**4. Nematode diseases of cucumber**

#### **4.1 Genus:** *Meloidogyne*

Members of the genus *Meloidogyne* have gained worldwide recognition as one of the major plant parasites constraining crops of primary economic importance [68]. *Meloidogyne* spp. are considered among the top five major plant pathogens and the first among the ten most important genera of plant parasitic nematodes in the world [18]. *M. arenaria*, *M. incognita* and *M. javanica* are reportedly dominant in Africa [69]. *Meloidogyne* spp. were among the nematodes found on cucumber field in Libya [70]. Aminu-Taiwo and Fawole [71] identified the effect of *Meloidogyne incognita* on cucumber in Nigeria bringing about remarkable yield reduction.

#### *4.1.1 Root Knot disease*

Root-knot is caused caused by *Meloidogyne* spp. All members of Cucurbitaceae family are susceptible. Typical symptoms observed on affected plants include stunted growth, pale green to yellow leaf colouration and wilting during the hot periods of the day [72]. This is due to reduced water uptake. Yield and quality of the fruit are greatly reduced. In heavy infections, plants will completely wilt and die as the nematode populations increase. When infected plants are removed from the

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*Current and Emerging Pests and Diseases of Cucumber (*Cucumis sativus *L.) in Africa*

on the roots. Secondary infection by other soil organisms is common.

fallow period and using plant extract with nematicidal property.

species known for causing downy mildew infections on plants.

generally [74]. The disease was reported on *C. sativus* L. in Egypt [75].

agents are other effective means of managing the disease.

soil, knobby, wart-like galls caused by the nematode can be seen singly or in clumps

Measures that have been used to manage root knot disease include the use of chemically formulated nematicides, crop rotation, soil fumigation, practice of

Members of the genus *Pseudoperonospora* are water moulds which include several

Downy mildew is one of the important foliar diseases of members of *Cucurbitaceae* family. Unlike other cucurbits, cucumber is more susceptible to downy mildew [73]. *Pseudoperonospora* spp. is the causative pathogen of downy mildew on cucurbits

Serious losses result from downy mildew of cucumber under unfavourable environmental conditions. Temperature and humidity have been identified as important factors for disease infection and development [76]. The transmission of the fungus is dependent on the presence of infected cucurbit hosts in cultivated fields. Symptoms of downy mildew in cucurbits are almost exclusively confined to the leaves. In cucumber, characteristic symptoms are angular chlorotic lesion on foliage. The underside of leaf turns grey-brownish to purplish black with high humidity.

Planting should be planned to coincide with the time that environmental factors are less favourable to disease infestation. Crop should also be closely monitored for early identification of incidence of the disease. Adoption of good phytosanitary measures, use of healthy planting materials, chemical fungicides and bio-control

Two genera (Erysiphe, Sphaerotheca) have been identified to cause powdery mildews which affect economically important crops, herbs and woody species [77, 78]. Members of the genera are obligate plant pathogenic fungi. *Erysiphe* is the largest in the family Erysiphaceae, comprising about 873 species. About 806 plant

Powdery mildew of cucumber is caused by either *Erysiphe cichoracearum* or *Leveillula taurica* (Erysiphales) and *Sphaerotheca fuliginea* [76]. Powdery mildew had been identified on cucumber fields in Nigeria [79]. There are reports on the presence of *Leveillula taurica* on cucumber fields in Kenya, Libya, Morocco and

*DOI: http://dx.doi.org/10.5772/intechopen.96692*

*4.1.1.1 Management of Root knot disease*

**5. Fungal diseases of cucumber**

**5.1 Genus:** *Pseudoperonospora*

*5.1.1 Downy mildew of Cucumber*

*5.1.1.1 Management of Downy mildew*

**5.2 Genera:** *Erysiphe, Sphaerotheca*

*5.2.1 Powdery mildew of Cucumber*

species are found in the genus *Sphaerotheca*.

soil, knobby, wart-like galls caused by the nematode can be seen singly or in clumps on the roots. Secondary infection by other soil organisms is common.
