In vitro induction of tetraploid garlic with trifluralin.

Garlic (Allium sativum) is propagated asexually. Since sexual cross breeding is almost impossible, means for effective breeding are not currently available and the available production cultivars are seriously aged and degenerated. A possible alternative for breeding is chemical induction. Trifluralin, a type of herbicide, has been reported to provoke chromosome doubling. However, this chemical had not been tested on garlic. We tested various trifluralin concentrations and treatment durations for efficiency in the induction of tetraploid garlic. A clove base of garlic with a stem cv. Gailiang was used as the ex-plant to induce calluses on Murashige and Skoog (MS) medium; the calluses were then inoculated onto MS medium containing different levels of trifluralin and cultured to induce chromosome number variation in vitro. Garlic calluses were effectively induced via the ex-plant and both shoots and roots differentiated well on MS medium containing 6-benzylaminopurine at 3.0 mg/L and indole-3-acetic acid at 0.1 mg/L. However, increases in trifluralin concentration and treatment duration reduced the survival rate and differentiation rate of calluses. Garlic callus cultured for 15 days on medium containing 100 µM trifluralin gave the highest rate of chromosome doubling. Through observation of chromosome number in the root apical cells and the morphology of guard cells on the leaf epidermis of the regenerated plantlets, it was clear that chromosome number variation was induced and tetraploids were produced in vitro by trifluralin treatment.

Cytomixis and meiotic abnormalities during microsporogenesis are responsible for male sterility and chromosome variations in Houttuynia cordata.

Houttuynia cordata (Saururaceae) is a leaf vegetable and a medicinal herb througout much of Asia. Cytomixis and meiotic abnormalities during microsporogenesis were found in two populations of H. cordata with different ploidy levels (2n = 38, 96). Cytomixis occurred in pollen mother cells during meiosis at high frequencies and with variable degrees of chromatin/chromosome transfer. Meiotic abnormalities, such as chromosome laggards, asymmetric segregation and polyads, also prevailed in pollen mother cells at metaphase of the first division and later stages. They were caused by cytomixis and resulted in very low pollen viability and male sterility. Pollen mother cells from the population with 2n = 38 showed only simultaneous cytokinesis, but most pollen mother cells from the population with 2n = 96 showed successive cytokinesis; a minority underwent simultaneous cytokinesis. Cytomixis and irregular meiotic divisions appear to be the origin of the intraspecific polyploidy in this species, which has large variations in chromosome numbers.