Spotlight on Lettuce Downy Mildew Spraying Fields with Metalaxyl Based Fungicides (Particularly When Metalaxyl-Insensitive Isolates Drive the Epidemics)

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Spotlight on Lettuce Downy Mildew Spraying Fields with Metalaxyl Based Fungicides (Particularly When Metalaxyl-Insensitive Isolates Drive the Epidemics)

Plant Health Services 2015 Fall Newsletter 3 information unveils a colossal health hazard associated with downy mildew infection in lettuce, and urges the development of efficient disease control strategies. The most effective method of controlling LDM is the development of resistant lettuce cultivars; breeding resistance into commercial lettuce takes time and foresight, but is more economically sustainable and effective than spraying fields with metalaxyl based fungicides (particularly Spotlight on Lettuce Downy Mildew when metalaxyl-insensitive isolates drive the epidemics). Over 30 single dominant genes (Dm genes) that confer Lettuce, Lactuca sativa L., is a booming industry with a multi- resistance to downy mildew have been identified (3). billion dollar production value in the US. But as is the case However, single Dm-gene based resistance has not been durable because B. lactucae rapidly evolves to break the with all commercial crops, lettuce is susceptible to a variety of plant pathogens that threaten crop viability. Today we will resistance of cultivated lettuce varieties. The International Bremia Evaluation Board (IBEB) has officially designated 32 take a closer look at Lettuce Downy Mildew (LDM), a widespread disease responsible for crop loss around the (Bl: 1-32) and 8 (CAI-VIII) different B. lactucae races in world. Europe and the US, respectively. Downy mildew in lettuce is caused by the oomycete Bremia Eurofins STA Plant Health Services offers LDM resistance lactucae Regel, an obligate parasite that primarily infects the screening services against California pathotypes CAV, CAVI, foliage of lettuce plants. B. lactucae is particularly infectious CAVII, & CAVIII. In addition, we now offer typing of field because its sporangia can travel long distances via wind isolates to help growers determine which race (known or patterns to new host plants. The pathogen causes yellowing novel) is present in their field. Please contact us for more and angular lesions on lettuce leaves that eventually turn information. brown and wither. These symptoms are often accompanied (1) Koike et al. 2007. Vegetable Diseases. p.302. (2) Simko et al. 2015. BMC by white sporulation on the underside (and sometimes on Microbiol. 15:19. (3) Simko et al. 2015. Phytopatholog y. 105:1220. top) of leaves. The infection can become systemic, which causes discoloration of leaves and the vascular system (1). B. lactucae prefers a moist climate and cool temperatures, this means that overcast coastal regions like Salinas Valley in California are at high risk for infection. Although B. lactucae is not lethal on its own, the infection weakens the plant’s immune system and opens the floodgates for other pathogens to enter. A 2015 study by Ivan Simko and colleagues at the USDA ARS in Salinas, California showed that the human enteric pathogens Escherichia coli and Salmonella enterica serovar typhimurium thrive in leaf lesions caused by B. lactucae (over a period of 48 hours) (2). This 1. Bremia lactucae sporangiophore bearing sporangia 2. Plant pathologist Laura Miles screening lettuce cultivars for downy mildew resistance RESULTS YOU CAN TRUST Eurofins STA Laboratories, Inc. 7240 Holsclaw Road • Gilroy, CA 95020 • (408) 846-9964 http://www.eurofinsus.com/grapevine-testing .

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Report of a Working Group on Leafy Vegetables: First Meeting
European Cooperative Programme for Plant Genetic Report of a Working Resources ECP GR Group on Leafy Vegetables First Meeting, 13-14 October 2005, Olomouc, Czech Republic L. Maggioni, A. Lebeda, I. Boukema and E. Lipman, compilers IPGRI and INIBAP operate under the name Bioversity International Supported by the CGIAR European Cooperative Programme for Plant Genetic Report of a Working Resources ECP GR Group on Leafy Vegetables First Meeting, 13-14 October 2005, Olomouc, Czech Republic L. Maggioni, A. Lebeda, I. Boukema and E. Lipman, compilers ii REPORT OF A WORKING GROUP ON LEAFY VEGETABLES: FIRST MEETING Bioversity International is an independent international scientific organization that seeks to improve the well- being of present and future generations of people by enhancing conservation and the deployment of agricultural biodiversity on farms and in forests. It is one of 15 centres supported by the Consultative Group on International Agricultural Research (CGIAR), an association of public and private members who support efforts to mobilize cutting-edge science to reduce hunger and poverty, improve human nutrition and health, and protect the environment. Bioversity has its headquarters in Maccarese, near Rome, Italy, with offices in more than 20 other countries worldwide. The Institute operates through four programmes: Diversity for Livelihoods, Understanding and Managing Biodiversity, Global Partnerships, and Commodities for Livelihoods. The international status of Bioversity is conferred under an Establishment Agreement which, by January 2008, had been signed by the Governments of Algeria, Australia, Belgium, Benin, Bolivia, Brazil, Burkina Faso, Cameroon, Chile, China, Congo, Costa Rica, Côte d’Ivoire, Cyprus, Czech Republic, Denmark, Ecuador, Egypt, Ethiopia, Ghana, Greece, Guinea, Hungary, India, Indonesia, Iran, Israel, Italy, Jordan, Kenya, Malaysia, Mali, Mauritania, Morocco, Norway, Oman, Pakistan, Panama, Peru, Poland, Portugal, Romania, Russia, Senegal, Slovakia, Sudan, Switzerland, Syria, Tunisia, Turkey, Uganda and Ukraine.
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Effector Identification in the Lettuce Downy Mildew Bremia Lactucae By
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Bremia Lactucae)
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