Losses of nitrogen from the soil/plant system not only reduce soil fertility and plant yield but can also create adverse impacts on the environment. Ammonia emissions into the atmosphere contribute to acid rain and represent an indirect source of nitrous oxide greenhouse gas emissions. Nitrate leaching losses into rivers and lakes can cause eutrophication resulting in excessive growth of aquatic weeds and algae, which can reduce fish populations and the recreational value of the water. Nitrate contamination of drinking water supplies can cause health risks. Legislation that is designed to limit nitrate leaching losses from land has become a constraint on agricultural land use in many countries. Nitrous oxide emissions into the atmosphere contribute to the depletion of the ozone layer and also make a significant contribution to climate change. This review describes the nitrogen cycle in temperate soil/plant systems, the processes involved in each of the individual nitrogen loss pathways, the factors affecting the amounts of losses and the methods that are available to reduce these losses. The review has shown that careful management of temperate soil/plant systems using best management practices and newly developed technologies can increase the sustainability of agriculture and reduce its impact on the environment.

Nitrogen losses from the soil/plant system: a review

Insect pathogens as biological control agents: Back to the future.

Sclerotinia sclerotiorum (Lib.) de Bary is a necrotrophic fungal pathogen causing disease in a wide range of plants. This review summarizes current knowledge of mechanisms employed by the fungus to parasitize its host with emphasis on biology, physiology and molecular aspects of pathogenicity. In addition, current tools for research and strategies to combat S. sclerotiorum are discussed. Taxonomy: Sclerotinia sclerotiorum (Lib.) de Bary: kingdom Fungi, phylum Ascomycota, class Discomycetes, order Helotiales, family Sclerotiniaceae, genus Sclerotinia. Identification: Hyphae are hyaline, septate, branched and multinucleate. Mycelium may appear white to tan in culture and in planta. No asexual conidia are produced. Long-term survival is mediated through the sclerotium; a pigmented, multi-hyphal structure that can remain viable over long periods of time under unfavourable conditions for growth. Sclerotia can germinate to produce mycelia or apothecia depending on environmental conditions. Apothecia produce ascospores, which are the primary means of infection in most host plants. Host range: S. sclerotiorum is capable of colonizing over 400 plant species found worldwide. The majority of these species are dicotyledonous, although a number of agriculturally significant monocotyledonous plants are also hosts. Disease symptoms: Leaves usually have water-soaked lesions that expand rapidly and move down the petiole into the stem. Infected stems of some species will first develop dark lesions whereas the initial indication in other hosts is the appearance of water-soaked stem lesions. Lesions usually develop into necrotic tissues that subsequently develop patches of fluffy white mycelium, often with sclerotia, which is the most obvious sign of plants infected with S. sclerotiorum.

Sclerotinia sclerotiorum (Lib.) de Bary: biology and molecular traits of a cosmopolitan pathogen.

Antagonistic fungi, trichoderma spp.: panoply of biological control

The Botryosphaeriaceae: genera and species known from culture

The study of gene function in filamentous fungi is a field of research that has made great advances in very recent years. A number of transformation and gene manipulation strategies have been developed and applied to a diverse and rapidly expanding list of economically important filamentous fungi and oomycetes. With the significant number of fungal genomes now sequenced or being sequenced, functional genomics promises to uncover a great deal of new information in coming years. This review discusses recent advances that have been made in examining gene function in filamentous fungi and describes the advantages and limitations of the different approaches.

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Approaches to functional genomics in filamentous fungi.

The rhizosphere competence of the biological control agent Trichoderma atroviride isolate C52 was studied on onion roots both in the glasshouse and in the field when introduced into soil in a range of formulations. Proliferation of T. atroviride in the rhizosphere was formulation-dependent. A pellet formulation maintained the fungal concentration at 105 cfu per g soil, whereas solid-substrate and seed-coating formulations gave concentrations of 104 and 101 cfu per g soil, respectively. To facilitate rhizosphere-competence studies, a UP-PCR band profile generated with primer L45 for isolate C52 was used to enable conclusive identification of T. atroviride C52 when recovered from soil. When isolate C52 was introduced into Sclerotium cepivorum-infested soil as both pellet and solid-substrate formulations, there was no statistically significant difference in the disease control between these treatments, but the pellet treatment doubled the percentage of healthy plants compared with the control treatment.

Effect of formulation on the rhizosphere competence and biocontrol ability of Trichoderma atroviride C52

Biocontrol of fungal plant pathogens through the use of mycoparasitic fungi is an environmentally sustainable approach to management of plant diseases. Mycoparasitism by Trichoderma spp. primarily involves production of cell‐wall degrading enzymes. Isolation and characterisation of the corresponding genes have revealed major insights into the underlying genetic basis of mycoparasitism, implicating various regulatory pathways such as carbon and nitrogen catabolite repression. A summary is presented here of the current state of knowledge in molecular regulation of mycoparasitism by Trichoderma species.

https://www.tandfonline.com/doi/pdf/10.1080/01140671.2003.9514263

Genetic basis of mycoparasitism: A mechanism of biological control by species of Trichoderma

Biological control of Pseudomonas syringae pv. actinidiae (Psa), the causal agent of bacterial canker of kiwifruit, using endophytic bacteria recovered from a medicinal plant

Mycoparasitism of fungal plant pathogens by Trichoderma species is a complex process that in- volves the production and co-ordinated secretion of cell-wall degrading enzymes. Genes implicated in my- coparasitism by Trichoderma atroviride contain motifs in the promoter region, designated MYRE1-MYRE4, that are proposed to act as binding sites for a global inducer of the mycoparasitic response. The aim of our study was to establish whether these motifs also were present in Trichoderma hamatum and whether the presence of these motifs could predict co-expres- sion when T. hamatum was confronted by a patho- gen. Using a combination of targeted, degenerate and inverse PCR, homologues of the mycoparasitism- related genes ech42 (chit42), prb1 and lam1.3 (xbg1.3-110), which encode an endochitinase, pro- teinase, and b-1,3-glucanase, respectively, were cloned and sequenced from T. hamatum. Alignment of the promoter regions of the three genes revealed identical regions in the chit42 and prb1 promoters, which were 6-9 base pairs in length and conserved in position. Specifically, the regulator y motifs MYRE1-MYRE4 were fully conserved, together with a fifth motif, identified by this research. A substrate as- say designed to investigate the response of these genes from T. harzianum and T. hamatum to a simple carbon source (glycerol) showed that, in contrast to chit42 and prb1, xbg1.3-110 was not expressed. Fur- ther comparison of the expression patterns of these three genes between T. harzianum and T. hamatum using the glycerol substrate assay showed that no

/pdf/co-expression-of-two-genes-a-chitinase-chit42-and-proteinase-jq9f497z1d.pdf

Hayley J. Ridgway

Papers

Approaches to functional genomics in filamentous fungi.

Effect of formulation on the rhizosphere competence and biocontrol ability of Trichoderma atroviride C52

Genetic basis of mycoparasitism: A mechanism of biological control by species of Trichoderma

Biological control of Pseudomonas syringae pv. actinidiae (Psa), the causal agent of bacterial canker of kiwifruit, using endophytic bacteria recovered from a medicinal plant

Co-expression of two genes, a chitinase (chit42) and proteinase (prb1), implicated in mycoparasitism by Trichoderma hamatum