with HIV (PWH) at highest risk for COPD have remained elusive. Biomarkers may reveal etiologic pathways and allow better COPD risk stratification. We performed a matched case:control study of PWH in the Strategic Timing of Antiretoviral Treatment (START) pulmonary substudy. Cases had rapid lung function decline (> 40 mL/year FEV1 decline) and controls had stable lung function (+ 20 to − 20 mL/year). The analysis was performed in two distinct groups: (1) those who were virally suppressed for at least 6 months and (2) those with untreated HIV (from the START deferred treatment arm). We used linear mixed effects models to test the relationship between case:control status and blood concentrations of pneumoproteins (surfactant protein-D and club cell secretory protein), and biomarkers of inflammation (IL-6 and hsCRP) and coagulation (d-dimer and fibrinogen); concentrations were measured within ± 6 months of first included spirometry. We included an interaction with treatment group (untreated HIV vs viral suppression) to test if associations varied by treatment group. This analysis included 77 matched case:control pairs in the virally suppressed batch, and 42 matched case:control pairs in the untreated HIV batch (n = 238 total) who were followed for a median of 3 years. Median (IQR) CD4 + count was lowest in the controls with untreated HIV at 674 (580, 838). We found no significant associations between case:control status and pneumoprotein or biomarker concentrations in either virally suppressed or untreated PWH. In this cohort of relatively young, recently diagnosed PWH, concentrations of pneumoproteins and biomarkers of inflammation and coagulation were not associated with subsequent rapid lung function decline. Trial registration: NCT00867048 and NCT01797367

Evaluating wheat for tolerance and resistance to root-lesion nematodes

Root-lesion nematodes are estimated to cost the Australian wheat industry AUD$260 million/year. Pratylenchus thornei is the dominant species in the north and P. neglectus in the south and west. We have tested wheat lines for tolerance to P. thornei on a dedicated 10-ha site of vertisolic soil near Jondaryan 170 km west of Brisbane. The site has been managed in a 4-year rotation of fallow-sorghum-wheat-wheat test plots, such that 2.5 ha are available each year with high P. thornei population and negligible other soil-borne wheat pathogens. About 2000 early-generation wheat lines are sown in unreplicated plots of 3 rows each 5 m long which are rated twice during the growing season for symptoms of nematode damage. Pre-release lines and varieties for the northern region are sown in plots of 7 rows by 8 m long in replicated experiments on two sowing dates. Yield of the lines/varieties determined from machine harvest is expressed as percentage of site mean yield (SMY) and averaged across trials and years. Tolerance indices derived from SMY have proved very predictive of varietal yield at independent sites infested with P. thornei, and are published annually in extension brochures. Resistance of wheat lines against P. thornei and P. neglectus has been assessed in replicated glasshouse experiments. The wheat lines are tested in pots of vertisolic soil inoculated with cultured nematodes and grown with optimum nutrition, water supply and temperature for nematode multiplication. After 16 weeks, nematodes are extracted from roots and soil from the bottom half of the pot and enumerated under a compound microscope. These methods have been used successfully to: (1) identify sources of resistance in wild relatives, landrace and synthetic hexaploid wheats, (2) characterise breeders' lines and varieties for resistance, (3) screen segregating progeny from backcross and topcross programs, and (4) characterise mapping populations for development of molecular markers to resistance genes

Optimising initial population density, growth time and nitrogen nutrition for assessing resistance of wheat cultivars to root-lesion nematode (Pratylenchus thornei)

