Faba bean is grown as a winter annual across the

Published January 14, 2016 Agronomic Application of Genetic Resources Adaptation of Autumn-Sown Faba Bean Germplasm to Southeastern Washington Erik J. Landry, Clarice J. Coyne, Rebecca J. McGee, and Jinguo Hu* ABSTRACT Information regarding the suitability of autumn-sown faba bean (Vicia faba L.) in southeastern Washington is lacking. Therefore, a variety trial testing the effects of two sowing dates was conducted for two seasons (2011 2012 and 2012 2013) at three locations: Central Ferry Research Farm (CF), Pomeroy, WA; Spillman Agronomy Farm (SF), Pullman, WA; Whitlow Farm (WF), Pullman, WA, with 20 northern European breeding lines, or cultivars, and U.S. Department of Agriculture-Agricultural Research Service National Plant Germplasm System (USDA-ARS NPGS) sourced germplasm accessions with predetermined winter-hardiness. Winter-hardiness and yield varied depending on location, timing of sowing, and genotype effects. Survival was greatest at CF where the extreme low air temperature was 6 C, yet multiple entries tolerated an extreme low of 14 C in Pullman. In both years, the second sowing at the CF location improved survival, whereas the first sowing was only beneficial at the Pullman locations when seedlings were established before the first hard frost. Providing a longer establishment and cold acclimation period was expected to optimize hardiness and yield potential. However, achieving two to three nodes before the first hard frost was difficult at dryland managed SF and WF locations where soil moisture was limiting. Across entries and site-years, the mean survival was 65% with a yield of 2800 kg ha 1. To realize the potential of autumn-sown faba bean in southeastern Washington, genotypes with earlier maturity than the northern European materials tested herein will be needed. Faba bean is grown as a winter annual across the Mediterranean and in parts of Australia and China, where winter temperatures generally remain above 5 C. True winter faba bean or winter field bean germplasm (Bond and Crofton, 1999) from northern Europe is small seeded (var. equine and minor) and can tolerate winter temperatures from 10 C (Evans, 1992) to 25 C (Picard et al., 1982). Generally, commercial cultivars from France and the United Kingdom can tolerate temperatures between 12 and 15 C without risk of crop failure (Herzog, 1989). Autumn-sown faba bean, like winter pea (McPhee et al., 2007), has the potential to become a new crop for southeastern Washington as temperatures generally remain above 20 C throughout winter. However, unlike winter pea, testing of known winter-hardy European faba bean cultivars and other identified genotypes with novel sources of winter-hardiness that are potentially adapted to southeastern Washington growing conditions is lacking. The diversification of cereal-dominated rotations with pulses can help reduce soil-borne diseases and provides N input (Jensen et al., 2010). Spring-sown faba bean has a high capacity to fix N and can yield more than many other cool-season pulses (Herridge et al., 1994). In southeastern Washington, the mean yield of spring-sown faba bean compared favorably with regional mean chickpea (Cicer arietinum L.) yield (Landry et al., 2015). Autumn-sown faba bean can have a higher yield potential and capacity to root and fix N than when spring sown (Herzog and Geisler, 1991). A winter crop can also show earlier development than a spring crop, making efficient use of seasonal moisture (Herzog, 1989) avoiding drought and heat stress (Hebblethwaite et al., 1983; Duc and Petitjean, 1995; Cutforth et al., 2007; Link et al., 2010). Experimental yields of autumn-sown faba bean in England have been reported as high as 9000 kg ha 1 (Roughley et al., 1983), but in production rarely yield over 7000 kg ha 1 (Stelling et al., 1994). Issues affecting adoption include weed pressure and controlling soil erosion throughout the winter and spring. High density sowing is one method to reduce erosion, weed pressure, and crop failure due to winter-kill (Murray et al., 1988). However, Published in Agron. J. 108:301 308 (2016) doi:10.2134/agronj2015.0028 Received 14 Jan. 2015 Accepted 30 Sept. 