Chromosome doubling in vine cacti hybrids.

Area of Science:

• Plant genetics
• Cactaceae family evolution
• Polyploidy in plants

Background:

• Selenicereus megalanthus is a tetraploid cactus species.
• Hylocereus species (H. undatus, H. polyrhizus) are diploid.
• Understanding interspecific hybridization in Cactaceae is crucial for crop improvement.

Purpose of the Study:

• Investigate hybridization outcomes between S. megalanthus and Hylocereus species.
• Determine the mechanism of polyploid formation in interspecific crosses.
• Analyze gamete viability and ploidy levels in resulting hybrids.

Main Methods:

• Performed reciprocal crosses between S. megalanthus (4x) and H. undatus (2x) / H. polyrhizus (2x).
• Analyzed pollen diameter variation to assess gamete viability and unreduced gamete frequency.
• Determined ploidy levels of resulting hybrid offspring.

Main Results:

• Crosses of S. megalanthus x H. undatus yielded viable hexaploids (6x) and 6x-aneuploid hybrids, not expected triploids (3x).
• Reciprocal crosses (Hylocereus x S. megalanthus) did not produce genuine hybrids.
• Pollen analysis indicated wide variation in S. megalanthus (tetraploid) and uniform pollen in H. undatus (diploid), suggesting a low frequency of unreduced gametes in the diploid.

Conclusions:

• Hexaploid formation in these crosses likely resulted from chromosome doubling of a triploid zygote.
• The fusion of unreduced gametes was not the primary mechanism for hexaploid formation.
• Ploidy level and gamete characteristics significantly influence hybridization outcomes in Cactaceae.