M.7 EMLA, and M.7A were most consistently in the 

 lowest category. Average internal concentrations 

 of ethylene, however, provide only a static look at 

 differences. It is acceptable to assume that fruit 

 with higher levels of ethylene are in fact riper, but 

 it is not clear how much riper. 



Plotting the rise in ethylene concentration over 

 time allows for direct comparison of the timing of 

 ripening. The rise up to one ppm is relatively slow; 

 however, ethylene concentrations increases rapidly 

 after they reach one ppm. Therefore, a simple 

 benchmark parameter to compare timing is when 

 the internal ethylene concentrations reaches one 

 ppm. Table 1 gives the averages from this experi- 

 ment. Generally, these data confirm the differences 

 found with overall ethylene concentrations, i.e. fruit 

 from trees on 0.3 and M.26 EMLA ripened earlier 

 than fruit from trees on other rootstocks (with the 

 exception of Mark, which was intermediate). The 

 difference between the earliest and the latest to 

 ripen was on average about three days. This differ- 

 ence is very small; however, the magnitude varied 

 from year to year and ranged up to as many as six 

 days. 



The timing of ripening varies to a significant 



degree from fruit to fruit. Therefore, a degree of 

 uncertainty exists about any assessment of ripen- 

 ing, even one as accurate as internal ethylene mea- 

 surement. To reduce this uncertainty, it is impor- 

 tant to measure other factors that change with rip- 

 ening. As apples ripen, starch is broken down into 

 sugar. So, during ripening, sugar (soluble solids) 

 concentrations increase and starch concentrations 

 decrease, giving two additional assessments of rip- 

 ening. Table 1 shows both the soluble solids con- 

 centrations and starch index values of fruit from 

 trees on these rootstocks. Generally, fruit from trees 

 on 0.3 and M.26 EMLA had relatively high sugar 

 concentrations and starch index values (low 

 amounts of starch), suggesting that these fruit were 

 riper at harvest than fruit from trees on most of the 

 other rootstocks. Both measurements confirm the 

 results from the ethylene measurements. 



Overall, these data suggest that 0.3 and M.26 

 EMLA advance ripening and that M.9/A.2, M.7 

 EMLA, M.7A, and OARl delay ripening. Mark is 

 less consistent in its effect. These results support 

 those with Delicious as the scion cultivar; however, 

 the magnitude of the differences were not as great 

 for Mcintosh as for Delicious. 



•J^ •J^ •J^ *Xa •Sa 

 #Y* *Y* *T* *T* *T* 



Fruit Notes, Spring, 1996 



