Linkage mapping and genomic prediction of grain quality traits in tropical maize (Zea mays L.)

The suboptimal productivity of maize systems in sub-Saharan Africa (SSA) is a pressing issue, with far-reaching implications for food security, nutrition, and livelihood sustainability within the affected smallholder farming communities. Dissecting the genetic basis of grain protein, starch and oil content can increase our understanding of the governing genetic systems, improve the efficacy of future breeding schemes and optimize the end-use quality of tropical maize. Here, four bi-parental maize populations were evaluated in field trials in Kenya and genotyped with mid-density single nucleotide polymorphism (SNP) markers. Genotypic (G), environmental (E) and G×E variations were found to be significant for all grain quality traits. Broad sense heritabilities exhibited substantial variation (0.18-0.68). Linkage mapping identified multiple quantitative trait loci (QTLs) for the studied grain quality traits: 13, 7, 33, 8 and 2 QTLs for oil content, protein content, starch content, grain texture and kernel weight, respectively. The co-localization of QTLs identified in our research suggests the presence of shared genetic factors or pleiotropic effects, implying that specific genomic regions influence the expression of multiple grain quality traits simultaneously. Genomic prediction accuracies were moderate to high for the studied traits. Our findings highlight the polygenic nature of grain quality traits and demonstrate the potential of genomic selection to enhance genetic gains in maize breeding. Furthermore, the identified genomic regions and single nucleotide polymorphism markers can serve as the groundwork for investigating candidate genes that regulate grain quality traits in tropical maize. This, in turn, can facilitate the implementation of marker-assisted selection (MAS) in breeding programs focused on improving grain nutrient levels.

Sustainable intensification of climate-resilient maize-chickpea system in semi-arid tropics through assessing factor productivity

Global trends show that the rapid increase in maize production is associated more with the expansion of maize growing areas than with rapid increases in yield. This is possible through achieving possible higher productivity through maize production practices intensification to meet the sustainable production. Therefore, a field experiment on "Ecological intensification of climate-resilient maize-chickpea cropping system" was conducted during consecutive three years from 2017-2018 to 2019-2020 at Main Agricultural Research Station, Dharwad, Karnataka, India. Results of three years pooled data revealed that ecological intensification (EI) treatment which comprises of all best management practices resulted in higher grain yield (7560 kg/ha) and stover yield compared to farmers' practice (FP) and all other treatments which were deficit in one or other crop management practices. Similarly, in the succeeding winter season, significantly higher chickpea yield (797 kg/ha) was recorded in EI. Further EI practice recorded significant amount of soil organic carbon, available nitrogen, phosphorus, potassium, zinc, and iron after completion of third cycle of experimentation (0.60%, 235.3 kg/ha,21.0 kg/ha,363.2 kg/ha,0.52 ppm and 5.2 ppm respectively). Soil enzymatic activity was also improved in EI practice over the years and improvement in each year was significant. Lower input energy use was in FP (17,855.2 MJ/ha). Whereas total output energy produced was the highest in EI practice (220,590 MJ ha-1) and lower output energy was recorded in EI-integrated nutrient management (INM) (149,255 MJ/ha). Lower energy productivity was noticed in EI-INM. Lower specific energy was recorded in FP and was followed by EI practice. Whereas higher specific energy was noticed is EI-INM. Each individual year and pooled data showed that EI practice recorded higher net return and benefit-cost ratio. The lower net returns were obtained in EI-integrated weed management (Rs. 51354.7/ha), EI-recommended irrigation management (Rs. 56,015.3/ha), integrated pest management (Rs. 59,569.7/ha) and farmers' practice (Rs. 67,357.7/ha) which were on par with others.

First report of Fusarium verticillioides causing Pokkah boeng disease on maize in India

Maize is a widely grown cereal crop in India and ranks third to wheat and rice in production (https://iimr.icar.gov.in). During a field survey in Kharif season in 2018, foliar chlorosis at the base and middle of leaves, and twisted top symptoms were observed in 40-50 days old maize plants in Belagavi district, Karnataka, India. Again during Kharif season in 2021, similar symptoms were observed on commercial maize hybrids and sugarcane at Agricultural Research Station, Sankeshwar Karnataka. The symptoms resembled Pokkah boeng disease of sugarcane (Vishwakarma et al. 2013). Symptomatic sugarcane and maize leaves were sampled, surface sterilized with 1.0% sodium hypochlorite, and 70% ethanol, and transferred on Potato dextrose agar, incubated for 10 days at 27±1°C. Fungal growth initiated with white mycelium later turned to pinkish-white with hyaline spores. The morphological features and sporulation patterns of maize and sugarcane samples were similar (e-Xtra 1). Microconidia were formed in long chains and clusters with oval to club-shaped, 0-septate, monophialide-borne microspores. DNA from representative pure culture isolates was extracted using the CTAB protocol (Doyle and Doyle, 1990). The ITS region of r-DNA was amplified with ITS1/ITS4 primers and sequenced. BLAST analyses of sequences of maize and sugarcane culture isolates at NCBI database revealed 100% homology with Fusarium verticillioides MK264336 (Lin et al., 2016). PCR amplification with Fusarium verticilliodes specific primers VER1/VER2 (Mule et al., 2004) confirmed the organism. CBS-KNAW Fungal Biodiversity Centre's Fusarium MLST database also revealed over 98.89% homology with Fusarium verticilliodes (NRRL 46612). The fungal isolates were named Fusarium verticilliodes maize isolate SNK 01 (ON110289) and Fusarium verticilliodes sugarcane isolate SNK 01 (ON564879), and their sequences were deposited in the GenBank. To test pathogenicity, artificial inoculation using maize isolate SNK 01 and cross-inoculation of sugarcane isolate SNK 01 were done on ten maize plants by spraying a conidial suspension (2×106 conidia ml-1) on nonwounded leaves. The plants sprayed with sterile water were used as control. After ten days, typical Pokkah boeng symptoms were observed in the plants inoculated with both maize and sugarcane isolates. Diseased leaves turned pale yellowish-green with small brown spots and a chlorotic appearance, further, these developed into stripes (e-Xtra 2). Wrinkling of leaves was noticed followed by splitting and rotting. No symptoms were noticed in the water-treated control. The pathogens re-isolated from diseased plants inoculated with maize and sugarcane isolates were similar morphologically and identical to the original isolates, fulfilling Koch's postulates. Hitherto, Fusarium verticilliodes was known to cause post-flowering stalk rot in maize. However, this is the first report of Pokkah boeng disease on maize in India caused by F. verticillioides. Considering the economic value of the maize crop, this identification can help develop appropriate disease management strategies to control the disease. References Lee, S. B., et al. 1988. A rapid, high yield mini-prep method for isolation of total genomic DNA from fungi. Fungal Genet. Newsl. 35:23-24. Lin, Z., et al. 2016. Deciphering transcriptomic response of Fusarium verticillioides in relation to nitrogen availability and the development of sugarcane Pokkah boeng disease. Sci. Rep. 6, 29692. Mule, G., et al. 2004. A Species-Specific PCR assay based on the Calmodulin partial gene for identification of Fusarium verticillioides, F. proliferatum and F. subglutinans. European J. Plant Path. 110:495-502 Vishwakarma, S.K., et al. 2013. Pokkah Boeng: an emerging disease of sugarcane. J. Plant Pathol. Microb. 4(3):170. https://iimr.icar.gov.in. Director's desk, ICAR-Indian Institute of Maize Research. (Accessed September 8, 2022).