Identification of New Bremia Lactucae Races in Lettuce in São Paulo State
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CASTOLDI R; CHARLO HCO; DALPIAN T; MELO DM; BOTELHO AP; BRAZ LT. 2012. Identification of new Bremia lactucae races in lettuce in São Paulo state. Horticultura Brasileira 30: 209-213. Identification of new Bremia lactucae races in lettuce in São Paulo state Renata Castoldi1; Hamilton César de O Charlo2; Tagli Dalpian3; Danilo M Melo1; Adelita P Botelho1; Leila T Braz1 1UNESP-FCAV, Depto Produção Vegetal, Rod. Prof. Paulo Donato Castellane s/n, 14884-900 Jaboticabal-SP; [email protected]; [email protected]; [email protected]; [email protected]; 2IFTM, R João Ribeiro 4000, Mercês, 38064-790 Uberaba- MG; [email protected]; 3CATI, Casa da Agricultura de Ibirá, Av Gabriel Sanches 725, 15860-000 Ibirá-SP; tagli.dalpian@cati. sp.gov.br ABSTRACT RESUMO Lettuce is the most consumed leafy vegetable in Brazil. However, Identificação de novas raças deBremia lactucae em alface no its production has faced increasing difficulties mainly due to the Estado de São Paulo infestation of producing areas with Bremia lactucae, the causing A alface é o grupo de hortaliças folhosas de maior consumo no agent of downy mildew, the worst disease in lettuce. The aim of Brasil. No entanto a dificuldade em produzi-la vem aumentando, this study was to identify B. lactucae races occurring in lettuce principalmente pela infestação das áreas de produção por Bremia producing areas of São Paulo state, during 2008 and 2009. Lettuce leaf lactucae, agente causador do míldio, principal doença da alface. O samples containing B. lactucae sporangia were collected in the major objetivo deste trabalho foi identificar as raças de B. lactucae que lettuce producing areas of São Paulo. Each sample was considered ocorreram nos municípios produtores de alface do Estado de São an isolate. After the multiplication of sporangia in the susceptible Paulo nos anos de 2008 e 2009. Para isso, coletaram-se folhas com cultivar Solaris, with subsequent inoculation in the differentiating esporângios de B. lactucae em municípios produtores de alface, sendo cultivars, the evaluations were performed on the same day of the que cada amostra foi considerada um isolado. Após a multiplicação first sporulation in the susceptible cultivar ‘Cobham Green (DM dos esporângios na cultivar suscetível Solaris, com posterior inocula- 0)’. In 2008 one new B. lactucae code was identified. SPBl:05 was ção nas diferenciadoras, realizaram-se as avaliações, no mesmo dia do the denomination proposed to it. In 2009 one another B. lactucae aparecimento da primeira esporulação na cultivar suscetível ‘Cobham code was identified, that is, 63/63/02/00, whose denomination was Green (DM 0)’. No ano 2008 identificou-se um novo código de B. proposed to be SPBl:06. lactucae em alface, à qual se propôs a denominação de SPBl:05. No ano 2009, outro código de B. lactucae foi identificado (63/63/02/00), ao qual se propôs a denominação de SPBl:06. Keywords: Lactuca sativa L, genes DM, downy mildew, resistance. Palavras-chave: Lactuca sativa, genes DM, míldio, resistência. (Recebido para publicação em 25 de abril de 2011; aceito em 14 de março de 2012) (Received on April 25, 2011; accepted on March 14, 2012) ettuce (Lactuca sativa), a member cities. The lettuce producing areas have which become yellow or necrotic after Lof the Asteraceae family, is a steadily increased in number during the the pathogen sporulation (Van Bruggen plant originating from Asia that was last years. & Scherm, 1997). The disease is usually introduced in Brazil in the XVI century The increment in lettuce production controlled by the application of systemic (Oliveira et al., 2004). Among the also caused increased production fungicides, but the continued use of leafy vegetables, lettuce is the most difficulties, even with more adequate these products, as well as the use of widely consumed in Brazil due to the environmental conditions such as vertical resistance, or environmental fact it is available year-round. In the autumn and winter seasons. There occur modification, though may result in the state of São Paulo, between January an increase of infestation of these areas selection of resistant pathogens which and July 2010, 29,297 tons of lettuce by Bremia lactucae, the causing agent may eventually end up by developing were commercialized, 47.34% of them of downy mildew, which is considered in new races capable of establishing formed by cultivars of the crispy group the worst problem affecting lettuce themselves even in resistant cultivars. So (Agrianual, 2011). production (Yuri et al., 2004). the most economical way of controlling The major lettuce producers are The species B. lactucae (Oomycetes) the disease consists in the use of found in the ‘green belt’ of São Paulo is a biotrophic parasite found in the resistant cultivars. city, such as Mogi das Cruzes, where is living cells of the host plant. This A previous study reported by Braz et located the greatest lettuce cultivation parasite survives only on living lettuce al. (2007), undertaken during 2003 and area (3.4 thousand ha) (IEA, 2010). plants (Michelmore & Ingram, 1982). 