Meloidogyne species: a diverse group of novel and important plant parasites

Two major genes for Na(+) exclusion in durum wheat, Nax1 and Nax2, that were previously identified as the Na(+) transporters TmHKT1;4-A2 and TmHKT1;5-A, were transferred into bread wheat in order to increase its capacity to restrict the accumulation of Na(+) in leaves. The genes were crossed from tetraploid durum wheat (Triticum turgidum ssp. durum) into hexaploid bread wheat (Triticum aestivum) by interspecific crossing and marker-assisted selection for hexaploid plants containing one or both genes. Nax1 decreased the leaf blade Na(+) concentration by 50%, Nax2 decreased it by 30%, and both genes together decreased it by 60%. The signature phenotype of Nax1, the retention of Na(+) in leaf sheaths resulting in a high Na(+) sheath:blade ratio, was found in the Nax1 lines. This conferred an extra advantage under a combination of waterlogged and saline conditions. The effect of Nax2 on lowering the Na(+) concentration in bread wheat was surprising as this gene is very similar to the TaHKT1;5-D Na(+) transporter already present in bread wheat, putatively at the Kna1 locus. The results indicate that both Nax genes have the potential to improve the salt tolerance of bread wheat.

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Major genes for Na+ exclusion, Nax1 and Nax2 (wheat HKT1;4 and HKT1;5), decrease Na+ accumulation in bread wheat leaves under saline and waterlogged conditions

Wheat crops usually yield more when grown after another species than when grown after wheat. Quantifying the yield increase and explaining the factors that affect the increase will assist farmers to decide on crop sequences. This review quantifies the yield increase, based on >900 comparisons of wheat growing after a break crop with wheat after wheat. The mean increase in wheat yield varied with species of break crop, ranging from 0.5 t ha–1 after oats to 1.2 t ha–1 after grain legumes. Based on overlapping experiments, the observed ranking of break-crop species in terms of mean yield response of the following wheat crop was: oats < canola ≈ mustard ≈ flax < field peas ≈ faba beans ≈ chickpeas ≈ lentils ≈ lupins. The mean additional wheat yield after oats or oilseed break crops was independent of the yield level of the following wheat crop. The wheat yield response to legume break crops was not clearly independent of yield level and was relatively greater at high yields. The yield of wheat after two successive break crops was 0.1–0.3 t ha–1 greater than after a single break crop. The additional yield of a second wheat crop after a single break crop ranged from 20% of the effect on a first wheat crop after canola, to 60% after legumes. The mean yield effect on a third wheat crop was negligible, except in persistently dry conditions. The variability of the break-crop effect on the yield of a second wheat crop was larger than of a first wheat crop, particularly following canola. We discuss the responses in relation to mechanisms by which break crops affect soil and following crops. By quantifying the magnitude and persistence of break-crop effects, we aim to provide a basis for the decision to grow continuous cereal crops, strategic rotations or tactically selected break crops. In many wheat-growing areas, the large potential yield increases due to break crops are not fully exploited. Research into quantifying the net benefits of break crops, determining the situations where the benefits are greatest, and improving the benefits of break crops promises to improve the efficiency of wheat-based cropping systems.

https://bioone.org/journals/crop-and-pasture-science/volume-66/issue-6/CP14252/Break-crops-and-rotations-for-wheat/10.1071/CP14252.pdf

Break crops and rotations for wheat

. Broadleaf break crops improve cereal yield through disease and weed control, increased nitrogen (N) availability and other mechanisms. In the rainfed farming systems of Australia the magnitude of the yield benefit is highly variable, yet is a major driver for adoption of break crops which are often less profitable and more risky than cereals. Declining area of break crops throughout Australia has re-ignited interest in better understanding the circumstances in which break-crop benefits can be maximised from a farming systems perspective. We compiled and analysed a database of 167 crop sequence experiments conducted throughout Western Australia in the period 1974–2007 to evaluate the impact on wheat (Triticum aestivum L.) grain yield from the use of narrow-leafed lupin (Lupinus angustifolius L.), field pea (Pisum sativum L.), canola (Brassica napus L.) or oats (Avena sativa L.), or following a long fallow where no crop had been sown the previous year. Adjusted for the years in which each was repr...

Break-crop benefits to wheat in Western Australia – insights from over three decades of research

