MINNESOTA RUST RESISTANCE BREEDING PROJECT 611 



PROCEDURE 



PHASE I. - MASS SELECTION AND FIELD SCREENING 



Selection Criteria 



Trees are selected only in areas of high rust infection in north- 

 eastern Minnesota. All sexually mature trees are selected if they have 

 an adequate cone crop and are 45 years of age or younger. Since the rust 

 was introduced into this area about 53 years ago, trees in age classes 

 45 or less may have been exposed to infection as seedlings and survived. 

 Older trees that are apparently free of the disease, show evidence of 

 having survived infection, or have cankers confined to branches are also 

 considered eligible for selection. 



Seed Collection and Propagation 



Collection of about 1,000 seedlots is planned. Seed collections in 

 1966 and 1967 total about 500 seedlots; another 500 seedlots will be 

 collected in autumn 1969. The plants are being propagated at the Eveleth 

 Nursery through cooperation of the U. S. Forest Service. 



Studies at the University of Wisconsin have demonstrated that there 

 is an age-related rust-susceptibility factor that should not be ignored; 

 the younger the plants the more susceptible they are. For this reason 

 the plants will be grown to the age of 2-2 (2 years in nursery, 2 years 

 in transplant beds) before transplanting to the test area. 



Inoculation (Screening) Tests 



Most previous tests of rust susceptibility of seedlings or clonal lines 

 have been done artificially in order to insure optimum conditions for infec- 

 tion. One possible result of such intensive treatments is that they may 

 far exceed any natural epidemic conditions and result in multiple infec- 

 tions that may cause the death of even highly resistant plants. 



Screen tests in this project will be carried out under optimum natural 

 conditions in a high infection area on the Tofte District, Superior National 

 Forest. Since most ribes {P.ibes spp.) plants now on the test area will be 

 destroyed during site preparation, plants of the eight native and two 

 naturalized species are being propagated and will be established on the 

 test area at the time of initial outplanting. 



Site Preparation and Planting 



The test site is an area of 2~0 sq. chains. Most of the area was 

 covered by a heavy sod which had been control-burned and will be periodi- 

 cally cultivated until planted. 



Spot treatment with simazine is planned around each white pine and 

 ribes plant immediately after planting. Other chemical or physical weed 

 control will be avoided unless necessary. 



The first outplanting on the test site (using 4-year-old stock grown 

 from 1966 and 1967 seed) will be made in spring 1972 ; the final outplanting, 

 using stock grown from 1969 seed, will be made in spring 1974. 



