Comparing the use of 2 marker systems- chemotaxonomic
markers and microsatellites- for litchi (Litchi chinensis
Sonn.) cultivar differentiation.
Paper Presenter: Madhvee MADHOU, MRC
M.Madhou1,2 and T.Bahorun2, I.Hormaza3
1. Mauritius Reseach Council, Rose Hill, Mauritius (Corresponding author,
email address mmadhou@mrc.intnet.mu)
2: Department of Biosciences, University of Mauritius, Reduit, Mauritius
3. Estacion Experimental la Mayora, CSIC, 29750, Algarrobo Costa,
Malaga, Spain
The litchi has been identified as a fruit of economic importance both for
local consumption and as an export crop. The European market absorbs
28 000 t of litchi yearly, the local export volumes accounting for less than
1% of this market ( Ministry of Agro Industry and Fisheries, 2007 ).
Moreover a number of new markets ( Dubai, South East Asia ) is opening
up. Consistently research efforts are directed towards the increased
production of good quality fruits to allow the local litchi industry to meet
existing export opportunities. It is further recognized that imported fruits
represent a major share in the local market as compared to local fruit
production (Ministry of Agro-Industry and Fisheries, 2007). The rising
global food and fuel prices are likely to have a negative impact on both
local fruit prices and consumption. Since fruits are known to play an
important role in the diet, litchi production is being encouraged by the
Government as a food security measure. It is widely recognized that
proper cultivar identification is of utmost importance in any litchi research
program (Degani et al., 2003; Viruel and Hormaza, 2004). Such
knowledge is essential to make optimal use of litchi genetic resources in
cultivation programs; a proper germplasm inventory will also contribute to
the conservation of local litchi cultivars and prevent genetic erosion. .Local
litchi cultivar identification is based a few phenotypic traits (Agricultural
Research and Extension Unit, 2002). Yet it is established that phenotypic
characterization is influenced by environmental conditions
(Anuntalabochai et al., 2002) and is of limited use; several reports have
highlighted the importance of both morphological and molecular tools for
proper litchi germplasm identification. Hence a study was initiated in 2002
to assess two techniques- chemotaxonomic (flavonoid profiles) and
molecular (microsatellites) markers - as support tools to be used in local
litchi cultivar identification. The investigation was conducted on seven
cultivars (Tai So, Bengal, Calcuttia Late, Huai Zhi, Bosworth 3 (B3), Hei
Ye, Hong Kong) originating from different agroclimatic regions (altitudes
50, 250 and 350 m from sea level respectively) of the island.
Chemotaxonomic markers, such as leaf polyphenolics, are a powerful
adjuct for the identification of a wide variety of plants (Bohm, 1987). The
leaf phenolic composition of the litchi is poorly documented. A wide range
of techniques (Quantitative bioassays, Thin Layer Chromatography, High
Pressure Liquid Chromatography) was used to provide a comprehensive
picture of the leaf phenolic profile of different cultivars. Phytochemical
data revealed that litchi leaves are particularly rich in flavanol and
flavonoid derivatives while phenolic acids were detected at lower levels.
However a significant degree of qualitative and quantitative variation was
detected among cultivars. Quantitative bioassays showed that the total
phenolic, total proanthocyanidin and total flavonoid contents of the
extracts varied widely among cultivars. B3, Bengal and Huai Zhi recorded
high total phenol ( over 40 mg Gallic Acid/g dw ) and high flavonoid
contents ( over 25 mg Quercetin/g dw ). It was also observed that the
cultivars ‘ Hong Kong ’ and ‘ Hei Ye ’ had lowest amounts ( less than 20
mg/g dw ) of the three classes of phenolic compounds.Consistently
detailed qualitative and quantitative analysis using Thin Layer
Chromatography and High Pressure Liquid Chromatography revealed that
cultivars with highest concentrations of phenolic compounds also recorded
complex phenolic profiles, in terms of composition and prominence. Based
on these variations cultivars were classified in decreasing order of
complexity: Huai Zhi > Yook Ho Pow > B3 > Bengal, Calcuttia Late > Tai
So ( from altitudes 250 and 350 m) > Hei Ye , Hong Kong > Tai So (
altitude 50 m) It was difficult to differentiate among profiles of firstly,
Calcuttia Late and Bengal and secondly, Hong Kong and Hei Ye . This is an
indication that these could be two cases of synonymies with similar
genotypes bearing different names. Interestingly the Tai So leaf extracts
from the lowest altitude had poorer profiles than other Tai So extracts
suggesting the presence of two genotypes classified under that cultivar
name.
Microsatellites are tandem repetitions of 1-6 bp nucleotide motifs found in
all genomes analysed to date and have been extensively used in cultivar
identification of many fruits (Wunsch and Hormaza, 2002). Twelve pairs of
litchi microsatellites (Viruel and Hormaza, 2004) were used to investigate
the genetic relationships among cultivars. It was revealed that all the
studied Tai So accessions had identical SSR profiles despite the observed
chemotaxonomic variations. Observations made in other plant species
have shown that plant phenolic composition can be influenced by the
environment (Alonso-Amelot, 2004; Mimura et al., 2004); it was
concluded the litchi leaf flavonoid profiles could be influenced by the
different environmental conditions prevailing at the lowest altitude.
Consistently with leaf flavonoid profiles similar SSR profiles were obtained
for firstly Calcuttia Late and Bengal, and secondly Hei Ye and Hong Kong,
hence revealing two cases of synonymies of litchi cultivar nomenclature.
In this case it could be deduced that chemotaxonomic profiles are good
indicators of genetic similarity. However due the variations obtained
among Tai So accessions from different climatic zones it was concluded
that litchi leaf phenolic profiles can be used as an identification tool when
all accessions originate from the same environmental conditions. In case
accessions originate from various regions the use of a more precise
marker such as microsatellites is recommended.
Keywords: Litchi, cultivar identification, chemotaxonomic markers,
Microsatellites
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