Genome size and nucleotypic variation in Malus germplasm.

Area of Science:

• Plant genetics and genomics
• Horticultural science
• Flow cytometry applications

Background:

• The genus Malus (apple relatives) comprises diverse species and subspecies with varying ploidy levels.
• Extensive Malus germplasm exists, but genome sizes have largely remained undetermined.
• Understanding genome size is crucial for characterizing genetic diversity within Malus.

Purpose of the Study:

• To determine the genome sizes of 100 Malus species and hybrid accessions.
• To identify the ploidy levels (diploid, triploid, tetraploid) within the analyzed Malus collection.
• To investigate the relationship between genome size and stomatal length in Malus.

Main Methods:

• Flow cytometry was employed to analyze nuclei extracted from leaf tissues of 100 Malus accessions.
• Propidium iodide staining was used, with maize (Zea mays) as an internal standard.
• Stomatal length, a nucleotypic parameter, was measured from leaf impressions of selected genotypes.

Main Results:

• Analysis identified 96 diploid, 3 triploid, and 1 tetraploid Malus genotype.
• Significant genome size differences were observed among ploidy types and within diploids (1.44-1.72 pg for diploids, 2.27-2.41 pg for triploids, 3.13 pg for tetraploids).
• A positive correlation was found between genome size and stomatal length (19.47 µm for diploid, 27.6 µm for tetraploid).

Conclusions:

• Flow cytometry is effective for determining ploidy and genome size in Malus germplasm.
• Malus accessions exhibit considerable variation in genome size and ploidy.
• Stomatal length serves as a reliable indicator of genome size variation in Malus.