Asatsuyu

Asatsuyu is a sencha cultivar selected from Uji zairai seedlings and registered in 1953 as Cha Norin No. 2 — the second cultivar named in Japan’s first round of tea variety registrations, immediately after Benihomare. It exists to answer a specific question: how close a seed-grown Uji-type tea can come, unshaded, to the flavour of a shaded gyokuro. Growers and researchers have called it 天然玉露, “natural gyokuro,” since that first registration bulletin, for a leaf colour and cup character that suggested shading effects the plant was producing on its own. Its long-term significance turned out to lie less in its own cultivation, which stayed marginal, than in its role as a parent: it is the pollen parent of both Saemidori and Tsuyuhikari, and the seed parent of Yutakamidori.

Lineage

• Uji zairai seed stand, Kyoto — an individual seedling selection from seed-grown Uji-type stock, not a controlled cross; no specific mother plant or pollen source is recorded.

Because Asatsuyu was picked out of an open-pollinated seedling population rather than bred, it has no recorded parents of its own — the same situation as Yabukita, selected from Shizuoka zairai seed the same registration year. What makes Asatsuyu unusual is the other end of the pedigree: it is a confirmed, named parent of three cultivars that between them anchor a large share of Japan’s post-Yabukita specialty tea. NARO’s own pedigree charts (茶品種ハンドブック) show it twice as a direct parent — as the pollen (male) parent of Saemidori (Yabukita ♀ × Asatsuyu ♂, crossed 1969) and, in the Shizuoka Tea Experiment Station’s own release paper, as the pollen parent of Tsuyuhikari (Shizu7132 ♀ × Asatsuyu ♂, crossed 1970). Shizu7132 is itself an open-pollinated Yabukita seedling, so Tsuyuhikari’s family tree runs Yabukita on both sides, once directly and once through Asatsuyu. Yutakamidori reverses the roles: it was raised as an open-pollinated seedling of Asatsuyu, with Asatsuyu as seed parent and the pollen source unrecorded.

Saemidori’s own descendants compound the pattern. NARO’s pedigree charts trace Kirari 31, Seimei, Kiyoka, Danshin 37, Saeakari and Haruto 34 all back through Saemidori to the same Yabukita × Asatsuyu cross of 1969 — meaning Asatsuyu’s genetic contribution recurs through a second and third generation of cultivars bred decades after Asatsuyu itself was registered.

History

The seedling that became Asatsuyu was grown from Uji-type seed sown at the Ministry of Agriculture and Commerce’s Agricultural Experiment Station, Tea Manufacturing Division, in Nishigahara, Tokyo. It was transplanted in 1921 (Taisho 10) to the ministry’s tea experiment station, by then relocated to Kanaya in Shizuoka — the institution’s line of succession runs through to today’s NARO Institute of Fruit Tree and Tea Science. Development was completed there in 1944 (Showa 19), under the working designation Kokucha U14 (国茶U14号).

It was registered in October 1953 as Cha Norin No. 2, one of fifteen cultivars named in Japan’s first round of tea variety registrations — ten for green tea (eight sencha, one tamaryokucha, one kamairicha) and five for black tea. The registration bulletin, 茶の品種登録と命名 (茶業研究報告 No. 2), gives its suitable range as northern Kyushu, the Chugoku region, and the prefectures near Shizuoka, and summarises it as a strong-growing, upright cultivar with long-elliptic, deep-green leaves, “excellent as a green tea, particularly as ordinary sencha, and known by the alternative name natural gyokuro.” The bulletin’s own naming rationale for that alternative name is short and specific: dark leaf colour, not chemistry.

