FALSE BLOSSOM was prevalent on three varieties in Wisconsin by 1906. The disease was first found in Massachusetts in 1914 and in New Jersey in 1915, and was general in those States by 1924. Apparently the disease ,Was carried there in infected vines from Wisconsin.
The disease gets its name from the abnormal character of the flowers, which, instead of hanging downward, become erect and have enlarged, greenish, and somewhat leaflike calyx lobes. The petals are shorter, broader, and reddish or greenish. The stamens and pistils are more or less malformed. No fruit is produced.
BY 1928 false blossom threatened to wipe out the cranberry industry in Wisconsin, Massachusetts, and New Jersey. It caused a reduction in the crop in Wisconsin and a downward trend in production in New Jersey,which began about 1924 and was strikingly evident by 1932. Many bogs in Massachusetts also were seriously affected.
Irene Dobrosky, a research worker in New Jersey, proved in 1927 that false blossom is caused by a virus carried by the blunt-nosed leafhopper. Earlier investigators had believed it was due to a disturbance in nutrition.
Dr. L. O. Kunkel, of the Boyce Thompson Institute, had suggested in 1924 that leafhoppers might be the carriers. A survey in 1925 and 1926 had shown that only one genus of leafhopper occurred in the regions in which false blossom was abundant and that it was not present in Washington and Oregon, where false blossom was found not to spread.
No cultivated varieties of cranberries are free from false blossom, but they vary in susceptibility. Howes is very susceptible. Shaw's Success, a variety not commonly grown, is the most resistant. Early Black and McFarlin are intermediate. The resistance is not an actual resistance that is due to opposition offered by the plant to infection by the disease. It is due, rather, to a difference in the preference of leafhoppers to feed on the different varieties.
The Department of Agriculture began a breeding program in 1929 to develop good, resistant varieties. Crosses in which one or both parents were known to be somewhat resistant to false blossom were made in Wisconsin and Massachusetts. From the crosses 10,685 seedlings have been grown. From a cross made at the New Jersey Agricultural Experiment Station 112 other seedlings have been grown. Forty of the more promising seedlings, including six from the New Jersey crosses, were selected in 1940. In addition 182 other selections were made in 1945, making a total Of 222 seedlings selected for a second test.
A selective feeding test; a "cafeteria test" for leafhoppers, to ascertain susceptibility to false blossom was made in 1945 on 362 seedlings selected in 1944. In the test leafhoppers that spread the disease were allowed a choice of different varieties on which to feed. Since the attractiveness of different varieties to leafhoppers seemed to be correlated with the rate of spread of the disease on those varieties in the field, the method was valuable in evaluating the probable resistance of the seedlings. Seedlings with the poorest ratings in the test were discarded, and 93 were included among the 182 selected in 1945 for a second test.
The 40 selections made in 1940 were planted in rod-square plots in New Jersey in 1941. Selections were made from them in 1945 and again in 1949. From the latter, three were named Beckwith, Stevens, and Wilcox. Plans for their distribution to growers in Massachusetts, New Jersey, and Wisconsin have been made so they can be tested on a large scale.
Further tests of the 40 selections of 1940, the 93 selections of 1945, and some others were started in Massachusetts, New Jersey, and Wisconsin, in the hope that new, healthier, and better varieties can be developed.
A PHYSIOLOGICAL DISEASE is one that injures or kills any part of a plant, without involving a fungus or other parasitic organism, or any disturbance of the normal growth or behavior of a plant. Such injury to flower buds and growing tips of cranberry vines, often severe enough to cause their death, was observed in 1919 as a result of flooding bogs in June to control insects. The most serious injury of this kind to cranberries is caused by winter flooding.
Cranberry bogs usually are flooded in winter as a protection against winter killing. The practice often hurts crop production. When submerged for a long time, cranberry vines may be so injured that their yield the following summer is reduced or destroyed.
The possibility that the injury might be due to a lack of oxygen in the flooding water was suggested by the fact that its lack caused injury to buds, flowers, and growing tips of vines in June flooding. Winter-flooding water often contains little or no oxygen. Injury occurs only on bogs on which the oxygen content of the water was very low at some time during the winter.
Investigations in Massachusetts proved that forms of injury not previously recognized as such are caused by a lack of oxygen during the winter. Observations in New Jersey showed that serious injury from winter flooding occurs there also.
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