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

Abstract

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 (P f /P i) 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.

Species Diversity of Pin Nematodes (Paratylenchus spp.) from Potato Growing Regions of Southern Alberta, Canada

“…The species was first found (but not described) in the glasshouse-grown lettuce from Belgium. The species causes damage to the root system, but this was not related to significant yield reduction in lettuce heads [34]. In the present study, same species was found in the potato growing region of southern Alberta.…”

“…Lower densities of identified species in the samples suggest that these are mild parasitic species and, as of yet, do not behave as potential pests. However, pin nematodes have a reputation of building high population densities in short periods, and, under favorable circumstances, can be a threat to their hosts [22,34]. Indeed, a higher incidence of root lesion nematodes (Pratylenchus spp.)…”

“…In the present study, same species was found in the potato growing region of southern Alberta. In the Belgian population, the authors noted the presence of a large proportion of pre-adults 51-96% and stated this might be due to soil disturbance [34]. The Canadian population also exhibits the same feature; the juveniles were observed in higher numbers than females.…”

Remarkable Cryptic Diversity of Paratylenchus spp. (Nematoda: Tylenchulidae) in Spain

“…This species has been recently described from Canada [ 21 ]; and it has also been reported in Belgium [ 22 , 24 ]. In the present study, the P. enigmaticus population from Spain matches with the original species description, except for minor differences in body length and a ratio; the Spanish population is slightly shorter than the original one (324–383 µm vs. 343–431 µm) and with smaller a ratio (17.6–21.6 vs. 21.7–28.7) ( Table 6 , Figure 12 ).…”

“…Pathogenicity has been found only on different crops for a few species such as P. bukowinensis Micoletzky, 1922 in celery ( Apium graveolens L.) [ 8 , 9 ]; Paratylenchus dianthus Jenkins & Taylor, 1956 in carnation ( Dianthus caryophyllus L.) [ 10 ]; Paratylenchus epacris (Allen & Jensen, 1950) Goodey, 1963 in black walnut ( Juglans nigra L.) [ 11 ]; Paratylenchus hamatus Thorne & Allen, 1950 in fig ( Ficus carica L.), pear ( Pyrus communis L.) and grapevine ( Vitis vinifera L.) [ 12 , 13 , 14 ]; Paratylenchus microdorus Andrassy, 1959 in red clover ( Trifolium pratense L.) and lettuce ( Lactuca sativa L.) [ 15 ]; Paratylenchus nanus Cobb, 1923 in garden balsam ( Impatiens balsamina L.) [ 16 ]; Paratylenchus neoamblycephalus Geraert, 1965 in Myrobalan plum ( Prunus cerasifera Ehrh.) [ 17 ]; Paratylenchus projectus Jenkins, 1956 in alfalfa ( Medicago sativa L.) and sunflower ( Helianthus annuus L.) [ 18 , 19 ]; Paratylenchus shenzhenensis Wang, Xie, Li, Xu, Yu & Wang, 2013 in Anthurium andraeanum Linden ex André [ 20 ]; and Paratylenchus enigmaticus Munawar, Yevtushenko, Palomares-Rius & Castillo, 2021 in lettuce [ 21 , 22 ]. Other species can be also pathogenic in crops, but further studies are necessary to confirm this.…”