Inheritance of susceptibility to Helminthosporium carbonum Race I. There are here submitted preliminary data on the linkage relations of the gene hm governing susceptibility to infection by H. carbonum Race I.

Earlier studies (Jour. Agri. Res. 63:331-334, 1941) and (Phytopathology 34: 214-222, 1944) have shown susceptibility to infection by H. carbonum Race I to be inherited as a monogenic recessive. Appropriate crosses were made by Dr. E. G. Anderson using a series of translocation stocks in which su endosperm was used as a translocation marker. The parents Pr and K61 are homozygous susceptible inbred lines of normal dent corn. The F1 material was backcrossed with pollen from double recessives (sugary susceptible plants). Kernel separations were made of the backcross progenies, planted in the greenhouse and seedling inoculated at the 3-4 leaf stage. One week after inoculation disease readings were made. The data in table 1 definitely indicate that the gene hm is located on chromosome 1.

In table 2 a summary is given of a four-point test involving 9 backcross progenies. Further studies are underway in which backcross progenies

p hm br × p hm br
+ +  + p hm br

will be used. A series of translocations all involving chromosome 1, and supplied by Dr. E. G. Anderson, will also be under observation in 1945.

Table 1. Segregation of seedlings in which su endosperm was used as a marker for translocations

  Number
kernels planted*		 Sugary Starchy Chi
Square		  
F1 Sug. St. Res. Sus. Res. Sus. Values Range of "P"
 
suT1-4a × Pr 1344 1149 921 317 190 912 767.0 < .01
K61 × suT1-4a 924 894 664 176 150 703 642.0 < .01
suT2-4a × Pr 408 475 173 207 234 341 3.1 .2 - .3
K61 × suT2-4a 541 675 223 259 319 344 3.6 .1 - .2
suT2-4c × Pr 566 512 266 239 245 238 1.5 .3 - .5
K61 × suT2-4c 516 511 240 237 248 237 .3 .5 - .9
suTuT4-5b × Pr 458 476 199 206 230 230 .1 .5 - .9
K61 × suTuT4-5b 250 273 120 114 133 139 .3 .5 - .9
Pr × suT4-6a 478 495 190 205 240 221 1.3 .5 - .9
K61 × suT4-6a 443 484 187 181 255 218 3.0 .2 - .3
Pr × suT4-8 336 437 157 161 224 188 .2 .5 - .9
Pr × suT4-9a 548 545 227 219 244 249 .8 .5 - .9
K61 × suT4-9a 252 251 114 109 115 128 3.2 .2 - .3
K61 × suT4-10b 257 245 127 125 112 119 .2 .5 - .9

*Also represents kernel ratio found on ears

 

Table 2. Four-point test for the gene hm, the F1 genotype being

hm + + + 
 + br f bm2
Progeny
No.		 Parental
Combinations		 Reg. 1 Reg. 2 Reg. 3 Reg. 1 & 2 Reg. 1 & 3 Reg. 2 & 3 Total
1 1 31 3 11 0 2 19 43 3 4 3 3 2 3 158
2 61 50 11 20 2 6 47 53 9 1 7 9 0 16 292
3 45 54 8 19 2 10 40 45 7 0 8 13 0 8 259
4 46 53 11 12 2 8 33 36 4 6 10 12 2 9 244
5 58 53 8 6 1 7 46 51 4 0 3 6 1 3 247
6 47 52 12 19 3 6 55 45 6 1 12 6 5 9 278
7 53 62 13 13 1 8 29 54 3 0 7 7 2 6 258
8 73 37 4 22 0 6 29 44 7 0 7 9 0 21 259
9 45 46 5 1 3 7 29 64 6 3 3 8 1 3 235
  459 438 75 134 14 60 327 435 49 15 60 73 13 78  
Total 897 209 74 762 64 133 91 2230
    9.4% 3.3% 34.2% 2.9% 6.0% 4.1%  

The indicated genetic map is:
hm 18.3 br. 10.3 f 44.3 bm2

Arnold J. Ullstrup and A. M. Brunson