Effects of Temperature Factors on Resistance against Pine Wood Nematodes in Pinus thunbergii, Based on Multiple Location Sites Nematode Inoculation Tests

Taiichi Iki,Masahiro Miura,Tomonori Hirao,Mineko Ohira,Atsushi Watanabe,Keiya Isoda,Masakazu G Iwaizumi,Taro Yamanobe,Manabu Kurita,Makoto Takahashi,Koji Matsunaga

doi:10.3390/f11090922

Taiichi Iki, Masahiro Miura + Show 9 more

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https://doi.org/10.3390/f11090922

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Abstract

Pine wilt disease (PWD) caused by the pinewood nematode (PWN) (Bursaphelenchus xylophilus (Steiner and Buhrer) Nickle) is a worldwide issue. Infection is considered to be promoted mainly by the increased air temperature, but it is important to investigate whether the effect of high temperature similarly influences the different ranks of resistant clone. In the present study, we conducted PWN inoculation tests using six common open-pollinated families of resistant Pinus thunbergii Parl. The tests were conducted at nurseries of five test sites across Japanese archipelago between 2015 and 2017. Our analysis focused specifically on temperature. Firstly, we examined the effects of test sites, inoculation year, and their interaction on unaffected seedling rate and found that the unaffected seedling rate of all tested pine families decreased as the cumulative temperature increased. We found that the unaffected seedling rate decreased as the cumulative temperature increased for all tested pine families. In general, higher cumulative temperatures were required for having an effect on the unaffected seedling rates of higher PWN-resistant families. Typically, early cumulative temperatures, i.e., 19 days after inoculation, had the greatest effect on the unaffected seedling rates of PWN-resistant pines. However, the relationship between cumulative temperature and predicted unaffected seedling rate follow similar rate for all families. Thus, the order of resistance level is maintained in terms of the cumulative temperature required for having an effect.

Highlights

Pine wilt disease is an epidemic disease caused by the invasive pinewood nematode, Bursaphelenchus xylophilus (Steiner and Buhrer) Nickle [1], and vectored by pine sawyer beetles, Monochamus alternatus Hope [2]
Our results suggest that a cumulative temperature of 25 °C or higher affects the unaffected seedling rate of resistant P. thunbergii after inoculation, which is the same temperature range with propagation of pinewood nematode (PWN) after inoculation [13,14]
P. thunbergii in the nurseries of five test sites from 2015 to 2017, in order to consider the effects of temperature factors on PWN resistance

Summary

Introduction

Pine wilt disease is an epidemic disease caused by the invasive pinewood nematode, Bursaphelenchus xylophilus (Steiner and Buhrer) Nickle [1], and vectored by pine sawyer beetles, Monochamus alternatus Hope [2]. Et Zucc., two major planted pine species in Japan, are susceptible to PWN [5]. Japanese pine forests have been seriously damaged by PWD. The disease has subsequently spread to every prefecture in Japan, apart from Hokkaido [7]. As the disease causes widespread damage, Japan began a tree breeding project in 1978 in order to select resistant pine varieties as a countermeasure against PWD. In the first breeding project, conducted from 1978 to 1984 in southwestern Japan, 16 and 92 resistant clones of P. thunbergii and P. densiflora were selected, respectively [8,9,10]. Up to March 2019, several related projects have led to the selection of 211 and 288 resistant clones of P. thunbergii and P. densiflora, respectively [11]

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