Evaluating Host Resistance to Limit Colletotrichum Coccodes on Onion
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HORTSCIENCE 53(7):916–919. 2018. https://doi.org/10.21273/HORTSCI12957-18 ley (Syn: Phoma terrestris)andFusarium basal rot incited by Fusarium oxysporum f. sp. cepae (H.N. Hansen) W.C. Snyder & H.N. Evaluating Host Resistance to Limit Hansen, but their response to C. coccodes has not been evaluated. The occurrence of this Colletotrichum coccodes on Onion pathogen constitutes a new challenge for í 1 2,3 onion growers in Michigan in maintaining Lina M. Rodr guez-Salamanca and Mary K. Hausbeck productivity and profitability and an integrated Department of Plant, Soil, and Microbial Sciences, Michigan State disease management strategy is needed. Onion University, East Lansing, MI 48824 growers historically have rotated with celery or carrot which are not recognized hosts of C. Additional index words. Allium cepa, anthracnose, cultivars, disease resistance coccodes and apply fungicides including stro- Abstract. Leaf and neck anthracnose is incited by Colletotrichum coccodes (Wallr.) bilurin products which were shown to limit í Hughes, a new foliar disease of onion (Allium cepa L.) in Michigan that has been observed disease in a field study (Rodr guez- in the state since 2010. Symptoms include elliptical lesions on the leaves, necks, or both Salamanca, 2013). In this study, we sought that appear bleached with a pale salmon to dark brown center. To develop an effective to investigate the response of 16 onion culti- integrated disease management strategy, field studies were conducted in 2011 and 2012 to vars to C. coccodes to limit leaf and neck evaluate 16 commercial onion cultivars for their susceptibility to the pathogen. The anthracnose under Michigan field conditions. incidence and severity of anthracnose were evaluated weekly following inoculation. Onion cultivars differed significantly in disease severity and incidence; differences Materials and Methods between years were also observed. ‘Hendrix’ had the lowest disease severity, whereas ‘Highlander’ and ‘Candy’ exhibited severe onion leaf and neck anthracnose symptoms. Field preparation, plant establishment, Using less susceptible onion cultivars combined with effective fungicides against C. and field maintenance. Cultivar trials were coccodes may limit crop losses for Michigan growers. direct-seeded in mineral soil, Oakville fine sand (Natural Resources Conservation Serv., n.d.), at the Southwest Michigan Research A range of pathogens can compromise Environmental conditions especially condu- and Extension Center, Benton Harbor, MI, on onion quality and yield (Carisse et al., 2011; cive to onion leaf and neck anthracnose in- 27 May 2011 and 10 May 2012. The field was Develash and Sugha, 1997; Schwartz and clude a minimum of 12 h at high relative previously planted to rye and vetch cover Mohan, 1995, 2008) and are a yearly threat humidity with temperatures higher than 20 °C crops in 2010 and to onion (C. coccodes– in Michigan. Onion leaf and neck anthrac- (Rodríguez-Salamanca et al., 2018). On to- inoculated plots) in 2011. Although Michi- nose incited by C. coccodes (Wallr.) Hughes mato, severe disease incidence incited by C. gan onions are produced primarily on muck was recently reported as a new disease, and coccodes is most often associated with high soils, some growers have moved a portion of growers in many Michigan counties observed rainfall during the growing season (Dillard, their acreage to mineral soils to avoid pink –1 significant symptoms in 2010 (Rodríguez- 1989). Disease incidence may also be in- root disease. Before bedding, 560 kg·ha of Salamanca et al., 2012) and continue to see creased by the use of overhead irrigation 8–21–29 fertilizer was applied with micro- symptoms yearly (Hausbeck, personal ob- (Raniere and Crossan, 1959). nutrients (0.5% Cu, 1% Mn and 0.5% Zn) and · –1 servation). The symptoms of onion leaf and C. coccodes has been reported to infect 50 side-dressed twice with 11 kg ha of foliar neck anthracnose incited by C. coccodes different hosts worldwide (Farr and Rossman, 20–20–20 fertilizer. The target seeding den- (Rodríguez-Salamanca et al., 2012) are dif- 2011) and 18 within the United States and is of sity was 18 plants per 30 cm. Onion cultivars ferent from the symptoms incited by Colleto- primary importance on tomato (Dillard, 1992) tested for their susceptibility to C. coccodes trichum gloeosporioides (Penz.) Penz. & Sacc and potato [Tsror (Lahkim) and Johnson, under field conditions during 2011 and 2012 included one red-colored bulb cultivar (Red- previously reported in the United States and 2000]. Seed extracted from tomato fruit in- wing) and 15 yellow-colored bulb cultivars the tropics, which is referred to as onion fected with C. coccodes may also be infested (Table 1). The 16 commercially available twister (Ebenebe, 1980; Nischwitz et al., with the pathogen (Ben-Daniel et al., 2010). C. cultivars were planted in a randomized com- 2008; Schwartz et al., 2015) or anthracnose coccodes can also infect weed species in the (Galvan, 2010; Haddad et al., 2003). Onion plete block design (RCBD) with four blocks. families Amaranthaceae, Asteraceae, Brassi- Each block was 5 m long and consisted of leaf and neck anthracnose symptoms include caceae, Euphorbiaceae, Poaceae, Malvaceae, oval lesions on the leaves and neck that differ a double row spaced 38 cm apart. A plot Oxalidaceae, and Polygonaceae (Anderson consisted of a double row of onions spaced 38 in appearance from other commonly occurring and Walker, 1985; Raid and Pennypacker, onion foliar diseases (Schwartz and Mohan, cm apart. 