The Vegetable Pathosystem

Ecology, Disease Mechanism, and Management

Mohammad Ansar, Abhijeet Ghatak, Mohammad Ansar, Abhijeet Ghatak

• Publisher: Apple Academic Press
• Year: 2019
• Print ISBN: 9781771887762
• eBook ISBN: 9780429663116
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Botany
• Index: Biological Sciences

Variability in vegetable pathogens is a critical issue, particularly in changing environments, as it presents challenges to accurate diagnoses and proper management. This book focuses on the diverse ecology of phytopathogens, covering the varying disease categories (acute, chronic, and emerging), the mechanisms involved in disease development, pathogen variability, and disease management. The book also discusses the preharvest and postharvest challenges that arise due to these phytopathogens.Key Features: • Provides an overview of phytopathogens that affect vegetables in various environmental conditions• Discusses how to manage vegetables affected by specific pathogens• Offers eco-friendly approaches to prevent postharvest diseases• Presents a comprehensive guide to identifying and addressing numerous diseases for individuals in the fields of horticulture

CHAPTER 1

Phytophtora Blight in Potato: A Challenge Ahead in the Climate Change Scenario

MEHI LAL^1*, SAURABH YADAV¹, V. K. DUA², and SANTOSH KUMAR³

¹Division of Plant Protection, ICAR – Central Potato Research Institute Regional Station, Modipuram, Uttar Pradesh, India

²Division of Crop Production, ICAR – Central Potato Research Institute, Shimla, India

³Division of Plant Pathology, Bihar Agricultural University, Sabour, Bihar, India

^*Corresponding author. E-mail: [email protected]

ABSTRACT

Potato is an important crop in the group of vegetable crops. It is being affected by various microorganisms apart from abiotic factors. Fungi, bacteria, viruses, nematodes, and phytoplasma are the main biotic factors, which causes tremendous loss to the potato crop. The pathogen, Phytophthora infestans (Mont.) de Bary, is a major fungus-like organism causing late blight which leads to 80% loss under improper management. The disease is severely challenged by various climatic factors, viz., temperature, relative humidity, rainfall, and CO₂ which are behaving in erratic manner in the past few years. The pathogen has adapted itself to higher temperature (up to 28°C) resulting in greater chances of spreading to larger area or persistence extended. Moreover, the level of resistance and susceptibility of the potato cultivars will also be changed in climate change scenario. Therefore, in the current perspective, control strategies should be modified or improved to sustainable management. Application of suitable fungicides coupled with suitable planting date and resistant cultivars taken into consideration. Moreover, advisories of forecasting models could also assist in the management of the late blight. Effects of temperature, CO₂, and rainfall on the pathogen are focused. Impact of these factors which are influencing the management strategies is discussed in this chapter.

1.1 INTRODUCTION

Potato (Solanum tuberosum) is a prominent vegetable crop and is grown in about 130 countries. It is the third most important food crop after rice and wheat (CIP Annual Report, 2015). It can be grown in temperate, tropical, and subtropical regions of the world. Potato is the world’s most important vegetable crop, with nearly 400 million tons produced worldwide every year, lending to stability in food supply and socioeconomic impact (Halterman et al., 2016). It is estimated that the increase in crop yield are 10–20% for C3 crops and 0–10% for C4 crops (Ainsworth and Long, 2005). Over the years, potato production has increased substantially in the developing countries. Today, China is the main producer of potato producing about 20% of global production (Staubli et al., 2008). It has been forecasted that the yield of potato will decrease by 18–32% due to changes in the climate. Past few years have witnessed a steady increase in national and international concern over the sustainability of the global environment. Climate change has emerged as the most prominent of the global environment issues, due to its harmful impact on the socioeconomic conditions of the human being. Climate change implies that the average conditions (mean and/or variability) are changing over time and may never return to those previously experienced (Coakley, 1988). Global climate has changed ever since the industrial revolution. The atmospheric concentrations of the greenhouse gases, carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O), have increased since 1750 due to human activity. In 2011, the concentrations of these greenhouse gases were 391 ppm, 1803 ppb, and 324 ppb, exceeding the preindustrial levels by about 40, 150, and 20%, respectively (IPCC, 2013). Global surface temperature change by the end of the 21st century is likely to exceed 1.5°C relative to 1850–1900 for all Representative Concentration Pathways (RCPs) scenarios except RCP2.6. It is likely to exceed 2°C for RCP6.0 and RCP8.5 and more likely than not to exceed 2°C for RCP4.5. Warming will continue beyond 2100 under all RCP scenarios except RCP2.6. Warming will continue to exhibit interannual to decadal variability and will not be regionally uniform (IPCC, 2013). It is expected to have serious consequences for mankind and the environment. The critical threshold is to be around 2°C increase of temperature (IPCC, 2007). CO₂ and temperature interactions are recognized as a key factor in determining plant damage from pests in future decade; likewise CO₂ and precipitation interaction will also be important. Globally, atmospheric CO₂ has been increased, and in northern latitudes mean temperature at many locations has increased to about 1.0–1.4°C with accompanying changes in pest and pathogen incidence and farming practices (Gregory, 2009).