2015 Available freely online through the author-supported open access option. Copyright 2016 by the American Society of Agronomy 5585 Guilford Road, Madison, WI 53711 USA All rights reserved E.J. Landry, C.J. Coyne, and J. Hu, Western Regional Plant Introduction Station, USDA-ARS and the Dep. of Crop and Soil Sciences, Washington State Univ., Pullman, WA 99164; R.J. McGee, Grain Legume Genetics Physiology Research, USDA-ARS and the Dep. of Crop and Soil Sciences, Washington State Univ., Pullman, WA 99164. *Corresponding author (Jinguo.hu@ars.usda.gov). Abbreviations: CF, Central Ferry Research Farm, Pomeroy, WA; SF, Spillman Agronomy Farm, Pullman, WA; USDA-ARS NPGS, United States Department of Agriculture-Agricultural Research Service National Plant Germplasm System; WF, Whitlow Farm, Pullman, WA. Agronomy Journal Volume 108, Issue 1 2016 301

wide spacing (before winter: 30 60 plants m 2 and after winter: 15 30 plants m 2 ) is recommended for grain production, as plants have a strong ability to produce reproductive branches and are less prone to lodging (Poulain, 1984; Link et al., 2010). In southeastern Washington winter faba bean would likely be sown into relatively dry soil in October, after harvesting spring wheat (Triticum aestivum L.) or barley (Hordeum vulgare L.). Late August to early October is the recommended sowing time for winter pea (Pisum sativum L.) in this region, as sowing much earlier results in slow germination, due to a lack of soil moisture, and late sowing increases winter-kill. Low soil moisture can also affect the stand establishment of winter wheat, resulting in a shorter cold acclimation phase and heightened risk of winter-kill (Young et al., 1994). According to Murray et al. (1988), winter faba bean seedlings should have two to three pairs of leaves and a strong root system going into winter. The objectives of this research were to evaluate the performance of northern European cultivars and breeding lines as well as identify adapted winter-hardy genotypes from the USDA-ARS NPGS faba bean collection. Multiple sowing dates were used to further understand the effects of establishment on winter-hardiness and yield of autumn-sown faba bean germplasm in southeastern Washington (Mwengi, 2011). MATERIALS AND METHODS The 20 entries (Table 1) used for this experiment included 10 cultivars and breeding lines from Europe with known winterhardiness, four NPGS accessions that were initially identified in 2008 and confirmed in 2009 as winter-hardy after field screening at CF in Central Ferry, WA, 46 39 5.1² N; 117 45 45.4² W and Washington State University s WF in Pullman, WA, 46 44 3.2² N; 117 7 25.8² W, a breeding line derived from a cross between a European winter-hardy line and a non-winter-hardy cultivar, and five bulk populations derived from the USDA-ARS NPGS faba bean collection. The four NPGS bulks were created as follows. In spring 2010, 466 NPGS accessions were evaluated in microplots of 15 to 20 plants each. Seeds bulked from 466 accessions were planted at high density (~65 seeds/m) at each of four locations (WF and SF near Pullman, WA, 46 41 45.1² N; 117 9 2.7² W, CF, and Dayton, WA, 46 38 8.1² N; 117 8 58.2² W) in October of 2010 to screen for additional winter-hardy materials from the collection. The percentage of winter survival was estimated from <1% in Pullman, approximately 5% in Central Ferry, to 5 to 10% in Dayton. The plants that survived were considered as potentially winter-hardy sources and were labeled as NPGS bulk WF, NPGS bulk SF, NPGS bulk CF, and NPGS bulk Dayton, respectively. The NPGS bulk original, was not selected and served as a non-hardy check. An autumn-sown variety trial was conducted for two seasons (2011 2012 and 2012 2013) across three locations CF, WF, and SF following a split-plot experimental design with three replications. The main plot was planting date and subplot was entry. Field sites represented different elevation and climatic zones of southeastern Washington, as well as field management. The CF location has a Chard silt loam soil (coarse-loamy, mixed, superactive, mesic Calcic Haploxeroll) and is characterized as low elevation (198 m) and irrigated (subsurface drip irrigation at 