331 Chapters
Medium 9781780643755

9: Nematophagous Bacteria as Biocontrol Agents of Phytonematodes

Askary, T.H., Editor CAB International PDF

9 

Nematophagous Bacteria as Biocontrol

Agents of Phytonematodes

Mohamed F.M. Eissa* and Mahfouz M.M. Abd-Elgawad

Phytopathology Department, National Research Centre, Giza, Egypt

9.1  Introduction

Plant-parasitic nematodes (PPN) are a severe constraint to agricultural production worldwide, in turn impacting international trade, social and economic development (Perry and

Maurice, 2013). A great deal of research has been done on phytonematodes and their hosts including many horticultural and field crops in tropical, subtropical (e.g. Luc et al., 2005), temperate (e.g. Evans et al., 1993) and other regions (e.g. Perry and Maurice, 2013). The nematodes can damage their host plants directly, act as vectors of viruses, or form disease complexes with other pathogens. In addition, nematode penetration of infected plants may facilitate subsequent infestation by ­secondary pathogens such as fungi and bacteria (Powell, 1971). Yet, due to their often subterranean habit and microscopic size, phyto­nematodes usually remain invisible to the naked eye (Ngangbam and Devi, 2012), which complicates their control. Monetary estimates of global annual yield losses caused by the nematodes demonstrated staggering figures whether in the past (e.g. Sasser and

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Medium 9781780641836

6 The Chemical Environment in the Soil Seed Bank

Gallagher, R.S., Editor CAB International PDF

6

The Chemical Environment in the Soil Seed Bank

Henk W.M. Hilhorst*

Wageningen Seed Lab, Laboratory of Plant Physiology,

Wageningen University, Wageningen, the Netherlands

Introduction

Soil is the natural physical and chemical environment of most seeds. Essentially, soil is a three-phase system consisting of solids, liquids and gases in varying proportions. In most soils the solids are predominantly mineral, derived from rock materials. Minerals are defined as solid, inorganic, naturally occurring substances with a definite chemical formula and general structure. It is evident that minerals may only affect seed behaviour when they are solubilized by water that penetrates the soil. In this respect the soil pH is an important factor. The soil matrix may also contain more readily dissolvable solutes, for example salts in saline environments. Direct chemical effects of rock-derived minerals on germination of seeds in the soil seed bank are unknown.

Solubilized minerals may inhibit germination non-specifically when they occur in high concentrations in soils. Also the effects of high salinity can be either osmotic or toxic. Soil may also contain organic matter.

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Medium 9781780642789

Sugarcane (Saccharum officinarum Linn.)

Kumar, P.; Sharma, M.K. CAB International PDF

SUGARCANE (Saccharum officinarum Linn.)

NITROGEN (N) DEFICIENCY

Symptoms

Plate 612. Die-back of an old leaf.

(Photo by Dr Manoj Kumar Sharma.)

1. In the nitrogen-deficient crop, stalks become short and slender

(Plate 614).

2. Fewer tillers are produced and overall growth of the plant is reduced.

3. The entire plant may become light green in appearance.

4. Nitrogen is a mobile nutrient in plants and in poor supply conditions it is easily mobilized from older to younger leaves.

5. The deficiency symptoms are primarily observed on older leaves (Plate 611).

6. Later, the entire plant turns chlorotic.

7. Older leaves may become uniformly pale green to yellow

(Plate 611).

8. Nitrogen deficiency causes die-back of older leaves (Plates 612 and 613).

9. Necrosis occurs on the tips and margins of recently matured old leaves.

Developmental stages

Stage I: In the early plant stage or mild deficiency, the entire plant appears uniformly light green.

Stage II: In prolonged deficiency, the older leaves turn uniformly yellow to dark yellow (Plate 611).

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Medium 9781845938291

21. Invasion of Exotic Arthropods in South America’s Biodiversity Hotspots and Agro-Production Systems

Pena, J.E., Editor CAB International PDF

21 

Invasion of Exotic Arthropods in

South America’s Biodiversity Hotspots and Agro-Production Systems

K.A.G. Wyckhuys,1 T. Kondo,2 B.V. Herrera,1 D.R. Miller,3

N. Naranjo4 and G. Hyman1

1

International Center for Tropical Agriculture CIAT, Recta Palmira-Cali,

Cali, Valle del Cauca, Colombia; 2Corporación Colombiana de Investigación

Agropecuaria,Corpoica, Colombia; 3Systematic Entomology Laboratory, Agricultural

Research Service, U.S. Department of Agriculture, Beltsville, Maryland 20705, USA;

4

Horticulture Research Center CIAA, Universidad Jorge Tadeo Lozano,

Bogota, Colombia

21.1  Introduction

Worldwide, exotic invasive species are of increased concern, and are responsible for environmental and economic problems. Although some exotic species are efficiently kept at bay through both biotic and abiotic processes, several lack effective natural enemies and undergo explosive population increases and geographic spread. Such species commonly transform and negatively affect (native) ecosystems, threaten biotic integrity and contribute to the disappearance of endangered species (Reid and Miller,

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Medium 9781780643731

8: The Impact of Ozone Pollution on Plant Defence Metabolism: Detrimental Effects on Yield and Quality of Agricultural Crops

Chakraborty, U., Editor CAB International PDF

8 

The Impact of Ozone Pollution on Plant

Defence Metabolism: Detrimental Effects on

Yield and Quality of Agricultural Crops

Fernanda Freitas Caregnato,1* Rafael Calixto Bortolin,1

Armando Molina Divan Junior2 and José Cláudio Fonseca Moreira1

1

Department of Biochemistry, Center for Oxidative Stress Research,

Federal University of Rio Grande do Sul (UFRGS), Porto Alegre; 2Laboratory of Plant Bioindication, Center of Ecology, UFRGS, Porto Alegre, Brazil

Abstract

Over the past decades, research on the negative effects of air pollutants on agricultural crops and agro-­ ecosystems point out for emission reduction strategies, with practical recommendations to increase the sustainability of agricultural and land management in an environment that is constantly changing. Agricultural production will need to keep pace with the growing food demand, which depends on many factors, including the future levels of air pollution, such as tropospheric ozone. The risk of negative effects of ozone on crop productivity created the need to improve our understanding on the mechanisms underlying ozone toxicity, and biotechnological advances are now starting to provide us with the necessary knowledge to safely develop and/or select crops varieties better adapted to ozone stress. Ozone phytotoxicity arises mainly because of its high oxidation potential to generate reactive oxygen species (ROS) in exposed plant tissue. After entering leaf stomata, ozone rapidly degrades into various ROS species, and plants reduce the oxidative damage by activation of antioxidant enzymes and accumulation of molecules that effectively scavenge ROS. If ROS production exceeds the plant’s capacity to detoxify it, deleterious effects at the cellular level may occur. The balance between the production and the scavenging of activated oxygen is thus crucial to plant growth maintenance and overall environmental stress tolerance. However, alterations in plant metabolism may lead to reduced crop yield and quality, directly or indirectly by exposing susceptible plants to stress factors. Secondary metabolites are constitutively synthesized and are of interest for human health and nutrition, especially because some of them are major sources of biologically active substances. However, they are also well known as plant defence molecules and their concentrations can be influenced by abiotic stresses such as ozone. Increased accumulation of plant secondary metabolites in leaves of forest trees in response to ozone exposure has been reported in several studies, while the changes on crop plants composition and nutritional quality need to be further studied and discussed to guide our efforts to select ozone-tolerant crops in an attempt to provide a secure food supply for a developing world.

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