Establishment of somaclonal variants of Robusta coffee with reduced levels of cafestol and kahweol.

Cafestol (caf) and kahweol (kah) are two diterpenes
uniquely associated with the unsaponified lipid fraction of
coffee brew and are reported to be responsible for an increase
in serum cholesterol and triglyceride levels. The plant growth
regulators (PGRs) indole-3-acetic acid (IAA), N6-
benzyladenine (BA), and thidiazuron (TDZ); the plant
growth-promoting agents silver nitrate, triacontanol (TRIA),
and coconut water; and some PGR antagonists such as lovastatin,
paclobutrazol, and 2,3,5-triiodobenzoic acid (TIBA)
were used to determine the variation of caf and kah in somatic
embryos of Robusta coffee (Coffea canephora, CxR variety).
Embryogenic (EG) medium was comprised of half-strength
Murashige and Skoog basal components (½MS) supplemented
with 2.85 μM IAA and 1.11 μM BA. After an 8-wk
culture, somatic embryos were subjected to diterpene extraction
and HPLC analysis of caf and kah profiles. TRIAsupplemented
(5 μg L−1) EG medium devoid of IAA reduced
the levels of caf and kah by 18–24 and 48–55%, respectively,
in coffee somatic embryos. Similarly, the combination of
2.85 μM IAA, 2.27 μM TDZ, and 5–10% coconut water in
½MS basal medium drastically reduced the caf and kah levels
in somatic embryos. There was 60–75% reduction in both caf
and kah in the presence of 5 μM TIBA, followed by 56–62%
reduction in the presence of 10 μM silver nitrate. In contrast,
there was 25–32% elevation of caf and kah in EG medium
supplemented with 5 μM paclobutrazol. In this study, for the
first time, somaclonal variants of C. canephora with reduced
levels of diterpenes caf and kah were established.
Furthermore, these lines exhibited consistency in their metabolite
profiles when cultivated under greenhouse conditions.
In-depth investigations at physiological level are warranted in
order to elucidate the actual mechanism of these PGR inhibitors
on alterations in endogenous pools of diterpenes in coffee
somatic embryos.