AAC Network hard red winter wheat

Abstract: AAC Network is a semi-dwarf hard red winter wheat (Triticum aestivum L.) cultivar that is well adapted across western Canada and eligible for grades of Canada Western Red Winter (CWRW) wheat. It was developed using wheat × maize pollen doubled haploid methodology. AAC Network was evaluated in the Western Canadian Winter Wheat Cooperative registration trials relative to CDC Buteo, Emerson, Moats, and AAC Elevate for 4 yr (2016–2019). Based on 44 replicated trials, AAC Network produced grain yield similar to AAC Elevate, the highest yielding check, with a protein concentration 0.9 units higher. AAC Network had fair to good winter survival, relatively late maturity, short straw with excellent lodging resistance, and high test weight. AAC Network expressed resistance to stem and stripe rust, moderate resistance to leaf rust and common bunt, and intermediate resistance to Fusarium head blight. In addition to increased grain protein concentration, AAC Network showed improvements in gluten strength and flour water absorption, and it maintained the excellent milling yield and low flour ash attributes of the CWRW wheat class.

High grain yield, fair to good winter survival, desirable agronomic traits, excellent end-use quality, and broad-spectrum disease resistance make AAC Network Canada Western Red Winter (CWRW) wheat well suited for production in all areas of western Canada. The name "Network" acknowledges the extensive web of highly committed individuals and organizations required to develop a new cultivar, take it to market, and make it successful for the sustainability and benefit of Canadian agriculture.

Disease Resistance Breeding Milestones
Wheat in western Canada is affected by numerous pathogens that can cause widespread epidemics and devastating economic losses through reduced productivity and marketability in a single season (Aboukhaddour et al. 2020). Over the past 25 yr, considerable breeding progress has been made in the level, diversity, and combinations of disease resistance available in hard red winter wheat cultivars for western Canada. This brief chronicle does not mention all of the disease-resistant cultivars registered but rather describes the first cultivars developed in western Canada expressing resistance to a particular pathogen and when initially combined with other types of resistance.
The first winter wheat cultivars developed and supported for registration in western Canada that expressed demonstrable major resistance to recognized critical disease threats were CDC Harrier with stem rust (Puccinia graminis Pers.: Pers. f. sp. tritici Eriks. & E. Henn.) resistance in 1997 (Fowler 1999b), followed in 1998 by CDC Falcon with resistance to stem rust and leaf rust (Puccinia triticina Eriks.) (Fowler 1999a) and AC Bellatrix with resistance to common bunt [Tilletia tritici (Bjerk.) G. Wint. in Rabenh. and Tilletia laevis Kühn in Rabenh.] (Thomas et al. 2012b (Thomas et al. 2012a) combined resistance to stripe rust (Puccinia striiformis Westend.) and the wheat curl mite (WCM; Aceria tosichella Keifer) vector of wheat streak mosaic virus. Flourish (Graf et al. 2012), recommended in 2010, brought together resistance to stem rust, leaf rust, and common bunt but regrettably proved to be highly susceptible to FHB. In the following year, Emerson was released, which combined the excellent rust resistance from McClintock with FHB resistance (Graf et al. 2013). Emerson was the first wheat cultivar of any type in Canada to be rated "resistant" to FHB, which may account for its enduring popularity with producers in the eastern prairie region. AAC Elevate (Graf et al. 2015), which was approved in 2014, was the first winter wheat cultivar to express the minimum recommended levels of resistance to all of the aptly termed Priority 1 diseases ("intermediate resistance" or better to all rusts and common bunt; "moderate susceptibility" or better to FHB), as well as resistance to WCM. Unfortunately, the stripe rust resistance shown at the time of registration was no longer effective when AAC Elevate became commercially available in 2017. Registered in 2019, AAC Network exceeded all of these minimum recommended disease resistance guidelines. It is a clear demonstration of how collaboration among plant breeders, pathologists, and scientists of many other disciplines from numerous institutions can lead to the successful mitigation of important threats to the Canadian field crop sector.

