Abstract
Background: Citrus cultivar improvement via conventional breeding strategies
is impeded by factors related to its reproductive biology. The orange is a hybrid between
pomelo (Citrus maxima) and mandarin (Citrus reticulata). Among various orange cultivars,
Valencia oranges have a bit of bitter tang mixed in with their sweetness, as Navel oranges
are, the most widely cultivated citrus species, quite sweeter, and also don't contain
any seeds. Tangelo mandarin orange cultivar is a hybrid of C. reticulata × C. maxima or
× C. paradisi.
Objective: The present study was undertaken to optimize the hormonal composition of the
media with regard to plant growth regulators for in vitro propagation of sweet orange cultivars
from nodal segment explants.
Methods: The nodal segment explants were collected from three citrus cultivars, Washington
Navel, Valencia and Tangelo. Murashige and Skoog (MS) medium supplemented with
sucrose and different concentrations of growth regulators was used for shoot proliferation
and root induction, and the optimum medium composition was assessed. The patent for
Citrus Tissue Culture was obtained from the Office of Research Affairs, Haramaya University.
Results: The results indicate that the highest shoot response was recorded for Washington's
navel with maximum shoot proliferation rate (99.75%), shoot number per explant (1.76),
shoot length (10.70 cm), leaf number per explants (3.54) after three weeks of culture. In all
experiments, no growth was observed for the basal MS medium. Phytohormone combinations
of IAA (1.2 mg/L) and kinetin (2.0 mg/L) were found to be the best for shoot proliferation.
Among the cultivars, there were significant differences for the highest rooting rate
(81.255), root number (2.22), and root length (2.95 cm) variables for Washington Navel.
The lowest rooting rate (48.45%), root number (1.47) and root length (2.26 cm) were observed
for Valencia. The highest rooting rate (84.90%), root number per microshoot (2.22)
and root length (3.05 cm) was on MS medium supplemented with 1.5 mg/L NAA.
Conclusion: A comparison of different concentrations of IAA and NAA on root induction
of microshoots from nodal segments of citrus cultivars demonstrated NAA was a more effective
hormone than IAA.
Graphical Abstract
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