V. Tests of Inbred Strains for Disease Resistance

Last spring seed of five inbreds furnished by Professor Hayes and eight by Professor Wiggans were sent to eight cooperators in various parts of this country. All these strains were supposed to be more or less resistant to smut. Some of them were shown to be less smut resistant than expected, several proved very susceptible to bacterial wilt (Stewart's disease) and a few susceptible to rust.

1. Smut.

I have attempted to present a summary of the observations on smut in tabular form, below:

Minnesota cultures grown under smut-epidemic conditions. Longfellow variety had 65.6% smut. H. K. Hayes.

Iowa season excellent for testing smut resistance; smut infection in general was one of the heaviest in several years. A. A. Bryan.

West Virginia check variety showed 75-80% smut. C. Burnham.

Notes of smut infection -

• Line C86-34, no smut reported; 214, little smut at Ames, Ia. only; 206, light smut at Morgantown, W. Va. and Ithaca, N.Y.; S283, light smut at St. Paul, Minn. and Ithaca, N.Y. only; S42, light smut at St. Paul, Morgantown, and Ithaca; 211, some smut at St. Paul and New Haven.
• Line 208, showed medium to high percentages of smut infection in most tests; at Morgantown, New Haven, and Ithaca, smut with one exception limited to light tassel infection, but at Ames five ears were smutted.
• Lines 212 and 213, showed heavy ear-smut infection in some tests.
• Line C70-34, little to no germination in all tests.

2. Rust.

Pasadena, Calif. Little smut in 1935, none on strains in test. Lines 208 and 211 very badly rusted; 209 moderately badly rusted; 210, 212, and 213 lightly rusted; 206 and 214 free from rust and easily the most desirable for this locality. E. G. Anderson.

Ithaca, N. Y. Lines S42 and 211 some rust; 208 much rust, but too late to injure plants very seriously. There is some rust present every year at Ithaca, but it usually comes too late to be a serious disease. During two widely separated seasons, however, when rust had been introduced inadvertently with seedlings transplanted from the greenhouse early in summer, a very severe epidemic occurred. Many of the more susceptible stocks were killed before flowering time. If conditions should arise by which early infection were brought about, rust would be our most serious disease. R. A. Emerson.

New Haven, Conn. "Apparently one of our inbreds, Connecticut 2, an inbred out of the Whipple variety of sweet corn, is completely susceptible to rust. We had no rust here during the years that we were inbreeding Whipples from 1925 to 1928. Sometime later, I think in 1929 or 1930, we noticed considerable rust on this one inbred. Aside from rust Connecticut 2 has proved to be our best Whipple inbred and the one we are using in a great many crosses. It is used as the pollen parent and is never damaged so much that it will not make sufficient pollen. It always makes a good crop of seed when planted early. Last year the Eastern States Farmers' Exchange at Springfield, Mass. planted about an acre of Connecticut 2 for increase. They planted this late in order to avoid contamination from the pollen of sweet corn growing near by. This field of Connecticut 2 was so badly damaged that it did not make a single ear. I am doing some convergent improvement on this inbred and using Rhoades method of inoculating the seedlings so I can get a similar inbred resistant to wilt." Of the inbreds in the cooperative test the only one seriously affected by rust was 208 in which about 80% of the leaf area was covered by rust pustules. Somewhat susceptible strains were, in order of susceptibility: 211, 30%; 209, 20%; 206, 213, and S283, 10%, the latter had a few scattered pustules on the leaves of all the plants. W. Ralph Singleton.

3. Bacterial blight (Stewart's disease).

Morgantown, W. Va. Lines S54 and 209 very susceptible to wilt; C86 and S42 poor plants, wilt (?) susceptible. Chas. Burnham.

Washington, D.C. At Arlington Farm, resistance to bacterial wilt is of much greater importance than smut resistance. We seem to have universally heavy infections of wilt and susceptible lines are almost completely wiped out. Such was the case this season. Dr. Wiggans' lines 206, 208, and 210 were outstandingly the most resistant. Merle T. Jenkins.

4. Lodging.

Washington, D.C. Lines 206, 208, and 210 looked better than everything else until late in the season. In the heavy storm we had in September, 206 and 210 lodged somewhat, whereas 208 remained erect. Merle T. Jenkins.

Morgantown, W. Va. Lines S283 and 211 no lodging; 206, 208, and 214 some lodging; 210 and 212 badly lodged. Chas. Burnham.

Ames, Iowa. Lodging recorded by grade: 1 = little or none, and 5 very much lodging. Roots and stalks noted separately to determine whether lodging due to weak roots or weak stalks.

A. A. Bryan.

5. Firing.

Ames. Line 209, top leaves burned badly just prior to tasseling. A. A. Bryan.

St. Paul. Line 213, some firing; 209, upper leaves rather heavily fired. H. K. Hayes.

6. Ear notes.

Ames.

A. A. Bryan.

St. Paul. Line 211, rather undesirable ears at harvest. H. K. Hayes.

Ithaca.

Obviously these inbreds differ widely in ability to produce sound and well filled ears at Ames and Ithaca. R. A. Emerson.

7. Summary.

The lines most generally resistant to smut are, in order of greatest resistance:- C86-34, 214, 206, S283, S42, 211. Line 208 showed the highest percentage of smut, but in most instances the infection was light and in the tassel only.

In rust susceptibility, line 208 showed the most infection, 209 and 211 much rust, and 206, 210, 212, 213, S42, and S293 some rust.

Bacterial blight was most injurious to lines S54, 209, C86, and S42. Lines 206, 208, and 210 were most resistant.

At both Ames and St. Paul, line 209 showed bad firing.

In set of seed, quality of ear, amount of lodging, there was little uniformity.

The following comments are of interest:

• Line 211, "excellent". A. A. Bryan, Ames.
• Under Arlington Farm conditions, I don't think there is any question but that 208 is by far the best line of the whole lot. M. T. Jenkins.
• [Lines 206 and 210 were good except for lodging.]
• The starred lines [206, 208, 211, 214] I consider good enough for use in crosses with genetic testers. C. R. Burnham.
• My choice of these lines would be about as follows, starting with the best; 214, 206, 210, 213, 211, 208, 212. E. G. Anderson.
• Line 208, very nice strain, vigorous. Lines S42, S283, 206, 210, 211, 212, 214, desirable types.
• C86-34 fair, 200 and 213 undesirable. H. K. Hayes.

From all these comments, it would seem that lines 206, 210, 211, 214 have rather wide adaptability and that, where rust and smut are not troublesome, line 208 may prove satisfactory. Sprague, however, reports that at Columbia, Mo., none of the lines have value.

8. Some cooperators have indicated a willingness to test these lines further and to include some of their own. Any of you, whether or not you helped in the test in 1935, who are willing to conduct a test in 1936, will be furnished seed in so far as it is available or can be obtained. If any of you have other inbred strains, thought to be highly resistant to diseases and which might be adapted to a relatively wide range of climatic conditions, I shall be glad to arrange for tests. We shall probably be unable, however, to handle any large number of strains.