Reactions of Canadian short-season soybean cultivars to three races

SHORT COMMUNICATION

Reactions of Canadian short-season soybean cultivars to three races of Phytophthora sojae S. Z. Zhang1,2, A. G. Xue2,5, J. X. Zhang2, E. Cober2, T. R. Anderson3, V. Poysa3, and I. Rajcan4 1

Soybean Research Institute, Key Laboratory of Soybean Biology of Chinese Education Ministry, Northeast Agricultural University, Harbin 150030, China; 2Eastern Cereal and Oilseed Research Centre, Agriculture and Agri-Food Canada, Ottawa, Ontario, Canada K1A 0C6; 3Greenhouse and Processing Crops Research Centre, Agriculture and Agri-Food Canada, Harrow, Ontario, Canada NOR 1GO; and 4Department of Plant Agriculture, University of Guelph, Guelph, Ontario, Canada N1G 2W1. Received 27 February 2009, accepted 23 October 2009. Zhang, S. Z., Xue, A. G., Zhang, J. X., Cober, E., Anderson, T. R., Poysa, V. and Rajcan, I. 2010. Reactions of Canadian short-season soybean cultivars to three races of Phytophthora sojae. Can. J. Plant Sci. 90: 207
210. Of 87 short-season soybean cultivars evaluated for reactions to three races (1, 3, and 5) of Phytophthora sojae Kaufmann and Gerdemann, 29 showed resistance to at least one of the three races. These resistant sources may be used for pyramiding Rps genes and deployment of P. sojae resistant soybean cultivars in Canada. Key words: Soybean, Glycine max, phytophthora root and stem rot, Phytophthora sojae Zhang, S. Z., Xue, A. G., Zhang, J. X., Cober, E., Anderson, T. R., Poysa, V. et Rajcan, I. 2010. Re´action des cultivars de soja a` cycle court canadiens a` trois races de Phytophthora sojae. Can. J. Plant Sci. 90: 207
210. Vingt-neuf des 87 cultivars de soja a` cycle court e´value´s pour leur re´action a` trois races (1, 3 et 5) de Phytophthora sojae (Kaufmann and Gerdemann) re´sistaient a` au moins une des races. Ces sources de re´sistance pourraient servir a` cumuler les ge`nes Rps et permettre le de´ploiement de cultivars de soja re´sistant a` P. sojae au Canada. Mots cle´s: Soja, Glycine max, pourridie´ scle´rotique duˆ a` Phytophthora, Phytophthora sojae

in Canada. Phytophthora root and stem rot was initially found in Ontario in 1954 (Hilderbrand 1959), but with the increased frequency of soybean production in crop rotations, it has become a predominant disease, spreading to all soybean production regions of Canada (Anderson and Tenuta 2003). The disease has been managed by the use of resistant cultivars, primarily with Rps1a, Rps1c, or Rps1k resistance genes, which provide resistance to Race 1, the predominant P. sojae race in Ontario from 1965 to 1973 (Anderson 1980). Several new races of P. sojae including races 3, 4, 5, 6, 7, 8, 9, 13, and 21 have been reported (Anderson 1980; Anderson and Buzzell 1992) and the disease has become more severe in Ontario and Quebec in recent years (Anderson and Tenuta 2003). A disease survey in Ontario in 2008 found that phytophthora root and stem rot was a major disease of soybean in central and eastern Ontario and western Quebec, where most of the short-season soybean is grown (Xue et al., unpublished data). There are more than 100 short-season soybean cultivars registered for commercial production in Canada. Although one of the major priorities of soybean breeding in Canada has been the improvement of disease resistance, particularly phytophthora resistance, the genetic

Phytophthora root and stem rot, caused by Phytophthora sojae Kaufmann and Gerdemann, is a destructive disease of soybean [Glycine max (L.) Merr.] worldwide (Wrather et al.1997). The disease can attack soybean plants at any stage of plant development, and commonly reduces yield by 10
40% (Anderson and Tenuta 2003). Pathogenic variation in P. sojae was first reported in 1958 (Kaufman and Gerdemann 1958), and to date at least 55 races have been identified based on their differential reactions to 13 host resistance alleles at seven loci (Leitz et al. 2000). Although a large number of physiologic races of P. sojae exist and new virulent races may develop in response to the release of resistant cultivars, the use of genetic resistance still remains the most effective strategy to reduce losses caused by the disease (Dorrance et al. 2008). Soybean has been grown as a cash crop in southwest Ontario since early 1940s, and to date the production has expanded to eastern Ontario, Quebec, and Manitoba, with the total area of annual production of 1.2 million ha 5

