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New Variants of Verticillium Dahliae Causing Sunflower Leaf Mottle and Wilt in Argentina

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New Variants of Verticillium Dahliae Causing Sunflower Leaf Mottle and Wilt in Argentina Journal of Plant Pathology (2017), 99 (2), 445-451 Edizioni ETS Pisa, 2017 445 NEW VARIANTS OF VERTICILLIUM DAHLIAE CAUSING SUNFLOWER LEAF MOTTLE AND WILT IN ARGENTINA G.E. Clemente1, M.E. Bazzalo2 and A.R. Escande1 1 FCA, UNMdP (Unidad Integrada Balcarce). Ruta 226 Km 73.5, (7620) Balcarce, Buenos Aires, Argentina 2 Advanta Semillas SAIC, Balcarce Research Station. Ruta 226 Km 60.5, (7620) Balcarce, Buenos Aires, Argentina SUMMARY INTRODUCTION The sunflower leaf mottle and wilt caused by Verticil- Argentina is a major sunflower producer in the world, lium dahlie Kleb. is a major disease of the crop. The popu- with an annual crop acreage of approximately 2.5 million lations of V. dahliae are variable and physiological races of ha in the last decade (Gutiérrez et al., 2012). Leaf mottle the pathogen have been reported in lettuce, pepper, spin- and wilt caused by Verticillium dahlie Kleb. has been re- ach, sunflower and tomato. The classification of V. dahliae ported as the most important sunflower disease in Ar- isolates based on their pathogenicity in differential sun- gentina and is endemic in the south of the province of flower genotypes to determine races of the pathogen gives Buenos Aires (Pereyra and Escande, 1994). The disease is useful information for growers and breeding programmes. also important in Canada, France, Germany, United King- Two new V. dahliae races causing sunflower leaf mottle dom and USA (Alabouvette and Bremeersch, 1975; Gulya, and wilt in sunflower hybrids previously known as resis- 2007; Alkher et al., 2009; Ganssmann, 2009). Sunflower tant were recognized. The sunflower inbred lines ADV29 yield losses of up to 30% have been reported in individual and ADV53 allowed to differentiate specific pathogenic- fields and the disease also reduces the oil content of grains ity patterns. One isolate that affected both genotypes was (Creus et al., 2007). Disease management is based on the postulated as race VArg3, and another group that did not use of no tillage and genetic resistance and currently 70% cause disease on either genotype was described as race of commercial hybrids are considered resistant (Quiroz et VArg4. Sunflower genotypes showing inverse differential al., 2008). reactions to races VArg3 and VArg4 were not found. How- Little is known about the sunflower resistance gene de- ever, the observed pathogenicity patterns could be consid- ployment in the region. One report by Bertero de Romano ered a phenotypic marker useful to identify the V. dahliae and Vázquez (1982) showed the susceptibility of the in- races VArg3 and VArg4 in monitoring studies. The current bred line HA89 (United States Department of Agriculture, presence of four races of V. dahliae affecting sunflower in USDA, USA) in some Argentinian regions. Two decades Argentina is discussed. later, the presence of V. dahliae races affecting sunflower was reported in experiments performed with commercial Keywords: genotypes, breeding, differential lines, resis- hybrids rather than sunflower inbred lines (Quiroz et al., tance, pathogen variability. 2001). The pathogenicity of another set of V. dahliae iso- lates was analysed on a set of two inbred lines (ADV29 and ADV53, Advanta Semilas, SAIC, Balcarce, Argentina) by Galella et al. (2004). Two races of V. dahliae were detected (VArg1 and VArg2) in different sunflower growing areas. The inbred line ADV29 was resistant to race VArg1, iden- tified as prevalent in Argentina, and susceptible to race VArg2. The inbred line ADV53 showed the inverse resis- tance pattern, being susceptible to race VArg1 and resis- tant to race VArg2. Evidence of variability of the V. dahliae population in Argentina was found based on DNA analysis by restric- tion fragment length polymorphism (RFLP) (Otero et al., 2004). Another way to describe the variability of V. dahliae populations is the Vegetative Compatibility Group (VCG) classification. Fungal strains that anastomose and form heterokaryons with one another are considered to be Corresponding author: G.E. Clemente vegetatively compatible and are assigned to the same group E-mail: [email protected] (Joaquim and Rowe, 1990). Markell et al. (2012) performed 446 Sunflower leaf mottle: races of Verticillium dahliae Journal of Plant Pathology (2017), 99 (2), 445-451 Table 1. Verticillium dahliae isolates and reference strains, pathogenic to sunflower, included in this study. Isolate Locality Geographic origin Fungal collection Collection year AND Andant center west of Buenos Aires province, Argentina. Plant Pathology, UIB1. 2001 ASC Hilario Ascasubi south of Buenos Aires province, Argentina. Plant Pathology, UIB. 2012 BOQ Belloq south east of Buenos Aires province, Argentina. Plant Pathology, UIB. 2011 COL Colón north west of Buenos Aires province, Argentina. Plant Pathology, UIB. 2001 PIE Pieres south east of Buenos Aires province, Argentina. Plant Pathology, UIB. 2011 VArg1 2 Orense south east of Buenos Aires province, Argentina. Plant Pathology, AS SAIC3. 