Red Cotyledon of lettuce study of abnormality shows seedling growth not always retarded, calls for modified germination requirements

Wesley H. Dempsey and James F. Harrington

Many lettuce seedlings with red coty- must have produced normal plants. Evi- ledons--seed leaves-produce normal dently a slight reddening of the cotyledon plants, and their general classification as is not serious enough to produce a weak abnormal is not justified. plant as long as the roots are normal. The high percentage of seedlings with To further test the effect of red coty- red cotyledons constitutes a new problem ledon on subsequent plant growth, trans- for California lettuce seed growers and plants were made from the germination seedsmen. Because of the inflexible rules tests of normal, abnormal C, and abnor- defining a normal seedling, seed analysts mal B seedlings. There were three repli- are forced to call reddening of the coty- cations of each lot. After four weeks ledons symptoms of abnormality. As a growth in flats in\the greenhouse all result, many lots are rated low in germi- plants appeared to be growing normally. nation even though most of the seedlings Fresh weight determinations were made are normal except for the reddening of of each treatment. The results are shown Red cotyledon condition in lettuce seedlings. the cotyledons. N is a normal seedling; c, b, and a are three in the following table. A slight but sig- An investigation was undertaken to de- categories of abnormal seedlings. nificant retardation of growth had oc- termine the effect of the red cotyledon curred among the B seedlings. condition on the production of lettuce high temperature and high humidity stor- Average Weight of Lots of Transplanted 54- plants. In addition to normal and dead age on the lot containing red cotyledon lings after Four Weeks Growth in the Green- seedlings, three categories of abnormal seed. There was a rapid increase in severe house. seedlings were tested. The categories red cotyledon abnormalities, and by the Avemge wei ht of each were: C seedlings showing a slight red- seventh day all seed were dead. In com- Group replicate o? twemty dening of the cotyledons, B seedlings parison with lots having no red cotyledon seedlings (Grams). having severe reddening and dead spots seed the deterioration was much more B ...... 43.1 C ...... 44.0 on the cotyledons, A seedlings having rapid indicating that seed with a high Normal ...... 48.7 dead root tips as well as dead or severely percentage of red cotyledon are less able * Least significant difference 19:14.72. deformed cotyledons. Effect of 90" F and 90% Relative Humidity for A sample of Great Lakes lettuce show- Varying Times on Seed Having the Red Cotyhsdon When the reddened area is localized ing a high percentage of red cotyledon Abnormality in Laboratory Germination Tests. in the middle base of the cotyledon, the was used in all tests with various samples Treat- Per cent germinants Nor- red cotyledon seedling produces normal ment Dead A B C ma1 showing no red cotyledon as checks. Be- I plants. The remaining green parts of the fore germination all lots of seed were Check ...... 7.5 6.5 17.5 55.5 13.0 cotyledon are able to grow and to photo- 12 hours .... 13.5 9.0 41.5 28.5 7.5 soaked in Chlorox for one minute and synthesize. With growth the normal part then rinsed for one minute. The seed was 1 day ...... 19.0 10.5 62.5 7.0 1.0 2 days ..... 19.0 21.5 56.5 3.0 0.0 of the cotyledon expands while the red- germinated at 68' F using six replica- 7 days .... .100.0 0.0 0.0 0.0 0.0 dened area does not, producing a curled tions of 50 seeds each. distorted effect. If the reddened portion Red cotyledon is apparently caused by to withstand the unfavorable storage of the cotyledon is more than one half neither a pathogenic organism nor by conditions of high humidity and high the total area, the seedling becomes re- growing conditions or variety. The ab- temperature. tarded in growth. If in addition there is normality is found in seed from many During the time that laboratory germi- root tip necrosis or the cotyledons do not growing areas and of all major lettuce nation tests were being made of the dif- emerge from the seed coat, severe retard- varieties. As the symptoms increase with ferently treated seed, other seed of the ing and death of the seedling results. age, storage conditions might be respon- same lots were sown in soil-filled flats in This study shows that many red coty- sible. An effort was made to induce red the greenhouse. The second table shows ledon seedlings produce normal plants cotyledon by subjecting seed to severe the percentage of normal plants in each indicatin the need for some modifica- storage conditions for varying periods. treatment after three weeks growth. Ap- tion of Be decision to classify all red The seed lots were stored at 90' F and parently most, if not all of the C abnor- cotyledon seedlings as abnormal. Possi- 90% relative humidity. Newly harvested mals and even many of the B abnormals bly some percentage of red cotyledon seed had as low as 25% normal seedlings seedlings could be reported as normal or Effect of 90" F and 90% Relative Humidity for after 16 days while older seeds showed a Varying Times on the Production of Normal Seed- red cotyledon could be reported as a sep- reduction of normal seedlings after only lings from Seed Having Red Cotyledon Abnor- arate part of the total germination as is 24 hours. However, lots showing no red mality in Soil Tests. done with hard seeds in beans. cotyledon at the beginning produced no Treat- Percentage of plants having red cotyledon seedlings a result of the ment four leaves after three weeks Wesley If. Dempsey is Research Assistant of as of Check ...... 73.0 Truck Crops, University California College storage treatment. The seeds of such lots of Agriculture, Davis. were either killed or root tip necrosis 12hours ...... 64.6 1 day ...... 51.6 James F. firrington is Assistant Professor of was the common abnormality produced. 2 days ...... 14.0 Truck Crops, University of California College The table below illustrates the effect of 7 days ...... 0.0 of Agriculture, Davis.

4 CALIFORNIA AGRICULTURE, JULY, 1951