Identification and inheritance of resistance to imidazolinone herbicides through induced mutagenesis and interactions between rhizoctonia root rot and selected herbicides in barley

Induced mutagenesis can be an effective way to increase variability in crop species. Crop resistance to a given herbicide can be of practical value to control weeds with efficient chemical usage. However, this type of production system with imidazolinone herbicides imposes 'plant-back' restrictions on rotational crops due to their soil residuals. In case of barley ( Hordeum vulgare), a common rotational crop following wheat ( Triticum aestivum), a period of 9--18 months is required. Thus, introduction of barley varieties showing resistance to imidazolinone herbicides will provide greater flexibility for barley production. The objective of the research was to identify resistance in barley for imidazolinone herbicides via induced mutagenesis. To achieve this objective, mutagenized barley cultivar Bob was screened for resistance, which identified a resistant mutant. Molecular analysis indicated a single point mutation leading to a serine 653 (AGC) to asparagine (AAC) amino acid substitution in the herbicide-binding site of the barley AHAS gene. Phenotypic characteristics of the mutant are promising and provide the basis for the release of new IMI-resistant barley cultivar(s).;The acceptance of reduced-till farming in the Pacific Northwest has resulted in increased use of herbicide for weed control, as well as, increased severity of Rhizoctonia root rot. Therefore, the objective of a second study was to assess injury symptoms on barley caused by the herbicides, imazamox or propoxycarbazone-sodium combined with the root rot pathogen, Rhizoctonia solani AG8 and to evaluate herbicide-pathogen relationships, as there are many crops that exhibit altered disease responses after application of herbicides. Negative impacts on plant growth parameters in the present study were generally caused by herbicide and/or the pathogen with interactions between them detected as well. This suggested sublethal levels of herbicides and pathogen altered severity of injury to root, and shoot dry weights and proportion of roots with disease symptoms, as the herbicide may predispose the plant to the pathogen. It was also observed that crown root initiation was increased by herbicide application. The observations and results indicated a complicated relationship between herbicides and pathogens when both are present at sublethal levels.