Ginger (Zingiber officinale Rosc.) is an important spice crop valued for its flavored and medical properties. It is susceptible to soil-borne diseases, which can cause considerable economic loss to growers. In vitro culture is feasible for the propagation of disease-free ginger plants, but has several disadvantages when producing seed rhizomes that can be commercially used, such as long cultivation cycles (usually 2–3 years) and occurrence of somaclonal variation. In this study, dynamic changes in the morphological characteristics of in vitro-propagated disease-free plants of ‘Wuling’ ginger were evaluated by continuous observation and measurement at 30-day intervals, and morphological variants were screened and characterized by agronomic, cytological, and molecular analysis at harvest. Results showed that the plants grew rapidly within 120 days after planting, and the most active growth period was from 60 to 120 days. Eight plants with clear and stable morphological differences were screened out from approximately 2000 plants grown in the field, and they could be classified into two groups (VT1 and VT2) based on tiller number, plant height, leaf color, and leaf shape. By flow cytometry analysis and chromosome counting, the VT1 was confirmed to be diploid, with the shortest plant height, the largest number of tillers and rhizome knobs, and the smallest tiller diameter and rhizome size among the three types of plants. The VT2 was mixoploid, consisting of diploid and tetraploid cells, with significantly reduced tiller number and rhizome knobs, significantly larger stomatal guard cells/apertures, and significantly lower stomatal density. SSR analysis detected DNA band profile changes in six out of the eight variants, including one plant of the VT1 and all the VT2 plants. The findings of this study might contribute to the commercial production of disease-free seed rhizomes in ginger, and the characterized somaclonal variants could provide useful germplasm resources for future breeding.
Aneuploids are valuable materials of genetic diversity for genetic analysis and improvement in diverse plant species, which can be propagated mainly via in vitro culture methods. However, somaclonal variation is common in tissue culture-derived plants including euploid caladium. In the present study, the genetic stability of in vitro-propagated plants from the leaf cultures of two types of caladium (Caladium × hortulanum Birdsey) aneuploids obtained previously was analyzed morphologically, cytologically, and molecularly. Out of the randomly selected 23 and 8 plants regenerated from the diploid aneuploid SVT9 (2n = 2x − 2 = 28) and the tetraploid aneuploid SVT14 (2n = 4x − 6 = 54), respectively, 5 plants from the SVT9 and 3 plants from the SVT14 exhibited morphological differences from their corresponding parent. Stomatal analysis indicated that both the SVT9-derived variants and the SVT14-originated plants showed significant differences in stomatal guard cell length and width. In addition, the variants from the SVT14 were observed to have rounder and thicker leaves with larger stomatal guard cells and significantly reduced stomatal density compared with the regenerants of the SVT9. Amongst the established plants from the SVT9, two morphological variants containing 3.14–3.58% less mean fluorescence intensity (MFI) lost one chromosome, and four variants containing 4.55–11.02% more MFI gained one or two chromosomes. As for the plants regenerated from the SVT14, one variant with significantly higher MFI gained two chromosomes and three plants having significantly lower MFI resulted in losing four chromosomes. Three, out of the twelve, simple sequence repeat (SSR) markers identified DNA band profile changes in four variants from the SVT9, whereas no polymorphism was detected among the SVT14 and its regenerants. These results indicated that a relatively high frequency of somaclonal variation occurred in the in vitro-propagated plants from caladium aneuploids, especially for the tetraploid aneuploid caladium. Newly produced aneuploid plants are highly valuable germplasm for future genetic improvement and research in caladium.
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