Diseases caused by Fusarium pathogens inflict major yield and quality losses on many economically important plant species worldwide, including cereals. Fusarium crown rot (FCR), caused by Fusarium pseudograminearum, is a cereal disease that occurs in many arid and semi-arid cropping regions of the world. In recent years, this disease has become more prevalent, in part as a result of the adoption of moisture-preserving cultural practices, such as minimum tillage and stubble retention. In this pathogen profile, we present a brief overview of recent research efforts that have not only advanced our understanding of the interactions between F. pseudograminearum and cereal hosts, but have also provided new disease management options. For instance, significant progress has been made in the genetic characterization of pathogen populations, the development of new tools for disease prediction, and the identification and pyramiding of loci that confer quantitative resistance to FCR in wheat and barley. In addition, transcriptome analyses have revealed new insights into the processes involved in host defence. Significant progress has also been made in understanding the mechanistic details of the F. pseudograminearum infection process. The sequencing and comparative analyses of the F. pseudograminearum genome have revealed novel virulence factors, possibly acquired through horizontal gene transfer. In addition, a conserved pathogen gene cluster involved in the degradation of wheat defence compounds has been identified, and a role for the trichothecene toxin deoxynivalenol (DON) in pathogen virulence has been reported. Overall, a better understanding of cereal host-F. pseudograminearum interactions will lead to the development of new control options for this increasingly important disease problem. Taxonomy: Fusarium pseudograminearum O'Donnell & Aoki; Kingdom Fungi; Phylum Ascomycota; Subphylum Pezizomycotina; Class Sordariomycetes; Subclass Hypocreomycetidae; Order Hypocreales; Family Nectriaceae; Genus Fusarium. Disease symptoms: Fusarium crown rot caused by F. pseudograminearum is also known as crown rot, foot rot and root rot. Infected seedlings can die before or after emergence. If infected seedlings survive, typical disease symptoms are browning of the coleoptile, subcrown internode, lower leaf sheaths and adjacent stems and nodal tissues; this browning can become evident within a few weeks after planting or throughout plant development. Infected plants may develop white heads with no or shrivelled grains. Disease symptoms are exacerbated under water limitation. Identification and detection: Fusarium pseudograminearum macroconidia usually contain three to five septa (22-60.5 × 2.5-5.5 μm). On potato dextrose agar (PDA), aerial mycelia appear floccose and reddish white, with red or reddish-brown reverse pigmentation. Diagnostic polymerase chain reaction (PCR) tests based on the amplification of the gene encoding translation elongation factor-1a (TEF-1a) have been developed for molecular identification. Host range: All major winter cereals can be colonized by F. pseudograminearum. However, the main impact of this pathogen is on bread (Triticum aestivum L.) and durum (Triticum turgidum L. spp. durum (Dest.)) wheat and barley (Hordeum vulgare L.). Oats (Avena sativa L.) can be infected, but show little or no disease symptoms. In addition, the pathogen has been isolated from various other grass genera, such as Phalaris, Agropyron and Bromus, which may occur as common weeds. Useful websites: https://nt.ars-grin.gov/fungaldatabases/; http://plantpath.psu.edu/facilities/fusarium-research-center; https://nt.ars-grin.gov/fungaldatabases/; http://www.speciesfungorum.org/Names/Names.asp.

https://bsppjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/mpp.12639

Fusarium crown rot caused by Fusarium pseudograminearum in cereal crops: recent progress and future prospects.

A DNA-based soil testing service operates in Australia to assist grain growers in predicting the likely extent of losses from various soilborne diseases well before a crop is planted. Growers, therefore, have the option of changing cultivars or modifying cropping programs in situations where the risk of crop loss is high. The service was launched in 1997 and although the initial focus was on wheat and barley, pathogens of rotation crops are now included. Key features of the service include a unique high-throughput DNA extraction system to process 500-g soil samples and a series of specific real-time PCR assays that allow a range of fungal and nematode pathogens to be quantified in a single soil sample. Tests for Heterodera avenae, Pratylenchus neglectus, P. thornei, Gaeumannomyces graminis var. tritici, G. graminis var. avenae, Rhizoctonia solani AG-8, Fusarium pseudograminearum, F. culmorum and the pea pathogens Mycosphaerella pinodes and Phoma medicaginis var. pinodella are available at present, while tests for Bipolaris sorokiniana, Ditylenchus dipsaci and Pratylenchus teres are in development. This paper discusses issues that were addressed in establishing the service (e.g. sampling strategies, extraction of DNA from soil, development of specific tests, disease risk categories) and explains the training and accreditation programs that have been established to ensure that results are interpreted adequately at the farm level. It also outlines research being conducted to extend the service to horticulture.

Development of a routine DNA-based testing service for soilborne diseases in Australia

Grape phylloxera, Daktulosphaira vitifoliae (Fitch) (Hemiptera Phylloxeridae) is a damaging pest of grapevines (Vitis spp.) around the world, and the management of this pest requires early detection of infestations. Here, we describe the development and validation of a sensitive DNA test for grape phylloxera that can be applied to soil. Species-specific primers were developed for grape phylloxera in the internal transcribed space region 2, and their specificity was confirmed after thorough screening by using a wide range of vineyard organisms and aphid genera. Preliminary testing of the detection limits of the grape phylloxera-specific primers was conducted using field-sourced soil types spiked with a known number of grape phylloxera. The assay was converted to a real-time polymerase chain reaction format (TaqMan MGB). This assay, in combination with DNA extraction from soil, can detect phylloxera crawlers added to soil. The assay was evaluated in the field at a recently detected grape phylloxera infestation site from the Yarra Valley in Victoria, Australia. The DNA assay proved to be substantially more sensitive than a standard ground survey for detecting grape phylloxera presence on vine roots in the infested vineyard. Moreover, unlike the ground survey, the assay provided quantitative information on grape phylloxera infestations, because grape phylloxera DNA concentrations in samples from vines closely matched the numbers of grape phylloxera crawlers collected with emergence traps placed at the base of vines. Unlike other detection techniques, the method can be applied at any time of the year, and it can be potentially modified to provide specific information on the virulence levels of the particular grape phylloxera genotypes responsible for any new infestations.

Developing and testing a diagnostic probe for grape phylloxera applicable to soil samples.

Meloidogyne fallax (Karssen, 1996) has been recorded for the first time in Australia from potato tubers and soil collected in the south-east of South Australia. Identification was based on morphological observations and DNA sequencing.

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Di Hartley

Papers

Development of a routine DNA-based testing service for soilborne diseases in Australia

Developing and testing a diagnostic probe for grape phylloxera applicable to soil samples.

First record of Meloidogyne fallax in Australia