A thorough study of a Paratylenchus sp. in glasshouse-grown lettuce: Characterisation, population dynamics, host plants and damage threshold as keys to its integrated management

In glasshouses practising monoculture of butterhead lettuce in Belgium, high densities of pin nematodes (Paratylenchus spp.) are frequently associated with reduced plant growth. Growers currently apply chemical soil disinfestation measures to manage this problem, although stricter phytosanitary regulations are forcing a shift towards integrated management. Efficient implementation of such management requires knowledge about the factors influencing nematode population dynamics, and the damage threshold for lettuce. The nematode populations in five Belgian glasshouses were monitored for at least 1 year by frequently soil sampling at 0–30 cm and 30–60 cm depth. An undescribed species of Paratylenchus was identified in all glasshouses based on morphological and molecular features. High nematode densities (>20,000 (100 ml soil)−1) occurred in winter and spring. Chemical soil disinfestation lowered these populations greatly, although up to 14% survived in the deeper soil layer. After soil steaming under negative pressure, no pin nematodes were found. After 2 months of black fallow pin nematode densities were reduced by 50%–76%. Lamb's lettuce, parsley and wild rocket were found to be poor hosts in a pot experiment, while reproduction factors (Pf/Pi) on lettuce cultivars varied between 1 and 3. In three experiments with butterhead lettuce ‘Cosmopolia’ in pots with a series of 9 or 10 densities of Paratylenchus sp. [up to 35,000 (100 ml soil)−1], no damage to lettuce heads was observed. However, root weight and root quality were reduced, and the corresponding damage thresholds were rather low [1,754 and 362 Paratylenchus sp. (100 ml soil)−1, respectively]. Management strategies such as crop rotation, soil disinfestation or fallow are recommended to avoid pin nematode population build-up.