Inheritance of Resistance to Sorghum Downy mildew (Peronosclerospera sorghi) in Maize (Zea mays L.)

Most efficient, viable and cost effective long-term strategy for the management of downy mildew in maize is possible through host plant resistance. A study was initiated with screening of 100 maize inbreds against downy mildew and study of inheritance of resistance. Diallel analysis was adopted using eight inbreds to understand the inheritance of downy mildew resistance in maize. Parents, UMI 57, UMI 62, UMI 39 and UMI 743 recorded positive gca effects, of which the effects of UMI 57 and UMI 743 were significant. Among the hybrids, UMI 57 × CM 500, UMI 13 × CM 500 and UMI 62 × UMI 118 recorded highly significant and positive sca effects. The hybrids UMI 743 × CM 500, UMI 13 × UMI 57 and UMI 13 × UMI 97 recorded highly significant positive reciprocal effects. Two hybrids viz., CM 500 x UMI 39, CM 500 × UMI 57 were found to be highly resistant (100%) to downy mildew with high grain yield. The hybrids CM 500 × UMI 97 (143.09 g), UMI 13 × UMI 57 (139.81 g) and CM 500 x UMI 39 (130.98 g) were also with high yield per plant with resistant reaction to downy mildew. Moderately resistant x resistant combination UMI 62 × UMI 743 recorded moderate reaction. The susceptible × highly resistant combination hybrid CM 500 × UMI 57 showed highly resistant reaction. Disease reaction of the parents and F₂s of eight crosses ranged from zero to 100 per cent. Genetic studies for downy mildew resistance have revealed the occurrence of monogenic, digenic and also the possible role of polygenic inheritance. All the downy mildew resistant hybrids were found to possess significantly higher concentration of total phenols, soluble protein, peroxidase and polyphenol oxidase. Hence these biochemical substances could have a possible role in the resistance behaviour of the genotypes against downy mildew.