A new cultivar of green tea ‘Kirari31’ was developed at the Tea Branch Facility, Miyazaki Agricultural Research Institute and released in 2013. ‘Kirari31’ was selected from seedlings of the crosses between ‘Sakimidori’ and ‘Saemidori’, which were created in 1994. The characteristics of ‘Kirari31’ are as follows : ‘Kirari31’ is early budding and plucking time of the first crop is about three days earlier than that in ‘Yabukita’. The shape of the plant is of intermediate type and its growth is vigorous. ‘Kirari31’ is fairly resistant to tea gray blight (Pestalotiopsis longiseta [Speg.] K.Dai & Ts.Kobay), but it is susceptible to tea anthracnose (Colletotrichum theae-sinensis [I.Miyake] W.Yamam) and tea blister blight (Exobasidium vexans Massee). It is slightly susceptible to bacterial shoot blight (Pseudomonas syringae pv. theae [Hori 1915] Young, Dye & Wilkie 1978). ‘Kirari31’ is resistant to cold injury damage in winter. The yield of ‘Kirari31’ is higher than that of ‘Yabukita’. Sencha, Kabusecha, and Gyokuro to make with ‘Kirari31’ is high quality, as indicated by the bright green color of tea and mild aroma and taste. The amino acid content in the processed tea is high, whereas the tannin content is low.
Required number of leaves and how to use ‘Phyto-traps’ were investigated to estimate the density of phytoseiid mites in an experimental tea plantation in Japan. Seasonal dynamics and species composition of phytoseiid mites in relation to spider mites will be estimated well on the basis of the total number of phytoseiid mites on 500 leaves. The mite-brushing machine is necessary for the 500-leaves inspection. In the cases of the inspection without the mite-brushing machine, it is desirable that the minimum number of leaves is determined by the preliminary investigation. For the phytoseiid mites in weak relation to spider mites, 30-50 traps are necessary to estimate mite density. It is better to set those traps out lower branches of tea trees, and keep those for 6-7 days. Traps should be collected in the morning or afternoon after setting those for a week. The dynamics of the number of phytoseiid mites are confirmed by the inspection of existence (or not) of phytoseiid mites in the traps. When phytoseiid mites exist in more than 70% of traps, the species composition may be estimated by the inspection of all mites in the traps.
Radiocesium release following the accident at the Fukushima Dai-ichi Nuclear Power Plant, operated by the Tokyo Electric Power Company, caused severe contamination of new tea plant shoots in many prefectures in eastern Japan in 2011. Consequently, many studies to reduce the radiocesium levels in tea have since been conducted. In this study, we investigated the radiocesium activity in tea leaves and stems classified through the refining process. The radiocesium activity in stems was 14% and 23% higher than those in ara-cha (unrefined tea) and tea leaves classified through the refining process, respectively. However, stems only make up approximately 10% of ara-cha, and thus only a minimal reduction of radiocesium activity in sen-cha can be expected by removing stems during the refining process.
This study investigated the cultivar differences in new shoot growth, hardening of leaves and component of first crop of five tea cultivars. ‘Tsuyuhikari’ had more opened leaves per day than the other four cultivars. The hardening of new leaves, the rate of increase in the yield per unit area and decrease in total nitrogen content in the new shoot differed with the cultivar. The hardening degree of the middle or lower leaf at the 4-5th leaf stage of ‘Tsuyuhikari’ and ‘Kousyun’ was lower and that of ‘Yamanoibuki’ and ‘Okuhikari’ was higher than that of ‘Yabukita’. The total nitrogen content in the new shoot of ‘Tsuyuhikari’ was higher at the optimum plucking time and decreased at a lower rate than that of ‘Yabukita’.
In collaboration with Matsumotokiko Co., Ltd., we have developed a novel method for pesticide reduction using a riding-type pesticide sprayer (the “Kagoshima-style” pesticide sprayer) in tea fields that makes use of a small fog nozzle and a ventilator. This pesticide sprayer facilitates a marked reduction in the pesticide spray volume. It can also be installed in the conventional riding-type pest control machines and tractors. In the first year of examination, this novel method provided results equivalent to those of conventional methods. The influence of pesticide reduction on pest management remains to be elucidated. However, this technology presents possibilities of practical use. We would also like to advance the improvement of this method in order to correspond to tea fields in every region of the country.
We investigated the relationship between the number of Trichogramma spp. captured by yellow sticky traps and the number captured by sticky suction traps on the plucking surface and in the space between hedges in tea fields. Our aim was to examine the usefulness of the former type of trap in Trichogramma spp. monitoring. Total number of adult Trichogramma spp. captured by yellow sticky traps and sticky suction traps per trap was 243.8 (the number of traps 12 ; sticky area 200cm2) and 1184.5 (the number of traps 2 ; sticky area 400cm2), respectively, during investigation period. Total number of Trichogramma spp. captured by yellow sticky traps per sticky area was 41% of total number of Trichogramma spp. captured by sticky suction traps. Seasonal changes in the numbers of Trichogramma spp. captured by the yellow sticky traps on the plucking surface, in the space between hedges, and the numbers averaged both parts were synchronized with the seasonal changes in the numbers captured by the sticky suction traps. These results suggested that the yellow sticky traps could be used instead of the sticky suction traps to investigate the occurrence of Trichogramma spp.
Method for the determination of the geographic origin of green teas was developed using sencha (most popular green tea in Japan) samples produced in Japan, China and Australia. Similarly, the method was also developed among Shizuoka, Mie and Kagoshima prefectures which accounted for about 75% of sencha production in Japan. Ten elements (Al, Ba, Cu, Fe, Mg, Mn, Ni, Rb, Sr, Zn) were analyzed in sencha samples originated in three countries or in three prefectures described above. Based on CDA (canonical discriminant analysis), 6 elements (Ba, Mg, Mn, Ni, Rb, Sr) were found to be effective in the determination of the geographic origin among three countries. After examining the samples not using for the modeling to elucidate the reliability of the got CDA model, it was classified 97% correctly. Similarly, based on CDA, 7 elements (Al, Cu, Fe, Mg, Ni, Rb, Zn) were found to be effective in the determination of the geographic origin among three prefectures. It was classified 95% correctly. Those results suggested that it could be possible to determine the geographic origin of sencha using the metal-element composition.