Doubled haploid (DH) technology is widely used in maize breeding because of its ability to produce 100% homozygous inbred lines within a short period of time. This efficiency has made DH technology an attractive tool for maize breeders, allowing its incorporation into breeding programs. This technology also facilitates advanced breeding techniques such as genome editing and the conversion of elite inbred lines into their cytoplasmic male sterility counterparts. The successful integration of DH technology into various maize breeding programs worldwide has spurred extensive research on the genetic basis and mechanisms underlying haploid induction, leading to the identification of key quantitative trait loci (QTL) aimed at improving efficiency and reducing costs. Additionally, new phenotypic markers are being explored for use along with the R1-nj marker to enhance the accuracy of haploid seed and plant identification. Efforts are underway to identify alternatives to colchicine, a toxic and carcinogenic compound commonly used for chromosome doubling. Nondestructive methods, such as nuclear magnetic resonance, Fourier transform Raman spectroscopy, and flow cytometry, are being developed to enable fast and accurate haploid identification and automate the process for large-scale breeding programs. As these advancements improve DH technology, the maize hybrid breeding paradigm is undergoing a substantial transformation. However, several challenges remain unaddressed.

In this study, 14 agricultural and phenotypic traits were used to analyze morphological variations among 10 near-isogenic lines (NILs) of colored waxy maize and 2 parental lines (HW3 and HW9) of the hybrid cultivar “Mibaek 2.” The results of principal component analysis indicated that on the first principal component axis, seed coat color, R value, V value, days of tasseling, L* value, and days of silking greatly contributed to the positive direction, whereas anthesis–silking interval and leaf width greatly contributed to the negative direction. On the second principal component axis, kernel row number and tassel color contributed to the positive direction, whereas setted ear length, ear length, and 100-kernel weight contributed to the negative direction. Thus, the morphological characteristics that greatly contributed to the first and second principal components might be useful for discrimination among the 10 NILs and 2 parental lines of “Mibaek 2.” Of the 10 NILs analyzed, 16CLP26 and 16CLP16 were considered useful breeding material for the development of colored waxy maize varieties with relatively high amounts of yield and anthocyanin. Collectively, these results are expected to provide useful information for the development and selection of lines for breeding colored waxy corn varieties at the Maize Research Institute, Gangwon-do Agricultural Research and Extension Services.

In order to develop a core set and new corn variety in Korea, we evaluated the morphological characteristics of 194 maize accessions by examining eight quantitative characteristics. On the evaluation of quantitative traits for 194 maize accessions, they showed the morphological variations in tassel length (35.1±5.0 cm), plant height (226.1±33.7 cm), ear height (86.3±22.6 cm), stem diameter (2.3±0.6 cm), leaf width (9.3±1.1 cm), ear length (14.5±2.4 cm), ear row number (14.1±1.9 row), and 100 kernel weight (24.9±4.4 g). The results of principal component analysis (PCA) indicated that the tassel length, plant height, and ear height greatly contributed to positive direction on the first principal component axis. One-hundred kernel weight contributed to negative direction on the second principal component axis. Thus these morphological characteristics, which contributed greatly in the first and second principal components, might be useful for discrimination among 194 maize accessions. In our study, seven accessions, such as IT026357, IT026441, IT027321, IT033271, IT033591, IT033597 and IT124273, particularly were measured high on yield-related traits. Consequently, the 194 maize accessions used in this study could be used as promising materials for maize breeding programs such as development of new hybrid in Korea.