Pace of climate change and the unpredictability of its characteristics are of great concern with respect to the pathogens and insect pests that reduce crop yield. The classic disease triangle recognizes the role of climate in the plant diseases, as no virulent pathogen can incite disease on a highly susceptible host if prevailed climatic conditions are not favorable. For epidemic conditions, fourth factor is time. How many times favorable conditions existed, it is also affecting the diseases’ development. All four factors (host, pathogen, environment, and time) are represented in disease tetrahedron or disease pyramid. Sometimes, a new component, human, is used in place of time in disease pyramid, but it should be considered a distinct new fifth component that influences the development of plant diseases directly and indirectly (Agrios, 2006). The climate change and global warming with increases in temperature, moisture, and CO₂ levels can impact all three legs of the plant disease triangle in various ways. Climate change could “alter stages and rate of development of the pathogen, modify host resistance, and result in changes in physiology of host– pathogen interaction” (Garrett et al., 2006). Climate influences all stages of host and pathogen life cycles as well as development of disease. Climate change and global warming will allow survival of plant and pathogens outside their existing geographical range. “The lack of action on climate change not only risks putting prosperity out of reach of millions of people in the developing world, it also threatens to roll back decades of sustainable development” (http://www.sciencemag.org/news/2012/11, Kim,19 November, 2012; a foreword to the report, Turn Down the Heat: Why a 4°C Warmer World Must be Avoided). The climatic factors including changes in temperature, rainfall and other atmospheric composition along with predominantly elevated CO₂ levels would accelerate the reproduction time of many plant pathogens and pests, thereby increasing their infection pressure on crop plants (Boonekamp, 2012).

The impact of climate change on the occurrence and activity of pathogens, pests, and diseases of agricultural crops have recently been considered more seriously. This is documented by the fact that renowned scientific journals in plant pathology (e.g., Annual Review of Phytopathology) published the papers focused on the implications of climate change for plant disease occurrence and management (Garrett et al., 2006). The range of plant pathogens and insect pests are mainly constrained by temperature, and the frequency and severity of weather events affecting the timing, intensity, and nature of outbreaks of most organisms (Yang and Scherm, 1997). It is well established that short- and long-term changes in climate will impact on which strains of pathogens prove most aggressive via their ability to grow and sporulate under particular environmental conditions. The change in environmental factors, particularly temperature and leaf wetness would influence the rate of progress at any stage of plant disease development (Agrios, 1997; Coakley et al., 1999). The late blight of potato, being a climate-dependent disease, might be more affected in climate change scenario.

As far as Indian scenario is concerned, losses in potato production due to late blight ranged between 5% and 90% depending upon various climatic conditions, with an average of 15% across the country (Collins, 2000). Tuber yield decline was significantly higher in unmanaged crop, which could go as high as 90% of total productivity in hilly regions. In the years, when disease appeared early in crop season due to heavy rains, late blight continued to build up throughout the crop duration resulting in crop losses up to 75% (Singh and Bhat, 2005). However, Lal et al. (2015) recently reported that yield losses were ranged 10–20% due to late blight during 2013–2014 in major potato growing states of the India. Potato late blight had become more severe in the recent years due to influx of a new population containing the A2 mating type especially in the United States (Goodwin et al., 1995). The worldwide late blight disease is re-emerging; therefore, this disease is constantly observed by the late blight researchers (Fry et al., 2015). The late blight disease is considered as an emerging disease; it is not only having importance in worldwide crop production but also pose severe threat on a local level, especially on small farms in developing countries (Subbarao et al., 2015). Phytophthora infestans is the most widely studied oomycete; about 1230 papers has beenpublished in the last 10 years (2005–2014) and is one of the top 10 oomycete pathogens studied using molecular techniques (Kamoun et al., 2015)