Pedigree and Breeding Method
AAC Network is an F 1 -derived doubled haploid (DH) cultivar that originates from the cross LG237/LG278 made in 2008. Both LG237 and LG278 were DH lines developed at AAFC LeRDC and tested in the Western Winter Wheat Cooperative (WWWC) registration trials as W481 and W476, respectively. LG237 was selected from the cross Patriot/CDC Falcon//AMW4AF7C.
LG278 has AMW4AF7C/Radiant//McClintock parentage. AMW4AF7C was derived from the cross IDO180*3/Cmc1// Norwin/A791191W-1 and was evaluated for registration as W334. CDC Falcon, McClintock, and Radiant are hard red winter wheat cultivars with regional registration for western Canada, whereas Patriot is a hard red winter wheat with regional registration for eastern Canada. An expanded pedigree of AAC Network illustrates ancestry to many of the original disease-resistant cultivars developed in western Canada (Fig. 1).
In 2010, wheat × maize pollination techniques were used to produce 366 DH lines from 33 F 1 plants. Ten DH lines were derived from the F 1 plant from which AAC Network originated. Evaluation of a first subset of 248 DH genotypes occurred in 2 m observation rows grown under irrigation near Lethbridge in 2011, resulting in the harvest of 64 lines based on winter survival, spring vigour, plant type, height, straw strength, stripe rust resistance, and general leaf health. In 2012, these selections were rated for disease resistance in artificially inoculated nurseries for stem and leaf rust in Winnipeg, MB, Canada, grown in collaboration with the University of Manitoba, and for stripe rust in Lethbridge. Resistance to common bunt was also evaluated in Lethbridge by planting inoculated seed into cold soil in mid-October. The remaining DH lines from this cross were evaluated in a similar manner in subsequent years.
Based on acceptable resistance to all of the diseases evaluated in 2012, 29 of the initial 64 selections were tested in single-replicate preliminary agronomic trials in Lethbridge in 2013. Favourable agronomic performance, continued resistance to the three rusts and bunt, and acceptable end-use quality prompted continued testing of three lines in 2014 and two lines in 2015. Evaluation for resistance to FHB and WCM colonization was also conducted for two or more years. Based on 10 site-years of replicated agronomic assessment across western Canada, LP855 entered the WWWC registration trial as W569 and was evaluated for 4 yr (2015/2016-2018/2019).
The performance of AAC Network in the WWWC registration trials was assessed relative to CDC Buteo, Emerson, Moats (Fowler 2012), and AAC Elevate. Agronomic test sites across western Canada were in Alberta (Beaverlodge, Lacombe, Lethbridge "dry land", Lethbridge "evergreen" (dry land + foliar fungicide), Lethbridge "irrigated", Olds, and Warner), Saskatchewan (Indian Head, Melfort, Saskatoon, and Swift Current), and Manitoba (Brandon, Carman, Portage la Prairie, and Winnipeg) through the collaborative efforts of AAFC, Alberta Agriculture and Forestry, and the University of Manitoba. Analyses of variance were conducted using a combined mixed effects model in which environments were considered random and genotypes were fixed. The least significant difference (LSD) test was used to identify significant differences from the check cultivars.
During registration testing, resistance to the major diseases of economic importance to winter wheat in both the eastern and western prairies was assessed by AAFC and the University of Manitoba. Supplementary checks were included in the various nurseries to aid in making accurate assessments. In addition, the agronomic trial collaborators recorded responses to various pathogens when differentials were observed. The adult plant reactions to stem and leaf rust were determined in artificially inoculated field nurseries conducted by the University of Manitoba in Winnipeg using race composites supplied by the AAFC Morden Research and Development Centre (MRDC) and reported using the modified Cobb scale (Peterson et al. 1948). The stem rust races used for one or more years included MCC (P0001), QTH (P0005), RHT (P0002), RKQ (P0003), RTH (P0007), TMR (P0006), and TPM (P0004) (Fetch et al. 2018. The leaf rust races were a representative mixture collected in western Canada during the previous field season (McCallum et al. 2019. Seedling reactions to individual races of stem and leaf rusts prevalent in Canada were also determined under controlledenvironment conditions by personnel at AAFC MRDC. The races of stem rust were the same as those used in the field nurseries whereas the leaf rust races used for one or more years included MBDS (12-3), MBRJ (128-1), MGBJ (74-2), TDBG (06-1-1), TDBG (11-180-1), and TJBJ (77-2). Stripe rust ratings were determined in irrigated, inoculated nurseries at AAFC LeRDC (Puchalski and Gaudet 2011). The reaction to common bunt was also estimated in nurseries conducted at AAFC LeRDC by planting into cold soil in mid-October. All seeds were inoculated with a composite of races that included L1, L16, T1, T6, T13, and T19 (Hoffman and Metzger 1976;Gaudet and Puchalski 1989). FHB response was