To whom correspondence should be addressed (e-mail: [email protected]). 207

208 CANADIAN JOURNAL OF PLANT SCIENCE

basis of resistance to phytophthora root and stem rot in most Canadian soybean cultivars has not been determined. The objective of this study was to evaluate 87 short-season soybean cultivars released in Canada for their reactions to three P. sojae races (races 1, 3, 5) common in Ontario. Resistant cultivars identified from this study could be used for future cultivar development for Canada and other short-season soybean production regions in the world. The three single zoospore P. sojae isolates, PS6, PS17, and PS44, representing races 1, 3, and 5, respectively, used in this study were isolated from diseased soybean plants in 2008. Races of these isolates were confirmed by challenging them on a set of eight differential lines each containing a single resistance Rps gene and the universal suscept Williams (rpsrps). The differential set included L75-6141 (Rps1a), L77-1863 (Rps1b), L75-3735 (Rps1c), PI103091 (Rps1d), Williams 82 (Rps1k), L83-570 (Rps3a), L89-1581 (Rps6), and L93-3258 (Rps7). The virulence formulae of the three P. sojae isolates in response to the eight differentials were rps7, rps1a rps7, and rps1arps1crps6rps7, confirming that PS6 was race 1, PS17 was race 3, and PS44 was race 5 (Anderson and Buzzell 1992; Dorrance et al. 2008). The P. sojae isolates were stored by transferring 5-mm mycelium plugs containing oospores to a sterilized solution of 10% glycerol in a cryovial. The cryovials were kept in 808C overnight before placing into liquid nitrogen. Before each inoculation, the pathogen isolates were brought to room temperature and immediately put in a warm water bath (308C) to avoid the formation of ice crystals. Inoculum was prepared by growing each P. sojae isolate on V8 juice agar in a 9-cm Petri dish at 258C for 7 d. The pathogen cultures were maintained on V8 juice agar and transferred every 2-mo during the course of this study. Eighty-seven short-season soybean cultivars (Maturity Groups I to 000) were evaluated for reactions to the three P. sojae isolates. These cultivars were 0800RR, 9004, 9063, 90A01, AC 0883, AC 2001, AC Albatros, AC Brant, AC Bravor, AC Colibri, AC Colombe, AC Cormoran, AC Glengarry, AC Harmony, AC Hercule, AC Orford, AC Pinson, AC Proteina, AC Proteus, Accord, Acme, Alta, Renfrew, Altona, Beechwood, Canatto, Capital, CeryxRR, Chikala, Comet, Crest, DH 3604, Dundas, Electron, Evans, Faucon, Flambeau, Heron, Kabott, Kamichis, Lanark, Mandarin, Maple Amber, Maple Arrow Brown, Maple Arrow, Maple Belle, Maple Donovan, Maple Glen, Maple Isle, Maple Presto Brown, Maple Presto, Maple Ridge Brown, Maple Ridge, McCall, Medallion, Merit, Micron, Montcalm, Morsoy, Nattawa, Nattosan, OAC 01-26, OAC Ayton, OAC Gretna, OAC Hanover, OAC Prudeme, OAC Raptor, OAC Wallace, OT03-10, OT03-12, OT04-11, OT04-13, OT05-15, OT05-17, OT06-13, OT06-17, OT06-22, OT0623, Pagoda, Portage, PS 44, RD 714, Rodeo, Roland, T2653, TNS, and Vansoy. Seeds of these cultivars were obtained from four public and private soybean breeding

