Incorporating disease resistance into cultivars is a primary focus of modern breeding programs. Resistance to pathogens is often introgressed from landrace or wild individuals with poor fruit quality into commercial-quality cultivars. Sites of multiple disease resistance (MDR) are regions or “hot spots” of the genome with closely linked genes for resistance to different pathogens that could enable rapid incorporation of resistance. An F2-derived F6 recombinant inbred line population from a cross between ‘Criollo de Morelos 334’ (CMM334) and ‘Early Jalapeno’ was evaluated in inoculated fruit studies for susceptibility to oomycete and fungal pathogens: Phytophthora capsici, P. nicotianae, Botrytis cinerea, Fusarium oxysporum, F. solani, Sclerotinia sclerotiorum, Alternaria spp., Rhizopus oryzae, R. stolonifer, and Colletotrichum acutatum. All isolates evaluated were virulent on pepper. Significant differences in disease susceptibility were identified among lines for each of the pathogens evaluated. P. capsici was the most virulent pathogen, while R. oryzae and one Sclerotinia isolate were the least virulent. Quantitative trait loci associated with resistance were identified for Alternaria spp. and S. sclerotiorum. Positive correlations in disease incidence were detected between Alternaria spp. and F. oxysporum, F. solani, and C. acutatum, as well as between C. acutatum and Botrytis spp., F. oxysporum, F. solani, and P. capsici. No sites of MDR were identified for pathogens tested; however, positive correlations in disease incidence were detected among pathogens suggesting there may be genetic linkage among resistance genes in CM334 and Early Jalapeno.
QTL mapping for sorghum downy mildew disease resistance in maize (Zea mays L.) in recombinant inbred line population of UMI79 X UMI936 (w)