10 min d 1 ) during the active growing season. Spillman and WF are higher in elevation (770 and 790 m, respectively), dryland managed, receiving an average 53 cm of rainfall annually, and Table 1. Faba bean entries, 100 seed weight (g), and country of origin, with percent winter survival for 2 yr at three locations (CF- Central Ferry Farm, WF- Whitlow Farm, and SF- Spillman Farm). Percent survival 2011 2012 2012 2013 Entry name 100 seed weight Origin CF WF SF CF WF SF 13 Diva 54.1 Germany 79 59 60 52 45 56 13 Karl/2-3 56.6 France 92 55 66 80 51 77 Clipper 64.0 UK 84 66 57 62 73 68 Côte d Or/2-3 52.3 France 89 83 73 68 56 71 Gö-Wibo-Pop 60.8 Germany 79 70 56 74 75 75 Hiverna 62.2 Germany 86 61 56 76 50 66 Hiverna/2-5EP1 57.2 Germany 73 50 55 71 64 68 Scout 60.6 Germany 81 60 56 74 71 71 Striker 59.4 UK 94 78 72 74 64 62 W6 12023 64.2 Bulgaria 92 68 59 70 53 82 W6 12024 65.1 Bulgaria 79 61 45 74 75 78 W6 12025 62.0 Bulgaria 88 64 57 64 65 68 W6 12028 60.5 Bulgaria 78 61 60 66 63 65 Wibo/1 60.0 Germany 90 73 68 59 71 73 F 3:5 88.2 Extra Precoce Violetto x Hiverna/2 88 74 55 71 63 71 NPGS bulk WF 58.3 Selection from WF 88 65 47 68 58 67 NPGS bulk CF 68.4 Selection from CF 88 45 45 58 49 68 NPGS bulk Dayton 75.8 Selection from Dayton, WA 82 38 34 61 54 70 NPGS bulk SF 73.1 Selection from SF 82 31 33 56 54 64 NPGS bulk original 71.2 Unselected check 69 9 28 35 9 32 SE ± 4.5 Seed originally obtained from Dr. Wolfgang Link, Georg-August-University, Göttingen, Germany. 302 Agronomy Journal Volume 108, Issue 1 2016

have heavier Palouse silt loam (fine-silty, mixed, mesic Pachic Ultic Haploxeroll) and Palouse Thatuna silt loam soils (fine-silty, mixed, superactive, mesic Oxyaquic Argixeroll), respectively. Treflan (a,a,a-trifluoro-2,6-dinitro-n,n-dipropyl-p-toluidine; Dow Chemical, Indianapolis, IN), to control monocot weeds and Thio-Sul ((NH 4 ) 2 S 2 O 3 ; Texas Sulfur Co., Borger, TX), to reduce bird damage to seedlings were applied at post-plant pre-emergence for all locations. Warrior ([1a(S*),3a(Z)]-cyano(3-phenoxyphenyl) methyl-3-(2-chloro-3,3,3-trifluoro-1-propenyl)-2,2-dimethylcyclopropanecarboxylate; Syngenta, Greensboro, NC) was used to control pea leaf weevil (Sitona lineatus) as necessary. Plot dimension varied by location due to subsurface drip irrigation constraints at CF, but area (2.7 m 2 ) was constant. Plots at WF and SF had four rows, while CF had two. Rows were spaced 35 cm apart at each location. Plot dimensions were 1.5 by 1.8 m at WF and SF and 0.75 by 3.6 m at CF, with a 40 cm space separating subplots. A Hege 120 planter was set for 48 seeds per plot, equivalent to 80 to 120 kg of seed ha 1 depending on seed size. Sowing density was toward the lower end of what is commercially recommended for autumn sowing (170 200 kg of seed ha 1 ) (Soper, 1956; Hebblethwaite et al., 1983; Link et al., 2010) to facilitate individual plant measurements. Seed stocks were obtained annually from the WF harvest of the previous year. Complete isolation was not practiced in an effort to allow gene flow between entries to potentially increase winter-hardiness, following a bulk method of selection. Therefore, entries were maternally/cytoplasmically distinct, but open to paternal gene flow. Percent survival was determined from the ratio of seed sown to stand count in spring. Mid-winter and spring stand counts were taken to estimate frost tolerance during early and late winter, but were not presented due to inconsistent stand establishment and delayed emergence at SF. Soil temperature, electrical conductivity, and moisture were collected at each of the three sites at three soil depths (2.5, 7.5, and 15 cm) using data loggers (EM-50, Decagon Devices, Pullman, WA) equipped with 5TE probes. Development was characterized as defined by Knott (1990). Early branching and height measurements were taken when plants started to bloom (203), and late branching and height just before harvest and leaf shedding (310 and 410) (Table 2). Number of branches and height measurements were based on 20 representative plants from each plot. Where less than 20 plants survived the winter, all remaining plants were scored. Total plot yield was extrapolated to kg ha 1. Plant yield (g