Abstract:
Cucumis sativus (Cucumber) is an edible fruit vegetable grown for its nutritional and economic values, but root-knot nematodes such as Meloidogyne incognita (MI) constitute a major constraint to its production. Nematicides, the most effective control option, are expensive and not environment friendly. Cultural practices such as crop rotation could reduce nematode infection but its effect on MI on cucumber has not been adequately documented. Therefore, biology, pathogenicity and management of Meloidogyne incognita with crop rotation were investigated.
A survey of plant-parasitic nematodes on cucumber in Lagos, Ogun, Osun, Oyo, Kaduna and Plateau States where cucumber is mostly cultivated was carried out using systematic sampling technique. Pathogenicity of M. incognita on Marketer, Ashley, Tokyo and Marketmore varieties of cucumber were assessed in pot and field experiments. Sixty-four one week-old seedlings of each variety was inoculated at four inoculum densities: 0, 10,000, 20,000 and 40,000 eggs of MI in pots (20 kg soil) using a 4x4 factorial arrangement in a completely randomised design in four replicates. On the field, split-plot design was used with main plots (nematode-infested and nematode-free) and sub-plots (cucumber varieties). Healthy and nematode-infected (unhealthy) cucumber roots of 5 weeks-old were processed for histopathology using standard procedures. Life cycle of MI in Marketer was studied to assess generation time (GT). Twenty-one economic crops were evaluated for resistance to MI (5,000 eggs/5kg soil) using Canto-Saenz’s host designation scheme (Resistant = Gall index (GI)≤2 and Reproduction Factor (RF)≤1; Susceptible = GI≥2 and RF≥1; Tolerant = GI≤2 and RF≥1). Potentials of three resistant crops were evaluated in rotation with cucumber for MI management in the field. Data were collected on fresh shoot weight (FSW), marketable fruit yield (MFY, t/ha), GT, GI and RF. Data were analysed using descriptive statistics and ANOVA at α0.05.
Eleven plant-parasitic nematode genera were identified and the most prevalent were Meloidogyne spp. (45.5%), while the least were Rotylenchus spp. (0.3%). The four cucumber varieties were susceptible and susceptibility was in order of Marketer (GI=4.0, RF=20) >Ashley (GI=3.8, RF=14) >Marketmore (GI=3.5, RF=10) >Tokyo (GI=3.0, RF=15). However, MI was highly pathogenic at 10,000 eggs/20 kg soil on all cucumber varieties with MFY ranged from zero (Marketer) to 32.5±9.9 t/ha (control). The MI infection significantly reduced FSW (62.1%) and MFY (77.7%) on the field. The M. incognita infection collapsed and shrank cells in the cortex, endodermis, vascular and formation of giant cells in unhealthy roots compared to healthy roots. The GT of MI was 30.0±0.0 days. Out of the 21 crops, 10 were resistant, 8 susceptible and 3 tolerant. Cucumber planted in rotation with resistant crops; marigold, sesame and maize each reduced GI by 75.0%, while FSW increased by 60.8% in marigold, 57.2% in sesame and 57.7% in maize. The MFY of cucumber planted after marigold and sesame increased by 96.0% each and 97.0% in maize compared to control (36.0%).
The cucumber varieties were susceptible to Meloidogyne incognita infection with more generations per growing season. However, cultivating cucumber in rotation with marigold, sesame or maize reduced Meloidogyne incognita infection in cucumber plots.
Keywords: Crop rotation, Cucumber fruit yield, Nematode infection, Meloidogyne incognita,
Words count: 500
