Exploring Polyploidization in Nigella sativa L.: An Applicable Strategy Towards Crop Improvement

A plant breeding program needs helpful markers, especially morphological ones, which can allow breeders to dispense with other markers, including cytological traits and flow cytometry. These markers can assist plant breeders in distinguishing diploid and tetraploid plants during the seedling stage. Therefore, the present study aimed to investigate and validate effective methodologies for the early identification of artificially induced polyploids in black cumin. Thus, we established an extensional program for black cumin breeding including producing seeds, active compounds, and flowers as ornamental plants. Field experiments on tetraploids and diploids were carried out to evaluate the morphological and yield traits of both plants. Also, some cytological studies and Gas Chromatography (GC) analysis were conducted to achieve these goals. The results showed the possibility of realizing diploid and tetraploid plants in early growing black seeds in the field (mainly after the first cotyledon leaves). This crucial outcome can support plant breeders in identifying polyploidy during the seedling stage without referring to biochemical markers, flow cytometry, and cytological traits. All morphological and yield-related traits were superior in diploid plants compared to tetraploids. The results showed that diploid and tetraploid plants exhibited plant heights of 116 cm and 95 cm, numbers of secondary branches of 112 and 22, numbers of flowers of 111.7 and 24.75, and shoot fresh weights of 610 g and 147.5 g, respectively. Furthermore, the number of seeds per capsule, seed yield per plant, and oil percentage in diploids were 97.5 seeds, 24 g, and 22.94%, compared with 35.25 seeds, 4.62 g, and 17.76% in tetraploids, respectively. This work used the cotyledon leaf shape as a morphological marker to distinguish the tetraploid and diploid plants, as diploids are typically taller with pointed cotyledons, whereas tetraploids are shorter with rounded cotyledon tips. This study will create great opportunities for plant breeders to save time and costs during their programs. Further studies on such suggested black cumin breeding programs are needed on diploids, triploids, and tetraploids.