Bulletin of The Iwate Agricultural Research Center No.17

Molecular approaches to identifying apple moths and to clarifying the genetic structure of the two-spotted spider mite in apple orchards
Hiroshi HADA
 There are two main pests in apple orchards of Iwate Prefecture, both extremely difficult to control. One is the group of fruit moths (Lepidoptera), whose internally feeding larvae directly attack the fruit, and the other is the leaf-feeding spider mites (Acari) that rapidly develop resistance to various kinds of chemicals. In this study, we first clarified the identification of three apple moth species, which are difficult to discriminate based on larval morphology alone: oriental fruit moth, Grapholita molesta (Busck), Grapholita dimorpha Komai, and peach fruit moth, Carposina sasakii Matsumura. Because their ecology (e.g., overwintering sites and feeding habits) is critically different, the first step of effective control is to accurately and easily identify the species using multiplex PCR (polymerase chain reaction). Next, we analyzed the genetic structure of populations of the two-spotted spider mite (Tetranychus urticae Koch) collected throughout Iwate Prefecture, to clarify how this particularly voracious mite developed simultaneous resistance to various acaricides. The results of this study will provide basic knowledge to effectively control both pests.
 For the multiplex PCR method to differentiate the three Japanese fruit moth species, a 1,342-bp fragment of mitochondrial cytochrome oxidase subunit I (COI) was sequenced in each species. The species showed consistent and diagnostic differences in the region of the COI gene, from which three species-specific forward primers were designed. The forward primers along with one universal reverse primer were used to selectively amplify DNA from specimens of diverse geographic origin for each corresponding target species. This method enabled easy, immediate, and accurate identification of these internally feeding Lepidoptera in apples and other fruits.
 Many T. urticae populations in apple orchards of Iwate Prefecture are resistant to multiple acaricides. Here, we investigated the simultaneous development of acaricide resistance in various mite populations, assessing their genetic structure. In principle, two scenarios are possible: (1) acaricide resistance developed in one or a few populations with a common geographical origin (e.g., an apple tree nursery) and subsequently spread widely, or (2) acaricide resistance developed in many geographically distant populations. To this end, we used four microsatellite loci to analyze the genetic structure of 11 T. urticae populations collected from eight commercial apple orchards, one apple tree nursery, one experimental apple orchard, and one hop farm. In the commercial orchards and nursery, acaricides were used 2-3 times every year; in the experimental apple orchard, acaricides were not used after transplantation; and in the hop farm, a propylene glycol emulsion was used 6-7 times per year.
 Our data showed that all 11 mite populations were genetically differentiated and that distance affected the genetic structure of mite populations (i.e., populations were more different with increasing distance). Additionally, the population collected from the nursery was genetically distinct from all other populations. These results indicated that mite populations were indigenous to the respective orchard and did not originate from the nursery. Our data also showed that F
IS values were higher in populations collected from commercial orchards in which acaricides were applied frequently than in those collected from orchards in which chemical acaricides were not applied, suggesting that recurrent chemical treatments increased the frequency of inbreeding in T. urticae populations. Overall, the results showed that the recurrent chemical treatments have a strong bottleneck effect on T. urticae populations, which probably accelerated the development of acaricide resistance. Thus, acaricide resistance is likely to develop in many geographically distant mite populations repeatedly. It is therefore important to monitor acaricide sensitivity of T. urticae populations in individual orchards to fine-tune effective spider mite control.
Breeding of a New Rice Variety "Konjikinokaze"
Yuki OTA, Tsutomu SASAKI, Hiromi SUGAWARA, Hisashi KOWATA, Shinsuke NAKAJO, Takuma KODATE, Tomoaki FUJIOKA, Akira ABE, Yasunori NONOUE, Sanae KAWADAI-ABE, Hiroyuki KANZAKI, Hideo MATSUMURA and Ryohei TERAUCHI
 A new rice variety "Konjikinokaze" was developed at Iwate Agricultural Research Center in 2016. To develop a new variety with superior eating quality, this variety was selected from the cross between "Hit1073", which is a low amylose line derived from mutant lines of "Hitomebore", and "Hitomebore" in 2010.
 "Konjikinokaze" has been tested as local line "Iwate118" since 2015, and it was adopted as a recommended variety in Iwate prefecture in 2017. Characteristics of "Konjikinokaze" are as follows:
(1) It belongs to the late-maturity group in Iwate, and its heading and maturing dates are the same as those of "Hitomebore".
(2) Its plant type is panicle-number type.
(3) Its amylose content in the endosperm is slightly lower than that of "Hitomebore".
(4) It has high tolerance to sterility caused by low temperature at the booting stage that is equivalent to "Hitomebore".
(5) It is presumed to possess a true resistance gene "Pii" for rice blast. Its field resistance to leaf blast is "slightly weak" and to panicle blast is "medium", that are the same of "Hitomebore".
(6) It has high eating quality. Its cooked rice is stickier and softer than "Hitomebore".
(7) Its grain yield is about 10% lower than that of "Hitomebore".
(8) Its grain appearance is equivalent to that of "Hitomebore".
Breeding of a New Rice Variety “Yuinoka” suitable for Daiginjo-shu (high quality sake) brewing
 “Yuinoka” is a new rice variety suitable for Daiginjo (top quality) sake brewering. It was developed at Iwate Agricultural Research Center in 2011. This variety was selected from the cross between “Aokei-sake140(Hanaomoi)” and “Yamadanishiki”.
 “Yuinoka” has been tested as local line number “Iwate-sake98” since 2009. It was officially registered by Ministry of Agriculture, Forestry and Fisheries of Japan in 2014 (registration no. 23454).
 The major characteristics of “Yuinoka” are as follows:

(1) It belongs to the late maturity group in Iwate, and its date of maturity is 6 days later than that of "Ginginga".
(2) The plant type is panicle number type. Its panicle number per unit area is more than that of "Ginginga".
(3) Its culm length shorter than that of "Ginginga".
(4) The lodging resistance is slightly inferior to "Ginginga".
(5) Its tolerance to sterility caused by low temperature before heading is inferior to that of "Ginginga" and classified into "slightly low".
(6) It seems to have no true resistant gene for blast disease. Its field resistance to leaf blast is slightly susceptible, and that to panicle is slightly resistant.
(7) Its yielding ability is lower than that of "Ginginga".
(8) The weight of 1000 grains is lighter than that of "Ginginga". Its white-core region is smaller than that of "Ginginga". Additionally, its white-core region located into the center of grain at high ratio, compared to "Ginginga". Its size and location result in excellent polishing character (less broken rice grain in high polishing ratio).
(9) The suitability for Daiginjo-shu (high quality sake) brewing is equivalent to that of "Yamadanishiki".
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