Rob Pyne1, Kathryn Homa 1,2, Bill Barney1,2, Andy Wyenandt1, and Jim Simon1
1 Department of Plant Biology and Pathology, Rutgers University 2 IR-4 Program
In 2010 a basil variety and breeding line trial was conducted as an initial screen for potential sources of genetic resistance to downy mildew caused by Peronospora belbahrii, a destructive pathogen of basil introduced in the US in 2009. This trial was expanded from 30 to over 40 varieties representing six different Ocimum species in 2011. Varying levels of disease susceptibility were observed with the highest tolerance associated with O. americanum, O. citriodorum, O. gratissimum, and O. tenuiflorum varieties and USDA-GRIN accessions. In contrast, the most severe symptoms and extensive sporulation were consistently observed in O. basilicum accessions, including the popular commercial sweet basil varieties.
In 2011 a breeding program for developing resistance to downy mildew in sweet basil was initiated at Rutgers University. Using data collected from field trials highly tolerant Ocimum spp. were selected for interspecific hybridization with Rutgers’ sweet basil breeding lines and a popular commercial variety. F1 hybrids were generated through purposeful crosses to transfer resistance from non-traditional basil species to the commercially important sweet basil varieties. A method for screening basil seedlings for susceptibility to downy mildew was developed under controlled conditions so as to confirm transmittance of resistance in progeny. Currently, a backcross breeding strategy is being pursued to breed out undesirable traits, but retain disease resistance. Crosses between species present issues of sterility, thus, a parallel strategy includes screening of new germplasm in order to identify a sweet basil (O. basilicum) genotype or mutant conferring resistance. This coming summer at the Rutgers Agricultural Research Center (RAREC) in Bridgeton, NJ F2 and backcross breeding populations will be evaluated for susceptibility to basil downy mildew. The purpose of this study is to determine the heritability of downy mildew resistance in basil and begin to characterize the gene action controlling its inheritance. Results will aid in effective selection for downy mildew resistance and improve effectiveness of future breeding strategies.
