The lesion nematode (Pratylenchus zeae), the stunt nematode (Tylenchorhynchus leviterminalis), the spiral nematode (Helicotylenchus dihystera), and the lance nematode (Hoplolaimus columbus) were major plant-parasitic nematode (PPN) species identified in the sugarcane fields on Kitadaito Island, Okinawa, Japan, for which real-time PCR primer sets were developed. Since the four PPN species ubiquitously inhabited Kitadaito, P. penetrans, which was confirmed to be absent in Kitadaito, was used as a benchmark to establish a soil calibration curve. Kitadaito soil samples were inoculated with juveniles and adults of P. penetrans at densities of , ,, and / g fresh soil, and a soil calibration curve was obtained: y = . x + . (y = Ct values, x = log (the number of P. penetrans)). The soil calibration curve was consistent with a calibration curve derived from serially diluted DNA samples of handpicked single P. penetrans (y = . x + . ), after adjusting the DNA dilution rates to the densities in soil. The results suggested that calibration curves developed using serially diluted DNA samples (y = . x + . , y = . x + . , y = . x + . , and y = . x + . for P. zeae, T. leviterminalis, H. dihystera, and H. columbus, respectively) may be appropriate to quantify target PPN in Kitadaito soil. Nematol. Res. ( ), -( ).

No abstract

The use of nematicides with reduced toxic side-effects against non-target free-living nematodes is a favorable option for farmers to control plant-parasitic nematodes. The nematicide fluensulfone was registered in several countries for the control of the root-knot nematodes, Meloidogyne spp. among other plant-parasitic nematodes. This study aimed to evaluate the nematicidal activity of fluensulfone against non-target nematode fauna in four field experiments, each under different conditions (soils types and plant hosts). Nematodes extracted from soil samples were classified and counted based on their morphological characters. Fluensulfone significantly reduced damage caused by root-knot nematodes to tomato and sweet potato plants, while overall non-target free-living nematode population densities were maintained at the same level as those in control. Different diversity indices (e.g., Shannon-Wiener H’, Simpson’s D, species richness, evenness J’, maturity indices) and principal component analyses in the four experiments showed that fluensulfone treatment kept a similar diversity level of non-target free-living nematode fauna to that of the non-treated control. The results suggested that fluensulfone may have minimal impact to free-living nematode fauna in both population density and diversity when the nematicide was applied to control Meloidogyne spp.

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 ca 50%, which is relatively high compared to other Japanese upland fields. Lesion (.Pratylenchus sp.), stunt (Tylenchorhynchus sp.) and spiral (Helicotylenchus sp.) nematodes were detected at mean densities of 48, 22 and 6 (20 g soil)-1 , respectively, from all the fields, and lance (Hoplolaimus 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.

loss observed around the globe, including reductions of -% in Australia, -% in Brazil, and more than % in South Africa in plant and ratoon crops. As indicated by Blair and Stirling ( ), many of previous nematode studies in sugarcane fields were in sandy soil, in which Meloidogyne may be the most important plant-parasitic nematode species (PPN). Bull ( and ) reported a yield decline of % in plant crop and -% or more in the ratoon crop in a sandy sugarcane field infested with Pratylenchus. Bond et al. ( ) reported that in sandy soil sugarcane fields w it h Tyle nchorhynchu s, Me socr icone ma a n d Pratylenchus, in Louisiana, USA, -% of yield decline was observed in both plant and ratoon crops. Furthermore, Cadet and Spaull ( ) showed a % yield increase by a nematicide application against Meloidogyne and Pratylenchus, and yields in the ratoon crop were correlated with those in the plant crop in sandy soil in South Africa.Yet, studies for nematode and sugarcane in clay soil have been limited. Dropkin ( ) reported that the Many field experiments have revealed sugarcane yield loss due to plant-parasitic nematodes, especially in sandy soil, but limited in clay soil. We previously reported a % sugarcane yield reduction in the plant crop in a heavy clay soil due to lesion nematodes suppressing the number of sugarcane tillers in the early growth stage (Kawanobe et al., ). Yet, it is unknown whether such early growth inhibition in plant canes will affect the ratoon crop yield in clay soil. The objective of this study was to examine the carry-over effect of yield decline from the plant crop to the ratoon crop in a field with high clay content (> %), in which early growth inhibition, possibly due to lesion nematodes, was observed in a plant crop of sugarcane. Though the Pratylenchus population density remained unchanged among treatments (fosthiazate-treated, kg and . kg/ ha at spring planting, and non-treated control), after months (July) from the spring planting until the harvest of the ratoon crop, our study showed a -% higher yield of the ratoon crop in the fosthiazate-treated crop than in the non-treated control. The result in the plant crop carried over to the ratoon crop, and implied that the healthier root growth of the plant canes achieved by a one-time nematicide application would carry-over to the ratoon crop. The result also suggested that the number of tillers and cane length observed at months (July) in the ratoon crop might adequately reflect nematode damage and offer a good explanation for the level of the ratoon crop yield. Nematol. Res. ( ), -. ( )