Frequency of heterotic hybrids in relation to general combining ability of parents in sweet corn.

The success of developing prominent hybrids directly depends on the selection of parents with good combining ability which can transfer desirable genes with additive effects to their progeny. The data of 42 hybrids generated using 7 × 7 full diallel design; their seven parents along with three check hybrids were subjected to combining ability analysis from the experiment that was carried out during rainy season 2019. The analysis of variance showed significant general combining ability, and specific combining ability mean sum of squares for all the thirteen characters studied. It is obvious from the results that three lines (SC Sel 2, SC Sel 1 and SC Sel 3) showed high overall general combining ability status, suggesting these lines as good general combiners across traits. Eighteen hybrids had high overall specific combining ability status, while nearly 52% (22 hybrids), 57% (24 hybrids) and 47% (20 hybrids) of crosses showed high overall mid-parent, better-parent and standard heterosis. The unique superiority of crosses involving high overall general combiner parent in the crosses highlighted the importance of using such parents to realize high heterotic crosses. A non-linear relationship between high overall specific combining ability status and heterotic status of hybrids was noticed. The probability of obtaining a cross with high standard heterosis was more with employing parents with high general combining ability status.

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).