Radiant
Abilene

Patriot
LG237 determined by staff at the University of Manitoba using a mist-irrigated field nursery with three replicates in Carman. Spray inoculation of each line occurred at 50% anthesis and again 3-4 d later using a suspension of F. graminearum macroconidia that contained equal quantities of two 3-acetyldeoxynivalenol (3-ADON) and two 15-ADON-producing chemotypes at a final concentration of 50 000 macroconidia mL −1 . Visual index (% incidence × % severity/100) rating typically occurred 18-21 d after anthesis or when symptoms were well developed (Gilbert and Woods 2006;Cuthbert et al. 2007). At maturity, a 50 g sample was harvested from each row to determine the percentage of fusariumdamaged kernels and to quantify the deoxynivalenol content using enzyme-linked immunosorbent assays. The response to WCM infestation was conducted each year using non-viruliferous mites under controlledenvironment conditions at AAFC LeRDC (Thomas and Conner 1986 , and physiological leaf spot were recorded at agronomic test sites expressing differential symptoms.

AAC Network
End-use quality analyses were conducted annually at the Canadian Grain Commission (CGC), Grain Research Laboratory (GRL), following protocols of the American Association of Cereal Chemists (2000). Following CGC determination of grain grade and protein concentration for the check cultivars at all of the agronomic test locations, a common site blending formula for the checks and all experimental lines was provided so as to produce composite samples in which the mean protein concentration of the checks was approximately 12.5%. Grain from test sites with serious downgrading factors was not included in the quality composites.

Grain yield and agronomics
Data from across the Canadian prairies, collected at 44 sites over 4 yr, established the agronomic performance of AAC Network relative to check cultivars of the CWRW class. Comparisons with Emerson were based on 33 site-years of data collected from 2017 to 2019. Data for CDC Falcon, a well-known cultivar in the eastern prairies and a Canada Western Special Purpose wheat check, are also reported. The mean grain yield of AAC Network was 102% of the CWRW check mean (nonsignificant) across all sites over 4 yr. Relative to specific checks, AAC Network had significantly higher grain yield than CDC Buteo (106%) and Emerson (107%) but was similar to Moats (101%), AAC Elevate (99%), and CDC Falcon (102%). On a regional basis, AAC Network was particularly well adapted to southern Alberta (Zone 1), where it was slightly higher yielding than all of the checks and 110% of the check mean (P ≤ 0.05). AAC Network also performed well in the eastern prairie rust area (Zone 4), where its yield was similar to AAC Elevate, the highest yielding check (Table 1).
AAC Network exhibited winter survival that was similar to the check cultivars. Heading date and maturity were later than the checks (P ≤ 0.05). The 2 d difference in maturity between AAC Network and CDC Buteo is similar to the long-term difference between Radiant and CDC Buteo (2.3 d) when they were tested together in the WWWC registration trials between 2005 and 2015 (77 direct comparisons over 9 yr, data not presented). AAC Network was shorter than all of the CWRW checks and 3 cm taller than CDC Falcon (P ≤ 0.05). Lodging resistance was similar to Emerson, AAC Elevate, and CDC Falcon and significantly better than CDC Buteo and Moats (P ≤ 0.05). The test weight and seed weight of AAC Network were within the range of the CWRW checks. AAC Network expressed higher grain protein concentration than all of the checks except Emerson (P ≤ 0.05). Grain protein yield per hectare was significantly greater than CDC Buteo, AAC Elevate, and CDC Falcon (P ≤ 0.05), and similar to Emerson and Moats (Table 2).

