VI Trends in Varieties
There are many varieties of sweetpotatoes cultivated in Japan which are mutations of varieties originally introduced into the country during the Edo to Meiji eras. Additionally, new varieties have continually been developed in response to ongoing needs. Before the war, when sweetpotatoes were used mainly for food, the delicious but low-yielding "Genji" and "Beniaka" varieties accounted for more than half of all plantings. During the war years, the high-yielding "Gokokuimo" and "Okinawa No. 100" found favor, as they were better suited for alcohol production. After the war, producers turned first to "Norin No.s 1 and 2" - both suitable for household and processing uses - when food was in extremely short supply; then subsequently to "Tamayutaka" and "Koganesengan" accounting for about half of production area during the period when higher-starch varieties moved into demand. Recently, demand has focused on sweetpotatoes for fresh consumption, as demand for higher-starch varieties has declined with the widespread availability of inexpensive corn starch.
1. Outline of varieties by use
Since sweetpotatoes are used for an extremely wide range of applications, individual varieties must be carefully matched with their intended purposes. At present, the general-use "Norin No. 1" and "Koganesengan" varieties are both very popular. Some of the different characteristics of leading varieties are outlined below.
(1) Varieties for fresh consumption
Red skinned sweetpotatoes have been used for fresh consumption for many years. The most popular types for fresh consumption tend to share certain characteristics: clear red to pinkish skin, spindly shape, light yellow to yellow flesh, dry powdery, fresh sweet, good texture feel. Especially in the Kanto area, powdery fleshed varieties are popular, making "Beniazuma" the market leader, followed by tasty "Benikomachi" and "Beniaka." In areas to the west of the Kanto area, the most popular varieties are "Kokei No. 14" and its mutants "Narutokintoki", "Tosabeni", "Kotobuki", and "Benisatsuma." [Note: The "Kotobuki" is produced in Miyazaki Prefecture.]
(2) Varieties for processed foods
Dried slices of steamed sweetpotatoes (Hoshiimo) have an ancient history. First produced in Shizuoka Prefecture, this product is now a local specialty of Ibaraki Prefecture. The best 'Hoshiimo' has no white center and has a soft, amber appearance when dried; in general, sticky varieties are regarded as best suited for drying. One popular choice is the smooth-shaped, high-yielding "Tamayutaka."
When it comes to making kinton (mashed sweetpotatoes tasting like sweetened chestnuts) or sweetpotato paste, "Kokei No. 14" and "Beniaka" are used instead. Both types are easy to peel, require little steaming, have low fiber levels, and low discoloration.
For roast sweetpotatoes, on the other hand, the important factors are taste, flesh quality, and yield when roasted. Highly storable varieties with less degradation and weight loss are suitable. "Norin No. 1" was formerly a popular choice for these reasons, but "Beniazuma" has now replaced it in the Kanto area.
(3) Varieties for starch-related products
For sweetpotatoes intended for use in starch-related products, the most important characteristic is high starch production per unit area. Starch factories desire high production yields, easy production and high product quality. "Koganesengan," released in 1966, was once grown across Japan owing to its high production and yield, but its poor storability proved to be a problem. It has since been replaced by the newer "Shiroyutaka" (1985) and "Shirosatsuma" (1986) varieties. The new "Satsuma Starch" (1994) variety, which contains extremely high levels of starch, is the latest candidate for popularity.
(4) Varieties for feed
The harvest season of sweetpotatoes is limited to only a few months, starting in September, and subsequent storage can be difficult. These factors make year-round utilization of sweetpotatoes difficult. Proper storage, however, enables sweetpotatoes to be stored for considerable periods. Tsurusengan (1981) is an improved variety exclusively for silage feed in summer. When mainly sweetpotatoes are used for feed, varieties for starch-related products can be utilized. Varieties adapted to a high level of fertilization should be selected, so they can be fertilized with manure.
2. Planting trends for major varieties
The relative shares of different sweetpotato varieties have changed greatly in the last 50 years. At present, the so-called "improved varieties" developed by national breeding programs have a dominant (over 90%) share of the market. Trends for the major sweetpotato types (classified by use) are described below.
(1) Varieties for fresh consumption
The tasty, high-yielding "Beniazuma" (1984) has grown in share steadily, while that of "Kokei No. 14" (1945) has remained almost unchanged. The traditional variety, "Beniaka" has lost share due to its difficult cultivation requirements, despite its good taste.
(2) Varieties for processed foods
The share of "Tamayutaka" (1960), used for dried, sliced steamed sweetpotatoes and produced mainly in Ibaraki Prefecture, has remained almost unchanged.
(3) Varieties for starch-related products
The "Shiroyutaka" (1985) and "Shirosatsuma" (1986), both of which feature high starch yields and high disease resistance, have added share at the expense of the general-purpose "Koganesengan" (1966).
○ Changes in shares of major varieties
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Bred varieties |
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Traditional varieties |
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(1) Breeding efforts
As part of an effort to develop better sweetpotatoes, national institutes and prefectural experiment stations are working to develop varieties having specific traits, with particular emphasis placed on product quality, ingredients, storability and processing performance. One challenge is to improve the sweetpotato's resistance to pests and diseases including soil diseases, viruses and nematodes.
Progress is underway to develop high quality sweetpotato varieties suitable for direct planting (bypassing the need to grow sprouts for transplanting). This is one part of the project begun in 1999, "Creating New Demand for Selected Crops through Development of High Quality Varieties and Farm Labor Reduction Technology."
(2) New varieties in recent years
There has been growing emphasis in recent years on the functionality of sweetpotatoes, including their suitability for used in processed foods. New varieties that address these considerations include "Benihayato" (1985), containing more carotene than carrots, the non-sweet "Satsumahikari" (1987), suitable for processed foods, "Ayamurasaki" (1995), the world's first variety bred especially for anthocyan pigment material, J-Red (1997), suitable for beverage production, Sunny Red (1998), suitable for powder production, and so on.
For starch-related products, the very-high-starch "Satsuma Starch" (1994) is now under cultivation. For shochu, "Joy White" (1994) provides shochu with a fruity aroma absent in conventional shochu.
○ New Varieties Released in Recent
Years
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Benihayato |
1985 |
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For food processing uses, high carotene content |
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Satsumahikari |
1987 |
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Low beta-amylase activity, light taste, good storability |
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High Starch |
1988 |
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Extremely high starch content, high starch yield |
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Beniotome |
1990 |
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Excellent appearance, high yield, high commercialization rate, good storability |
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Healthy Red |
1993 |
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Slightly high carotene content, good appearance and taste, suitable for steamed, dried, sliced sweetpotato |
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Satsuma Starch |
1994 |
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Extremely high starch content, high starch yield |
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Joy White |
1994 |
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Provides shochu with a fruity aroma. |
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Ayamurasaki |
1995 |
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For anthocyan pigment material |
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Elegant Summer |
1996 |
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Petiole can be used as a vegetable. |
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J-Red |
1997 |
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High carotene content, low starch content, high-yield, suitable for beverage processing |
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Harukogane |
1998 |
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Excellent appearance, good taste, suitable for fresh market |
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Sunny Red |
1998 |
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High carotene content, resistant to root-knot nemotode, suitable for powder production |