Genetics of Resistance in Lettuce to Races 1 and 2 of Verticillium Dahliae from Different Host Species
Total Page:16
File Type:pdf, Size:1020Kb
Euphytica (2017) 213:20 DOI 10.1007/s10681-016-1813-0 Genetics of resistance in lettuce to races 1 and 2 of Verticillium dahliae from different host species German V. Sandoya . Suraj Gurung . Dylan P. Short . Krishna V. Subbarao . Richard W. Michelmore . Ryan J. Hayes Received: 23 June 2016 / Accepted: 2 December 2016 / Published online: 23 December 2016 Ó Springer Science+Business Media Dordrecht (outside the USA) 2017 Abstract Race 1 resistance against Verticillium originating from hosts other than lettuce. This indi- dahliae in lettuce was originally shown in the cultivar cated that cultivars resistant to race 1 and the breeding La Brillante to be conditioned by a single dominant lines derived from them would also be resistant to race gene (Verticillium resistance 1, Vr1). Multiple, mor- 1 isolates from other hosts; similarly, the partial phologically diverse sources of germplasm have been resistance would be effective against race 1 and 2 identified as resistant to race 1. In this study, allelism isolates from hosts other than lettuce. Nevertheless, tests indicated that resistance in these different lettuce there were specific interactions that warrant further cultivars is closely linked or allelic to the Vr1 gene. study. Although race 1 currently predominates in the The Vr1 gene is defeated by race 2 isolates of V. major lettuce production area of the Salinas Valley, dahliae. Only partial resistance to race 2 isolates is CA, breeding lettuce for resistance to V. dahliae available in a few plant introductions (PIs). Green- should take both races into account. house and field experiments conducted with these PIs demonstrated partial resistance to V. dahliae race 1 as Keywords Breeding Á Disease Á Disease resistance Á well as race 2 isolates from lettuce. Cultivars resistant Diversity Á Genetic Á Host-pathogen interaction Á to race 1 and PIs with partial resistance to race 2 were Lactuca sativa Á Vegetable Á Verticillium wilt challenged with several race 1 and 2 isolates G. V. Sandoya Á R. W. Michelmore The Genome Center and Department of Plant Sciences, S. Gurung University of California, Davis, One Shields Avenue, Sakata Seed of America, Salinas, CA 93907, USA Davis, CA 95616, USA D. P. Short Present Address: Division of Plant and Soil Sciences, West Virginia G. V. Sandoya University, Morgantown, WV 26506, USA Everglades Research Education Center, Horticultural Sciences Department – IFAS, University of Florida, Belle Glade, R. J. Hayes (&) FL 33430, USA National Forage Seed Production Research Center, United States Department of Agriculture, USDA, 3450 SW S. Gurung Á D. P. Short Á K. V. Subbarao Campus Way, Corvallis, OR 97331, USA Department of Plant Pathology, University of California, e-mail: [email protected] Davis, 1636 E Alisal St., Salinas, CA 93905, USA 123 20 Page 2 of 12 Euphytica (2017) 213:20 Introduction single aggressive isolate each of race 1 (VdLs16) and race 2 (VdLs17), Hayes et al. (2007) identified seven Fifty percent of the lettuce consumed in the USA is cultivars from a diversity of lettuce types that were grown in the Salinas Valley of California and is worth completely or highly resistant to race 1 but susceptible more than $1 billion annually (Anonymus 2014). to race 2 (Hayes et al. 2007). Only partial resistance to Verticillium wilt, caused by the soil borne fungus race 2 of Verticillium wilt is known in lettuce (Hayes Verticillium dahliae Kleb., is a destructive disease of et al. 2011b). Plant introductions (PIs) 169511, lettuce in coastal California with the potential to 171674, 204707 and 226641 were shown to express severely reduce lettuce production in the region a lower incidence of Verticillium wilt compared to cv. (Subbarao et al. 1997). Symptoms of the disease Salinas when challenged with either the race 1 isolate include wilting of outer leaves, discoloration of the VdLs16 or race 2 isolate VdLs17 (Gurung et al. 2015; root vascular system, and ultimately plant death. Even Hayes et al. 2011b). though all lettuce types are susceptible, wilting is more The majority of V. dahliae isolates recovered from pronounced and economically damaging in iceberg the Salinas Valley are race 1 (Gurung et al. 2014); lettuce (Vallad et al. 2004). however, extensive crop production with Vr1 carrying Feasible methods for control of Verticillium wilt of cultivars, reduced fumigation, and inadvertent impor- lettuce are limited. Crop rotation is generally not tation of novel isolates could cause shifts in the effective since the pathogen is able to colonize a predominant populations in the future (Atallah et al. diverse range of dicotyledonous crops and weeds 2011; Short et al. 2014). Identifying new resistance (Atallah et al. 2011). This includes crops commonly genes, including among race 1 resistant cultivars (strawberry, artichoke and spinach) or occasionally would broaden the genetic base of resistance (Ye and (tomato, potato, eggplant and pepper) grown in Smith 2008). Additionally, the efficacy of