plant 1 ), pods plant 1, and mature branches plant 1 were based on five representative plants at harvest. Early and late branch number and height measurements, pod number, and per plant yield for each entry are included as a supplement. Yield stability was estimated according to Finlay and Wilkinson (1963) as the regression coefficient (b i ) of each individual entry s site-year yield across the mean yield of all entries at each site-year. Ecovalence (W i 2 ) (Becker and Léon, 1988) was transformed into a variation coefficient (VCW i 2 ) according to Stelling et al. (1994) to weigh variation according to yield. The mean yield and b i of each entry were used to visualize reliability indices. Survival, phenological characteristics, and yield least squares means (LS-means) were compiled and analyzed using an ANOVA with PROC MIXED (SAS Institute, 2008). Entry, location, sowing date, and year were treated as fixed effects and block and block sowing date (main plot) were considered random effects within the model following a split-plot experimental design. Treatment mean comparisons were assessed based on Fisher s Least Significant Differences (LSD) test at P = 0.05. RESULTS Daily minimum air (Fig. 1) and minimum monthly temperatures over the winter (Table 3) at WF and SF were colder than at CF, aligning with 30-yr averages and record minimum temperatures. The lowest temperature throughout this trial was just below 14 C on 13 Jan. 2013 at WF. The lowest soil temperature at sowing depth (7.5 cm) was 3.1 C at SF during this same cold period, which was slightly colder than WF ( 2.2 C). The active growing season in 2012 was very similar to the 30 yr average, but 2013 temperatures were generally above normal. Percent survival reflected winter severity, with a greater survival at CF (74.8%) than at either SF (60.7%) or WF (58.4%). Percent survival was also slightly greater across entry, location, and sowing date for the 2011 2012 (65.5%) compared to the 2012 2013 (63.7%) season. Percent survival responded to year, location, and sowing date effects (Table 4). For 2012 2013, the second sowing at CF generally improved survival and appeared to be less affected by Pea Enation Mosaic and Bean Leaf Roll viruses, which are vectored by late-season aphid migration. The second sowing possibly escaped infection as emergence was largely after the first hard frost. A lack of soil moisture at both SF and WF delayed germination and autumn growth, limiting the effect of planting date on winter survival. The first sowing at WF showed a slight improvement in overwintering as compared to the second for both seasons. However, at SF there was no clear trend. The Table 2. Phenological sampling and final harvest dates for Whitlow Farm (WF), Spillman Farm (SF), and Central Ferry Research Farm (CF) in 2011 2012 and 2012 2013. Year and location Sowing dates Early branching, height, and flowering Branching and height at maturity Harvest date of sampling 2011 2012 WF 29 Sept./13 Oct. 9 June 19 Sept. 20 Sept. CF 30 Sept./14 Oct. 9 April 5 July 20 July SF 7 Oct./21 Oct. 9 June 19 Sept. 20 Sept. 2012 2013 WF 25 Sept./10 Oct. 4 June 26 Aug. 27 Aug. CF 28 Sept./12 Oct. 18 April 12 July 19 July SF 5 Oct./19 Oct. 6 June 26 Aug. 16 Sept. Agronomy Journal Volume 108, Issue 1 2016 303

Table 3. Minimum air temperature at three locations (Central Ferry farm-cf, Whitlow Farm-WF, and Spillman Farm-SF) for two winter seasons (2011 2013) and 30-yr average (daily) minimum air and record minimum temperatures for Ice Harbor and Pullman, WA, (NOAA, 2013) by month. Ice Harbor was chosen for comparison with the CF because of its geographic and meteorological similarities. Minimum temperature 30-yr min. Record low 2011 2012 2012 2013 Month Ice Harbor Pullman Ice Harbor Pullman CF WF SF CF WF SF C Oct. 5.1 2.3 8.3 13.9 1.3 1.0 1.6 1.8 3.7 3.0 Nov. 1.6 0.7 18.9 25.6 1.3 4.4 4.6 2.3 6.3 4.4 Dec. 2.3 4.0 25.6 35.6 5.8 9.0 9.8 2.7 12.4 10.8 Jan. 1.9 2.9 25.6 33.9 5.9 8.3 8.8 5.9 14.1 14.5 Feb. 1.3 2.2 25.6 31.1 3.3 12.6 11.7 2.3 6.6 5.5 Mar. 1.8 0.1 12.2 20.0 3.1 3.7 4.5 3.4 6.7 6.1 April 4.9 2.1 5.6 10.6 1.6 1.6 1.5 1.9 6.9 6.5 Table 4. Percent survival, branch number and height at maturity, pod number, yield