A Comparison of Six Strains of M.9 

 Over 1 Years 



Wesley Autio, James Krupa, and Jon Clements 



Department of Plant & Soil Sciences, University' of Massachusetts 



Serious interest in the use of clonal, dwarfing 

 rootstocks for apples developed in the United States 

 only in the latter half of the 1900's. The use of dwarf 

 apple trees, however, dates back more than 2,000 

 years, and the identification of potentially useful 

 materia] for rootstocks likely began about 500 years 

 ago. L"p through the 1800's, these rootstocks were 

 categorized as either Doucin (semidwarf) or Paradise 

 (full dwarf). The variety of clones within these two 

 categories and the misidentification of clones led the 

 researchers at the East Mailing Research Station in 

 Kent, England to collect, name, and properly describe 

 24 different apple rootstocks. They were given the 

 names East Mailing I through East Mailing XXIV. 

 One of these rootstocks, EM. IX (later changed to M.9) 

 was originally found in France in 1 879. It originated as 

 a chance seedling and was given the name Jaune de 

 Metz. Subsequently, it became known as the fully 

 dwarf rootstock of 

 choice, and now is 

 the most widely 

 planted apple root- 

 stock in the world. 



All living organ- 

 isms are subject to 

 occasional mutation 

 in their genetic code. 

 Apples are no excep- 

 tion. Obvious ex- 

 amples of random 

 mutations (or sports) 

 are seen in some 

 varieties more than 

 others. Delicious, 

 Gala, and Jonagold, 

 for example, are 

 prone to obvious 

 skin-color mutations. 

 Marshall Mcintosh 

 is a random mutation 



of Rogers Red Mcintosh found at Marshall Farms in 

 Fitchburg, MA. Rootstocks also express mutations 

 from time to time. Since much of the plant is belov^ 

 ground, however, most mutations are not obvious, and 

 even ones that may be beneficial are lost. Even so. 

 several genetically different strains of M.9 have been 

 characterized over the years. Until relatively recently. 

 U.S. growers have had access only to M.9 and M.9 

 EMLA. In the last 1 or more years, other strains have 

 entered the U.S. market, most notably M.9 

 NAKBT337. These strains offer some variation in the 

 grafted tree. Likely, the most obvious difference is in 

 the degree of dwarfing, but other characteristics may 

 change with mutations. It is important for nurseries 

 and growers to understand strain differences, so that 

 the best possible rootstocks and management systems 

 are used. 



In 1994, the NC-140 Multistate Research 



100 

 _ 90 

 80 



E 

 a 



70 - 

 60 - 



c 

 o 



■^ 50 



0) 



tf) 

 in 



V) 



o 



c 



3 



40 

 30 - 

 20 

 10 

 



be 



cd 



cd 



M.26 

 EMLA 



M.9 

 Pajam 2 



M.9 M.9 M.9 M.9 M.9 M.27 



RN29 Pajam 1 EMLA T337 Fleuren EMLA 



56 

 Figure 1. Trunk cross-sectional area of Gala apple trees on various strains of M.9 

 and on M.26 EMLA and M.27 EMLA, after 10 growing seasons. Bars topped by 

 different letters are signficantly different at odds of 19: 1 . 



22 



Fruit Notes, Volume 68, Spring, Summer, & Fall, 2003 