resistance in rotation with lettuce (Bhat and Subbarao 1999). lettuce germplasm when challenged with V. dahliae Fumigation can reduce pathogen levels; however, isolates from diverse crops, particularly those com- the availability of fumigants is decreasing and monly rotated with lettuce, was unknown. As high- pathogen populations may return to pre-fumigation levels of resistance and race non-specific resistance is levels in as few as three lettuce crops (Short et al. generally more valuable, additional information on 2015). isolate specificity would be useful for prioritizing The most sustainable control method is to develop germplasm within current breeding efforts. Therefore and deploy resistant lettuce cultivars (Hayes et al. the objectives of this research were to determine: (1) 2007). There are two characterized races of Verticil- the allelic relationships of resistance in germplasm lium dahliae of lettuce (Vallad et al. 2006). The resistant to race 1 and (2) the effectiveness of resistant heirloom Batavian cultivar (cv.) La Brillante pos- lettuce germplasm against V. dahliae isolates origi- sesses the single dominant gene Verticillium resis- nating from diverse hosts other than lettuce. tance 1(Vr1), which confers complete resistance to race 1 isolates (Hayes et al. 2011c). Isolates that cause disease on Vr1 carrying germplasm are known and are Materials and methods designated as race 2 (Hayes et al. 2011c; Maruthacha- lam et al. 2010). Tomato also has two races of V. Description of experiments dahliae, where the Ve1 resistance gene interacts with the avr1 V. dahliae effector (de Jonge et al. 2012). In a Several trials were conducted in either the greenhouse handful of other crop species a single major gene or field using a diverse range of V. dahliae isolates confers high level resistance to Verticillium wilt (Mert (Table 1). The lettuce cultivars used in testing or as et al. 2005). However in other crops such as potato, parents were previously reported as resistant to race 1 multiple major Verticillium wilt resistance genes have (Hayes et al. 2007) or partially resistant to race 2 been reported (Jansky et al. 2004). (Hayes et al. 2011b). The field trials were grown in a Multiple lettuce accessions and cultivars possess race 1 artificially infested field site at the USDA-ARS resistance to race 1 isolates, though the genetic basis of Station in Salinas, CA using standard procedures for this resistance was unknown in most cases. Using a lettuce production on the Central Coast of California 123 Euphytica (2017) 213:20 Page 3 of 12 20 Table 1 Isolates of Isolate Originating host Geographical origin Racea Verticillium dahliae used in this study along with their VdLs16 Lettuce (Lactuca sativa L.) CA Race 1 hosts and geographic origin CS1616 Artichoke (Cynara scolymus L.) CA Race 1 and race classification based on Short et al. (2014) LE1087 Tomato (Solanum lycopersicum L.) CA Race 1 CL1 Watermelon (Citrullus lanatus L.) CA Race 1 VdLs17 Lettuce (L. sativa L.) CA Race 2 SM1 Eggplant (Solanum melongena L.) CA Race 2 VD57 Mint (Mentha longifolia L.) WA Race 2 CB86.7.2 Potato (Solanum tuberosum L.) WA Race 2 CF40 Pepper (Capsicum frutescens L.) CA Race 2 CF156 Pepper (C. frutescens L.) CA Race 2 303 Spinach (Spinacia oleracea L.) WA Race 2b G2D5 Spinach (S. oleracea L.) WA Race 2 a Short et al. (2014) PD494 Strawberry (Fragaria ananassa L.) CA Race 2 b Determined in this PD410 Strawberry (F. ananassa L.) CA Race 2b research (Ryder 1999; Hayes et al. 2007). In greenhouse and &5 kg of potting mix. The second method of inoc- field trials, the first set were aimed at determining the ulation involved pipetting a 2 9 106 conidia/ml allelism of resistance in cv. La Brillante and five other suspension into each plug-tray cell. The conidia and race 1-resistant cultivars. The second set tested PIs suspension were produced using the methods of that were partially resistant to race 2 and two lettuce Vallad et al. (2006). Control plants for each lettuce isolates (VdLs16 and VdLs17, race 1 and 2 respec- cultivars were mock inoculated with sterile water and tively) under greenhouse conditions and against race 1 grown in a non-replicated block. in field conditions. The third set of were conducted with nine race 1-resistant cultivars plus four race 2 Disease assessment partially resistant PIs against 14 race 1 or race 2 isolates of V. dahliae isolated from diverse hosts. Disease symptoms depend on plant development, and unless otherwise stated, assessments of greenhouse Greenhouse experiments experiments were done when plants began to flower. Disease severity (DS) of each plant was evaluated by Seed germination longitudinally cutting the taproot and examining the leaves and root vascular tissue for symptoms typical of Seeds were germinated in Sunshine No. 4 plug mix V. dahliae. Each plant was rated on a 0 to 5 rating scale, (Sun Gro Horticulture, Canada) in 341 or 200 cell plug where 0 = roots with no discoloration; 1 = 1–25% of trays (each cell was 19 9 19 9 60 mm) and incu- the taproot with vascular discoloration; 2 = 26–50% bated in the dark at 10 °C for approximately 48 h.