per plant, and plot yield across 20 faba bean populations in 2011 2012 and 2012 2013 in response to two autumn sowing dates at three locations (CF- Central Ferry Farm, WF- Whitlow Farm, and SF- Spillman Farm). Letters separate significantly different least square means (LS-means) (P 0.05). Year Location Planting date Percent survival Branch no. Height Pod no. Per plant yield Plot yield % cm g kg ha 1 2011 2012 CF 30 Sept. 82.9A 5.5A 83.6B 56.0A 66.0A 5961.0B 14 Oct. 85.2A 4.5B 84.3B 45.6B 57.2B 6618.2A 2012 2013 28 Sept. 59.1CDEF 3.3D 47.1E 21.4D 7.7G 754.1G 12 Oct. 72.1B 3.9C 58.8D 31.0C 26.0E 2065.1EF 2011 2012 WF 29 Sept. 62.0CD 2.8E 90.1A 28.7C 49.6C 4518.7C 13 Oct. 55.0EF 2.7EF 87.9AB 27.7C 47.5C 3714.7D 2012 2013 25 Sept. 60.6CDE 2.1G 64.5C 17.5D 15.9F 1853.8F 10 Oct. 55.9DEF 2.1G 65.3C 18.0D 17.0F 1964.2F 2011 2012 SF 7 Oct. 55.5DEF 3.4D 91.0A nd 32.6D 2519.3E 21 Oct. 52.6F 3.0DE 83.5B nd 29.9DE 2450.7E 2012 2013 5 Oct. 63.9C 2.3FG 51.5E nd 7.2G 880.8G 19 Oct. 70.8B 2.2G 50.5E nd 6.6G 902.2G nd = not determined. Fig. 1. Daily low air temperature through the 2011 2012 and 2012 2013 winter seasons from weather stations located at Central Ferry (CF), Whitlow (WF), and Spillman (SF) Farms. 304 Agronomy Journal Volume 108, Issue 1 2016

sowing date at SF was a week later than at WF for both seasons (Table 1). As a result, emergence at SF was delayed until early December and the second sowing was not fully rated until late March, whereas, both sowing dates emerged and were rated by early November at WF. The soil at SF was also drier because of the previous spring wheat crop, whereas WF was fallowed. No single entry stood out across all site-years or in any one location across years for winter survival (Table 1). Many of the entries exceeded 70% survival compared to the original bulk/ unselected check, which averaged 30% across all treatments. The W6 accessions were comparable to proven European lines and bulk populations were only statistically inferior to the hardiest of entries. The WF bulk population was on average comparable to elite northern European lines, suggesting that winter-hardy genotypes are present in the NPGS collection and may serve as a novel source for improving winter-hardiness. Plot yield, like percent survival, was dependent on the genetic background (G), environmental conditions (E), and G E interaction, ranging from more than 8000 kg ha 1 to less than 100 kg ha 1. Across locations, 2011 2012 (4297 kg ha 1 ) was more productive than 2012 2013 (1403 kg ha 1 ), mainly as a result of greater per plant pod number and percent survival. Across years, the first sowing at CF yielded less than the second sowing (Table 4), as a result of higher survival and lower visible viral symptoms than in the second sowing. The yield at both Pullman locations did not respond to different sowing dates, apart from the first sowing at WF in 2011 2012, which was likely the result of greater percent survival. At SF in 2012 2013 percent survival did not compensate for low plant productivity. Plot yield of individual entries varied across year and location, but not sowing date. However, all 12 sowing date location mean plot yields were included to estimate yield stability (Fig. 2). Four contrasting entries were chosen based on their differential reliability indices. Scout had the highest mean yield across site years (3391 kg ha 1 ), with optimal or dynamic stability (b i = 1.02), and moderate VCW i 2 (682.7), whereas the NPGS Dayton bulk had the lowest mean yield (2299 kg ha 1 ), apart from the original bulk, with optimal stability (b i = 1.05), but high VCW i 2 (1478.4). Alternatively, 13 Karl/2-3 showed the most static stability (b i = 0.75), apart from the original bulk, but had a low mean yield (2485 kg ha 1 ) and high VCW i 2 (1315.9). The F 3:5 population was the most responsive (b i = 1.33) and had a high mean yield (3146.0 kg ha 1 ) and VCW i 2 (1896.9). Not all static entries had low yields, for example, Striker had a mean yield of 3002 kg ha 1 and a b i of 0.85. However, the majority of lines with a mean yield >3000 kg ha 1 were also responsive (b i = >1.0). Wibo/1 and Hiverna/2 had the lowest VCW i 2 at Fig. 2. Scatter plot of plot yield for each of 20 faba bean populations by mean plot yield for each of 12 sowing date location interactions. Regression lines are included for four entries. Agronomy Journal Volume 108, Issue 1 2016 305

