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W latach 2005-2009 badano zdolność kiełkowania stratyfikowanych nasion jabłoni otrzymanych z programów krzyżowań wykonanych w latach 2004-2008. Łącznie było to 121 kombinacji zapyleń, z użyciem 28 form rodzicielskich. Nasiona uzyskane z programów krzyżowań odkażano 0,1% roztworem fungicydu Benlate (poprzez zamoczenie na 24 godz.) i poddawano stratyfikacji. Stratyfikacja polegała na jednoczesnym wysiewie wszystkich nasion do małych doniczek plastykowych (tace wielokomórkowe) o wymiarach 5,5 cm x 5,5 cm i pojemności 90 cm3, napełnionych mieszaniną substratu torfowego, ziemi kompostowej i piasku w stosunku 1:1:1 (1 nasiono do 1 doniczki) i umieszczeniu ich na 30 dni w zwykłej chłodni o temperaturze 1-2°C. Po tym okresie doniczki z wysianymi nasionami ustawiono na parapecie w szklarni w celu kiełkowania, zapewniając sztuczne doświetlanie (16 godz.) i temperaturę ok. 20°C. Generalnie najlepiej kiełkowały nasiona z programu krzyżowań wykonanego w 2005 roku, średnio 81%, przy czym najwięcej skiełkowanych nasion stwierdzono w rodzinach: ‘Free Redstar’ x ‘Retina’ (89%), ‘Free Redstar’ x ‘Szampion’ (87%) i ‘Free Redstar’ x ‘Pinova’ (85%), natomiast najsłabiej kiełkowały nasiona z programu krzyżowań wykonanego w roku 2007 (średnio 14%, w rodzinie ‘Free Redstar’ x ‘Ligol’ (12%)) i w roku 2006 (średnio 22%, w rodzinach: ‘Ligolina’ x ‘Szampion’ (13%), ‘Ligolina’ x ‘Ligolina’ (17%), ‘Ariwa’ x J-79 (18%)).
To investigate the photoinhibition of photosynthesis in ‘Honeycrisp’ apple (Malus domestica Borkh. cv. Gala) leaves with zonal chlorosis, we compared pigments, CO₂ assimilation and chlorophyll (Chl) a fluorescence (OJIP) transient between chlorotic leaves and normal ones. Chl and carotenoids (Car) contents, Chl a/b ratio, and absorptance were lower in chlorotic leaves than in normal ones, whereas Car/Chl ratio was higher in the former. Although CO₂ assimilation and stomatal conductance were lower in chlorotic leaves, intercellular CO₂ concentration did not differ significantly between the two leaf types. Compared with normal leaves, chlorotic ones had increased deactivation of oxygen-evolving complexes (OEC), minimum fluorescence (Fₒ), dissipated energy, relative variable fluorescence at L-, W-, J- and I-steps, and decreased maximum fluorescence (Fm), maximum quantum yield for primary photochemistry (Fv/Fm or φRₒ/ABS), quantum yield for electron transport (ETₒ/ABS), quantum yield for the reduction of end acceptors of photosystem I (PSI) (uRo and REₒ/ABS), maximum amplitude of IP phase, amount of active photosystem II (PSII) reaction centers (RCs) per cross section (CS) and total performance index (PItot,abs). In conclusion, photoinhibition occurs at both the donor (i.e., the OEC) and the acceptor sides of PSII in chlorotic leaves. The acceptor side is damaged more severely than the donor side, which possibly is the consequence of over-reduction of PSII due to the slowdown of Calvin cycle. In addition to decreasing light absorptance by lowering Chl level, energy dissipation is enhanced to protect chlorotic leaves from photo-oxidative damage.
The aim of the present study was to estimate the relationship between the crop load, number of fruits produced per unit of trunk cross-sectional area (TCA), the average fruit weight and the yield of 'Jonagold' apple trees. The trees apple (Malus domestica Borkh. cv. 'Jonagold') grafted on P 60 rootstock were planted at 3.5 x 1.25 m spacing. In order to achieve a high diversity of fruit load, light (L) as well as heavy (H) thinning were applied. The fruitlets were not thinned in the control (Control) trees. The yield and average fruit weight depended on the applied thinning. The correlation coefficient between crop density (CD) and yield was positive, whereas that between CD and average fruit weight was negative. The mean fruit weight was influenced not only by the number of fruit per unit of trunk cross- sectional area but also by the age of a tree.
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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