Plant-parasitic nematodes in sugarcane fields in Kitadaito Island (Okinawa), Japan, as a potential sugarcane growth inhibitor

<jats:p>Sugarcane is the main industrial crop in Kitadaito Island (Okinawa), Japan, and the objective of this study was to estimate potential damage to sugarcane by plant-parasitic nematodes (PPN). We selected 15 sugarcane fields with the same cultivar and cropping type in Kitadaito Island. Various kinds of PPN were found in all the fields and the proportion of PPN to the total nematode number was <jats:italic>ca</jats:italic> 50%, which is relatively high compared to other Japanese upland fields. Lesion (<jats:italic>Pratylenchus</jats:italic> sp.), stunt (<jats:italic>Tylenchorhynchus</jats:italic> sp.) and spiral (<jats:italic>Helicotylenchus</jats:italic> sp.) nematodes were detected at mean densities of 48, 22 and 6 (20 g soil)<jats:sup>−1</jats:sup>, respectively, from all the fields, and lance (<jats:italic>Hoplolaimus</jats:italic> sp.) and ring nematodes from half of the fields. The results suggested that sugarcane fields in Kitadaito Island were ubiquitously infested with a variety of PPN with a relatively high abundance. One of the fields was studied further to examine the potential relationship between PPN and sugarcane plant growth. Since no nematicide is registered for sugarcane fields in Japan, an appropriate agrochemical was selected by testing its efficacy against PPN before evaluating the relationship between a PPN community and sugarcane growth. The results of a 10-week pot experiment for sugarcane growth showed that the number of PPN decreased by applying a nematicide fosthiazate, and that sugarcane seedling biomass was significantly greater by 34-63% in soils with applied nematicide than in non-applied control soils, suggesting that PPN may suppress sugarcane growth in Kitadaito Island.</jats:p>