this special issue of fungal genetics and biology describes a comprehensive effort to develop methods and expertise to tackle one of the world s most serious fungal diseases of wheat .
the series of papers within this issue are designed to provide a resource for a new generation of plant pathologists who we hope will be inspired to investigate the biology of septoria blotch of wheat and develop new and durable disease control strategies .
wheat is the world s most widely cultivated crop and is responsible for providing about a quarter of the calories to humankind .
global wheat production was more than 700  million tons in 2013 , with the european union and china producing the largest harvests , and wheat being cultivated across most of the temperate regions of the planet ( gurr and fones , 2015 ; rudd et al . , 2015 ) .
as well as being the most widely grown crop , wheat is also the most traded food on the international markets  indeed more wheat is traded than all other crops combined . along with rice and maize ,
there are many threats to wheat productivity , including the availability of high quality land for cultivation , which is threatened by urbanisation , the sustainable use of fertilisers , which are used in enormous quantities , especially in europe , and the prevalence of diseases .
wheat diseases , such as septoria blotch , provide an ever - present threat to wheat production and if they could be controlled effectively , would provide a much - needed boost to productivity that will be required to satisfy increasing global demand for food in the next two decades ( courbot et al . , 2015 ;
what then are the essential pre - requisites to allow us rapidly to understand the biology of zymoseptoria tritici ? what requirements are necessary to allow a fungal pathogen to be regarded as a model system ( perez - nadales et al . , 2014 ) and for new insights into the underlying mechanisms of infection and virulence to be understood ?
the last 20  years have seen pathogens , such as the corn smut fungus ustilago maydis and the rice blast fungus magnaporthe oryzae , for example , emerge as model systems ( dean et al . , 2012 ) .
in both cases , this required the development of many tools , which took many years .
it is by considering these issues that this collection of reviews and primary publications has been put together .
arguably , the first pre - requisite to being able to investigate any disease is a comprehensive description of the life cycle of the organism and the spatial and temporal dynamics of the infection process . for z. tritici
this means a cell biological investigation of what happens from the moment a spore germinates on the leaf surface , to its location of a stoma and invasion of underlying leaf tissue .
using live cell imaging approaches , facilitated by the tools generated and described elsewhere in this special issue , the cell biology of infection is addressed , with an emphasis on the developmental biology of the fungus , its dimorphic growth habit , its ability to perceive and respond to the leaf surface , and its ability to undertake developmental transitions during its establishment of a wheat infection ( steinberg , 2015 ) . without a  road - map of how an infection proceeds , it is difficult to identify points of disease intervention or to understand how any single gene product , or family of proteins ( from the pathogen or its host ) , might be important in disease .
the next essential pre - requisite for the model pathogen tool - kit is the ability to test the function of any gene . without an ability to construct mutants ,
it is hard to carry out any reverse genetic approach to test the importance of any selected biological process .
therefore , a high frequency transformation system is essential , with a ready supply of selectable marker genes to allow multiple constructs to be expressed , and the ability to carry out targeted mutations ( kilaru and steinberg , in 2015 ; kilaru et al . , 2015a ; schuster et al . ,
the latter can be dramatically improved by development of a strain of z. tritici in which the non - homologous dna end - joining pathway is impaired ( sidhu et al .
coupled to this , it would be advantageous to have a means by which the function of a gene could be attenuated but without complete loss of function , such as virus - induced gene silencing , and the ability to regulate genes driven by a set of highly controllable promoters by which gene expression can be predictably controlled ( kilaru et al .
the latter will also provide the means to over - express , or mis - time the expression of a given gene to tests its function , or requirement ( cairns et al . , 2015 ) .
next , a means by which gene products can be localised using expression of fluorescently - labelled fusion proteins is essential , preferably with optimised fluorescent markers , calibrated and tested for the pathogen and in amenable vectors , with easy cloning strategies for ready construction ( kilaru et al .
