1V66] H A W K I N S : POTATO VARIETIES 253

NEWS AND REVIEWS

P O T A T O V A R I E T I E S - - T H E P A S T AS A K E Y T O T H E F U T U R E IN C O N N E C T I C U T

A R T H U R H A W K I N S 1

The variety of potato grown is a prime factor in obtaining efficiency in production. The variety factor is related to other factors in obtaining higher yields at lower cost per unit of marketable potatoes. The factors other than just being a natural higher yielding variety for the climate at hand include susceptibility or resistance to disease and insects, tolerance to heat and drought, length of growing season required, response to soil reaction ( pH) and nutrients, resistance to bruising, and storage quality.

These are variety factors the grower must consider in addition to the tuber characteristics which make the variety aeeptable to consumer or processor.

The history of well known varieties gives a clue to characteristics required of new varieties, if they are to serve and survive.

A LESSON FROM HISTORY

Green Mountain displaced by Katahdin. For the past fifteen years the Katahdin variety has been the primary potato variety grown in Con- necticut. It is planted on about 90% of the Connecticut potato acreage, with Kennebec and Chippewa varieties next in importance - - with Green Mountain on only about 1% of the acreage. Back in 1940 about 95% of the Connecticut potato acreage was Green Mountain plus Irish Cobbler and other varieties including some acreage of the newly developed Chip- pewa.

Why the change to Katahdin? The Katahdin developed and re- leased by U S D A in 1935 was tried commercially in Connecticut in the early 1940's as seed became available. This variety is resistant to mild mosaic, field resistant to leaf roll, and is resistant to tuber net necrosis and stem end browning, in contrast to Green Mountain which is sus- ceptible to most of the common potato diseases.

Katahdin develops tubers of satisfactory shape and good storage ability even if subjected to hot, dry growing conditions. In addition to being especially acceptable for boiling and french fries, it produces good-colored potato chips. Although the Green Mountain was especially good for baking, its susceptibility to internal tuber discoloration, and irregular shape, frequently made it more difficult to market than Katahdin.

By 1948 as seed became available and its popularity assured, Katahdin was planted on nearly 50% of the commercial acreage in Connecticut.

In 1949, in one of the hottest and driest seasons, when little irrigation was practiced, Katahdin proved its superiority over Green Mountain. The growing season favored development of stem-end jelly rot in long-type tubers as in the Green Mountain variety. Katahdin produced considerably higher yields of marketable tubers. As a result, Katahdin nearly displaced the entire Green Mountain acreage in 1950.

1Potato Specialist, the University of Connecticut, Storrs, Conn. Reprinted from 1966 Connecticut Potato Yearbook.

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Growers learn to grow Katahdin. The Katahdin variety was found to be much more susceptible than Green Mountain to toxic conditions which occur in excessively acid soil, especially if the soil is low in organic matter. Experiments conducted by the Storrs Agricultural Experiment Station, University of Connecticut, on commercial potato farms showed the need for liming soil up to the point of favoring scab, and plowing in organic matter from green manure crops to reduce toxic soil conditions.

More careful hilling is required for the Katahdin variety to reduce greening of tubers and field frost. Katahdin is less susceptible to blight, and has smaller vines. The reduced vine growth favors weed growth, but this has been overcome with the use of weed control chemicals as necessary.

POTATO VARIETY TRIALS

Potato variety tests have been conducted annually since 1948 by the Storrs Agricultural Experiment Station and Extension Service, University of Connecticut in cooperation with commercial growers in the Connecticut River Valley.

Performance information was obtained on newly released varieties and on promising numbered selections in comparison with standard varieties. Marketable yields, internal tuber discolorations, specific gravity, and chipping quality were determined.

Results: The unadaptability of many new varieties was shown by these tests and growers were cautioned about trying new varieties not adapted to Connecticut conditions. Those that were promising were sug- gested for trial.

Results of variety tests show the importance of testing varieties at more than one location in one year, and the need for testing varieties for at least three or four years before recommending them for trial.

The Ontario varietv when released was of special interest because of its resistance to scab. Iic produced high yields in six tests in three years 1948-1950. But it was only in the third year, 1950, that under hot soil conditions internal drought spot was noted in the tubers. At one location 1855 of the tubers had red to brown discoloration of the flesh, while at the second location 809o had this discoloration.

The Saco variety was found to be a high producer of higher specific gravity potatoes under good weather conditions but produced a very high percentage of non-marketable ill-shaped potatoes in a poor growing season.

Mohawk produced good yields of higher dry matter potatoes similar to Green Mountain but of better shape. However, it produced a high percentage of large tubers with hollow-heart under ideal tuber developing conditions. Prevention would require closer seed spacing and attention to vine-killing as needed to check size of tubers. Excellent yields were obtained with irrigation in 1961 but with 8% hollowheart at 9-inch spacing.

Many varieties tried have produced tubers of higher dry matter and satisfactory appearance but yields were 25% or more lower than Katahdin grown under the same conditions. Such varieties included: Avon, Canso, Cherokee, Delus, Keswick, Merrimack, Plymouth. Other varieties that did not yield well included Blanca, Emmet, Early Gem, Onaway, Navajo, Keeweenaw and Tawa.

