No abstract

Maize is the third most important crop worldwide after rice and wheat (Hoisington and Melchinger 2004). It is affected by several pests and diseases. Among the diseases, sorghum downy mildew (SDM), caused by Peronosclerospora sorghi [(Weston and

Sorghum downy mildew (SDM), caused by the biotrophic fungi Peronosclerospora sorghi, threatens maize production worldwide, including India. To identify quantitative trait loci (QTL) associated with resistance to SDM, we used a recombinant inbred line (RIL) population derived from a cross between resistant inbred line UMI936 (w) and susceptible inbred line UMI79. The RIL population was phenotyped for SDM resistance in three environments [E1-field (Coimbatore), E2-greenhouse (Coimbatore), and E3-field (Mandya)] and also utilized to construct the genetic linkage map by genotyping by sequencing (GBS) approach. The map comprises 1516 SNP markers in 10 linkage groups (LGs) with a total length of 6924.7 cM and an average marker distance of 4.57 cM. The QTL analysis with the phenotype and marker data detected nine QTL on chromosome 1, 2, 3, 5, 6, and 7 across three environments. Of these, QTL namely qDMR1.2, qDMR3.1, qDMR5.1, and qDMR6.1 were notable due to their high phenotypic variance. qDMR3.1 from chromosome 3 was detected in more than one environment (E1 and E2), explaining the 10.3% and 13.1% phenotypic variance. Three QTL, qDMR1.2, qDMR5.1, and qDMR6.1 from chromosomes 1, 5, and 6 were identified in either E1 or E3, explaining 15.2%–18% phenotypic variance. Moreover, genome mining on three QTL (qDMR3.1, qDMR5.1, and qDMR6.1) reveals the putative candidate genes related to SDM resistance. The information generated in this study will be helpful for map-based cloning and marker-assisted selection in maize breeding programs.

TNAU maize hybrid Co 6 (CMH-08-282) is a high yielding single cross hybrid (UMI 1200 x UMI 1230) and matures in 110 days. It is suited for cultivation both under irrigated (June - July & November - December) and rainfed (September - October) conditions. A total of 100 adaptive research trials, 16 multi location trials, 138 on farm trials, 9 station trials and 49 All India trials were conducted with single cross hybrid CoH(M) 5 as check and popular private maize hybrids viz., 900 M (G ) and NK 6240 as checks. Under irrigated condition, it recorded a mean grain yield of 7359 kg/ha with 28.2, 10.6 and 8.2 per cent increased grain yield over the existing hybrid Co(H)M 5 (5739 Kg/ha), 900 M (G) (6656 Kg/ha) and NK 6240 (6803 Kg/ha) respectively. Under rainfed conditions the same hybrid recorded a mean grain yield of 4906 kg/ha with 16.6, 19.0 and 21.6 per cent increased grain yield over checks viz., CoH(M) 5 (4209 Kg/ha), 900 M (G) (4121 Kg/ha) and NK 6240 (4034 Kg/ha) respectively. It recorded a highest yield of 13273 Kg/ha (JH Agri, Bangalore) and 19 tonnes of fodder under irrigated condition. It exhibited a multiple disease resistance against the Sorghum downy mildew, Turcicum leaf blight and Post flowering stock rot and moderately resistant to stem borer. It possesses high starch (76.30 %), high protein (11.25%) and high beta-carotein (0.48 mg/100g) with moderate level of fat (4.65 %) and crude fibre (1.25%) than the check hybrids. Grains are bold, orange yellow, semi dent in texture. It recorded a high shelling (81%) with high test weight (400 g /1000 seeds). Hybrid seed production is much easier since male and female parents can be sown simultaneously for flowering synchronization. In view of high yielding with stable performance across environments, it has been released as new hybrid during 2012 for commercial exploitation in the state of Tamil Nadu.