APS_July2019

J ournal of the A merican P omological S ociety

184

evaluated in Oregon were scored resistant to EFB, presenting contrasting results to our data (note that progenies 09030 and 09031 had similar ratios of resistant to susceptible trees visualized in both studies). However, in general our results confirm reports from Oregon that the OSU 495.072 source of re- sistance is transmitted in a dominant man- ner and controlled at a single locus. Our somewhat varied responses with the different susceptible parent may indicate interactions with uncharacterized modifying factors pres- ent or absent in some parental combinations, of which further work will elucidate. These interactions could also explain the abundance of seedlings rated 3, which indicates a use- ful level of tolerance, and was not expected based on the choice of known susceptible parents used in the crosses.  Further, in respect to placing the R -gene on LG 6, Muehlbauer et al. (2018) exam- ined the EFB response of 1,319 seedlings from 31 different full-sib progenies expected to segregate for the ‘Gasaway’ R -gene in either a 1 resistant: 1 susceptible or 3 resis- tant: 1 susceptible ratio based on prior work in Oregon. They found that the number of trees remaining free of EFB was much less than the expected ratio. In contrast, nearly all progeny of OSU 495.072 tested in New Jersey segregate as in Oregon, and the parent trees, unlike ‘Gasaway’, also remain free of EFB. This indicates that the R-gene in OSU 495.072, while located on LG 6, is different than the ‘Gasaway’ gene, as was suggested by Colburn et al. (2015). Corylus americana ‘Rush’. ‘Rush’, a wild hazelnut selection from Pennsylvania, has a long history of use in breeding hybrid ha- zelnuts. It was a parent in the first crosses with C. avellana starting in the early 1900s, from which selections were made and clon- ally propagated, and of which many open- pollinated seedling populations were subse- quently grown (Crane et al., 1937; Grimo, 2011; Molnar, 2011; Molnar et al., 2005, 2015; Reed, 1936; Slate, 1961; Thompson et al., 1996). Grower reports in the eastern U.S.

source still mapped to a single locus. Based on its demonstrated ability to resist EFB from multiple locations and placement on a different LG than ‘Gasaway’, ‘Ratoli’ pres- ents a very promising option for breeding eastern U.S. adapted cultivars and potential gene pyramiding. Corylus avellana OSU 495.072. OSU 495.072 was selected from plants grown from seeds sent to OSU in 1989 from the N.I. Vavilov Research Institute of Plant In- dustry in St. Petersburg, Russia. It is believed that the seeds originated from a cultivar col- lection in southern Russia. Sathuvalli et al. (2010) determined it to be resistant to EFB in Oregon through greenhouse inoculations. Later, Colburn et al. (2015) examined segre- gation patterns of progeny in Oregon when crossed with a susceptible parent and also mapped the location of the R -gene using co- segregation with SSR markers. While their results showed that most progenies held an abundance of resistant seedlings that did not fit either a 1:1 or 3:1 segregation ratio, resis- tance was mapped to a single locus on LG 6 in the same region where the ‘Gasaway’ R - gene is located. The authors suggested that resistance was likely part of a cluster of dif- ferent resistance genes in the same region.  Six OSU 495.072-related progenies to- taling 317 seedlings were examined in this study. Note that three progenies (09029, 09030, and 09031) were from the similar crosses examined in Colburn et al. (2015). When all six progenies were pooled, the OSU 495.072 population fit a 1:1 resistant: sus- ceptible segregation ratio (Table 2; Fig. 1). However, there was some interesting varia- tion among progenies, which is likely from the susceptible parent’s contribution. Four of six fit the expected 1: 1 model (09030, 09031, 08525, and 09569), whereas progeny 09567 had an abundance of resistant seedlings with 38 of 49 rated 0 (77.6%). In contrast, prog- eny 09029 held only 17 of 48 free of EFB (35.4%). This progeny is especially interest- ing, as Colburn et al. (2015) reported that 41 of 60 trees from this same parental cross