Pratylenchus thornei is a major pathogen of wheat in Australia. Two glasshouse experiments with four wheat cultivars that had different final populations (Pf) of P. thornei in the field were used to optimise conditions for assessing resistance. With different initial populations (Pi) ranging up to 5250 P. thornei/kg soil, Pf of P. thornei increased to 16 weeks after sowing, and then decreased at 20 weeks in some cultivar x Pi combinations. The population dynamics of P. thornei up to 16 weeks were best described by a modified exponential equation P f (t) = aP i e kt where P f (t) is the final population density at time t, P i is the initial population density, a is the proportion of P i that initiates population development, and k is the intrinsic rate of increase of the population. The cultivar GS50a had very low k values at Pi of 5250 and 1050 indicating its resistance, Suneca and Potam had high k values indicating susceptibility, whereas intolerant Gatcher had a low value at the higher Pi and a high value at the lower Pi. Nitrate fertiliser increased plant growth and Pf values of susceptible cultivars, but in unplanted soil it decreased Pf. Nematicide (aldicarb 5 mg/kg soil) killed P. thornei more effectively in planted than in unplanted soil and increased plant growth particularly in the presence of N fertiliser. In both experiments, the wheat cultivars Suneca and Potam were more susceptible than the cultivar GS50a reflecting field results. The method chosen to discriminate wheat cultivars was to assess Pf after growth for 16 weeks in soil with Pi ~1050–5250 P. thornei/kg soil and fertilised with 200 mg NO3–N/kg soil

Stunted cotton (Gossypium hirsutum L.) fully recovers biomass and yield of seed cotton after delayed root inoculation with spores of an arbuscular mycorrhizal fungus (Glomus mosseae)

In the northern grain and cotton region of Australia, poor crop growth after long periods of fallow, called ‘long-fallow’ disorder, is caused by a decline of natural arbuscular-mycorrhizal fungi (AMF). When cotton was grown in large pots containing 22 kg of Vertisol from a field recently harvested from cotton in Central Queensland, plants in pasteurised soil were extremely stunted compared with plants in unpasteurised soil. We tested the hypothesis that this extreme stunting was caused by the absence of AMF and examined whether such stunted plants could recover from subsequent treatment with AMF spores and/or P fertiliser. At 42 days after sowing, the healthy cotton growing in unpasteurised soil had 48% of its root-length colonised with AMF, whereas the stunted cotton had none. After inoculation with AMF spores (6 spores/g soil of Glomus mosseae) and/or application of P fertiliser (50 mg P/kg soil) at 45 days after sowing, the stunted plants commenced to improve about 25 days after treatment, and continued until their total dry matter and seed cotton production equalled that of plants growing in unpasteurised soil with natural AMF. In contrast, non-mycorrhizal cotton grown without P fertiliser remained stunted throughout and produced no bolls and only 1% of the biomass of mycorrhizal cotton. Even with the addition of P fertiliser, non-mycorrhizal cotton produced only 64% of the biomass and 58% of the seed cotton (lint + seed) of mycorrhizal cotton plants. These results show that cotton is highly dependent on AMF for P nutrition and growth in Vertisol (even with high rates of P fertiliser), but can recover from complete lack of AMF and consequent stunting during at least the first 45 days of growth when treated with AMF spores and/or P fertiliser. This corroborates field observations in the northern region that cotton may recover from long-fallow disorder caused by low initial levels of AMF propagules in the soil as the AMF colonisation of its roots increases during the growing season

What is the impact of winter grain crops on Pratylenchus thornei grown in rotation with tolerant and intolerant wheat?

Management of the root-lesion nematode, Pratylenchus thornei (Pt), is central to wheat production in the northern grain region of Australia and relies on rotation with resistant crops and growing tolerant wheat cultivars. We determined the residual populations of Pt to 90 cm soil depth after winter grain crops and their impact on the growth of subsequently planted tolerant and intolerant wheat cultivars. A weed-free fallow and 5–6 cultivars each of faba bean, chickpea, barley and wheat were treatments on two areas of land, 1) 4,500 Pt/kg soil at 0–45 cm after 7 months fallow after wheat and 2) 2,100 Pt/kg soil at 0–45 cm following 14 months fallow after sorghum. Six months after harvest there were 10,000–22,700 Pt/kg soil 0–45 cm after most barley, faba bean and commercial wheat cultivars; 2,600–6,000 Pt/kg soil 0–45 cm after wheat cvv. QT9050, GS50a, chickpea cv. PBA Hattrick and fallow. There was a negative, linear relationship between Pt (to 90 cm) and biomass of the intolerant wheat cv. Strzelecki (max. R2 = 0.70 P<0.001 at 0–45 cm). There was no impact of residual Pt on the tolerant wheat cv. EGA Wylie. The tolerance of cv. EGA Wylie was robust but breeding resistant barley, faba bean and wheat will improve management options