1966] HAWKINS: POTATO VARIETIES 255

Following are comments on varieties which have produced well under certain conditions, and are compared with Katahdin:

Chippewa: Early, yields well on soils with good moisture holding capacity or with ample irrigation. Avoid planting on droughty soils. Usually lower specific gravity. Good for boiler. Not generally good for long time storage.

Kennebec: Resistant to blight in vines only. Very susceptible to verticillium wilt, and to pink eye of tuber. Sets tubers close to surface, subject to greening and field frost. Thin skin greens easy; bruises easy; requires very careful handling. Requires careful attention to storage management. Consistently outyields Katahdin under good growing con- ditions. Since it sets fewer tubers per hill, space seed 8 inches for good growing conditions. On lighter soils it develops irregular-shaped tubers, growth cracks, and jelly-end rot unless soils are irrigated as necessary. This variety requires uniform growing conditions more likely available on heavier soil or where supplemental water can be applied to lighter soils as needed. Growers are cautioned not to grow this variety where verti- cillium wilt has been or might be expected to be a problem.

Pungo: Medium late variety; russetty skin; resistant to late blight. Usually slightly higher dry matter than Katahdin. Under fast growing conditions tubers may become irregular in shape but not as deep-eyed as Cobbler. Only under good growing conditions will it outyield Katahdin.

Teton: Produces yields similar to Katahdin, with about the same dry matter. Since it sets tubers deeper in the soil there is less problem with exposed tubers. Tuber shape is similar to Katahdin but with a deep blossom-end cluster of eyes. Teton was suggested for trial in 1957; several growers tried it and were pleased with it. However, seed has since become unavailable from seed producing areas.

Houma: Resistant to verticillium wilt. Produces a large vine that is very susceptible to late blight. Tubers are of higher dry matter than Katahdin. It produces as good or better yields than Katahdin under good growing conditions. Under hot, dry conditions the yields and tuber shape are not a~" good as Katahdin. Since it produces a large number of tubers per hill, seed needs to be spaced 11 inches or farther as compared with nine inches for Katahdin. Saranac, highly resistant to verticillium wilt, proved very promising in good seasons but was found unadaptable during hot dry seasons.

REQUIREMENTS OF FUTURE POTATO VARIETIES

Resistance to Verticillium wilt and scab are requirements of the future potato variety along with high yielding ability of marketable tubers with consumer and processing acceptance and the other desirable variety char- acteristics outlined in the opening paragraph.

Verticillium wilt control. The most important potato production prob- lem in recent years is Verticillium wilt control. This problem has become of increasing importance with the production of potatoes more frequently on the same land, as compared with longer rotations with tobacco in previous years.

Verticillium wilt build-up in the soil occurs faster with the susceptible Kennebec variety, especially if the seed is infected. This is also a problem

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in the areas which supply the seed. Increased Verticillium wilt in the areas producing seed also plays a part in increased Verticillium wilt in the seed brought in.

Current control includes: a) rotation with crops not susceptible to the disease such as tobacco, grass sods, millet, and corn, b) the planting of less susceptible varieties and c) use of seed clean or low in Verticillium wilt infection. Investigations are underway on the use of less costly soil fumigation materials for control of this disease and nematodes on infected soils.

Scab resistance. When resistance to both Verticillium wilt and scab are bred with high yielding ability of marketing potatoes, efficiency of production should increase considerably.

Potato soils are now kept acid for control of scab. Field observations on lime-rate plots in Connecticut showed that Vr wilt became more severe, as well as scab in a susceptible variety, where large amounts of lime had been applied.

If a potato variety was resistant to both diseases, higher amounts of lime could be applied to eliminate the toxic soil problem associated with 'highly acid soil. Less phosphorus is required for potatoes on less acid soils; phosphorus could be used more efficiently. At present much of the phosphorus applied on acid soils is used to counteract the toxic soil con- ditions which would be corrected at much less cost with lime. Also enough magnesium limestone could be applied to supply ample magnesium for the potato. Until a suitable scab resistant potato variety is available, potato soils will of necessity have to be maintained acid.

The possibilities of a suitable variety resistant to both Verticillium wilt and scab was proven with the development of the Ona variety. In addition it is also resistant to late blight and virus A. Ona in 1964 pro- duced higher yields than other commercial varieties at a location in Con- necticut highly infected with Verticillium wilt. Where the disease was not a problem, Katahdin and Kennebec produced higher yields of market- able sized potatoes than Ona in test plots in 1964 and 1965 in Connecticut.

Since Ona is a very late variety and sets a large number of tubers per hill, cultural practices may possibly be modified to promote earlier maturity and larger tubers and yields of marketable-size potatoes.

Thirty-seven seedlings (unnamed varieties) which had proven to be superior in some characteristics in preliminary tests elsewhere were compared on two farms in Connecticut in 1965. Two of the seedling selections that were resistant to both Verticillium wilt and scab, produced higher yields than Katahdin at both locations tested in 1965. One of them produced tubers with specific gravity about the same as Katahdin while the other had a considerably higher specific gravity and produced good quality chips. Several other selections of the 37 tested appeared worthy of further trial in larger plots in 1966.