Heterosis for Resistance against Sorghum Downy Mildew [Peronosclerospora sorghi (Weston and Uppal) C.G. Shaw] Infection in Maize (Zea mays L.)

Background: Sorghum downy mildew (SDM) of maize caused by the fungus Peronosclerospora sorghi (Weston and Uppal) C.G. Shaw is one of the most important diseases of maize and it remains vital constraint in maize production. Since maize is the highly cross pollinated crop, exploitation of heterosis is one of the breeding methods to increase the production. Negative values in the expression of heterosis indicate a contribution towards resistance which is highly needed in order to have reduced incid ence of sorghum downy mildew in maize hybrids.Methods: The materials selected as parents for the present study consisted of nine maize inbred lines which comprised of three resistant (UMI102, UMI936(w) and UMI285), three moderately resistant (UMI176, UMI13 and UMI57) and three susceptible (UMI79, UMI432 and UMI467) inbreds to SDM incidence. Nine inbred lines were crossed in all possible combinations including reciprocals in diallel fashion and the resultant seventy two hybrids along with their parents and the check (COH(M)5) were raised and evaluated for resistance against SDM under glass house condition. The extent of heterosis was estimated over mid parent, better parent and popular check hybrid.Result: Analysis of variance for sorghum downy mildew incidence revealed highly significant differences among parents and hybrids indicating greater diversity among the genotypes for sorghum downy mildew incidence under study. Out of seventy two hybrids, only three hybrids namely UMI 13 x UMI 936 (W), UMI 467 x UMI 936 (W) and UMI 432 x UMI 936 (W) exhibited three types heterosis significantly in negative direction.

Peronosclerospora sorghi (sorghum downy mildew).

P. sorghi causes sorghum downy mildew, which can result in severe economic losses of both sorghum and maize. It has been a particularly invasive pathogen: it was introduced to the Americas where it has spread on both sorghum and maize causing considerable damage (Frederiksen et al., 1973). Quarantine restrictions probably maintained the USA free of sorghum downy mildew until the early 1960s (Reyes et al., 1964; Frederiksen, 1980a). Information on the spread of the disease and the damage it causes is available in the literature reporting its spread in the USA (Frederiksen et al., 1970) and elsewhere in the Americas (Frezzi, 1970; Grobman, 1975; Burtica et al., 1992).