regulators on
direct shoot regeneration are shown in Table 3. Direct shoot
regeneration was observed within 14 days of culture. Shoot
buds emerged directly from the cut end of the region near to
petiole on cotyledon explants. Multiple shoot was formed
directly within 21 day of culture initiation (Fig. 1). According
to percentage of direct shoot regeneration , different plant growth regulators combinations showed different responses.
Thus, the best result was obtained in M1 and M7 medium
with 0.54 µM NAA, 0.44 µM BA (72% direct shoot
regeneration) and 0.1 µM NAA, 0.44 µM BA (65% direct
shoot regeneration), respectively. Higher concentrations of
NAA and BA did not increase the number of direct shoot
regeneration. These results are similar to those obtained by
Hunter and Burritt (2002), who produced the greatest number
of shoots when 0.54 µM of NAA used in combination with
0.44 µM of BA. Similarly, Kanamoto et al. (2006) obtained
high shoot regeneration from leafy explants cultivated on
medium supplemented with 0.1 mgl-1 NAA and 0.1 mgl-1
BA. Webb et al. (1984) showed that cotyledon age can
influence the regeneration response; with older cotyledons has less ability for direct shoot regeneration than younger
ones. According to Hunter and Burritt (2002), cotyledon age
influences the shoot-forming ability of cotyledon explants but
in a genotype manner. But in the present study, explants age
did not have a significant effect on direct shoot regeneration
in two lettuce landraces. The present study also showed that
lettuce genotypes did not have a significant effect on direct
shoot regeneration. The relative influence of the genotypes on
tissue response has been a matter of controversy. Vasil and
Vasil (1986) suggested that the differential response of the
genotypes may be due to differential expression, which in
turn, depends upon the spatial and temporal distribution of
their physiological and developmental stages. To identify the
relationship between callus induction and direct shoot regeneration, Pearson’s correlation coefficient was computed.
Pearson’s correlation coefficient identified that callus
induction was correlated with direct shoot regeneration.
These variables were positively correlated (0.408), and the
correlation was statistically significant at the 0.05 level. This
result is not similar to that of Ampomah-Dwamena et al.
(1997), who reported no correlation between callus
production and shoot regeneration. Three regions (middle,
near to petiole and petiole) on cotyledon explants were also
tested to identify the best region for direct shoot regeneration.
According to obtained results to identify the best region for
direct shoot regeneration, petiole of cotyledons did not show
significant response to growth regulators. On the other hand,
middle parts of cotyledon showed significant response to
growth regulators and produced callus. But the best region
for direct shoot regeneration in lettuce was the region near to
petiole on cotyledon explants which showed high significant
response to growth regulators (Fig. 1). In conclusion, our
study revealed that the effect of growth regulators
combinations on callus induction was genotype and explant
age-dependent. The highest number of callus was obtained
using 2.7 µM NAA and 4.4 µM BA. It also showed that
direct shoot regeneration significantly decreased with
increasing BA concentration. However, the use of BA less
than 1 µM increased direct shoot regeneration in two
genotypes. Positively significant correlation was observed
between callus induction and direct shoot regeneration. It was
also shown in our study that the best region for direct shoot
regeneration on cotyledon explants of lettuce is near to
petiole. This adventitious origin of shoots directly from the
region near to petiole of cotyledons may aid the use of
genetic engineering to improve horticultural characteristics. If
propagation through tissue culture can be done efficiently on
a large scale in plant breeding programs, it may be used to
produce F1 hybrids to use the hybrid vigour. This
regeneration protocol will be useful not only for further
research studies such as Agrobacterium mediated genetic
transformation or protoplast fusion studies, but also for
commercial nurseries to produce virus-free plants and
agricultural practices that could reduce pesticides application
and increase production.
regulators on direct shoot regeneration are shown in Table 3. Direct shoot regeneration was observed within 14 days of culture. Shoot buds emerged directly from the cut end of the region near to petiole on cotyledon explants. Multiple shoot was formed directly within 21 day of culture initiation (Fig. 1). According to percentage of direct shoot regeneration , different plant growth regulators combinations showed different responses. Thus, the best result was obtained in M1 and M7 medium with 0.54 µM NAA, 0.44 µM BA (72% direct shoot regeneration) and 0.1 µM NAA, 0.44 µM BA (65% direct shoot regeneration), respectively. Higher concentrations of NAA and BA did not increase the number of direct shoot regeneration. These results are similar to those obtained by Hunter and Burritt (2002), who produced the greatest number of shoots when 0.54 µM of NAA used in combination with 0.44 µM of BA. Similarly, Kanamoto et al. (2006) obtained high shoot regeneration from leafy explants cultivated on medium supplemented with 0.1 mgl-1 NAA and 0.1 mgl-1BA. Webb et al. (1984) showed that cotyledon age can influence the regeneration response; with older cotyledons has less ability for direct shoot regeneration than younger ones. According to Hunter and Burritt (2002), cotyledon age influences the shoot-forming ability of cotyledon explants but in a genotype manner. But in the present study, explants age did not have a significant effect on direct shoot regeneration in two lettuce landraces. The present study also showed that lettuce genotypes did not have a significant effect on direct shoot regeneration. The relative influence of the genotypes on tissue response has been a matter of controversy. Vasil and Vasil (1986) suggested that the differential response of the genotypes may be due to differential expression, which in turn, depends upon the spatial and temporal distribution of their physiological and developmental stages. To identify the relationship between callus induction and direct shoot regeneration, Pearson’s correlation coefficient was computed. Pearson’s correlation coefficient identified that callus induction was correlated with direct shoot regeneration. These variables were positively correlated (0.408), and the correlation was statistically significant at the 0.05 level. This result is not similar to that of Ampomah-Dwamena et al. (1997), who reported no correlation between callus production and shoot regeneration. Three regions (middle, near to petiole and petiole) on cotyledon explants were also tested to identify the best region for direct shoot regeneration. According to obtained results to identify the best region for direct shoot regeneration, petiole of cotyledons did not show significant response to growth regulators. On the other hand, middle parts of cotyledon showed significant response to growth regulators and produced callus. But the best region for direct shoot regeneration in lettuce was the region near to petiole on cotyledon explants which showed high significant response to growth regulators (Fig. 1). In conclusion, our study revealed that the effect of growth regulators combinations on callus induction was genotype and explant age-dependent. The highest number of callus was obtained using 2.7 µM NAA and 4.4 µM BA. It also showed that direct shoot regeneration significantly decreased with increasing BA concentration. However, the use of BA less than 1 µM increased direct shoot regeneration in two genotypes. Positively significant correlation was observed between callus induction and direct shoot regeneration. It was also shown in our study that the best region for direct shoot regeneration on cotyledon explants of lettuce is near to petiole. This adventitious origin of shoots directly from the region near to petiole of cotyledons may aid the use of genetic engineering to improve horticultural characteristics. If propagation through tissue culture can be done efficiently on a large scale in plant breeding programs, it may be used to produce F1 hybrids to use the hybrid vigour. This regeneration protocol will be useful not only for further research studies such as Agrobacterium mediated genetic transformation or protoplast fusion studies, but also for commercial nurseries to produce virus-free plants and agricultural practices that could reduce pesticides application and increase production.
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