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Determination of nornicotine in leaf and plants used for seed production for air-cured tobacco |
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By Lowell Bush |
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Questions
Selection level Information has been obtained from four (4)
countries. Presently France
has a 15% upper limit on cured leaf and a 10% limit on plants selected as
progenitors of breeder’s seed, Japan has a 5% limit on plants used for
seed production, the USA has a 15% limit on cured leaf from cultivar
evaluation and Zimbabwe has a 10% limit on cured leaf and a 3% limit on
plants used for seed production. Sampling in France, Japan and Zimbabwe is done on an
individual plant basis of plants used for seed production.
Cured leaf of a potential line for commercial production in France,
USA and Zimbabwe is on a composite sample from a population of plants
grown for agronomic evaluation. Protocols for sampling In France the 15% upper limit is on a composite
sample from about 50 plants grown in a trial plot to evaluate agronomic
performance. The 10% upper
limit for seed production is on an individual plant basis.
The limit values are for nornicotine. In Japan the seventh (7th) leaf from the
top is harvested 35 days after topping and cured.
Lamina of cured leaf from individual plants is analyzed for
nicotine and nornicotine. In the USA potential new cultivars are evaluated in
Minimum Standards Program for agronomic and alkaloid content. At seven (7) locations a minimum of 40 plants are grown in
each of 3 replications. After
air-curing a 500g sample, representing a weighted distribution of all
grade or stalk positions, is taken from several plants from each replicate
and one composite sample is made for each location.
Alkaloid determination is done on the lamina only.
If the total secondary alkaloids content is less than 15% the
breeder’s seed may be used to produce Foundation seed and then certified
seed for the producer without further evaluation. In Zimbabwe commercial leaf crops must have
nornicotine as a percent of total alkaloids of 10% or less.
However, the upper limit for breeder seed is 3% nornicotine of
total alkaloids on an individual plant basis.
In Zimbabwe breeder’s seed is used to produce certified seed for
growers. Plants are topped to
16 leaves and the top 6 leaves of each plant are harvested and air-cured.
Seed is bulked only from plants with nornicotine less then 3% of
total alkaloids. Analytical methods Gas chromatographic and HPLC procedures were used to
determine individual alkaloids or nornicotine by colorimetry with isatine. In the USA, Foundation seed has been recently produced from individual plants with less than 5% of nornicotine of nicotine + nornicotine content. One leaf is sampled from individual plants, treated with 2-chloroethyl phosphonic acid (ethephon) and “air-cured” for approximately 10 days (lamina must be yellow after the “curing”. Individual plants are used for Foundation seed production only if nornicotine content is less than 5% of nicotine + nornicotine content. The threshold value for selection may be lower for some genotypes.
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