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4: Cassava Brown Streak

Tennant, P.; Fermin, G. CABI PDF

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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15: Rice Tungro

Tennant, P.; Fermin, G. CABI PDF

15

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

Tennant, P.; Fermin, G. CABI PDF

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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17: Mealybug Wilt Disease

Tennant, P.; Fermin, G. CABI PDF

17

Mealybug Wilt Disease

Cherie Gambley1* and John Thomas2

Department of Agriculture and Fisheries, Stanthorpe,

Queensland, Australia; 2Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, Brisbane,

Queensland, Australia

1

17.1  Introduction

Mealybug wilt disease (MWD) is a serious field disease of pineapples worldwide that was first described in Hawaii in 1910 (German et al.,

1992). Depending on the age of the plant at the onset of the disease, reductions in fruit yields range from 30% to 55% in Hawaii (Sether and

Hu, 2002a). The disease is often referred to as isolated wilt as it typically occurs in secluded patches within the crop or along the edges

(Sether et al., 2010) as shown in Fig. 17.1.

MWD is thought to be caused by a complex involving viruses, mealybugs and ants. The viruses are transmitted by mealybugs, which in turn are tended by ants. Although a number of distinct viruses have been associated with the disease, the identity of the causal agent(s) has not been determined unequivocally.

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3: Wheat Dwarf

Tennant, P.; Fermin, G. CABI PDF

3

Wheat Dwarf

Isabelle Abt1,2 and Emmanuel Jacquot1*

INRA-Cirad-SupAgro Montpellier, Montpellier, France;

Bayer S.A.S./Bayer CropScience, Lyon, France

1

2

3.1  Introduction

Cereals can be infected by a vast range of pathogens of which Wheat dwarf virus (WDV, family Geminiviridae, genus Mastrevirus), the aetiological agent of wheat dwarf disease

(WDD), is one of the most damaging of all.

WDV is exclusively transmitted from plant to plant by leafhoppers. Very few options are available for the farmers to control this pathogen in the field. Indeed, the lack of genetic resistance against WDV in cereal germplasm, the rare sources of genetic tolerance and the absence of anti-viral molecules lead to the use of indirect management methods such as the modification of cultivation practices and/ or use of insecticides to protect cereal crops from WDV infections.

Even though WDD can be associated with important economical and agronomical impacts, scientific knowledge on this pathosystem and the epidemiology of the disease are still limited. Only a few studies on WDV have been published after three decades between the first report of wheat dwarf-like symptoms back in the 1960s and the description of WDD outbreaks in the 1990s (e.g. Vacke,

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