RUST RESISTANCE IN WINTER-WHEAT VARIETIES. 5 



When sprays of urediniospore decoction were used in the study at 

 Manhattan, Kas., a small knapsack pressure sprayer was employed. 

 All sprays were applied in the evening; if possible during periods of 

 moist, cloudy weather. The plants were first sprayed with water 

 and then with the urediniospore spray. Sprays of urediniospores 

 were found to be unreliable, however, because of the hot dry winds 

 which frequently occur in Kansas during the late spring and early 

 summer. In order partially to overcome this difficulty, removable 

 canvas covers were placed over a wooden framework which was 

 built over the plats. These covers were used the day following the 

 urediniospore sprays and aided materially in retaining moisture. 

 They were easily handled by one man, being unrolled from a long 

 strip of wood and drawn over the nursery plats, to be fastened at 

 the corners as shown in Plate II, figure 1. 



Several attempts have been made to inoculate plants in the rust 

 nursery in the fall. Not only was it difficult to obtain satisfactory 

 infection, but it was of doubtful value in view of the fact that it is 

 questionable whether stem rust lives over winter in Kansas to any 

 great extent (17). 



On account of the unsatisfactory results obtained with the uredin- 

 iospore sprays, the infection-center method of obtaining an epidemic 

 was tried. This method is somewhat similar to inoculating plants 

 in the field, but it is much simpler and more certain to give satis- 

 factory results. The inoculated seedlings are carried from the green- 

 house to the plats, where they spread the infection. Numerous 

 infection centers were located in each plat, so as to provide ample 

 spore material (PL II, fig. 2). 



Most of the rust cultures for these experiments were grown on 

 seedlings in 2|-inch flowerpots, two seedlings in each pot. Fre- 

 quently 4-inch pots were used, as they held more seedlings and did 

 not dry out so rapidly. It was found that if small galvanized-iron 

 pans were placed between the rows of wheat in the rust nursery 

 early in the spring and filled with pots of inoculated seedlings, a 

 most successful center of infection could be established. (PI. II, 

 fig. 2). The pans were kept filled with water at all times. 



As soon as the seedlings died or the rusted leaves no longer produced 

 urediniospores, the pots were replaced with a new set. In this man- 

 ner the wheat plats were continually exposed to rust infection. It 

 recently has been found that if plants in the heading stage are inocu- 

 lated in the greenhouse and used in place of seedlings for the centers 

 of infection, their usefulness in the field continues longer than that 

 of seedling plants; hence, they are much more satisfactory. It was 

 found also that wherever the centers of infection were located the 

 rust obtained a start and spread rapidly from the centers to all 

 adjacent plants. 