2001 VArg24 Energía south east of Buenos Aires province, Argentina. Plant Pathology, AS SAIC. 2001 VB05 Balcarce south east of Buenos Aires province, Argentina. Plant Pathology, AS SAIC. 2005 VGA Villalonga south of Buenos Aires province, Argentina. Plant Pathology, UIB. 2011 VUSA5 Fargo North Dakota, USA. Plant Pathology, AS SAIC. 2003 1 UIB: Unidad Integrada Balcarce, FCA (UNMdP)-EEA INTA, Balcarce, Buenos Aires, Argentina. 2 and 4 Used in this study as reference strains of races VArg1 and VArg2 of V. dahliae, respectively, reported by Galella et al. (2004). 3 AS SAIC: Advanta Semillas SAIC, Balcarce Research Station (Balcarce, Buenos Aires, Argentina). 5 Used in this study as a reference strain of V. dahliae for molecular identification of Argentinean V. dahliae isolates. a VCG classification of Argentinian V. dahliae isolates ob- arrangement of microsclerotia on SPT medium (Soil tained from sunflower, reporting the presence of groups Pectate Tergitol agar; Kantzes, 1980) and by polymerase 1B, 2B, 4A, 4B and 6. chain reaction (PCR) with primers reported by Nazar et al. The classification of V. dahliae isolates based on their (1991). The strain VUSA was used as a V. dahliae reference pathogenicity in differential sunflower genotypes and the strain to check the identity of the Argentinean isolates by determination of races of the pathogen give useful infor- PCR tests. The V. dahliae isolates were grown in flasks mation for growers and breeding programmes. The objec- containing Malt Extract Broth (Raper and Thom, 1949) tive of this research was to analyze the pathogenicity of for 7 days in darkness at 25 ± 2°C, with a 250 rpm rotation V. dahliae isolates affecting sunflower hybrids previously speed. The mixture of V. dahliae conidia and mycelium known as resistant on differential sunflower inbred lines was filtered through cheesecloth, washed with sterilized to define races of the pathogen in the province of Buenos distilled water twice, and grounded with a pestle and mor- Aires, Argentina. tar containing liquid nitrogen. Total DNA was extracted by the Cenis (1992) procedure. PCR amplifications were performed in a total volume of 25 μl PCR reaction mixture MATERIALS AND METHODS (1× PCR buffer, 1.5 mM MgCl2, 0.2 mM of each dNTP, 0.5 μM of each primer, 2 U of Taq DNA polymerase, 0.01- Fungal isolates and reference strains. Seven V. dahliae 0.05 μg of DNA and ultrapure water). As a negative con- isolates from plants with leaf mottle of hybrids previously trol, a reaction with 1 μl of sterilized ultrapure water was known as resistant, growing in areas of the Buenos Aires included. The amplification was performed in a program- Province, Argentina, were characterized in this study (Ta- mable thermocycler Eppendorf Mastercycler® (Eppendorf ble 1). The isolates were obtained from portions of petioles AG, Hamburg, Germany). The PCR protocol consisted of and piths of sunflower plants colonized by V. dahliae and 10 min at 94°C, 30 cycles of 1 min at 94°C, 1 min at 55°C cultured on homemade Potato Dextrose Agar (PDA). Fun- and 1 min at 72°C, and a final extension for 10 min at gal colonies were purified in two steps: i) by sub-culturing 72°C. The amplification products were analysed after frac- hyphal tips on PDA and ii) by monoconidial cultures ac- tionation by agarose gel (2%) electrophoresis and stained cording to Singleton et al. (1993). Only isolates of proved with a 0.5 mg/ml ethidium bromide solution (Sharp et al., pathogenicity in the susceptible cultivar Cauquén, tested 1973), rinsed with distilled water and visualized with a UV as described below, were included in this study. Reference transilluminator (UVP, Upland, Canada; 302 nm). strains VArg1, VArg2 (Galella et al., 2004) and VUSA (Fargo, ND, USA) were also included (Table1). V. dahliae V. dahliae inoculum production. Brown rice grains isolates and reference strains were kept in sterilized brown were moistened with distilled water (100:45, w:v, g:ml) and rice grains colonized by microsclerotia at room tempera- sterilized by autoclaving (121°C, 1 atm, 15 min). Isolates ture or under refrigeration (4 to 7°C). were grown on PDA plates for 7 days (25 ± 4°C, darkness). PDA plugs colonized by V. dahliae were taken from the Isolates identification. The V. dahliae isolates were margins of colonies and transferred to flasks containing identified according to the taxonomic reports for the spe- sterilized brown rice grains. Cultures were grown for 15 cies (Smith, 1965; Hawksworth and Talboys, 1970). The days (25 ± 4°C, darkness). Distilled water was added to isolates identities were verified on the basis of colony mor- collect conidia and the suspension was filtered through phology, conidiophore formation, conidial production, cheesecloth to discard mycelia. Conidia were counted with Journal of Plant Pathology (2017), 99 (2), 445-451 Clemente et al. 447 Table 2. Pathogenicity of Verticillium dahliae isolates AND, ASC, BOQ, COL, PIE, VB05 and VGA. Severity of V. dahliae sunflower leaf mottle and wilt V.
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