A parent more consequential than a cultivar

Asatsuyu’s own footprint stayed small, but the two crosses made from it in 1969 and 1970 turned out to matter far more. Saemidori, crossed at Makurazaki in Kagoshima with Yabukita as the seed parent and Asatsuyu as the pollen parent, was registered under Cha Norin No. 40 in 1990 and separately under the Plant Variety Protection Act (No. 2881) in 1991 — it went on to become one of the most widely planted specialty cultivars in Japan and a parent in its own right several times over. Tsuyuhikari, crossed the following year at the Shizuoka Tea Experiment Station from Shizu7132 (a Yabukita seedling) and Asatsuyu, was selected by individual selection in 1979, trialled for local adaptability from 1991 to 1997, adopted as a Shizuoka Prefecture recommended cultivar in 2001, and registered under the Plant Variety Protection Act in 2003; the release paper credits it with high yield, cold hardiness better than Yabukita’s, and fair resistance to tea anthracnose. Yutakamidori, grown from open-pollinated Asatsuyu seed at the national tea experiment station, never received the same formal registration but is documented in NARO’s pedigree charts as a parent of later cultivars including Kanaemaru (2022).

Characteristics

Field data complicates the budding-time question. The 1953 registration bulletin classed Asatsuyu as 中生種, medium-season. Field trials tell a different story: in a 1991 comparison of 13 cultivars planted at Mizobe in Kagoshima, Asatsuyu and Yutakamidori budded earliest of all, ahead of Sayamakaori (itself roughly two days ahead of Yabukita) and Yabukita itself. Modern secondary sources consistently describe it as 早生, early — this record follows the trial data as the better-sourced and more specific claim, while noting the bulletin’s older classification as a documented disagreement rather than silently overriding it.

That early budding comes at a cost the same trial documents directly. A late-frost event in the spring of 1990 damaged nine of the thirteen cultivars under test to some degree, and the paper singles out Asatsuyu and Yutakamidori — the two earliest budders — for the most conspicuous bud damage, worse than Yabukita’s. Field survival tells the same story from a different angle: four years after planting, Asatsuyu had the lowest bush survival of the five cultivars in its test group — 67.50 on the paper’s arcsin-transformed scale, roughly 85% untransformed, below Yabukita (83.07, roughly 98%) and Toyoka, Kanayamidori and Yutakamidori (90.00, full survival). It was poor enough that the researchers excluded Asatsuyu from that year’s harvest and yield measurements altogether, rather than report figures from a badly thinned plot. A separate 1996 varietal survey rated it susceptible to slightly susceptible to tea gray blight. Together this is a reasonably direct documentary basis for the cultivar’s reputation as low-yielding and disease-prone: it is not simply a repeated rumour, but the outcome recorded in at least one controlled multi-year trial.

The cup is where Asatsuyu earns its reputation. Processed as ordinary or deep-steamed sencha, it gives a bright, lush green liquor and a grain-and-nori-toned umami character that tasting notes compare to shaded teas — the origin of “natural gyokuro.” How well-founded that comparison is chemically is harder to pin down than the tasting notes suggest. The 1953 registration bulletin’s own stated reason for the nickname is leaf colour, not amino acid content, and this research did not turn up a controlled study directly comparing Asatsuyu’s theanine or free-amino-acid levels against other unshaded sencha cultivars to establish shading-like chemistry as the mechanism. What the literature does show is that Asatsuyu has long been treated as a serious reference point for amino-acid quality: a 1984 study used it as the baseline cultivar against which a spontaneous mutant’s free amino acid content (105.8–332.9% of Asatsuyu’s) and tannin content were measured. That is evidence Asatsuyu’s amino-acid profile has been taken seriously enough to build comparisons on, but it falls short of proving the specific “gyokuro without shading” mechanism. On present evidence, “natural gyokuro” is best treated as a long-standing, officially adopted descriptive name — predating any modern marketing use by decades — whose stated basis is visual (leaf colour) and whose implied biochemical basis (amino acids standing in for theanine-rich, shade-grown character) is plausible and consistent with how the cultivar is used, but not something this research could confirm with a direct comparative assay.

None of this made Asatsuyu a commercial success on its own terms. It is grown today mostly in warm, frost-light districts — Kagoshima is the region most often cited, though this research could not independently source a cultivation-area or regional-share figure to put a number on it. What did succeed, decisively, is its genetics: crossed twice in 1969 and 1970 while its own plantings were struggling with survival and frost, it became the pollen parent behind Saemidori and Tsuyuhikari, and through Saemidori’s own many offspring, one of the two cultivars — with Yabukita — that most of Japan’s post-war specialty sencha traces back to.