5 



CAN ROOTSTOCK AFFECT APPLE RIPENING AND QDALITY?^ 



Wesley R. Autio 



Department of Plant and Soil Sciences 



University of Massachusetts 



Interest in the effects of rootstocks on fruit ripening and quality began 

 a number of years ago. In 1930 Wallace (7) published data suggesting that 

 apples from trees on M.9 rootstocks had higher soluble solids (sugar) levels 

 and did not store as well as fruit from trees on other rootstocks. However, if 

 fruit from trees on M.9 were harvested earlier than others, then similar 

 storability was obtained, suggesting that M.9 encouraged earlier ripening. In 

 1944 Hewetson (4) published similar results using Mcintosh trees with various 

 interstocks. Fruit from trees with an M.9 interstock matured and colored 

 earlier. Perry and Dilley (6) confirmed these results using the ethylene 

 climacteric as an index of ripening. In their study Empire apples on MM. Ill 

 with an M.9 interstock entered the climacteric significantly sooner than those 

 on MM. Ill alone. 



Lord et al. (5) used the ethylene climacteric and soluble solids as the 

 primary indices of Empire apple ripening and compared various interstock- 

 rootstock combinations with M.26, M.9, and M.27. They found few consistent 

 differences with respect to the percentage of fruit in the ethylene climacteric 

 5 days after harvest. However, consistent differences existed in soluble 

 solids content. Fruit from trees on M.27 had significantly higher soluble 

 solids than fruit from trees on M.26, with fruit from trees on M.9 intermediate 

 between the two. These results suggested that M.27 encouraged earlier ripening 

 than M.26, and possibly M.9. 



Fallahi et al. (2, 3) compared the ripening and quality of fruit from 

 Golden Delicious trees on seedling roots, M.l, M.7, M.26, MM. 106, and OAR 1. 

 Using ethylene measurements they found that fruit from trees on M.26 appeared 

 to ripen earliest, and those from trees on OAR 1 ripened substantially later 

 than those from all other trees. However, OAR ] also had the highest percent 

 soluble solids, which is difficult to explain. 



It is difficult, from the small number of studies, the small range of 

 rootstocks used in each study, and the somewhat inconsistent results to compose 

 a clear picture of the effects of rootstock on apple ripening and quality. The 

 objective of this study was to use a range of rootstocks, from the very 

 dwarfing M.27 to the very vigorous MAC 24, to assess rootstock effects on 

 ripening, size, and quality. 



Materials and Methods 



Starkspur Supreme Delicious trees on 9 rootstocks (Ott.3, M.7 EMLA, M.9A 

 EMLA, M.26 EMLA, M.27 EMLA, M.9, MAC 9 (Mark), MAC 24, and OAR 1) were planted 

 in a randomized complete block design with 10 replications at the University of 



^This work was supported in part by a grant from the International Dwarf 

 Fruit Tree Association. 



