Seasonal change in susceptibility of Pinus densiflora to Bursaphelenchus xylophilus infection, determined from the number of nematodes passing through branch sections

Abstract

AbstractPine wilt disease by Bursaphelenchus xylophilus has been causing devastating damage to Pinus densiflora and P. thunbergii forests in Japan. Reforestation using resistant trees is one of the most effective control measures. In this study we examined the seasonal change in the number of nematodes passing through 5 cm long P. densiflora branch sections during 24 h, to determine the season of greatest susceptibility when resistant candidates can be identified easily. We inoculated 200 nematodes of each of four B. xylophilus and one B. mucronatus isolate on the cut end of individual branch sections. The overall seasonal change in the number of nematodes passing was similar among the five isolates. Peaks occurred in August and between December and February for four isolates. A virulent isolate, T-4, exhibited remarkable fluctuations, with the highest peak in August, suggesting that a test in August with T-4 is most informative. Another study showed that the passage ability, which is a measure of the dispersal ability in branches, was low for eggs and second-stage propagative juveniles and high for other developmental stages. This indicates that the composition of developmental stages in the inoculum is important when comparing the numbers of passing nematodes obtained on different occasions and in different places.