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4: Cassava Brown Streak

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4

Cassava Brown Streak

James P. Legg,1* P. Lava Kumar2 and Edward E. Kanju1

International Institute of Tropical Agriculture,

Dar es Salaam, Tanzania; 2International Institute of Tropical Agriculture, Ibadan, Nigeria

1

4.1  Introduction: Disease and Symptoms

4.1.2  Symptoms

4.1.1  First reports and disease aetiology

The earliest studies investigating virus diseases of cassava were initiated in the north-­ western part of what is now Tanzania during the 1930s. It was during this period that a ‘mosaic’-like disease was observed with characteristics that were distinct from cassava mosaic disease (CMD), which had been described several decades previously

(Warburg, 1894). The cassava ‘brown streak’ disease (CBSD), like CMD, appeared to be a graft-transmissible systemic condition, but unlike CBSD, it produced distinctive foliar symptoms that were most prominent on lower mature leaves and was associated with an unusual root rot phenomenon (Storey, 1936). Although Storey

(1936) considered the disease to have a viral aetiology, it was not until several decades later that molecular studies identified the causal viruses (Monger et al., 2001a) and Koch’s postulates were fulfilled (Winter et al., 2010). For much of its history,

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16: Sweet Potato Virus Disease

Tennant, P.; Fermin, G. CABI PDF

16

Sweet Potato Virus Disease

Augustine Gubba* and Benice J. Sivparsad

Department of Plant Pathology, School of Agricultural, Earth and Environmental Sciences, University of KwaZulu-Natal,

Pietermaritzburg, South Africa

16.1  Introduction

Sweet potato is ranked as the seventh most important food crop in the world (Woolfe,

1992; FAOSTAT, 2012). Among the major starch staples, it has the largest rates of biomass and nutrient production per unit area per unit time (Woolfe, 1992). Because of its good performance under adverse farming conditions and high carbohydrate and vitamin content, sweet potato has been identified as an ideal starch staple in subsistence economies (Mukasa et al., 2003; Wambugu, 2003;

Naylor et al., 2004; Loebenstein et al., 2009).

Virus infection is the main limiting factor in sweet potato production worldwide

(Allemann et al., 2004). Moreover, viral diseases rank second after sweet potato weevils as restraining biotic factors and can cause considerable yield reduction of up to

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15: Rice Tungro

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Rice Tungro

Indranil Dasgupta*

Department of Plant Molecular Biology, University of Delhi,

New Delhi, India

15.1  Introduction

Rice tungro bacilliform virus (RTBV) and

Rice tungro spherical virus (RTSV) are two viruses responsible for the rice tungro disease (RTD). The disease has been known for almost a half a century and has been intensively investigated across various countries in Asia. Today, a large volume of information is available on the viruses, their transmission by insect vectors, their gene functions, the pathological response in rice plants upon infection, and the rice genes that mediate resistance to the viruses. This chapter summarizes what is known about the pathogens and the disease, and discusses the prospects of conventional and biotechnological approaches to controlling RTD − mainly by strengthening the RNA-based defence pathway in rice.

15.2  Disease Symptoms

RTD is characterized by orange–yellow foliar discoloration and stunting of plants to

­almost half the normal size upon maturity

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13: Tomato Yellow Leaf Curl

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13

Tomato Yellow Leaf Curl

Cindy-Leigh Hamilton,1 Sudeshna MazumdarLeighton,2 Icolyn Amarakoon3 and Marcia Roye1*

Biotechnology Centre, The University of the West Indies,

Mona Campus, Jamaica; 2Department of Botany, Delhi

University, Delhi, India; 3Department of Basic Medical

Sciences, The University of the West Indies, Mona

Campus, Jamaica

1

13.1  Introduction

Tomato yellow leaf curl virus (TYLCV), a geminivirus of the genus Begomovirus and the family Geminiviridae, has impacted

­tomato (Solanum lycopersicum) cultivation world­ wide in tropical and subtropical regions for many years (Picó et al., 1996). The virus was first reported in the Jordan Valley,

Israel, in the 1940s. Years later, it was isolated

(Czosnek et al., 1988) and sequenced (Navot et al., 1991), and was among the first begomoviruses shown to consist of a single genomic

DNA molecule. TYLCV also infects several other economically important crop plants including pepper (Capsicum spp.), bean (Pha­ seolus vulgaris) and tobacco (Nicotiana spp.), as well as numerous weed species (Roye et al.,

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5: Cassava Mosaic

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5

Cassava Mosaic

Olufemi J. Alabi,1* Rabson M. Mulenga2 and James P. Legg3

Department of Plant Pathology & Microbiology, Texas A&M

AgriLife Research and Extension Center, Weslaco,

Texas, USA; 2Zambia Agriculture Research Institute,

Mount Makulu Central Research Station, Lusaka, Zambia;

3

International Institute of Tropical Agriculture,

Dar es Salaam, Tanzania

1

5.1  General Introduction

The global cassava development strategy launched by the Food and Agriculture

Organization of the United Nations in Rome in 2000 concluded that:

. . . cassava could become the raw material base for an array of processed products that will effectively increase demand for the crop and contribute to agricultural transformation and economic growth in developing countries (http://www.fao.org/ ag/agp/agpc/gcds/).

Although cassava is currently consumed by over 800 million people in Africa and is the third most important source of calories in the tropics, the vision of the Food and Agriculture

Organization would nevertheless represent a major increase in the global significance of a crop that is still largely cultivated by resource-poor farmers utilizing traditional farming tools and practices. A native to South

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