, 2015c ; mehrabi et al . , 2015 ; schuster et al . , 2015a ; sidhu et al .
this provides the means to carry out live cell imaging of a pathogen undergoing infection and directly observing the position , fate and turnover of a gene product , which is absolutely pivotal to understanding its function . but this will make no sense without some context , so having the ability to unequivocally identify organelles , such as nuclei , er , golgi bodies , peroxisomes , and mitochondria is essential ( schuster et al . , 2015b ; kilaru et al . , 2015b ; guo et al .
, 2015a , b ) . also , to understand intracellular trafficking it is necessary to be able to identify and track the movement of endosomes , secretory vesicles and the associated components of the actin and microtubule cytoskeleton and their corresponding motor proteins , so that the transport of proteins and the regulation of such processes can be studied ( guo et al . , 2015a , b ; kilaru et al . , 2015c ; schuster et al .
when considered together , these tools will therefore allow rapid elucidation of gene function in z. tritici , as rapidly as in any fungal pathogen studied today .
so far , of course , we have only considered addressing the functions of individual genes as opposed to gene families and the function of the whole genome and the corresponding , context - dependent proteomes that are expressed during pathogenesis . to address these
requires first of all a detailed understanding of the genome ( goodwin et al . , 2011 ; testa et al . , 2015 ) and its inherent , strain - to - strain variation , and how this correlated with pathotype .
understanding the role , for example , of accessory , or supernumerary chromosomes , as opposed to the core , invariant gene repertoire of the genome will be key ( mcdonald et al . , 2015 ) . an ability to analyse global patterns of gene expression , proteomic and metabolomics data sets during infection , will also be necessary so that the total expressed proteome can be defined and sub - sets associated with the effector repertoire of the pathogen , proteins required for symptom development and those necessary for fungal proliferation can be readily classified , define and then functionally analysed ( ben mbarek et al .
methods to define transcriptional networks by chromatin immuno - precipitation coupled to next generation sequencing to define targets genes downstream of transcription factors , will also allow networks of gene expression to be distinguished readily ( soyer et al . ,
protein interactions between fungal proteins , but also between fungal proteins that act upon host plant proteins , is also essential , with the ready availability of yeast two - hybrid libraries and associated bespoke protocols to z. tritici ( ma et al . , 2015 ) finally ,
of course we need to consider the plant host and within this context , transgenic wheat lines expressing organelle - specific markers are already available and being constructed to augment host - pathogen cell biological analysis , while detailed analysis of sources of resistance can guide plant breeding strategies such that durable combinations of resistance genes can be identified and introduced into elite , high yielding commercial wheat cultivars ( brown et al . , 2015 ) .
with wider knowledge of the fungal pathogen population and prevailing virulence specificities , should some the ability to breed for exclusion of the most prevalent , prevailing pathotypes of the fungus ( vallet et al . , 2015 ) , providing a direct route to disease control at least in the medium term .
the new methods and resources presented in this special issue mean that the z. tritici research community now has , arguably , the same level of research tools as any fungal model system .
this is remarkable , because it has happened in a very short period of time in response to an acute need , articulated by growers and the agricultural biotechnology industry .
an integrated programme has been funded and undertaken to carry out this method development and to begin to apply the newly acquired expertise to understanding this disease .
many research questions immediately present themselves . what is the purpose of the morphogenetic plasticity exhibited by z. tritici and how are these dimorphic transitions regulated
how is long - distance control of pathogenesis - associated gene expression achieved and how does the fungus perceive and respond to the internal plant tissue environment during infection ? how is sporulation triggered and correctly regulated ? all of these questions can now be addressed and the answers provided will result not only in many of the fungicide targets of the future , but also perhaps to some longer - term strategies for broad spectrum disease control .
so , to those of you reading this commentary who have never previously considered studying z. tritici , or perhaps not even considered studying a fungal pathogen before , think of the obstacles that have just been removed .
 septoria blotch of wheat is one of the world s most serious plant diseases , which is difficult to control due to the absence of durable host resistance and the increasing frequency of fungicide - resistance . the ascomycete fungus that causes the disease , zymoseptoria tritici , has been very challenging to study 
 . 
 this special issue of fungal genetics and biology showcases an integrated approach to method development and the innovation of new molecular tools to study the biology of z. tritici . when considered together 
 , these new methods will have a rapid and dramatic effect on our ability to combat this significant disease . 