and pathology programs in Canada in 2008. The 87 cultivars were each grown in four replicates in 12-cmdiameter plastic pots containing a sterilized soil:peat: perlite mixture (1:1:1) with five plants per pot in growth chambers at 258C day and 208C night temperature with a 16-h photoperiod at a light intensity of 360 mmol m 2 s 2. Plants were watered twice weekly from the bottom of the pot. The potting mixture contained sufficient nutrients to support healthy plant growth for the course of the experiments. Plants were inoculated using the hypocotyl wound inoculation technique described by Kaufmann and Gerdemann (1958) at the first-node stage, which occurred 7 d after planting. Seedlings were slightly incised with a blade along the hypocotyls and a weft (10 10 mm) of aerial mycelium was obtained from the margin of a 7-d-old P. sojae culture on V8 juice agar was inserted into the longitudinal wound. After inoculation, the plants were placed in a mist chamber with 100% relative humidity at 248C with 12-h light for 3 d, and then returned to the growth chambers. The cultivar reaction to each race was determined with five plants per pot and four replicated pots for each cultivar and isolate combination in each experiment. The replicated pots of each cultivar within an experiment were arranged in a complete randomized design and the experiment was conducted twice. In each experiment, four pots of soybean cultivar Williams (rpsrps), which has no resistance genes and is susceptible to all known P. sojae races, were wounded and inoculated with each of the three P. sojae races in the same manner, and four pots of Williams were wounded and inoculated with V8 Juice agar. These pots were included as checks to verify the suitability of environmental conditions for infection and disease development and the existence of possible extraneous airborne inoculum, respectively. The number of dead plants was determined for each test cultivar 5 d after the inoculation and cultivar responses to each race were classified as resistant, intermediate, and susceptible reactions, based on mortality levels of 525, 26
50, and 50%, respectively. The resistance scale was similar to that described by Dorrance et al. (2008) for P. sojae race identification. Williams plants that were wounded but inoculated with V8 juice agar without the pathogen did not show disease symptoms and grew normally during the course of the experiment, while Williams plants inoculated with each of the Phytophthora isolates died within 72 h after inoculation, suggesting that the environmental conditions were appropriate for the disease infection and development. The percentage of mortality for the 87 soybean cultivars to each of the three P. sojae races in both experiments ranged from 0 to 100%. Based on percentage of plant mortality averaged over the two experiments, 29 cultivars were resistant (525% mortality) to at least one of the three races (Table 1). Of the resistant cultivars, AC Brant, AC Orford, Beechwood, Maple Arrow, Maple Donovan, and OAC Gretna were resistant to all

ZHANG ET AL. * RESISTANCE TO PHYTOPHTHORA SOJAE IN SOYBEAN Table 1. List of 29 short-season soybean cultivars that showed resistance (525% of seedling died) to at least one of the three Phytophthora sojae races tested Seedling mortality (%)z Cultivar AC Pinson Accord OAC 01
26 OAC Ayton OAC Wallace 90A01 AC Proteina AC Proteus Canatto Kamichis Maple Arrow Brown Merit Nattosan OT 05
15 PS44 RD714 AC Bravor Alta Electron Evans Maple Belle Maple Presto Brown Madallion AC Brant AC Orford Beechwood Maple Arrow Maple Donovan OAC Gretna

Race 1

Race 3

Race5

23 0 100 100 55 46 56 69 56 44 86 59 33 100 33 87 0 25 24 22 0 0 41 0 24 0 0 24 0

100 100 0 0 0 50 94 94 50 90 76 69 88 82 29 94 29 75 41 54 60 77 0 0 18 13 15 25 0

77 100 100 100 100 0 20 0 25 13 0 4 5 0 0 11 0 25 0 5 0 0 5 0 0 5 0 0 0

Resistance to Race 1 Race 1 Race 3 Race 3 Race 3 Race 5 Race 5 Race 5 Race 5 Race 5 Race 5 Race 5 Race 5 Race 5 Race 5 Race 5 Races 1, Races 1, Races 1, Races 1, Races 1, Races 1, Races 3, Races 1, Races 1, Races 1, Races 1, Races 1, Races 1,

5 5 5 5 5 5 5 3, 3, 3, 3, 3, 3,

5 5 5 5 5 5

z

Values are the average of two experiments, 20 plants in FOUR replicate pots of each experiment.

three races; AC Bravor, Alta, Electron, Evans, Maple Belle, and Maple Presto Brown were resistant to races 1 and 5; Medallion was resistant to races 3 and 5; and 90A01, AC Pinson, AC Proteina, AC Proteus, Accord, Canatto, Kamichis, Maple Arrow Brown, Merit, Nattosan, OAC 01-26, OAC Ayton, OAC Wallace, OT05-15, PS 44, and RD 714 were resistant to only one of the three P. sojae races. The intermediate plant response was observed for 15 cultivars in 19 cultivar and race combinations. AC Hercule was the only cultivar showing the intermediate reaction to all three P. sojae races, suggesting that this cultivar may have strong partial resistance to P. sojae. Partial resistance is characterized as incomplete resistance and it is believed to be controlled polygenically and may be more durable for phytophthora resistance in soybean (Dorrance et al. 2008; Mideros et al. 2007). These cultivars have not been reported previously to possess resistance to phytophthora root and stem rot and may be used in resistance breeding for development of new soybean cultivars in Canada. It is worth mentioning that several lines with self colored testae, natural mutatations from cultivars with yellow testae, showed different reactions to the three

