Yield efficiency (lbs/in 2 TCSA) 



MWD 



Drainage class 



Figure 3. Cumulative yield efficiencies (1986-88) of Marshall Mcintosh trees on M.7A, M.26, 

 M.9/MM.106, and M.9/MM.111 planted in 1982. Drainage class: SED = somewhat 

 excessively drained; WD = well drained; MWD = moderately well drained; SPD = somewhat 

 poorly drained; and PD = poorly drained. 



trees on each rootstock in each soil grouping. 

 Overall, the most efficient trees were on the WD 

 and MWD soils; however, dramatic differences 

 existed among rootstocks. Trees on M.7A were 

 the least efficient on all soils, with a gradual 

 decline in efficiency as soil moisture increased 

 from the WD to the PD categories. The trees on 

 M.26, M.9/MM.106, and M.9/MM.111 were 

 similarly efficient on the SED, WD, and MWD 

 soils, and trees on M.26 and M.9/MM.106 were 

 the most efficient and similarly efficient on the 

 SPD and PD soils. As the soil moisture increased 

 beyond the MWD category, the trees on M.9/ 

 MM. Ill declined in efficiency. 



These results lead to several conclusions. 

 M.26 and M.9/MM.106 produced the most con- 

 sistently efficient tree, across all soils. In fact, 

 these two rootstocks produced trees which did 

 not decline in efficiency as the soil moisture 

 increased beyond the WD category. This result 

 must be qualified, however, since both M.26 and 

 MM. 106 are very sensitive to collar rot, which is 

 prevalent in wet soils. Over eight years, this 

 study did not show significant numbers of either 

 of these rootstocks lost to collar rot; however, 

 more time will be required to assess longevity 

 adequately on the wettest soils. It would be best 

 to avoid these two rootstocks on SPD and PD 



12 



Fruit Notes, Summer, 1991 



