Resistance to Helminthosporium turcicum from Tripsacum floridanum incorporated into corn

Many years ago Walton Galinat provided me with seed of a corn inbred crossed with T. floridanum. The hybrid expressed chlorotic-lesions (resistance) to the leaf blight caused by H. turcicum. The corn inbred was susceptible. The resistance persisted through backcrosses to susceptible corn. Resistant plants, however, were poor plant type and often partially fertile. After more generations of backcrossing and selfing with selection for resistance, normal looking and fertile corn plants with resistance were obtained. These can be identified as corn-T. floridanum (CTf) selections. The CTf selections have been used in backcross breeding and several inbreds with resistance from CTf obtained.

When crossed with susceptible inbreds, such as Hy-2 and Oh43, segregation for resistant (R), intermediate resistant (R-), or susceptible (S) lesion types has been regular and that of a single dominant gene as shown by the following data:
 
Population Observed Ratio Expected

Ratio

 P

Value
R R- S
Hy-2 x CTf F2 54 105 56 1:2:1 0.90 - 0.95
Oh43 x CTf F2 103 183 98 1:2:1 0.50 - 0.70
(Hy-2 x CTf) Hy-2 0 101 112 0:1:1 0.30 - 0.50
(Oh43 x CTf) Oh43 0 95 105 0:1:1 0.30 - 0.50
(Hy-2 x CTf) CTf 226 224 0 1:1:0 0.90 - 0.95

Homozygous plants are the most resistant.

Two other dominant gene loci, Ht and Ht2 (A. L. Hooker, Crop Science 17:132-135, 1977), for chlorotic lesion resistance to H. turcicum are known. When inbreds having Ht or Ht2 are crossed with CTf the CTf resistance segregates independently as shown by the following data:
 
Population
Observed Ratio
 Expected Ratio P Value
R S
Ht Ht x CTf F2 211 15 15:1 0.80 - 0.90
(Ht Ht x CTf) Oh43 150 58 3:1 0.30 - 0.50
Ht2 Ht2 x CTf F2 284 17 15:1 0.50 - 0.70
(Ht2 Ht2 x CTf) Oh43 282 95 3:1 0.90 - 0.95

All evidence indicates that the resistance in CTf came from T. floridanum and that it segregates in a manner similar to that of a single dominant gene. I propose that it be given the symbol Ht3.

A. L. Hooker

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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