Mapping of QTL affecting resistance against sorghum downy mildew (Peronosclerospora sorghi) in maize (Zea mays L)

Sorghum downy mildew (SDM) is one of the most destructive diseases of maize (Zea mays L) in South-East Asia. Understanding the genetic basis of downy mildew resistance (DMR) could increase the efficiency of breeding for disease resistant germplasm. The objectives of this study were to determine the number, genomic positions and genetic effects of quantitative trait loci (QTL) conferring resistance to SDM. The study included 251 F2:3 families derived from a cross between the two inbreds, Nei9008 (Thailand) and CML289 (CIMMYT), resistant and susceptible, respectively. Individuals in the population were genotyped for simple sequence repeat (SSR) and phenotypic resistance data were evaluated as percentage disease incidence in replicated field trials at three environments by Triple Lattice design. Heritability across environments was 94.3%. Traits were analyzed within and across environment using composite interval mapping. Nine QTLs were identified for resistance to SDM, one QTL each on chromosome 2, 3, 4, and 6, three QTLs on chromosome 5, and two QTLs on chromosome 9. Just one QTL on chromosome bin 5.07 came from the susceptible parent, all others from the resistant parent, Nei9008. The QTLs in chromosome bins 2.09 at umc1736, 5.03 at bnlg1902, and 6.01 at bnlg1867 had major effects and were consistent over all environments. A common map shows intriguing collocations of SDM QTLs with those for other disease and insect resistance QTLs from literature. As several consistent QTLs for downy mildew resistance are available now, an avenue is open for pyramiding multiple genes by marker assisted selection (MAS) that may control different mechanisms for resistance