Apple species and cultivars differ in nuclear (2C) DNA content and ploidy level. The majority of these genotypes
are diploids, but there are some triploids and a few tetraploids. Nuclear DNA content is a specific feature and
its flow cytometric evaluation can be helpful in differentiating taxa. For many apple genotypes – including all the
Polish ones, these characteristics are not known. 2C DNA was evaluated in relation to leaf, flower, fruit, pollen
grain and stomata sizes as well as to the flowering time for seventy genotypes (including 46 Polish cultivars) gathered
in the gene bank of the Research Institute of Horticulture, Skierniewice, Poland. For standard cultivars with
the known chromosome number, 2C value was 1.71 pg for diploid cultivar ‘Alwa’ (2n=2x=34), 2.55 pg for triploid
‘Boskoop’ (3x=51), and 3.37 pg for tetraploid genome (4x=68) of mixoploid ‘McIntosh 2x+4x’. In 61 cultivars
(including 41 Polish ones), the nuclear DNA content ranged from 1.58 to 1.78 pg indicating their diploid chromosome
number. Five cultivars were identified as triploids (‘Bursztówka Polska’, ‘Pagacz’, ‘Rapa Zielona’, ‘Rarytas
Śląski’ and ‘Witos’) owing to their nuclear DNA amount ranging between 2.42 and 2.58 pg. Leaf, flower, fruit,
stomata and pollen grain sizes were on average significantly larger in triploids. Thus, in 3x plants the mean leaf
surface was 49.1 cm², flower diameter – 52.4 mm, fruit weight – 204.7 g, stomata length – 32.1 μm and pollen
grain diameter – 33.7 μm, whereas in diploids – 36.0 cm², 46.1 mm, 162.7 g, 28.4 μm and 30.7 μm, respectively.
Pollen grain viability was on average significantly higher in diploids (75.6%), compared to triploids (22%). These
results confirm that in apple, as in many other plant species, the higher ploidy level of triploids is generally
associated with increased sizes of pollen grains, stomata, flowers, fruits and leaves but decreased pollen viability.
No clear correlation between ploidy level and flowering time was found. In the case of mixoploid apple genotypes
possessing diploid and tetraploid genomes, some phenotype observation is helpful in describing the ploidy level
of the histogenic layers, L1 and L2. Small stomata sizes (similar to diploid) indicate diploid L1 and larger leaf
sizes, compared to diploid counterparts, show tetraploid L2. The results will be used for breeding, in which it is
important to determine maternal and paternal genotypes as well as the direction of the crossing that is of great
importance in obtaining seeds and materials for further selection.
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