By R. B. WiLcox, associate pathologist^ Division of Fruit and Vegetable Crops and
Diseasesj Bureau of Plant Industry, United States Department of Agriculture,
and C. S. BECKWITH, associate entomologist in cranberry and blueberry investiga-
tions. Department of Entomology, New Jersey Agricultural Experiment Station^
INTRODUCTION
Varieties of the cranberry (Vaccinium macrocarpon Ait.) under commercial culture differ widely in their susceptibility to the false- blossom disease. Fracker (5) ^was probably the first to mention this fact in a publication; he states that in the inspection of Wisconsin bogs for this disease, in the course of regulatory work, a few varieties had '^practically clear records^\ Stevens (7), summarizing present knowledge of varietal susceptibility, includes the Howes and Cen- tennial among the sorts that are very susceptible to false blossom, and says that the Early Black shows a fair degree of resistance under varied field conditions and the McFarlin shows marked resistance. Beckwith (2) classifies the Centennial and Champion as ''only slightly less susceptible'' to false blossom than the Howes. The evidence upon which to judge the Champion is less conclusive than that relating to the other sorts; this variety, in New Jersey, is not so generally affected as either Howes or Centennial, but it has become badly diseased in some instances when exposed to heavy infection. On the basis of field observations it may therefore be said that the five varie- ties mentioned fall into the following descending order of susceptibility to false blossom: Howes and Centennial, Champion, Early Black, and McFarlin.
Varietal resistance to false blossom is almost certain to play a large part in the future of the cranberry industry, especially in the develop- ment of new commercial forms. Up to the present time the only method for judging the resistance of a variety has been to watch its behavior under exposure to natural infection for several years It has not been known whether the resistance of McFarlin is due to natural protection against attacks of the insect vector ^or to inhibition of the spread and survival of the false-blossom virus within the plant tissues; or whether this variety may be a symptomless carrier of the disease.
INTRODUCTION
Varieties of the cranberry (Vaccinium macrocarpon Ait.) under commercial culture differ widely in their susceptibility to the false- blossom disease. Fracker (5) ^was probably the first to mention this fact in a publication; he states that in the inspection of Wisconsin bogs for this disease, in the course of regulatory work, a few varieties had '^practically clear records^\ Stevens (7), summarizing present knowledge of varietal susceptibility, includes the Howes and Cen- tennial among the sorts that are very susceptible to false blossom, and says that the Early Black shows a fair degree of resistance under varied field conditions and the McFarlin shows marked resistance. Beckwith (2) classifies the Centennial and Champion as ''only slightly less susceptible'' to false blossom than the Howes. The evidence upon which to judge the Champion is less conclusive than that relating to the other sorts; this variety, in New Jersey, is not so generally affected as either Howes or Centennial, but it has become badly diseased in some instances when exposed to heavy infection. On the basis of field observations it may therefore be said that the five varie- ties mentioned fall into the following descending order of susceptibility to false blossom: Howes and Centennial, Champion, Early Black, and McFarlin.
Varietal resistance to false blossom is almost certain to play a large part in the future of the cranberry industry, especially in the develop- ment of new commercial forms. Up to the present time the only method for judging the resistance of a variety has been to watch its behavior under exposure to natural infection for several years It has not been known whether the resistance of McFarlin is due to natural protection against attacks of the insect vector ^or to inhibition of the spread and survival of the false-blossom virus within the plant tissues; or whether this variety may be a symptomless carrier of the disease.
There is no accumulation of evidence based on insect collections to
indicate whether the blunt-nosed leaf hopper is relatively more
abundant on Howes and Centennial bogs than on those of McFarlin
or Early Black. In New Jersey, as a result of both natural conditions
and cultural practices, such as the use of flood water for frost protec-
tion in June, the leaf-hopper population often varies greatly on plants
of one variety, in a single bog, and even within the space of a few feet.
Comparison between varieties in the field, therefore, is frequently
misleading. A preliminary test showed little to be gained through
casual observation of caged insects.
The present paper is a report of more careful experiments to deter- mine whether the false-blossom vector prefers to feed on the ^'suscep- tible'^ varieties of cranberries rather than on those which are con- sidered resistant; in other words, whether unattractiveness to the insect is a factor in the resistance of certain varieties. These experi- ments form part of an attempt by the senior writer to find a quicker and more reliable means of testing varietal resistance.
The present paper is a report of more careful experiments to deter- mine whether the false-blossom vector prefers to feed on the ^'suscep- tible'^ varieties of cranberries rather than on those which are con- sidered resistant; in other words, whether unattractiveness to the insect is a factor in the resistance of certain varieties. These experi- ments form part of an attempt by the senior writer to find a quicker and more reliable means of testing varietal resistance.
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