Category Archives: REVIEW ARTICLE

Ergot of cereals: Toxins, pathogens and management

Posted on 13 April 2024 by

This review article focuses on recent progress in understanding the toxins, pathogens and management of ergot, an important disease of cereals that affects food safety.

Abstract

Ergot is a fungal disease of many plants but is perhaps most commonly associated with domesticated grasses or cereals, such as rye, wheat, barley, oat, sorghum, millet, maize and rice. Ergot is of historical significance, having been reported for several millennia, but is also of concern in modern agricultural production systems. Caused by many different species within the genus Claviceps, the fungi cause the production of sclerotia, which are typically dark in colour, in place of healthy grain. The sclerotia contain toxins that can make the grain unsafe for consumption by humans or livestock. Ergot can be managed both preharvest as well as postharvest to minimize the presence of sclerotia and their associated toxins in food and feed systems. In this review, we provide a detailed update on our current knowledge of ergot on cereals, with a focus on recent advances in our understanding of fungal toxins and their regulation, pathogen biology and disease management.

The coffee leaf rust pandemic: An ever‐present danger to coffee production

Posted on 13 March 2024 by nAthina Koutouleas, nDavid B. Collinge, nEric Boan

The history of the fungal disease coffee leaf rust is highlighted along with recent epidemics and future scenarios. Possible causes of these outbreaks are also examined.

Abstract

Coffee leaf rust (CLR) is caused by the biotrophic pathogenic fungus Hemileia vastatrix. Despite being the most researched coffee disease, mysteries still exist relating to its epidemiology and biology. The objective of this work is to highlight past and present events concerning this prominent coffee disease. We start with an historical overview of the homeland of Coffea arabica, the Afromontane forest of south-west Ethiopia, and then follow its journey across the globe linked to colonial trade and power struggles. We report the relevance of CLR to coffee production today, with a focus on the Americas and summarize unproven hypotheses in relation to the cause of recent epidemics. We present an original hypothesis concerning the first major outbreak occurring in 1869 in Ceylon (Sri Lanka), based on geopolitical connections to global trade. We review old and new options for management of the disease. The likelihood of a yet undetected alternate host of H. vastatrix is also considered as an additional piece of the epidemiological puzzle. Finally, we reflect on the interactions between H. vastatrix and a changing climate. By better understanding past events, linked to CLR, we may be better prepared for future outbreaks.

An emergent plant‐parasitic nematode in Brazil: Aphelenchoides besseyi. Current status and research perspectives

Posted on 13 March 2024 by

We review the biology, life cycle, host range and management solutions of an emergent pathogen in Brazil, all in the context of the landmark events leading to the rise of Aphelenchoides besseyi (Created using Biorender).

Abstract

Aphelenchoides besseyi is an emerging and yet overlooked plant parasite of many economically important crops, including cotton, soybean and common bean. It presents an economic risk to these crops in several countries, notably in Brazil. Although first reported infecting strawberries in the United States as early as 1942, it was only identified to be the causal agent of green stem and foliar retention (GSFR) disease in Brazil in 2017. Currently, there are no chemical nematicides registered in Brazil against A. besseyi, and no known sources of genetic resistance. Here, we review the biology of A. besseyi, its spread across Brazil, its relevance to the country's current and future agriculture and the limited control measures. We describe control measures that have been successfully used to manage infestations of other plant-parasitic nematodes and could potentially be extended to use in the control of A. besseyi. We also review and discuss potential future control measures, such as RNA interference and genome editing, for the development of crops with enhanced resistance to A. besseyi.

Research progress on the resistance mechanism of host pine to pine wilt disease

Posted on 13 March 2024 by

We provide an overview of the resistance mechanism of pines against Bursaphelenchus xylophilus infection through histopathological characteristics and physiological, biochemical and molecular response mechanisms.

Abstract

Pine wilt disease, caused by Bursaphelenchus xylophilus, is a major quarantine forest disease that has resulted in massive economic losses as well as ecological disaster. Therefore, it is imperative to study the defence response mechanism of host pine trees to infection by B. xylophilus to understand further the internal causes of pine tree death and to find control strategies. For many years, systematic research has been carried out on the pathophysiological response of pine trees to pine wilt disease. However, due to the complexity of the occurrence and development of pine wilt disease, the specific response mechanisms of different tree species have remained unclear. This paper attempts to provide an overview of the resistance mechanism of host pine trees against B. xylophilus infection through the perspectives of histopathological characteristics, physiological and biochemical responses, and molecular response mechanisms, which provide a theoretical reference for further investigating the disease resistance mechanism of pine trees to pine wilt disease and lay the foundation for the prevention and quarantine of pine wilt disease.

