^ June 1933 
Rust Resistance in a Marquis-Kota Cross 
1001 
One of the problems which it was hoped to solve was the discovery 
of a greenhouse test of F3 seedlings which would give an accurate esti¬ 
mate of the behavior of Marquis X Kota Fg families under field con¬ 
ditions. As no such test was available, the larger part of the Marquis 
X Kota material was grown in the rust nursery and an artificial epidemic 
of stem rust induced by the use of the available biologic forms of stem 
rust which were present in the greenhouse and which were known to 
have been found in the spring-wheat region. The forms of rust used 
for the field epidemic in 1922 are those listed in Table i, with the 
exception of Form XXVII, which was originally collected in Barges, 
France, and Form XXXIV which was collected in South Africa. These 
two forms were not used for the nursery epidemic. 
Between 25 and 50 plants were grown in the field nursery from each 
selected Fg family. The rust infection was heavy on susceptible types, 
as shown by the infection on Marquis, and consequently the determina¬ 
tion of those Fg families which had the Kota type of resistance to the 
nine biologic forms in question could be made with accuracy. 
EXPERIMENTAI, RESUETS 
DWARF PLANTS OBTAINED IN THE Fg PROGENY 
The Fg material of the Marquis X Kota cross grown in the plant¬ 
breeding nursery in 1921 was not severely infected with stem rust and, 
therefore, was used for the greenhouse studies. Considerable material 
also was grown in the rust nursery. With most hybrid material in which 
Kota had been used as one parent, dwarf plants appeared in the Fg 
generation. The frequency of the appearance of such plants was 
determined for the Fg progeny which grew in the rust nursery in 1921. 
Of a total of 787 Fg plants, 666 were of normal type and 121 were dw^s. 
Seed from some of these dwarfs was sown in the greenhouse and only 
dwarf plants resulted. The results may be explained genetically by 
the assumption that one of the parents contains two factors, one for 
dwarf habit and the other which inhibits the expression of the dwarf 
factor. On this basis a 13:3 ratio of normals and dwarfs is expected in 
Fg. The number of dwarfs expected in a population of 787 would be 
147. The number of dwarf plants obtained was somewhat less than 
the expectation for a 1313 ratio. 
THE AWNEESS or bearded CHARACTER IN REEATION TO SEED 
CHARACTERS 
Kota is a bearded wheat, while Marquis has short apical awns and is 
commonly classified as awnless. The F^ hybrids have somewhat longer 
apical awns than Marquis. At harvest time some of these tip awns 
were broken off and it was impossible to separate the awnless from the 
hybrid types with certainty. For this reason awnless and apically- 
awned (hybrid) forms were placed together. In an earlier study of a 
cross between Marquis and Preston, experimental data gave reason 
for the belief that the awn was an important physiological organ under 
the conditions of the experiment. Accordingly a somewhat similar 
study was made of the Kota X Marquis plants (Tables II, III, IV). 