1987). The pathogen produces abundant acer- 1995). The onion leaf and neck anthracnose Weed control was achieved by hand vuli and sclerotia on senescent tissues of lesions range about from 0.2 to 0.6 cm in weeding and herbicides were applied as infected plants including tomato (Dillard and width · 0.4 to 3 cm in length and have needed following current recommendations Cobb, 1998), potato (Nitzan et al., 2008), and a characteristic bleached appearance that in- (Bird et al., 2012). Insects, including thrips cludes a salmon- to brown-colored center. some weed species (Raid and Pennypacker, and armyworms, were controlled with appli- 1987). Acervuli give rise to abundant black cations of methomyl (2.3 L·ha–1). The plants globose microsclerotia that have setae (Sutton, had overhead mist irrigation (94.6 L·ha–1)2d 1980). Conidia are produced from acervuli each week for 1–2 h to promote leaf wetness Received for publication 6 Feb. 2018. Accepted for and moisture from rain or irrigation is neces- conducive to C. coccodes dispersal and in- publication 3 May 2018. sary for their release (Dillard, 1992). Sclerotia fection in the field. This work was supported by MSU GREEEN may remain in the soil for up to 1 year in Inoculum preparation, inoculation, and GR11-030 and GR11-020 and the Michigan Onion potato fields [Farley, 1976; Tsror (Lahkim) disease ratings. Several C. coccodes iso- Committee. and Johnson, 2000] and survive associated lates recovered from onion leaves in 2010 We thank all the members of the Hausbeck Lab for with host debris or alone for up to 8 years in and maintained in long-term storage in the their valuable help; special thanks to A. Worth and tomato fields (Dillard and Cobb, 1998). Hausbeck laboratory culture collection were J. Munoz for guidance with statistical analysis assistance. About 40 onion cultivars are available to used as inoculum. The Michigan C. coccodes 1Former Graduate Research Assistant. Michigan growers from various seed sup- isolates 7–1–1–3 (Newaygo Co.), 8–1–1–1 2Professor. pliers. Some of these cultivars offer resistance (Ottawa Co.), 24–1–1–2 (Ionia Co., NRRL 3Corresponding author. E-mail: hausbec1@msu. to pink root incited by Setophoma terrestris accession number 62808), 31–1–2–2 (Calhoun edu. (H.N. Hansen) Gruyter, Aveskamp, & Verk- Co.), 34–1–6–1 (Kent Co.), and 38–1–3–1 916 HORTSCIENCE VOL. 53(7) JULY 2018 | BREEDING,CULTIVARS,ROOTSTOCKS, AND GERMPLASM RESOURCES (Eaton Co., NRRL accession number 62809) rinsed three times with distilled water, and cultivars (Table 2). The values for these two were obtained from infected and symptomatic allowed to air dry for 1 h. Isolations were cultivars were significantly different from foliage of onions. conducted on 25% strength PDA and cultures each other in 2012, with ‘Highlander’ having Isolates were transferred from long-term were incubated at 22 ± 2 °C for 14 d under the highest SAUDPC value, whereas in 2011, storage onto 50% strength potato dextrose continuous light. their mean SAUDPC values were similar agar (PDA) and incubated at 22 ± 2 °C for 7 d. Statistical analysis. Final disease inci- (Table 2). A total of 120 plates (20 plates per isolate) dence was analyzed using a generalized lin- After plating, C. coccodes colonies de- with at least 70-mm-diameter fungal growth ear model with a Logit link function and veloped from foliar lesions 5 d after iso- was blended with 500 mL 0.001% tween in binomial distribution. Incidence and sever- lations were conducted, and microsclerotia water and strained through a 19-L paint ity values were used to calculate the area were observed 14 d later. Among cultivars, strainer. This process was repeated until all under the disease progress curve (AUDPC); microsclerotia were not evident on onion 120 fungal plates were used. A total of 25 L IAUDPC and SAUDPC for incidence and roots at the time of field collection. After of inoculum was prepared per trial. The severity, respectively, and yield was ana- incubating onion root isolations for 2 weeks, conidial suspension was adjusted to 2 · 105 lyzed using the PROC MIXED and PROC microsclerotia were observed on cultivars conidia/mL (Rodríguez-Salamanca et al., GLIMMIX procedure of the SAS statistical Bradley (15% of the roots), Marco (15%), 2018) and placed in plastic carboys (Nalgene, analysis software (SAS Institute, Inc., Cary, Livingston (10%), Stanley (10%), Vespucci Rochester, NY).