Coffee wilt disease: The forgotten threat to coffee

Posted on 13 March 2024 by nLily D. Peck, nEric Boan

This review describes a series of hugely damaging outbreaks of coffee wilt disease across Africa over the past century, and evaluates strategic successes and failures in tackling its second wave. Photo: G Hakiza.

Abstract

Coffee is attacked by several highly damaging pests and diseases, which include coffee wilt disease (CWD). Despite a devastating impact in recent years, CWD receives little attention and its importance is downplayed or simply ignored. Memories are short and knowledge of past outbreaks fragmentary. Nearly two decades after the last major outbreaks, CWD has quietly faded into the background. This review describes a series of outbreaks of CWD across Africa, from Uganda to Guinea, from the first discovery in the 1920s to a hugely damaging recurrence that began in the 1970s and lasted through to the 2000s. This second wave had devastating impacts on growers and communities in the Democratic Republic of Congo and in Uganda. This review examines the origins of the disease, how and why it spread, and attempts to manage the outbreaks. Recent work on new pathogen variants is also considered. This review aims to recount these events and to evaluate the strategic successes and failures at national, regional and international levels in tackling the second wave of CWD.

Weather‐based models for forecasting Fusarium head blight risks in wheat and barley: A review

Posted on 13 March 2024 by

There is a need for comprehensive but user-friendly weather-based models for FHB, FDK and mycotoxin prediction in small-cereal crops with a focus on simplicity and real-time application to aid in effective disease management.

Abstract

Fusarium head blight (FHB) is one of the most devastating crop diseases worldwide, significantly reducing the yield and quality of small-cereal crops such as wheat and barley when favourable weather conditions exist during anthesis. Additionally, FHB-associated mycotoxins significantly impact global food and feed safety. Controlling FHB with fungicides applied near anthesis reduces visual FHB symptoms and associated mycotoxin production, thereby lowering disease-related costs. However, when weather conditions are unfavourable for FHB occurrence, fungicide application can be costly and environmentally undesirable. Thus, fungicides should be used sparingly only when the pathogen is present and weather conditions are favourable. Modelling of FHB risk using weather data has grown rapidly in recent decades and plays an essential role in integrated crop disease management. In this review, several weather-based FHB models are selected and described in detail. The models were developed globally for assessing the real-time risk of FHB epidemics in various regions/countries. Most of these models are site-specific and predict FHB visual observations such as the incidence and severity of FHB, Fusarium-damaged kernels (FDK), and also deoxynivalenol (DON) levels. The review also highlights the limitations of these existing models, including their narrow applicability, low accuracy for high-risk contamination situations, and omissions of certain factors. Also discussed are potential avenues for improvement and enhanced predictive capabilities including consideration of additional disease risk factors as well as a broader range of varieties. These predictive models can assist producers, regulatory agencies, and industry to mitigate potential food and feed security and safety concerns.

Barley powdery mildew control in Western Australia and beyond

Posted on 23 February 2024 by

This review discusses the challenging nature of barley powdery mildew and management strategies used in Western Australia, and the wider context of how scientists and breeders have responded to epidemics.

Abstract

Australia is one of the largest barley exporters in the world, with Western Australia accounting for some 40% of national production. The crop is predominantly grown in the south and south-west of the state in winter and spring, where temperate conditions and higher rainfall levels are more suited to barley than northern and eastern regions. Between 2007 and 2013, prolonged outbreaks of barley powdery mildew (BPM) occurred. This was brought about by a combination of the extensive use of susceptible cultivars and an over-reliance on a small number of single mode-of-action demethylation inhibitor fungicides, which select for mutations in the C14α-demethylase (Cyp51A) gene. This review highlights the steps taken to reduce losses to BPM, breeding efforts to introduce resistance into cultivars and the success of pre-breeding research to find new and durable resistance genes. We also draw comparisons with powdery mildew in Australian wheat, where similar factors are leading to substantial outbreaks.

Pine wilt disease: A global threat to forestry

Posted on 8 February 2024 by

This review describes the global impact, biology and management of pine wilt disease and includes interviews with those directly involved in tackling the problem in Portugal.

