Control of bottom rot in hydroponic lettuce, caused by strains of Botrytis cinerea with multiple fungicide resistance

Phytopathologia Mediterranea Firenze University Press www.fupress.com/pm The international journal of the Mediterranean Phytopathological Union Research Paper Citation: M. Chatzidimopoulos, A.C. Pappas (2019) Control of bottom rot in hydroponic lettuce, caused by strains of Botrytis cinerea with multiple fungicide resistance. Phytopathologia Mediterranea 58(3): 507-517. doi: 10.14601/ Phyto-10826 Accepted: July 25, 2019 Published: December 30, 2019 Copyright: © 2019 M. Chatzidimopoulos, A.C. Pappas. This is an open access, peer-reviewed article published by Firenze University Press (http:// www.fupress.com/pm) and distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Control of bottom rot in hydroponic lettuce, caused by strains of Botrytis cinerea with multiple fungicide resistance Michael CHATZIDIMOPOULOS1, Athanassios C. PAPPAS2 1 Department of Agriculture, Crop Production and Rural Environment, Laboratory of Plant Pathology, University of Thessaly, Fitokou Street, 384 46, N. Ionia, Volos, Greece 2 Present address: 17 Bizaniou, 1156 69 Papagos, Greece *Corresponding author: Summary. For two consecutive growing periods, fungicide-resistant Botrytis cinerea strains were detected in high proportions in glasshouse-grown lettuce, but at variable frequencies. Pre-transplanting fungicide sprays applied on two successive occasions reduced disease severity and increased the number of healthy plants without leaving detectable residues above accepted MRLs at harvest. In some instances, the disease was further decreased when pre-transplanting applications were combined with one or two further sprays applied soon after transplanting. The fungicide mixture of fludioxonil + cyprodinil was the most effective against the disease and provided better control of B. cinerea isolates in situ. These treatments gave satisfactory disease control despite the predominance of multi-fungicide resistant B. cinerea populations. Keywords. Fungicides, grey mould, fludioxonil, cyprodinil, chlorothalonil. Competing Interests: The Author(s) declare(s) no conflict of interest. Editor: Jean-Michel Savoie, INRA Villenave d’Ornon, France. INTRODUCTION Bottom rot of butterhead lettuce (Lactuca sativa L.) caused by Botrytis cinerea Pers. :Fr. is the most common disease problem in hydroponic lettuce production in Greece, during the late autumn to early spring period. Infections can start in nurseries and spread systemically (endophytically) in plants, without early visible symptoms (Sowley et al., 2010). Botrytis head rots are less common and, in most cases, follow the appearance of ‘tip burn’ symptoms, due to inadequate transport of calcium into emerging leaves. These rots can be avoided by keeping calcium in balanced nutrient solutions, using cultivars which are less susceptible to ‘tip burn’, and manipulating the environment (Morgan, 1999; 2012). Good ventilation practices reducing excess of moisture combined with application of fungicides give adequate control of infections caused by Botrytis cinerea (Dik and Wubben, 2007). In addition to multi-site fungicides such as thiram, compounds with site-specific modes of action against grey mould in lettuce crops are currently registered in Greece. These include anilinopyrimidines (cyprodinil Phytopathologia Mediterranea 58(3): 507-517, 2019 ISSN 0031-9465 (print) | ISSN 1593-2095 (online) | DOI: 10.14601/Phyto-10826 508 and pyrimethanil), the phenylpyrrole fludioxonil, the succinate dehydrogenase inhibitor (SDHI) boscalid and the quinone outside inhibitor (QoI) pyraclostrobin. Two commercial fungicide formulations with widespread use against B. cinerea in lettuce are Signum® (26.7% boscalid + 6.7% pyraclostrobin; BASF) and Switch® (25% fludioxonil + 37.5% cyprodinil; Syngenta). However, the use of fungicides for B. cinerea control in various crops has been associated with the development of fungicide resistance (Hahn, 2014). High levels of resistance against site-specific fungicides are the result of gene mutations at positions encoding their target sites. For example, the point mutations G143A, H272R, and F412S, which lead to changes in the target proteins CytB, SdhB, and Erg27, confer high resistance of the pathogen to, respectively, the QoI, SDHI, and hydroxyanilide fungicide classes (Leroux, 2007). Multi-drug resistance (MDR) is another mechanism associated with fungicide resistance in B. cinerea. This involves mutations leading to over-expression of efflux transporters such as the ATP-binding cassette (ABC) and the major facilitator superfamily (MFS), allowing weak resistance towards fungicides with unrelated modes of action (Kretschmer et al., 2009). Very often, MDR and specific fungicide resistance types are coupled (Leroch et al., 2013; Fernández-Ortuño et al., 2014; Rupp et al., 2016). The presence of B. cinerea strains with multiple fungicide resistance to all site-specific classes of fungicides have been reported in different parts of the world, especially for small fruits (Weber, 2011; Amiri et al., 2013; Fernández-Ortuño et al., 2014). Recent surveys made on lettuce crops in Greece and Germany have also demonstrated increasing threats from emergence of multiple fungicide resistance in B. cinerea populations (Chatzidimopoulos et al., 2013; Weber and Wichura, 2013). Current trends in agriculture demand fewer chemical applications, while maintaining profitable high-quality production with low pesticide residues. The limited number of registered fungicide formulations against bottom rot of lettuce forces growers to make repeated seasonal sprays with the one fungicide. Some studies have also shown that pesticide residues are detected in greater amounts in leafy vegetables compared to other crops (Skovgaard et al., 2017). Multiple applications may compromise reduced pesticide strategies, which aim to delay the development of resistance and reduce pesticide residues. The present study was undertaken: (i) to evaluate the efficacy and timing of applications with current botryticides against multi-resistant B. cinerea strains; (ii) to detect and measure possible fungicide residues at harvest; and (iii) to determine effects of different compounds against selected resistant isolates of the pathogen in situ. Michael Chatzidimopoulos, Athanassios C. Pappas MATERIALS AND METHODS Host plant material The 2-year experiments were carried out in a commercial lettuce glasshouse located at Krokion, Magnesia, Greece. The glasshouse was surrounded by cereal crops and olive trees, which were unlikely to be sources of B. cinerea inoculum. Pelletized lettuce seeds (Lactuca sativa ‘Penelope’; ‘butterhead’ type, Rijk Zwaan), pre-treated with thiram were used in all tests. Seeding, germination and emergenc (...truncated)