484.8 and 480.2, respectively, showing their yield stability was highly predictable. The F 3:5 population mean yield was among the highest under favorable conditions, 8070 kg ha 1 at CF and 4827 kg ha 1 at WF in 2011 2012, but among the lowest at SF, 1252 kg ha 1 in 2011 2012 and 437 kg ha 1 in 2012 2013. This dynamic response may be explained by the earlier flowering, pod set, and maturity observed for this population, as compared to European entries, improving yield potential at CF, but leading to shattering at SF. The paternal parent Extra Precoce Violetto is a relatively short early flowering large seeded Mediterranean type when spring sown under dryland conditions. In general, number of branches, height, and pods per plant (Table 4) contributed to per plant yield, while survival influenced plot yield. Taller plants at maturity with more branches tended to set more pods than shorter plants with fewer branches. Plants shorter than 50 to 60 cm at maturity were generally low yielding and likely stressed due to biotic and/or abiotic factors. European materials were generally later to regrow than the F 3:5 and bulk populations. For example, the F 3:5 population was one of the tallest (31.5 cm) and most branched (2.4) of any entry at flowering, whereas, 13 Karl/2-3 was among the shortest (24.9 cm) least branched (2.0) entry across site-years. However, at maturity, 13 Karl/2-3 was taller (73.2 vs. 57.8 cm), had a higher mean branch number (3.7 vs. 3.1) and pod number (32.0 vs. 22.9), but lower yield per plant (23.2 vs. 28.5 g) as compared to the F 3:5 population. The F 3:5 population typically had larger pods and seeds (88.2 g 100 seeds 1 ) than 13 Karl/2 3 (56.6 g 100 seeds 1 ) explaining this discrepancy between pod number and yield per plant. The NPGS Dayton and SF bulks, like the F 3:5 population, had high yields at CF and WF, but were among the lowest yielding at SF. Interestingly, they also were relatively earlier maturing and had above average seed sizes of 75.8 and 73.2 g 100 seeds 1, respectively. Early flowering and maturity may have been advantageous at CF and WF where plants were threshed by hand, but limiting at SF, where the use of a plot combine delayed harvest for 2 to 3 wk after WF, increasing the incidence of pod dehiscence. DISCUSSION Winter faba bean has been a mainstay of English agriculture since 1825 (Bond and Crofton, 1999), reportedly introduced as a small seeded Russian bean (Lawes et al., 1983). The crop is relatively unknown in the United States and has received little attention in southeastern Washington, which is a major pea, lentil (Lens culinaris L.), and chickpea growing region (Slinkard and Blain, 1988). French landrace Côte d Or has been cultivated since at least 1812 and is considered hardy to at least 18 C (Bond et al., 1994; Link and Bond, 2011). Older winter cultivars (Banner, Côte d Or, Webo, and Hiverna) tolerate up to 14 C (Herzog, 1988). More recently, Arbaoui et al. (2008) concluded that cultivars Hiverna/2, Hiverna, Karl, Bulldog/1, and Gö-Wibo-Pop were consistently winter-hardy across 12 European environments. Mwengi (2011) found Gö-Wibo-pop to be the hardiest and Hiverna/2, W6 12024, and W6 12026 to be reasonably hardy for the Palouse region. It would appear that a rhizosphere temperature between 7 C (Mwengi, 2011) to 9 C (Saxena, 1982) determines survival of even the hardiest genotypes, rather than ambient temperature alone, since snow cover can mediate air temperature (Link et al., 2010; Link and Bond, 2011). The lowest air temperature experienced in our study was 14.5 C, which corresponded to a soil temperature of 3.1 C at seed depth. While winter temperatures were not extreme enough to conclusively distinguish northern European materials, average survival was between 63 and 73% for the majority of European entries, there was sufficient selection pressure to separate them as a group from the bulk population entries (50 65%). In 2013 2014 for example, the lowest air temperature recorded in Pullman was 25 C