Abstract

Pines are the most economically important trees in the world and, together with eucalyptus, they dominate commercial forests. But the success of a relatively small number of widely planted species, such as Pinus pinaster, the maritime pine, comes at a price. Pines are attractive to damaging pathogens and insect pests, including the pinewood nematode (PWN), Bursaphelenchus xylophilus, the causal agent of pine wilt disease (PWD). Originally described in Japan, PWD has caused widespread destruction to forests in countries such as China, Taiwan, Portugal, Spain and the United States. PWN causes irreparable damage to the vascular system of its pine hosts, leading to mortality within 3 months. Pine sawyer beetles (Monochamus spp.) are key vectors of PWD, introducing the PWN to healthy trees during feeding. Other organisms contribute to PWD spread and development, including bacteria, fungi and bark beetles. Control measures include tree felling to prevent vector transmission of PWN, insecticide treatments, trapping of Monochamus spp. and tree breeding for plant resistance. The PWN is a quarantine pathogen and subject to regular legislation and phytosanitary measures aimed at restricting movement and preventing introduction to new areas. Current research is investigating the use of biopesticides against PWN and Monochamus spp. This review examines the biology, epidemiology, impact and management of PWD through published research, grey literature and interviews with people directly involved in the management of the disease in Portugal.

How does vector diversity influence the transmission efficiency of yellow dwarf virus? Perspectives from a review

Posted on 3 February 2024 by nDaniel J. Leybournen

Aphids vary in their ability to transmit an important cereal virus; however, the underlying processes are unclear. Here three mechanisms that potentially explain this variation are proposed.

Abstract

Cereals are some of the most important global crops that contribute directly and indirectly to the production of food for human consumption. Cereal aphids can cause significant damage to wheat, barley and oats, particularly via the transmission of plant viruses that cause devastating plant diseases, such as yellow dwarf disease. High levels of yellow dwarf disease can result in yield losses of around 20%, rising to 80% if infection is severe. Yellow dwarf disease is caused by multiple viruses, including viruses within the families Tombusviridae and Solemoviridae. These include yellow dwarf virus species within the genus Luteovirus (Barley yellow dwarf virus) and Polerovirus (Cereal yellow dwarf virus, Wheat yellow dwarf virus, Maize yellow dwarf virus). Some yellow dwarf virus species are primarily vectored by one aphid species whereas others can be transmitted by multiple vectors. Biological diversity within a given vector species (e.g., genotype, biotype) can influence virus transmission efficiency. However, it is unclear what biological factors drive this variation within a given vector species. Understanding how biological variation in vector populations influences virus transmission efficiency can help to identify biological traits that underpin successful transmission in competent vector populations. Here, the available literature on yellow dwarf virus transmission efficiency is synthesized and significant variation in yellow dwarf virus transmission efficiency is detected between different populations for several vector species. Three biological mechanisms that potentially underpin this variation are proposed.

Ash dieback: From Asia to Europe

Posted on 2 February 2024 by nDáire Carroll, nEric Boan

This report gives an overview of the outbreak, spread, research and response to ash dieback, a disease of European ash (Fraxinus) caused by the fungal pathogen Hymenoscyphus fraxineus.

Abstract

Ash dieback is a disease caused by the fungal pathogen Hymenoscyphus fraxineus. Since its emergence in the 1990s, this pandemic disease has spread throughout much of the native range of its host species, the European ash (Fraxinus excelsior). Where present, it can kill up to 85% of ash trees. The loss of these trees has had an enormous impact, particularly in Britain and Ireland where they formed an integral component of wood and farmland, supporting complex communities of other species. Thanks in part to widespread public interest, the ash dieback pandemic has also had a large political impact, leading to changes in the management of plant diseases. Now, three decades after the emergence of the disease, ambitious projects to breed tolerant plants, and evidence of natural selection for resistance, give hope for the recovery of European ash. The aim of this review is to provide an overview of the history of the ash dieback pandemic, from its emergence to current efforts to mitigate its effects. We discuss the emergence of ash dieback and the wide body of research that has led to our current understanding of the disease. We question which aspects of the disease have led to it holding a particular interest to the public. With a focus on the islands of Britain and Ireland, we discuss how this has driven changes in the management of plant diseases, which may give hope for the control of emerging pathogens in the future.