The genus Setosphaeria consists of an important group of species that includes pathogens of monocots, such as the maize pathogens Setosphaeria turcica (causal agent of Northern Leaf Blight, NLB) and Setosphaeria rostrata (causal agent of Rostratum Leaf Spot). Setosphaeria is sister to the related maize pathogen Cochliobolus heterostrophus, and to the wheat pathogens, Pyrenophora tritici-repentis and Mycosphaerella graminicola. Sequencing of S. turcica provides the opportunity to understand the interaction between a hemibiotrophic pathogen and its host, maize, and also provides an opportunity to study vascular pathogenesis, allowing researchers to identify key differences between vascular and non-vascular pathogens on a genome-wide level.
To date, at least seven races of S. turcica have been identified. As with all hemibiotrophs and biotrophs, the expectation is that genes involved in the pathogen/plant battle are continually evolving. As new fungal effector molecules (secreted disease factors) are deployed, the host deploys new plant resistance genes. Within the past years, new races have emerged which overcome common sources of NLB resistance, and NLB is once again in focus as a major constraint to worldwide maize production. Through sequencing efforts, the biology of S. turcica will be better understood so that breeders can make a more informed decision about the deployment of resistance. The advanced knowledge of pathogenesis will serve to enhance NLB breeding efforts.
Northern Leaf Blight, caused by S. turcica, is a major disease of maize, both in the United States and internationally, and poses a significant production constraint. In a survey of 10 maize-producing countries of sub-Saharan Africa, NLB posed a maize production constraint in 40% of the area. If disease occurs before flowering, yield losses can exceed 50%. Yield loss is due to extensive leaf damage during the grain-filling period, and to increased susceptibility to stem rot, caused by Diplodia maydis. Yield loss is mainly due to the lack of available carbohydrates due to the extensive leaf damage during the grain-filling period. The deployment of host resistance remains the most effective strategy for S. turcica management. Efforts to isolate and utilize host resistance loci will be more efficient when informed by insights on pathogenic mechanisms.
There is an extensive collection of S. turcica field isolates available which may be used for analyses of natural variation. Sexual crosses can be made in the laboratory. Transformation is possible with S. turcica, allowing molecular manipulation of candidate fungal genes.