and the averaged survival of bulk and European entries were not discernable (~50%) across WF and SF locations. The majority of European entries tested were largely smaller seeded, later to flower, tended to have fewer branches, and were shorter at flowering, while taller at maturity than the bulk populations. The WF selected bulk did not follow this trend however, supporting the claim that early spring regrowth and large seeds limit winter-hardiness (Ney and Duc, 1997, Patrick and Stoddard, 2010). This association between hardiness, small seed size, late flowering, and yield may not be complete though. The F 3:5 population, for example, while still segregating for many traits did have the largest mean seed size of all entries tested, was the earliest to flower and mature, overwintered with a mean 70% survival, and had a mean plot yield >3000 kg ha 1. Having yields comparable to the most productive European materials suggests that these traits may have an advantage in our warmer and drier climate as compared to northern Europe. The advantage of these two traits were particularly apparent at CF and WF, where the F 3:5 population was among the highest yielding. However, at SF, this population performed poorly, possibly due to early maturity induced dehiscence. Similar conclusions can be drawn about the CF, Dayton, and SF bulk populations. Whether or not adapted genotypes are present in these materials will require further testing and selection. The two primary selection events overwinter occur at the beginning and end of winter (Link et al., 2010). The first period of selection coincides with the first autumn frosts and depends directly on the development of cold acclimation and extent of frost tolerance. Sufficient seedling development, storage of photosynthetic reserves, and cold acclimation before hard frosts has been understood for some time to increase winter-hardiness of winter wheat (Janssen, 1929) and winter pea (Etève, 1985). Frost tolerance is a major component of winter-hardiness in faba bean as well (Arbaoui et al., 2008). Herzog (1987) showed the importance of establishment in that frost tolerance increased between the first and second leaf of the faba bean seedling during cold acclimation. The second abiotic stress period encompasses the many vicissitudes of winter: inter and intracellular ice formation, frost heaving, water logging, wind injury, freeze-drying (inability to absorb water from the frozen soil), and loss of frost tolerance through dehardening (Herzog, 1988) and resumption of growth (Annicchiarico and Iannucci, 2007). Precipitation in southeastern Washington is normally scarce during late September and early-october when sowing winter faba bean would be ideal based on daily low air (<8 C) and soil (<10 C) temperatures (Murray et al., 1988). Without adequate soil moisture, stand establishment, winter-hardiness, 306 Agronomy Journal Volume 108, Issue 1 2016

and yield of faba bean (Herzog and Geisler, 1991) like winter wheat (Young et al., 1994) can be affected. Earlier sowings were generally more appropriate than later for overwintering at the Pullman locations, even though low soil moisture delayed germination. Optimal cold acclimation would be expected if soil moisture supported prompt germination and seedling development. At the warmer CF location, where soil moisture was adequate for germination, a delayed sowing in mid-october avoided late season virus pressure on emerging seedlings. Without virus pressure, early-october sowing, when mean air temperature is still above 5 C, results in luxuriant growth susceptible to freezing injury. Ideally, seedlings going into winter should have two pairs of leaves and a strong root system (Hebblethwaite et al., 1983; Murray et al., 1988), which indicates acquisition of freezing tolerance and accumulation of storage reserves. Sowing date did not have a consistent effect on plot yield except at the CF location, where the second sowing generally out yielded the first, primarily as a result of virus pressure in 2012 2013. Pod set was the main determinant of yield per plant as is commonly the case (Lawes, 1978; Chaieb et al., 2011), but advantages associated with early sowing (McEwen et