2014a, b, 2016a, 2017b) reflect that of other sexually reproducing fungal pathogens, including the closely related V. The degree and distribution of genetic diversity observed within and among populations of V. effusa have a race structure based around the pecan cultivar on which they originated and other closely related cultivars however, the race structure has not been fully examined ( Conner and Stevenson 2004 Converse 1960). Additionally, there is a history of the resistance breaking down as the pathogen population adapts to host resistance ( Goff et al. Although scab-resistant pecan cultivars are available, they are often not preferred by either growers or consumers for agronomic or nut quality reasons. effusa has developed resistance to several major classes of fungicides recommended for its management, including both single-site and multisite chemistries ( Seyran et al. Pecan scab is a challenging disease to manage ( Bock et al. As the fruit are produced, they can become infected, and the earliness and severity of infection will dictate the degree of yield loss ( Gottwald and Bertrand 1983 Stevenson and Bertrand 2001). In seasons conducive to the disease, the pathogen can reproduce asexually in as little as 7 to 9 days, and this can happen multiple times throughout the growing season ( Latham 1982). In the spring, as conditions become favorable for sporulation, conidia spread to the expanding leaves and cause infection on the foliage. The primary source of inoculum, thought to be conidia, comes from overwintering lesions on shoots and shucks from the previous year ( Demaree 1924). effusa relies on wind and rain splash to spread conidia early in the season ( Gottwald and Bertrand 1982). Much of the acreage in the southeastern United States is planted to susceptible cultivars and, thus, the disease is a major concern in most years. Since the mid-19th century, pecan has been cultivated mostly as clonal cultivars on rootstocks, although some production of native trees still exists. The native extent of pecan is thought to be primarily the Mississippi watershed area ( Worley 2002), while the remaining Carya spp. are native to the southeastern United States but pecan is the only cultivated species. tomentosa) in Illinois ( Winter 1885), and is described causing disease on C. Venturia effusa was first isolated from mockernut ( C. 2010a), whereby infection by the pathogen can cause serious and even catastrophic yield loss when conditions are favorable for an epidemic ( Gottwald and Bertrand 1983 Stevenson and Bertrand 2001). The disease is caused by the plant-pathogenic fungus Venturia effusa (G. The combined cost of the damage and disease control measures was $78.7, $25.7, and $65 million in these 3 years, respectively. Estimated crop losses in the state of Georgia alone were 15, 10, and 12% in 2013, 2014, and 2015, respectively ( Brock and Brenneman 2013, 2014, 2015). Koch) in the southeastern United States ( Demaree 1924). Scab is the most prevalent disease of pecan ( Carya illinoinensis (Wang.) K. This is an open access article distributed under the CC BY-NC-ND 4.0 International license. The apparent equilibrium of the MAT idiomorphs provides impetus for a renewed effort to search for the sexual stage of V. Analysis of this collection revealed the frequency of the MAT idiomorphs is in a 1:1 equilibrium of MAT1-1: MAT1-2. A hierarchical sampling protocol representing region, orchard, and tree allowed for analysis of MAT structure at different spatial scales. effusa collected from 11 populations of pecan across the southeastern United States. A multiplex polymerase chain reaction screen was developed to amplify MAT1-1-1, MAT1-2-1, and a conserved reference gene encoding β-tubulin, and used to screen 784 monoconidial isolates of V. The MAT locus spanning the flanking genes was amplified and sequenced from a subset of 14 isolates, of which 7 contained MAT1-1-1 and the remaining samples contained MAT1-2-1. The MAT1-1-1 locus is flanked by two conserved genes encoding a DNA lyase ( APN2) and a hypothetical protein. inaequalis, we identified a single MAT gene, MAT1-1-1, in a draft genome of V. Using the mating type ( MAT) idiomorphs from V. effusa are typical of a sexually reproducing fungal pathogen, and comparable with other dothideomycetes with a known sexual stage, including the closely related apple scab pathogen, V. However, the degree and distribution of genetic diversity observed within and among populations of V. effusa is currently known only by its asexual (conidial) stage. Fusicladium effusum), causal agent of pecan scab, is the most prevalent pathogen of pecan ( Carya illinoinensis), causing severe yield losses in the southeastern United States.