Disease resistance
Upon the request for support to register W569 (AAC Network), the Prairie Recommending Committee for Wheat, Rye and Triticale (PRCWRT) Disease Evaluation Team examined 3 yr of disease ratings. Note that as AAC Network was included as a year 4 entry in the 2018/2019 WWWC registration trial, these disease resistance data are also presented. Overall, AAC Network was rated as resistant to the prevalent races of stem rust and stripe rust, moderately resistant to leaf rust and common bunt, and intermediate in resistance to FHB. Barring significant disease pressure from FHB and changes to the prevalent races of rust and common bunt in western Canada, AAC Network is unlikely to require fungicide treatment for the Priority 1 diseases. In environments where FHB infection is expected, a crop management approach integrating cultivar resistance, foliar fungicides, and escape from infection remains the best control strategy (Ye et al. 2017;Beres et al. 2018). Based on natural infection at a limited number of agronomic trial sites, the reaction to leaf spotting diseases was within the range of the checks; powdery mildew infection was somewhat lower than the best check (Tables 3 and 4). AAC Network did not express resistance to WCM (data not presented).

End-use quality
Three years of end-use suitability testing by the CGC, GRL and evaluation by the PRCWRT Quality Evaluation Note: All means are weighted by the number of tests. LSD, least significant difference includes variation from the appropriate genotype × environment interaction. a Zone 1: Southern Alberta sites (Lethbridge "dry land", Lethbridge "irrigated", Lethbridge "evergreen" (dry land + foliar fungicide), and Warner); Zone 2: Parkland sites (Beaverlodge, Lacombe, Olds, and Melfort); Zone 3: Semi-arid prairie site (Swift Current); Zone 4: Eastern prairie rust-hazard sites (Brandon, Carman, Indian Head, Portage la Prairie, Saskatoon, and Winnipeg).  Note: LSD, least significant difference includes variation from the appropriate genotype × environment interaction.
a Team established that AAC Network had quality eligibility for all grades of the CWRW wheat class. AAC Network produced grain of higher protein concentration than all of the checks except Emerson and with an improvement in gluten strength, had much improved farinograph and bake absorption, and maintained the excellent milling yield and low flour ash attributes desired for the CWRW wheat class (Table 5).

Other Characteristics
Seedling: leaf sheath and blade glabrous. Plant: juvenile growth habit semi-prostrate; flag leaf blade glabrous, medium glaucosity, mid-long, mid-wide, highly recurved; flag leaf sheath glabrous, medium glaucosity; auricle anthocyanin colouration absent or very weak; culm neck straight to weakly curved, hollow, anthocyanin intensity at maturity absent or very weak.
Kernel: medium red, texture medium hard, medium size.

Maintenance and Distribution of Pedigreed Seed
The development of AAC Network Breeder Seed followed a standard head-row derivation approach to preserve the purity of its DH derivation. Progeny plots originating from 66 uniform head rows, produced under isolation at Lethbridge in 2018, were grown at the AAFC Seed Increase Unit in Indian Head in 2019. Following the elimination of 12 progeny lines, the remaining 54 plots were inspected, harvested in bulk, and cleaned to form 831 kg of Breeder Seed, which was released to pedigreed seed growers in the fall of 2019. Bulking of the Breeder Seed occurred eight generations after the harvest of the original DH plant. Breeder Seed of AAC Network will be maintained by the AAFC Seed Increase Unit. All other pedigreed seed classes will be multiplied and distributed by SeedNet Inc., P.O. Box 1062, Lethbridge, AB T1J 4A2,  www.seednet.ca. Rated using a 1-9 scale: 1 = disease free, 9 = very severe symptoms. Fusarium-damaged kernels = damaged kernel weight/total weight × 100.