**2.3 Genus:** *Crinivirus*

*Cucumber Economic Values and Its Cultivation and Breeding*

Use resistant varieties for planting and avoid planting close to old cucurbit fields. Phyto-sanitation, use of virus-free planting materials and pesticide for control of

*Papaya ringspot virus* (PRSV) has great economic importance for cucurbit and papaya cultivation worldwide. The designated biotype for cucurbits is PRSV-W. The virus has been reported on cucurbits in Tunisia [44], Egypt [45], Morocco [46] and South Africa [47]. Early season infection may lead to poor fruit set while late season infection may result to blotchy fruit. The virus can be transmitted through movement of farm workers and machinery from one place to another and by aphids. At initial stage, symptoms can appear as vein clearing of leaves followed by the development of dark-green mosaics. In cucumber, leaves are distorted along the

Management of infection on cucurbits can be achieved by using resistant varieties for planting. Insecticide applications may also reduce aphid numbers in the field. Other practices may include the use of mulches and elimination of volunteer

Viruses in this genus have wide host range, infecting over 1200 plant species worldwide [48]. Virions are icosahedral particles of approximately 29 nm in diameter, made of subunits of single capsid protein numbered 180 [49, 50]. The genus consists of three linear positive-sense single stranded RNA molecules. The major *Cucumovirus* infecting *C. sativus* L. in Africa is *Cucumber mosaic* 

The first report of cucurbits-infecting virus was obtained on *Cucumber mosaic virus* in 1916. CMV is of great importance in temperate and tropical regions of the world [51]. Report of CMV infection on cucurbits in Africa were established in Tanzania and South Africa [36]. Over 80 species of aphids in more than 30 genera transmit CMV in a non-persistent manner but *Aphis gossypii* and *Myzus persicae* are the most efficient [52, 53]. Rapid spread of the virus has been attributed to the attraction of CMV-infected plants to aphids [54]. Transmission through seed, parasitic weeds such as dodder *Cuscuta* spp. and mechanically have also been established [50, 55, 56]. CMV causes typical mosaic symptoms in cucumber which include mosaic on leaves or fruit, stunted growth, deformed fruit, yellow spot and

The use of certified seed for planting, regular weeding and disinfection of hands and farm tools are effective ways to manage CMV. Aphid population should also be

kept under control through regular spraying with insecticide.

the vectors have also been employed in the management of MWMV.

*2.1.3.1 Management of MWMV*

*2.1.4 Papaya ringspot virus (PRSV)*

*2.1.4.1 Management of PRSV*

**2.2 Genus:** *Cucumovirus*

*2.2.1 Cucumber mosaic virus (CMV)*

margins.

weed hosts.

*virus* (CMV).

wilting (**Table 1**).

*2.2.1.1 Management of CMV*

**184**

The genus *Crinivirus* comprises of members with cross-banded flexuous particle, five gene nodule and infection that is restricted to the vascular tissues [57]. A typical member of this genus infecting cucurbits in Africa is *Beet pseudoyellows virus*.

### *2.3.1 Beet pseudo-yellows virus (BPYV)*

*Beet pseudo-yellows virus* has a broad host range including cucurbits, ornamentals and weeds. BPYV particles are approximately 12 nm wide and 1500–1800 nm long [58]. BPVY has been reported in South Africa [11]. The genome is made up of two linear positive sense, single stranded RNA of about 7.6 to 8 kb, both required for infectivity [57]. Typical BPVY symptoms may be confused with physiological disorders. Symptoms appear first on older leaves as yellow spots which develop into yellow blotchy raised areas between veins, which remain green. Subsequently, younger leaves become affected but the fruit remain intact.

#### *2.3.1.1 Management of BPYV*

Prevention of incidence of whitefly infestation, practising crop rotation and regular weeding are recommended ways of managing BPVY. Elimination of intercropping of old and young plants and good sanitation are also effective.