209

P. sojae races from their mother cultivars. For instance, Maple Arrow was resistant to all three P. sojae races while it’s mutant Maple Arrow Brown was resistant to race 5 only. Maple Presto was susceptible to all three races but it’s mutant Maple Presto Brown showed a resistance response to races 1 and 5. It is not know if further mutations, beyond the testa color, affecting phytophthora reactions are present in these self-colored seed lines. All Canadian commercial soybean cultivars have yellow testae that lack pigmentation. Further studies are needed to verify the roles and importance of testa color in soybean cultivar reactions to P. sojae races. Phytophthora root and stem rot is best controlled by planting disease-resistant cultivars and the importance of incorporating P. sojae resistance in soybean has been recognized by breeding programs in Canada for more than 50 yr. The results of this study demonstrated that a number of sources of resistance to P. sojae are available in short-season soybean, and these should be suitable for use in breeding programs in the colder regions of Canada and the world. However, due to the highly variable nature of P. sojae reported in Canada (Anderson 1980; Anderson and Buzzell 1992), preference should be given to the use of germplasm with high level of partial resistance. The race-specific resistance exhibited by the 29 cultivars is likely controlled by a specific gene(s), and may be overcome when the appropriate virulence gene(s) are selected in the pathogen populations. Cultivars with high levels of incomplete resistance, such as AC Hercule, may be more desirable as sources of resistance for soybean breeding programs dealing with P. sojae populations in Canada. Although the Canadian soybean breeding programs have been relatively successful in breeding cultivars with race-specific resistance to P. sojae, as demonstrated by identification of 29 cultivars resistant to one to three common races in Canada in the present study, little effort has been reported on the integration of racespecific resistance and partial resistance. The use of genotypes with race-specific resistance and partial resistance to P. sojae in a breeding program will enable the pyramiding of genes in subsequent generations to give high levels of durable resistance. Further studies are needed on methods of quantifying levels of partial resistance to phytophthora root and stem rot and the host-pathogen relationships by exposing these genotypes with partial resistance to many different P. sojae races. Anderson, T. R. 1980. Incidence of Phytophthora root-rot of soybeans in Essex Co., Ontario in 1979. Can. Plant Dis. Surv. 60: 33
34. Anderson, T. R. and Buzzell, R. I. 1992. Diversity and frequency of races of Phytophthora megasperma f. sp. glycinea in soybean fields in Essex County, Ontario, 1980
1989. Plant Dis. 76: 587
589. Anderson, T. R. and Tenuta, A. 2003. Phytophthora Rot. Pages 155
156 Pages
in K. L. Bailey, B. D. Gossen, R. K. Gugel

210 CANADIAN JOURNAL OF PLANT SCIENCE and R. A. A. Morrall, eds. Diseases of field crops in Canada. Canadian Phytopathological Society. Dorrance, A. E., Berry, S. A., Anderson, T. R. and Meharg, C. 2008. Isolation, storage, pathotype characterization and evaluation of resistance for Phytophthora sojae in soybean. Plant Health Progress. Online. doi: 10.1094/PHP-2008-0118-01-DG. [Online] Available: http://www.plantmanagementnetwork.org/ sub/php/diagnosticguide/2008/soybean/ [2008 Jan. 18]. Hilderbrand, A. 1959. A root and stalk rot of soybeans caused by Phytophthora megasperma Drechsler var. sojae. Can. J. Bot. 37: 927
957. Kaufmann, M. J. and Gerdemann, J. W. 1958. Root and stem rot of soybean caused by Phytophthora sojae. Phytopathology 48: 201
208.

Leitz, R. A., Hartman, G. L., Pedersen, W. L. and Nickell C. D. 2000. Races of Phytophthora sojae on soybean in Illinois. Plant Dis. 84: 487. Mideros, S., Nita, M. and Dorrance, A. E. 2007. Characterization of components of partial resistance, Rps2, and root resistance to Phytophthora sojae in soybean. Phytopathology 97: 655
662. Wrather, J. A., Anderson, T. R., Arsyad, D. M., Gai, J., Ploper, L. D., Porta-Puglia, A., Ram, H. H. and Yorinori, J. T. 1997. Soybean disease loss estimates for the top 10 soybean producing countries in 1994. Plant Dis. 81: 107
110.