Mint plant named ‘Saksham’

Plants – Commercial herbaceous vegetable or herb plant – Mint

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Plant Patent

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PP013279

ABSTRACT:

BOTANICAL/COMMERCIAL CLASSIFICATION
Mentha arvensis
Linn./Japanese Mint Plant.
VARIETAL DENOMINATION
cv. Saksham.
FIELD OF INVENTION
The present invention is related to the development of a novel high menthol producing plant obtained through a unique method of screening of the somaclones in poison agar medium containing toxic level of menthol. The selected plant is tolerant to high concentration of menthol in cultures and hence possesses property of accumulating more menthol per unit leaf mass due to shifted feed back inhibition by menthol as end product. The essential oil yield from the said plant is high coupled with the property of being rich in menthol. This plant is unique and clearly distinct from all other existing varieties of
Mentha arvensis
L. The new variety was initially designated GRB 30. The new variety has been named as ‘Saksham’ (meaning capable) which can be propagated vegetatively through suckers for commercial cultivation.
BACKGROUND OF THE INVENTION
Mentha arvensis
Linn. Var
piperescens
. Holmes (menthol or Japanese mint) is a highly valued industrial crop due to menthol, which is purified by crystallisation through freezing from its essential oil. In the varietal improvement programs, the genetic alternations leading to enhancement in the menthol content in the essential oil and improving other adaptive characters determining the yield and quality of essential oil are most desirable. Menthol is produced from geranyl pyrophosphate through a series of intermediates and the level of production of the high value product menthol is controlled through feed back inhibition of the accumulated end product (which is menthol here). It appears that beyond a certain limit of menthol during the biosynthesis the enzymes involved are inhibited by the end product preventing further forward reaction. Also, monoterpenes are known to be cytotoxic to plant tissues, by inhibiting respiration and photosynthesis by drastically affecting the mitochondria, golgi bodies etc and decreasing cell membrane permeability (Brown J T, Hegarty P K, Charlwood B V, 1987. The toxicity of monoterpenes to plant cell cultures. Plant Science 48: 195-201). Monoterpenes are either sequestered in the plants in specialized structures like glandular hairs in Pelargonium (Brown J T, Charlwood B V, 1986, Differentiation and monoterpene biosynthesis in plant cell cultures. In Morris P, Scragg A, Stafford A and Fowler M, ed Secondary Metabolism in Plant Cell Cultures. Cambridge University Press, Cambridge, 1986, p. 68), trichomes in Mentha or stored in the form of non-toxic glycoside derivatives in vacuoles e.g. Rosa spp. The end product toxicity in such cases can be related to the feed back inhibition to regulate the extent of monoterpenes that can be accumulated within tolerance limits. Menthol, the major component of the essential oil, which is considered to be cytotoxic to the plant, could be so due to toxicity mechanism related to the end product. To this corollary, the level of menthol accumulated in leaf tissues may be linked to the level of menthol tolerance. Uncoupling of these two factors may thus deregulate the rate-limiting step in the production of menthol. With this rationale, the applicants attempted to screen the somaclones available with us and tested to select clones tolerant to high level of menthol with the possibility of selecting high menthol yielding clones. It was assumed that through certain alternate mechanism cellular components may escape toxicity and damaging effect of higher menthol in the tissues by circumventing feed back inhibition level. Such a condition may lead to more menthol accumulation in the trichomes of the regenerated menthol tolerant plant which indeed happened and the applicants could screen out a stable high menthol containing clone showing enhanced tolerance to menthol in vitro.
OBJECTS OF THE INVENTION
The main object of the invention is to develop a new and distinct plant through tissue culture, said plant being capable of producing higher menthol with high essential oil yield as well as herbage yield.
Another object of the invention is to develop a new plant which possesses better vegetative growth with high regenerability.
Still another object of the invention is to retain certain original characters of the parent plant.
SUMMARY OF THE INVENTION
This invention provides a new and distinct mint plant of
Mentha arvensis
‘Saksham’, developed through tissue culture, possessing the following combination of characters namely producing higher amount of menthol with high essential oil yield as well as herbage yield; possesses better growth and vegetative growth with high regenerability; has distinct molecular profile by random amplified polymorphic DNA (RAPD); retains the characteristics of tolerance to leaf spot, rust and powdery mildew as in the parent variety ‘Himalaya’; and has light greenish leaves, pinkish white flowers like the parent plant ‘Himalaya’. This new plant is able to produce higher herbage, oil and menthol yield per unit area as compared to other existing improved varieties.
The new plant ‘Saksham’ of the present invention was produced at the Central Institute of Medicinal and Aromatic Plants field station Pant Nagar, Lucknow, India.
The new variety of the present invention commonly produces a significant number of suckers, and has been asexually reproduced at the same location in India by division. The ‘Saksham’ plant is firmly fixed in its characteristics and has been found to reproduce true to type through successive generations of such asexual reproduction.
DETAILED DESCRIPTION
The invention provides a new and distinct mint plant of
Mentha arvensis
‘Saksham’, developed through tissue culture, possessing the following combination of characters:
a) Produces higher amount of menthol (83% of oil) with high essential oil yield (0.8 to 1.0%) as well as herbage yield (at least 1.83 Q per 100 m
2
),
b) Possesses better growth and vegetative growth with high regenerability covering at least 77 cm canopy area and a height of at least 72 cm in a maximum of 100 days,
c) Has a distinct molecular profile by random amplified polymorphic DNA (RAPD) using 20 random primers distinguishing the plant from the other existing varieties,
d) Retains characteristics of tolerance to leaf spot, rust and powdery mildew as in the parent variety ‘Himalaya’.
e) Has light greenish leaves (138B), pinkish white flowers (56C) like the parent plant ‘Himalaya’, and
f) Produces higher herbage, oil and menthol yield per unit area as compared to other existing improved varieties.
The applicants used the plant ‘Himalaya’ (U.S. Plant Pat. No. 10,935), an elite mint genotype for large scale screening of in vitro raised clones (Khanuja S P S, Shasany A K, Dhawan S, Sushil Kumar, 1998, Rapid procedure for isolating somaclones of altered genotypes in
Mentha arvensis.
J medicinal and Aromatic Plant Sciences 20:359-361) to select clones tolerant to high menthol concentration in the medium (An efficient in vitro selection procedure for large scale screening of mint clones to isolate high menthol genotypes. Khanuja et al, Procedure patent pending, 1999).
While testing the tolerance of in vitro regenerates in presence of menthol in the MS based medium (Murashige T and Skoog F, 1962, A revised medium for rapid growth and bioassay with tobacco tissue cultures;
Physiol. Planta.
15 473-497), the initial toxicity symptoms were first observed at the menthol concentration of 40 &mgr;g ml
−1
menthol after 7 days. The immediate symptoms of menthol toxicity were observed at menthol concentration of 70 &mgr;g ml
−1
within 24 hours. Here it was immediate chlorophyll loss and irreversible wilting of the shoots, non-rescuable even by culturing these regenerates in normal medium without menthol. Lowest survival was detected at a concentration of 70 &mgr;g ml
−1
, where only 1% shoots could survive. Since at 50 &mgr;g ml
−1
concentration of menthol, also typical symptoms of toxicity were observed, a stepwise selection pressure of menthol concentration in the medium was

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