Conservation agriculture has been proposed as a widely adapted set of management principles that can assure more sustainable agricultural production. Conservation agriculture removes the emphasis from the tillage component alone and addresses a more enhanced concept of the complete agricultural system. Applying conservation agriculture essentially means altering literally generations of traditional farming practices and implement use. Within the framework of agricultural production, high soil quality equates to the ability of the soil to maintain a high productivity without significant soil or environmental degradation. A comparative soil quality evaluation is one in which the performance of the system is determined in relation to alternatives. Inconsistent effects of a reduction in tillage on the variation in total porosity with depth may be related to differences in traffic on different sites, or on soil quality at the time tillage was reduced or stopped.

Conservation agriculture, improving soil quality for sustainable production systems?

Summary
Bipolaris sorokiniana (teleomorph Cochliobolus sativus ) is the causal agent of common root rot, leaf spot disease, seedling blight, head blight, and black point of wheat and barley. The fungus is one of the most serious foliar disease constraints for both crops in warmer growing areas and causes significant yield losses. High temperature and high relative humidity favour the outbreak of the disease, in particular in South Asia's intensive ‘irrigated wheat–rice’ production systems. In this article, we review the taxonomy and worldwide distribution, as well as strategies to counteract the disease as an emerging threat to cereal production systems. We also review the current understanding of the cytological and molecular aspects of the interaction of the fungus with its cereal hosts, which makes B. sorokiniana a model organism for studying plant defence responses to hemibiotrophic pathogens. The contrasting roles of cell death and H 2O2 generation in plant defence during biotrophic and necrotrophic fungal growth phases are discussed.

Bipolaris sorokiniana, a cereal pathogen of global concern: cytological and molecular approaches towards better control‡

Tropical and subtropical highlands of the world have been densely populated and intensively cropped. Agricultural sustainability problems resulting from soil erosion and fertility decline have arisen throughout this agro-ecological zone. We assessed practices that would sustain higher and stable yields for wheat (Triticum aestivum L.) and maize (Zea mays L.) in this region. A long-term experiment (randomized complete block) was started in 1991 under rainfed conditions in the volcanic highlands of central Mexico (2240 m a.s.l.;19.31°N, 98.50°W; Phaeozem). Our objective was to determine infiltration, soil moisture content, root diseases and nematode populations at the end of 12 years of 16 management treatments from a factorial arrangement of: (1) four rotations (monocropping and rotation of maize and wheat), (2) two tillage (conventional tillage [CT] and zero tillage [ZT]) and (3) two crop residue management practices (residue retention and removal). Water infiltration and soil moisture levels were greater under ZT when residue was left in the field then when residue was removed. Higher infiltration rates and favourable moisture dynamics supported up to 30% yield increase. A significantly higher incidence of root rot was found in monoculture of maize under ZT than CT. Residue retention significantly increased maize root rot incidence compared to residue removal. Rotation of maize and wheat decreased the incidence of maize root rot up to 30%. In general, the incidence of root disease was lower in wheat (up to 3 on a scale of 7) than in maize (up to 3.93 on a scale of 4) for all treatment. In maize, both non-parasitic and parasitic nematodes increased under ZT; however, in wheat no effect of tillage was seen. Incidence of root rot and parasitic nematode populations were not correlated with yield. Although root diseases may have affected crop performance, they affected yield less than other critical plant growth factors such as infiltration and water availability. Both environmental conditions and microflora played a key role in the biology and expression of soil pathogens. In the semi-arid and rainfed subtropical highlands of central Mexico, positive effects were observed with zero tillage, crop rotations and crop residue retention, compared with common farming practices.

Infiltration, soil moisture, root rot and nematode populations after 12 years of different tillage, residue and crop rotation managements

Crown rot of wheat and barley in the Pacific Northwest is caused by a complex of Fusarium pseudograminearum, F. culmorum, F. avenaceum, Bipolaris sorokiniana, and Microdochium nivale. Yield-loss estimates were made by evaluating yield components on tillers collected from commercial fields and sorted by disease severity classes, and by comparing yields for field plots inoculated with F. pseudograminearum with yields in naturally infested soil. Increasing crown rot severity caused an increase in grain protein content and reduction in grain yield, kernels per head, kernel weight, test weight, tiller height, and straw weight. Crown rot reduced winter wheat yield as much as 1,550 kg/ha (35%, $219/ha) in commercial fields, with a 13-field mean of 9.5% ($51/ha). Inoculation reduced yields as much as 2,630 kg/ha (61%, $372/ha) over that caused by the native pathogen flora. Rain-induced crusting of the soil surface greatly amplified preemergence damping-off caused by F. pseudograminearum. Crown rot caused the greatest losses during seasons of lowest precipitation but also damaged crops under wet conditions. Aboveground symptoms were not always apparent under conditions of moderate infection and yield constraint. Damage from crown rot in the Pacific Northwest is more widespread and damaging than previously recognized.

https://apsjournals.apsnet.org/doi/pdf/10.1094/PD-89-0595

Crop Damage Estimates for Crown Rot of Wheat and Barley in the Pacific Northwest.

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.

In southern Queensland, crown rot caused by Fusarium graminearum Group 1 and common root rot caused by Bipolaris sorokiniana are common soilborne diseases of wheat and barley The incidence of these diseases was measured in the susceptible wheat (Triticum aestivum L) cultivar, Hartog which was grown under no tillage, reduced tillage (two tillage operations plus herbicides) and where stubble was retained or removed by burning (1984-1986) or physically removed (1987-1993) Primary tillage was with blade, disc or chisel implements The level of crown rot and common root rot was higher where stubble was retained than where it was removed There was a significant interaction in incidence of crown rot between stubble management and some types of tillage Where there was no tillage, incidence of crown rot was significantly higher where stubble was retained (322%) than where it was removed (47%) whereas under disc tillage, there was no significant difference in disease level between stubble treatments (12-17%) Incidence of crown rot was not affected by the type of tillage employed The incidence of deadheads (heads without grain) caused by crown rot was lowest in the no tillage plots (43%) and highest in the reduced (193%) and conventional (122%) disc tillage stubble retained treatments Available soil water (depth of 12 m) at sowing and anthesis was lowest in the conventional disc stubble retained plots and highest in the no tillage stubble retained plots It is hypothesised that the high levels of deadheads were due to moderate to high levels of disease and low available soil water at planting and anthesis Although incidence of crown rot was high under no tillage, incidence of deadheads was lower than in other treatments due to the higher availability of soil water Severity of common root rot was lower in stubble removed, than in stubble retained, treatments and also lower in no tillage than in any of the other tillage treatments (C) 1997 Elsevier Science BV

R.B. McNamara

Papers

Crown rot and common root rot in wheat grown under different tillage and stubble treatments in southern Queensland, Australia