Discussion
Finding new oil crops is necessary to meet increasing market demands,
and also to diversify our current oil crops. Results presented here
indicate that bitter fennel, due to its potential to produce high
amounts of oil with a high percentage of unsaturated fatty acids, is a
good candidate as a new seed oil crop. The 50 Iranian fennel landraces
exhibited considerable diversity for oil yield, with Sari, Haji Abad,
Meshkin Shahr, Moqhan, Kohin, Alamot, Marvdasht, Fasa, Saqez, and
Rafsanjan producing the highest oil yields.
The main oil compositions in the twelve studied fennels were oleic acid
and linoleic acid, which is similar to previous studies on fennel
(Rezaei Chiyaneh et al., 2020; Hayat et al., 2019; Sayed Ahmad et al.,
2018; Agarwal et al., 2018; Rebey et al., 2016; Nguyen et al., 2015;
Acimovic et al., 2015; Bogdanov et al., 2015; Barros et al., 2010;
Vidrih, et al., 2009; Cosge et al., 2008; Singh et al., 2006; Gupta et
al., 1995; Reiter et al., 1998). It is reported that oleic acid is also
one of the major fatty acids in other Apiaceae members, such as dill,
celery, cumin, coriander, and carrot (Gao et al., 2016; Uitterhaegen et
al., 2016; Sowbhagya, 2014; Amin et al., 2010; Saleh et al., 2009). The
oleic acid chemotypes originated from regions with a dry and warm
climate and the high linoleic acid chemotypes from regions with a humid
and cool climate. This pattern shows potential evolutionary adaption of
biochemical pathways to the environmental condition experienced by
ancestors for a long time. Changes in fatty acid profiles by factors
related to climate have been observed in many plant species (Mustiga et
al., 2019; Raziei et al., 2018). One reason for such a pattern could be
the partially shared biosynthetic pathway for oleic acid and linoleic
acid, which may be by environmental factors. These factors may shift the
pathway more toward one of the components and reduce the other one’s
production (negative correlation between oleic and linoleic acids). A
pattern like what we found here, can help breeders in high throughput
preliminary screening programs.
It has been reported that temperature is positively associated with
palmitic, arachidic, and stearic acid concentrations while increasing
temperature negatively impacts linoleic and oleic acid concentrations
(Mustiga et al., 2019). Also, Raziei et al (2018) reported that lower
temperature can increase the production of unsaturated fatty acids, such
as oleic and linoleic acids. Hixson
and
Arts (2016) reported that phytoplankton temperature is negatively
associated with omega-3 fatty acids, such as linolenic acid, while
positively is associated with omega-6 fatty acids, such as linoleic. For
the most part, our results are compatible with these previous studies,
except about oleic acid, which was similar to what Hixson
and
Arts (2016) reported, but opposite of what Mustiga et al (2019) and
Raziei et al (2018) reported. Definitely, analyzing a higher number of
samples from different climates could clarify potential relationships
between temperature and oleic acid production.
The fennel landraces comprising group 1, compared to those in group 2,
had the higher amounts of monounsaturated fatty acids (62.6±0.9% vs
55±1.2%) and also saturated fatty acids (8.8%±0.7 vs 6.1%±0.6), while
those from group 2 had more polyunsaturated acids than those in group 1
(37.1%±1.2 vs 28.5%±0.4). Compared to those in group 1, the landraces
from group 2 originated from cool/wet climates, had a higher ratio of
unsaturated to saturated fatty acids, (15.6±1.6 vs 10.8±0.8), which
makes them healthier sources of oil for human use. Among the twelve
fennels landraces profiled, Qazvin, Sari, Rafsanjan, Meshkin Shahr, and
Chahestan landraces had the highest ratios of omega-3 to omega-6 (0.11,
0.06, 0.06, 0.05, and 0.05, respectively) fatty acids.
Taking all these points into consideration, the Meshkin Shahr landrace,
with high ratios of unsaturated to saturated fatty acids (15.85), and
omega-3 to omega-6 (0.05) has great potential among all the evaluated
landraces as a potential source of edible oil. This landrace was also
the highest oil yielding landrace. Therefore, we recommend it for
further studies to be considered as a high yielding source of healthy
edible oils.