C.6 



Bud.9 



M.26 EMLA 



P.2 



P.22 



10/1 



10/8 10/15 10/22 



Date of log ethylene 



10/29 



Figure 1. The effect of various dwarfing and ultradwarfing rootstocks on the ripening of Starkspur 

 Supreme Delicious fruit in 1990. The date of log ethylene approximates the date of the beginning 

 of ripening. 



Clearly, trees on P.2, C.6, and Bud.9 have per- 

 formed very well so far. Additionally, trees on P. 16 

 and P.22 have been very yield efficient; however, 

 growth has been poor and trees have become spur- 

 bound. Trees on P.16 and P.22 will not remain yield 

 efficient because of these problems. The protocol of 

 the experiment has not allowed us to thin fruit from 

 these very small trees which are overfruiting, nor 

 has it allowed staking of the trees until they fall over. 

 The lack of staking severely limits the growth and 

 development of these trees. 



Ripening of fruit from these trees was assessed 

 in 1990 (Figure 1). One year of data is not adequate 

 to make clear conclusions regarding ripening; how- 

 ever, dramatic differences existed in 1990. Fruit 



from trees on P.2 ripened 1 week later than those 

 from trees on C.6, and fruit from trees on P.22 

 ripened approximately 9 days later than those from 

 trees on P.2. If this effect is consistent, we may be 

 able to utilize these rootstocks to expand the harvest 

 season dramatically; however, several additional 

 years of data are required to assess this effect accu- 

 rately. 



Study of the rootstocks in this planting will 

 continue for several years to assess performance as 

 well as potential barriers to their use commercially. 

 A new planting is scheduled to be established in 1993 

 which will include several new dwarfing rootstocks, 

 some of which have not been released prior to their 

 use in this planting. 



Fruit Notes, Spring, 1991 



