Royal Red Delicious Apple
Dead spur is a malady originally associated with Red Delicious which results in the death of the fruiting spurs on the 3-year and older wood. The disorder was originally associated with water stress to the weak-dying spurs which was believed to be caused by a hormone imbalance. We have shown that aminoethoxyvinylglycine (AVG) applied in the fall resulted in less spur death, and many of the weaker spurs appeared normal. AVG inhibits ethylene formation and may reduce IAA levels. The results with AVG support the findings of previous work associating a growth regulator imbalance with dead spur. However, additional evidence indicates dead spur is probably transmissible. This paper also reports the finding of virus-like particles in the proto-xylem of dead spur affected tissue. One particle is 22 nm wide and 257 nm long. The other particle is 2.8 – 5.5 nm wide and 85 nm long. Neither of these particles are claimed to be the incitant of dead spur. These particles are associated with dead spur and are found in material from dead-spur affected trees and not in material from unaffected check trees.