Late blight of potato caused by P. infestans still remains the leading threat to potato cultivation globally. This notorious pathogen is known to break host resistances across Solanum spp. and has the ability to develop resistance to chemical fungicides in a very short span of time. The pathogen possesses this quality owing to very large genome size of about 240 Mbps (Hass et al., 2009) which is largely composed of transposons. Consequently, it is also expected that this pathogen will quickly adapt itself to changed climatic conditions and will continue to play havoc in potato-growing regions across the globe. There are some reports that the P. infestans is introduced in different places by seeds. Pamella et al. (2004) reported that the introduction (40%), weather (41%), and farming techniques (19%) are the important factors for fungi in spreading emerging infectious disease. Fungal diseases such as those caused by Ustilago and Sclerotia species are not expected to be affected by climate change because of their monocyclic nature. However, polycyclic diseases such as those caused by Colletotrichum, Peronospora, Phytophthora, and Puccinia species, each additional disease cycle multiplies inoculums many fold, so an increased duration of growing season in Ontario (Canada) would be expected to result in an increased number of disease cycles and inoculums. Primary inoculums will be increased for disease established in tomato late blight whereas potential duration for epidemic of potato late blight will be increased in Ontario (Boland et al., 2004). Zargarzadeh et al. (2008) observed that there were significant correlations between climatic factors, particularly temperature and rainfall, with the incidence of the late blight. The late blight appearance, favorable period, and delay in appearance of late blight in western Uttar Pradesh were predicted using base line for the year 2000. It is clearly indicated that earliest late blight appearance during the potato crop season was predicted during 13 October to 1 November in baseline year 2000 and is expected to be delayed by 0–8 days in 2020 and 10–21 days in 2055 (Fig. 1.1) (Dua et al., 2015).

FIGURE 1.1 (See color insert...

Table of contents

• Cover
• Half Title Page
• Title Page
• Copyright Page
• Series Page
• About the Editors
• Table of Contents
• Contributors
• Abbreviations
• Preface
• Introduction
• Acknowledgments
• 1. Phytophtora Blight in Potato: A Challenge Ahead in the Climate Change Scenario
• 2. Pathosystem in Cowpea: An Overview
• 3. A Population Genetics Perspective on Ecology and Management of Phytophthora Spp. Affecting Potato, Tomato, and Pointed Gourd in India
• 4. Phytoplasma in Vegetable Pathosystem: Ecology, Infection Biology, and Management
• 5. Ralstonia solanacearum: Pathogen Biology, Host–Pathogen Interaction, and Management of Tomato Wilt Disease
• 6. Nematodes: Pest of Important Solanaceous Vegetable Crops and Their Management
• 7. Effect of Fungal Pathogen on Physiological Function of Vegetables
• 8. Foilar Fungal Pathogens of Cucurbits
• 9. Yellow Vein Mosaic of Okra: A Challenge in the Indian Subcontinent
• 10. Disease Dynamics and Management of Vegetable Pathosystems
• 11. Mechanism of Microbial Infection in Vegetables Diseases
• 12. Virus Diseases: An Inimitable Pathosystem of Vegetable Crop
• 13. Begomovirus Diversity and Management in Leguminous Vegetables and Other Hosts
• 14. Biology and Molecular Epidemiology of Begomovirus Infection on Cucurbit Crops
• 15. Diversity of Potyviruses and Their Extent in Vegetable Pathosystem
• 16. Soilborne Microbes: A Culprit of Juvenile Plants in Nurseries
• 17. Biological Control of Postharvest Diseases in Vegetables
• 18. Postharvest Handling and Diseases and Disorders in Bulb Vegetables
• 19. Management of Soilborne Diseases of Vegetable Crops Through Spent Mushroom Substrate
• Color insert of illustrations
• Index