RUST RESISTANCE IN WINTER-WHEAT VARIETIES. 23 



1526) and Khapli emmer (C. I. No. 4013) seemed to show more con- 

 sistently the type designated as R3. Khapli emmer (C. I. No. 4013) 

 is the only variety of spring wheat so far studied that under all 

 conditions seemed to exhibit a high degree of resistance in the field 

 and in the greenhouse. Even this variety, however, may be classed 

 at times as R.2 instead of R3. The seedlings of the so-called wild 

 wheat of Palestine, Triticum hermonis Cook (C. I. No. 3109), really 

 a form of emmer, all proved to be susceptible. 



The purple color mentioned under "Remarks" occurred in some 

 varieties and surrounded the uredinia. It does not appear con- 

 sistently in any one variety. Environmental conditions seem to 

 affect its production. 



COMPARISON OF NURSERY AND GREENHOUSE RESULTS. 



In general, the results of the greenhouse inoculations were similar 

 to those produced under field conditions in the rust nursery. All of 

 the winter-wheat varieties were found to be susceptible except 

 Kanred, PIO66, and P1068. Kansas No. 2390, which appeared to be 

 partially resistant in the rust nursery, gave no evidence of being 

 resistant in the greenhouse. 



In the nursery, results on rust behavior usually are obtained on 

 varieties in the heading stage, but in the greenhouse the seedling 

 stage is most commonly used. Determining the resistance of varie- 

 ties as seedlings is the most convenient method, particularly when a 

 number of distinct biologic strains of rust are being used. It perhaps 

 is the most severe test that can be given a variety and should always 

 serve as a check on nursery results. The results thus obtained, 

 however, scarcely can be considered as the sole criteria of the actual 

 field resistance or susceptibility of a variety; in fact, plants showing 

 certain effects when inoculated in the seedling stage in the green- 

 house may respond very differently to the same rust when they are 

 subjected to it in the heading stage under field conditions. No 

 definite statements as to the cause of these differences can be made 

 at this time. The same factors causing resistance or susceptibility 

 may operate in all stages of growth, but the reaction of the host and 

 parasite at various stages of development may be different. 



It is possible that time of maturity may have an important 

 influence on the extent of the rust on a given variety, but if the rust 

 is epidemic before the plants reach the heading stage there can be 

 no doubt as to the plants having been exposed to infection. The 

 differences perhaps are due to complex factors in the developmental 

 stages in a variety, which may cause a different response to rust 

 infection. To whatever cause these differences in behavior in the 

 seedling and heading stages may be due, the behavior of any variety 



