Screening late maize hybrids against the pathogenic fungus Fusarium verticillioides (Sacc.) Nirenberg

Fusarium verticillioides (Sacc.) Nirenberg causes maize ear rot in all maize-growing regions of the world and produces mycotoxins that contaminate maize grains. Therefore, it is considered an important species in terms of food health for both animal and human in the world. One of the best approaches to address this disease is to identify highly tolerant or resistant genotypes that can be used for genetic improvement. In this experiment, the resistance of 16 late maize hybrids was evaluated for cob resistance, silk channel resistance, and resistance in the germination stage using three inoculation methods. The objective of the current study was to select the genotype with high resistance in all three developmental stages.

The seeds of 16 late maize hybrids were obtained from the Maize and Forage Crops Research Depatment (MFCRD), Seed and Plant Improvement Institute (SPII), Karaj, Iran, and were planted in a randomized complete block design with three replications in the research field of MFCDR, in 2021. To inoculate the plants, the Kj7 isolate collected from infected maize cobs in the field of MFCDR was used. Maize hybrids were screened with three methods. In the first method, the resistance of the studied hybrids was evaluated by the rolled paper method at the germination stage. In the second method, the cob resistance was assesed by creating a wound in the middle of the cob and injecting spore suspension, and in the third method, silk channel resistance was investigated by injecting spore suspension into the silk channel seven days after the appearance of silks. Data statistical analysis was done by analysis of variance and comparison of means with Duncan's test using SAS software.

The results of analysis of variance and comparison of means showed that there was a significant difference among the studied 16 maize hybrids in terms of disease resistance with all three methods of artificial contamination. According to disease severity measurement in all three evaluated methods, the hybrids H3, H8, H11, H12 and H13 were selected as hybrids with high resistance against pathogenic fungi. These hybrids showed suitable resistance against all main methods of fungal infection and were superior hybrids compared to the other hybrids evaluated in this study in terms of resistance to maize ear rot caused by F. verticillioides. The implementation of these screening assays in maize breeding programs can be effective for classifying the degree of flexibility of maize germplasms to fusarium head rot.

The results of this experiment indicated that to evaluate the fusarium ear rot resistance of maize genotypes, the cob resistance method can be used as the main evaluation method especially in dry regions. Silk channel resistance can be used as a control method to evaluate the possible sensitivity of resistant or semi-resistant genotypes in humid areas where contamination with this method is important. Also, due to the different reaction of a number of hybrids investigated at the germination stage in this study and the possibility of the fungus growing as an endophyte in the plant, it is recommended to evaluate the new cultivars being introduced at this growth stage. Finally, hybrids should be introduced as resistant to this disease, which have shown a suitable reaction to the fungus in all three methods.