Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/22/2006
Publication Date: 3/22/2006
Citation: Carson, M.L. 2006. Response of a maize synthetic to selection for components of partial resistance to exserohilum turcicum. Plant Disease. 90:910-914. Interpretive Summary: Resistance of corn to the potentially devastating disease northern corn leaf blight can be expressed as a delay in the appearance of the characteristic lesions of the disease. This resistance trait, called increased latent period, along with another resistance trait, smaller lesion size, was selected for in corn breeding populations for three generations or selection cycles. Resistance to northern leaf blight improved an average of more than 20% per cycle when increased latent period was selected for. This rate of improvement in resistance is comparable to or better than rates reported when plants are selected for reduced disease severity later in the growing season. Resistance improved somewhat less when plants with smaller lesion sizes were selected. Selection for increased latent period length is an easy, effective method of improving resistance to northern leaf blight in corn. Unlike conventional approaches to selection where plants are evaluated for northern leaf blight resistance some time after flowering, this approach can be done prior to flowering, allowing control of both male and female plants selected for interbreeding the next generation.
Technical Abstract: A synthetic population of maize was created using five inbred lines varying in their level of partial resistance to northern leaf blight. This synthetic was then subjected to three cycles of recurrent phenotypic selection with pollen control for either increased latent period length or decreased lesion length. A selection intensity of ca. 10% was used in each selection cycle. The original synthetic and three selection cycles for the two components of partial resistance were evaluated in field trials in the summers of 1999 and 2001 and in greenhouse trials. Selection for increased latent period was more effective in improving resistance to NLB (20-27% gain/cycle) (as measured by area under the disease progress curve) than was selection for decreased lesion length (14-18% gain/cycle). Responses in AUDPC to selection for either component of resistance were linear in the 1999 field trial but were quadratic (decreased response in advanced cycles) in the 2001 trial. Selection for increased latent period length in the field resulted in a 0.6 day increase in latent period per selection cycle when measured in the greenhouse. Selection for decreased lesion length in the field did not significantly alter latent period in the greenhouse. These results support using latent period length as an effective means of improving partial resistance to northern leaf blight in maize populations. Selection for decreased lesion length is considered less desirable as it is not as easily measured and is somewhat less effective in improving levels of resistance.