Fruit Count, Fruit Weight, and Yield Relationships in `Delicious' Apple Trees on Nine Rootstock

Annual yields per tree for 'Starkspur Supreme Delicious' apple (Malus domestica Borkh.) trees on nine size-controlling rootstocks were related linearly to number of fruit per tree at harvest each year, independent of rootstock. Mean fruit weight was inversely and less closely related to number of fruit per tree when adjusted for tree size (fruit load). Annual yield-fruit count data for 9 years analyzed together showed that the number of fruit per tree was the principal factor determining yield, regardless of rootstock or tree age. A curvilinear relationship between yield and fruit count per tree during 9 years suggests that the sink strength of an apple crop is nearly, but not precisely, proportional to the number of fruit per tree