Fungal pathogens in pome fruit orchards and causal agents of postharvest decay

Apples and pears (pome fruit) are important deciduous fruit species cultivated on a worldwide scale. Mild and humid climatic conditions favour fungal diseases on pome fruit. Pome fruit may remain for up to 12 months in storage, during which fruit rot diseases may develop. This thesis presents a number of new and emerging postharvest disease on apples and pears, and the important lenticel spot disease of pome fruit, caused by Fibulorhizoctonia psychrophila, in more detail. Typically, the causal pathogens of postharvest diseases infect fruits during the growing season and remain quiescent until disease symptoms occur after several months of storage. Epidemiological knowledge of these diseases is limited. This thesis describes Taqman PCR assays for quantification of N. alba, N. perennans, C. malorum and C. luteo-olivacea in environmental samples. Substrate colonization varied considerably between orchards. The temporal dynamics of these pathogens was followed in apple and pear orchards. Knowledge on population dynamics is essential for the development of preventative measures to reduce risks of fruit infections during the growing season. Fruit tree canker caused by Neonectria ditissima is a serious problem in apple production regions with climates with moderate temperatures and high rainfall throughout the year. A novel method for screening of apple and pear trees at the nursery stage for latent fruit tree canker infections caused by N. ditissima to be used prior to planting in orchards is described. As apple cultivars differ in their levels of susceptibility to N. ditissima, the appropriateness of two resistance parameters were examined. A new parameter, Lesion Growth Rate (LGR), appeared the best with respect to reproducibility and statistical significance. The presented methods can be used to develop strategies for the control of European fruit tree canker. Dead dormant flower buds of pear is a common phenomenon of economic importance in the major pear production areas of Europe. No indication was found that growth regulation can prevent the occurrence of dead flower buds, nor that P. syringae pv. syringae is the causal agent of dead flower buds disease in the Netherlands. We concluded in this thesis that dead flower buds of pear in the Netherlands should be regarded as a fungal disease caused by A. alternata SC and potentially also A. arborescens SC which may be controlled by specific fungicide applications. Finally, it is argued that postharvest diseases should be regarded as complex problems that require multiple interventions at different stages of the disease process in a systems intervention approach for their control. Such approach requires a deep understanding of the epidemiology of the causal agents in the orchard, fruit defense mechanisms, and the molecular biology of host-pathogen interactions in order to develop novel disease control methods.</p

Pesticide Exposure of Residents Living Close to Agricultural Fields in the Netherlands:Protocol for an Observational Study

Background: Application of pesticides in the vicinity of homes has caused concern regarding possible health effects in residents living nearby. However, the high spatiotemporal variation of pesticide levels and lack of knowledge regarding the contribution of exposure routes greatly complicates exposure assessment approaches. Objective: The objective of this paper was to describe the study protocol of a large exposure survey in the Netherlands assessing pesticide exposure of residents living close ( Methods: We performed an observational study involving residents living in the vicinity of agricultural fields and residents living more than 500 m away from any agricultural fields (control subjects). Residential exposures were measured both during a pesticide use period after a specific application and during the nonuse period for 7 and 2 days, respectively. We collected environmental samples (outdoor and indoor air, dust, and garden and field soils) and personal samples (urine and hand wipes). We also collected data on spraying applications as well as on home characteristics, participants' demographics, and food habits via questionnaires and diaries. Environmental samples were analyzed for 46 prioritized pesticides. Urine samples were analyzed for biomarkers of a subset of 5 pesticides. Alongside the field study, and by taking spray events and environmental data into account, we developed a modeling framework to estimate environmental exposure of residents to pesticides. Results: Our study was conducted between 2016 and 2019. We assessed 96 homes and 192 participants, including 7 growers and 28 control subjects. We followed 14 pesticide applications, applying 20 active ingredients. We collected 4416 samples: 1018 air, 445 dust (224 vacuumed floor, 221 doormat), 265 soil (238 garden, 27 fields), 2485 urine, 112 hand wipes, and 91 tank mixtures. Conclusions: To our knowledge, this is the first study on residents' exposure to pesticides addressing all major nondietary exposure sources and routes (air, soil, dust). Our protocol provides insights on used sampling techniques, the wealth of data collected, developed methods, modeling framework, and lessons learned. Resources and data are open for future collaborations on this important topic

Correction to: Latent postharvest pathogens of pome fruit and their management: from single measures to a systems intervention approach

This erratum is published as vendor overlooked many corrections in the original publication. The original article has thus been updated with the corrections.</p

Latent postharvest pathogens of pome fruit and their management: from single measures to a systems intervention approach

Postharvest diseases of pome fruit are typically caused by a wide diversity of fungal pathogens, and the list of confirmed causal agents is still growing. There is considerable knowledge on the epidemiology of wound pathogens, such as Botrytis cinerea and Penicillium expansum. In contrast, knowledge on the occurrence of the different postharvest diseases caused after latent (quiescent) infections during long-term storage and their epidemiology is limited. Well-known pathogens causing postharvest losses after latent infections are Neofabraea spp. and Colletotrichum spp., but in many cases the causal agents that occur in a specific region remain unknown and their control relies on the routine use of fungicide applications. However, due to the growing concern over the use of synthetic fungicides, alternative control measures are highly desired. Over the past years the use of physical treatments, natural compounds, and biocontrol agents have been investigated as alternatives. However, no single method has emerged that can robustly and reliably control postharvest diseases of pome fruit in practice. In this review it is argued to approach latent postharvest diseases as complex problems that require multiple interventions at different stages of the disease process in a systems intervention approach for their control. Such approach requires a deep understanding of the epidemiology of the causal agents in the orchard, fruit defence mechanisms against pathogens, and the molecular biology of host-pathogen interactions in order to develop novel disease control methods in which the deployment of resistant cultivars can be a cornerstone.</p