al., 1988; Pilbeam et al., 1990) were inconsistent. We did not observe the increase in branch number in response to an early sowing date as shown by Herzog (1989), likely because of the shorter hardening period. Seasonal effects on yield were more pronounced than sowing date. The colder winter and warmer summer of 2012 2013 likely led to a reduction in yield, not completely attributable to percent survival. A late spring frost during April 2013 coincided with regrowth at both Pullman locations. While this did not reduce percent survival, it is unclear if it had limited yield potential through restricting branch number and height. Frost, once growth has resumed in spring, is just one of the many possible causes for loss of yield potential (Lawes, 1978; Bond et al., 1994). Most likely the drought conditions of 2013, limited stem elongation (Dantuma and Grashoff, 1984), biomass (Loss et al., 1997a), and yield (French, 2010), particularly at SF, which was severely affected due to a drier site location than in 2012. Gasim and Link (2007) found that many of these same varieties tested herein were more than 50 cm taller and generally yielded more than 4000 kg ha 1 in northern Europe. Shorter determinant spring-type varieties have been found to have more yield stability than indeterminate types under drought stress conditions (De Costa et al., 1997). Although not determinant, the early flowering and shorter F 3:5 population showed greater phenotypic stability in height, pod number, and yield per plant than taller northern European entries. Therefore, combining the winter-hardiness of northern European germplasm with the earlier flowering and more determinant height and maturity of Mediterranean germplasm (Link et al., 1996) could provide adapted genotypes which maximize yield potential under the terminal drought conditions of southeastern Washington. A stable faba bean variety for southeastern Washington will need adequate winter-hardiness and productivity (i.e., pod set) under diverse moisture limiting conditions. Sufficient winter-hardiness appears to be present within current northern European winter faba bean cultivars, as well as in the USDA germplasm. The majority of European entries expressed sufficient winter-hardiness and yield comparable to trials in southwestern Australia (Loss et al., 1997b) and across continental Europe (Arbaoui et al., 2008; Ghaouti and Link, 2009), but lower than in the UK (Link et al., 2010) and Germany (Gasim and Link, 2007). The yield of winter faba bean may respond more favorably to an even precipitation pattern throughout the growing season as experienced in northwestern Europe, indicated by the taller plant heights reported by Gasim and Link (2007) than observed here under low humidity/terminal drought conditions. The characterization of an ideal ecotype, which maximizes both yield potential and winter-hardiness across the diverse environments of southeastern Washington, will require further test environments with larger field-scale plot sizes and selection of more homogeneous populations than the bulk populations used here to minimize site-year error and within entry variance, respectively. ACKNOWLEDGMENTS This research was supported by USDA-ARS CRIS Project 5348-21000-026-00D and NIFA MultiState Project W006 to Jinguo Hu and Scholarship from the ARCS Foundation to Erik Landry. We gratefully acknowledge the assistance with planting and plot maintenance by Jarrod Pfaff, Sean Vail, and Wayne Olson. We would also like to thank Lisa Taylor for technical assistance. Mention of trademarks, proprietary products, or vendors does not constitute a guarantee or warranty of products by USDA and does not imply its approval to the exclusion of other products that may be suitable. All programs and services of the USDA are offered on a nondiscriminatory basis, without regard to race, color, national origin, religion, sex, sexual orientation, age, marital status, or handicap. REFERENCES Annicchiarico, P., and A. Iannucci. 2007. Winter survival of pea, faba bean and white lupin cultivars in contrasting Italian locations and sowing times, and implications for selection. J. Agric. 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