Release of inbreds with high Gibberella ear rot resistance
--Reid, LM and Hamilton, RI

The first inbreds (CO387, CO388, and CO389) from the Plant Research Centre's ear rot breeding program have been released. Their development began as a result of observations in the Ontario Soil and Crop Improvement Association (OSCIA) half acre plots of eastern Ontario, Canada, in the fall of 1986 during a Gibberella ear rot (pink mold, Fusarium graminearum) epidemic. Four hybrids were significantly less infected, one of which was the single cross hybrid CO272 X CO265. The source for this resistance has now been shown to be CO272, an inbred which appears to possess a single dominant gene for resistance to infection through the silk (Reid et al., J. Hered. 85:118-121, 1994). A component of this resistance may be a buildup of the wax layer on CO272 silk (Bergvinson and Reid, MNL 69:114, 1995). CO272 was developed from (BS10 x CO109) CO1092 beginning in 1975. BS10 was formerly known as BSTE (Iowa two ear synthetic). CO109 was developed by Dr. F. Dimmock from the cultivar Early Butler in the 1950's. CO265 was developed by Dr. L.S. Donovan from the 1970's commercial hybrid Pioneer 3990 (75 RM).

In the development of the new lines, CO272 was used as the donor parent followed by inbreeding, inoculation and resistance screening for several generations. Artificial inoculations were conducted by injecting 2 ml of a 5 x 105 spores/ml macroconidial suspension of F. graminearum into the silk channel 6 days after pollination. At harvest, only those ears with no visible symptoms of infection on the kernels were selected and advanced to the next generation. In test crosses with susceptible checks, outstanding resistance to artificial infection via the silk has been evident.

CO387 was developed from the CO272 X CO266 hybrid. CO387 has reddish-brown dent-flint kernels and a similar silking date as CM105. CO388 and CO389 were developed from the backcross population of (CO272 X B73) CO272. CO388 has orange dent kernels and CO389 has yellow-orange flint kernels. Both are similar in silking date to A632. All three inbreds will be released under a research agreement to the corn seed industry. 

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