Combining Ability for Husk Extension and Corn Earworm Resistance.

Corn earworm (Helicoverpa zea) is an important pest for organic sweet corn growers. Earworm larvae feed on corn silks and ears, making the ears unmarketable. Organic growers have few earworm management options, and breeding for earworm resistance is one promising option for reducing the damage caused by corn earworm on organic farms. Two potential traits for increasing resistance to corn earworm are long husks and maysin, a flavonoid present in some corn silks that delays earworm larval development. We conducted two studies to assess the potential of husk length and/or maysin to improve sweet corn resistance to corn earworm.

The first study used a North Carolina Design II mating design to calculate the general and specific combining ability of long- and short-husk parents and maysin and non-maysin parents. We grew the parents and progeny in a total of five environments in 2016 and 2017. We artificially inoculated the corn silks with earworm eggs, measured maysin content in the silks, and evaluated ears at harvest for husk length, earworm damage, and earworm larval maturity. The 2016 results showed that the crosses with significantly longer husks had significantly lower earworm damage.

The second study was a recurrent selection experiment, in which we selected for long husks over three seasons, from 2014 to 2016. In 2017, we will evaluate these cycles of selection for husk length and earworm resistance to determine if the selection resulted in improvements in husk length and/or earworm resistance. We will also compare the selection cycles to commercially available sweet corn varieties. The results of these two studies emphasize the importance of husk characteristics in earworm resistance, and will contribute to the development of new earworm resistant sweet corn varieties for organic agricultural systems.