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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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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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14: Tristeza

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14

Tristeza

Latanya C. Fisher,1 Paula Tennant2 and Vicente J. Febres1*

Horticultural Sciences Department, University of Florida,

Florida, USA; 2Department of Life Sciences, The University of the West Indies, Mona Campus, Jamaica

1

14.1  Introduction

­resistant sour orange rootstock in the Mediterranean and the Americas. This particular

Citrus tristeza virus (CTV) is the most eco- rootstock had excellent agronomic qualities nomically devastating viral plant pathogen such as cold hardiness, enhancement of fruit and is responsible for the death and loss of quality and high adaptability to adverse soil productivity of approximately 100 million conditions (Moreno et al., 2008). However, citrus trees worldwide (Timmer et al., 2000; CTV outbreaks grew problematic to the citrus

Moreno et al., 2008; Saponari et al., 2013). industry due to: (i) the loss of trees and proReports of the CTV epidemics have been re- duction that occurred from CTV-susceptible corded in several countries, including ­Argentina, genotypes grafted on the widely used sour

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10: Sugarcane Mosaic

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10

Sugarcane Mosaic

Laura Silva-Rosales,1* Ricardo I. Alcalá-Briseño2 and Fulgencio Espejel1

Plant-Virus Interaction Laboratory, Department of Genetic

Engineering at Cinvestav-Unidad Irapuato, Guanajuato,

Mexico; 2Department of Plant Pathology, University of Florida,

Gainesville, Florida, USA

1

Monocot species, in particular grasses, are cultivated over large areas worldwide for human and animal consumption and lately for biomass energy production. However, viruses like

Sugarcane mosaic virus (SCMV), alone or in conjunction with other viruses or microorganisms, have emerged in some regions as devastating problems for their cultivation. Here we present the taxonomy, distribution, diversity and economic importance of this virus that infects maize and sugarcane as well as provide some insights into its evolution. Efforts to obtain resistance through classical breeding and transgenic approaches are also described.

10.1  Structure, Taxonomy and Diversity

SCMV, a member of the genus Potyvirus in the

Potyviridae family of plant viruses, belongs to the replication group IV. As such, its genome consists of a single-stranded (+) RNA molecule. Its length of 9.6 kb is encapsidated by approximately 2,000 monomers of the coat protein (CP) forming flexuous filaments of about 750 nm in length (Riechmann et al.,

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2: Banana Bunchy Top

Tennant, P.; Fermin, G. CABI PDF

2

Banana Bunchy Top

Niyongere Célestin,1* Aman Bonaventure

Omondi2 and Guy Blomme3

ISABU, Bujumbura, Burundi; 2BIOVERSITY International,

Bujumbura, Burundi; 3BIOVERSITY International,

Addis Ababa, Ethiopia

1

2.2  Importance of Banana as the

Main Host Plant of Banana Bunchy

Top Disease

2.1  Introduction

Banana bunchy top disease (BBTD) is caused by Banana bunchy top virus (BBTV), which is transmitted by the aphid vector Pentalonia nigronervosa Coquerel and through infected planting materials. It is one of the most economically important diseases in many banana-producing areas of Africa, Asia and the South Pacific (­ Furuya et al., 2005; Hooks et al., 2009). Between 1913 and 1920, the banana-growing industry in Australia was almost completely destroyed by the disease

(Magee, 1927; Hooks et al., 2009). In the

1990s, the first severe outbreak of BBTD in Africa was estimated to have reduced banana production in the Nkhatabay and Nkhotakota districts of Malawi from 3500 ha to about 800 ha (Soko et al., 2009; Kumar et al., 2011). In the Great Lakes countries of Africa, about 90% yield loss has been reported in severely BBTD-infected banana plantations in the Rusizi valley in Burundi

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