Temperature response of root-lesion nematode (Pratylenchus thornei) reproduction on wheat cultivars has implications for resistance screening and wheat production

The root-lesion nematode Pratylenchus thornei is a major pathogen of wheat and other field crops, particularly in the northern grain region of sub-tropical eastern Australia. Research was conducted into the temperature requirements of P. thornei for reproduction on wheat to increase the reliability of selection in resistance tests for wheat breeding. Final population densities (Pf) of P. thornei were determined on four wheat cultivars (Gatcher, GS50a, Potam and Suneca) at fortnightly intervals from 8 to 18 weeks at a range of six soil temperatures (15, 20, 22.5, 25, 27.5 and 30 ºC) in a glasshouse experiment. Pratylenchus thornei had the highest Pf in the temperature range 20–25 ºon all wheat cultivars at all growth times after sowing, with no nematode reproduction measured at 30ºC and very little at 15ºC. The wheat cv. GS50a consistently produced lower Pf than cvs Gatcher, Potam and Suneca in the optimum temperature range 20–25ºC. In carrot disc cultures, P. thornei had an optimum temperature of 25ºC with little reproduction at 17.5ºC and none detectable at 30ºC. A standard soil temperature of 23ºC was chosen to maximise differences in nematode reproduction between resistant and susceptible wheat genotypes for selection in wheat breeding, and to improve reproducibility among successive experiments. The relationships derived from these experiments will be valuable for simulation of P. thornei reproduction in crop growth models. They also indicate that early sowing of wheat into cool soil (≤15ºC) in farmers’ fields of the northern grain region should favour wheat growth over nematode reproduction and increase grain yield

Field inoculation with arbuscular-mycorrhizal fungi overcomes phosphorus and zinc deficiencies of linseed (Linum usitatissimum) in a vertisol subject to long-fallow disorder

Background and aims: Long-fallow disorder is expressed as exacerbated deficiencies of phosphorus (P) and/or zinc (Zn) in field crops growing after long periods of weed-free fallow. The hypothesis that arbuscular-mycorrhizal fungi (AMF) improve the P and Zn nutrition, and thereby biomass production and seed yield of linseed (Linum usitatissimum) was tested in a field experiment. Methods: A factorial combination of treatments consisting of ± fumigation, ±AMF inoculation with Glomus spp., ±P and ±Zn fertilisers was used on a long-fallowed vertisol. The use of such methods allowed an absolute comparison of plants growing with and without AMF in the field for the first time in a soil disposed to long-fallow disorder. Results: Plant biomass, height, P and Zn concentrations and contents, boll number and final seed yield were (a) least in fumigated soil with negligible AMF colonisation of the roots, (b) low initially in long-fallow soil but increased with time as AMF colonisation of the roots developed, and (c) greatest in soil inoculated with AMF cultures. The results showed for the first time in the field that inflows of both P and Zn into linseed roots were highly dependent on %AMF-colonisation (R2 = 0.95 for P and 0.85 for Zn, P < 0.001) in a soil disposed to long-fallow disorder. Relative field mycorrhizal dependencies without and with P+Zn fertiliser were 85 % and 86 % for biomass and 68 % and 52 % for seed yield respectively. Conclusions: This research showed in the field that AMF greatly improved the P and Zn nutrition, biomass production and seed yield of linseed growing in a soil disposed to long-fallow disorder. The level of mycorrhizal colonisation of plants suffering from long-fallow disorder can increase during the growing season resulting in improved plant growth and residual AMF inoculum in the soil, and thus it is important for growers to recognise the cause and not terminate a poor crop prematurely in order to sow another. Other positive management options to reduce long fallows and foster AMF include adoption of conservation tillage and opportunity cropping