2004 in the state of São Paulo, showed Other small areas are also found all over The lesions caused by mildew are of the race SPBl:01 to be the predominant São Paulo state, mainly near the major light green color or slightly chlorotic one. In the same study, the authors Hortic. bras., v. 30, n. 2, abr. - jun. 2012 209 R Castoldi et al. verified the lettuce genes R-17, R-18, Echaporã, Marilia, Botucatu, and Bauru. few sporulating lesions. and R-38 to be capable of conferring Each sample was considered an isolate All the materials showing resistance to the race SPBl:01. More and the number of collected isolates susceptibility (with positive sign), recently, a study carried out in 2006 and during the years of 2008 and 2009, were to a given isolate had their values 2007 showed the existence of three new 35 and 49 were respectively. added within each group (from 1 to 4), races, SPBl:02, SPBl:03, and SPBl:04, The samples were put in plastic resulting in four distinct numbers, each to which the lettuce genes R-17, R-18, bags, identified and stored in thermos one separated by a bar, that identifies R-37, and -38 were verified to confer to be transported to the Plant Breeding the different groups. This numerical resistance (Souza et al., 2011). Laboratory of the Department of Plant sequence was then called “Sextet” Code. In California, USA, four main B. Production, where the sporangia were lactucae pathotypes were found which multiplied in plants of the ‘Solaris’ RESULTS AND DISCUSSION were identified by the determination cultivar, a susceptible one to obtain the of their virulence with the help of necessary amount of sporangia for the In 2008, the results showed the differentiating cultivars (Schettini et differentiation test. existence of four codes of B. lactucae in al., 1991). The next phase consisted in the the lettuce producing regions of São Paulo According to the Plantum (2010), sowing of seeds of the 21 differentiating state, namely 63/63/03/00, 63/63/33/00, the International Bremia Evaluation cultivars in 11 x 11 x 3.5 cm plastic 63/63/51/00, and 63/63/19/00. The Board (IBEB) evaluated several lettuce boxes lined with paper employed for sextet code 63/63/03/00 was the most isolates during 2009 and showed the germination tests. This paper was wet frequent one (48.57% of the isolates) existence of 27 races of B. lactucae in and divided in four equal parts. In each (Table 1). Europe, and the majority of the foci were one of these parts, approximately 40 The sextet code 63/63/03/00 was caused by new races whose importance seeds of each differentiating cultivar reported by Souza et al. (2011) too, was restricted to the local where they were sown and maintained for 15 days at who found it in 2006 in a low level of were found. a temperature of 13ºC and a photoperiod frequency but enough to give origin to of 12 hours, in a seed germinator. After The IBEB notes that although the a new race named SPBl:04. Therefore, that period, the collected isolates were seed companies submit seeds with this race should be a focal point in inoculated according to technique of resistance to the races Bl:1 to Bl:27, lettuce breeding programs, since Illot et al. (1987). The sporangia used this is not totally secure against the its virulence genes were capable of in the procedure were obtained by pathogen, because it provides to the breaking down the resistance of lettuce washing infected tissues of the host producer only temporary protection, genotypes developed by Souza, which is plants after being stirred in distilled as through mutation, the combination resistant only to the race SPBl:01. This water. A suspension containing 5 x 104 of several genes existing in the same race was disseminated very efficiently sporangia/mL was used to be sprayed cultivar may be broken (Plantum NL, since 2006, when it was first reported on the seedlings. 2010). in the county of Bauru. However, two Thus, the aim of this study was to Following the inoculation, the boxes years late, it was found in seven other identify B. lactucae races occurring in were taken back to the germinator and municipalities of São Paulo state in lettuce producing areas of São Paulo kept at 13ºC in darkness for the first 6 addition to Bauru. This fact justifies the state during 2008 and 2009 aiming to hours. After that period, the photoperiod necessity of a constant monitoring of support the lettuce breeding program was adjusted to 12 hours.