Vegetos
https://doi.org/10.1007/s42535-023-00793-0
RESEARCH ARTICLES
Grain level characterization of widely cultivating traditional and new
improved rice (Oryza sativa L.) varieties of Sri Lanka using physical
and chemical test methods
Madara Dilrukshi Wijesekara Samaranayake1 · Walimuni Kanchana Subhashini Mendis Abeysekera2 ·
Ilmi Ganga Namali Hewajulige1 · Hewa Pathiranage Preethi Sudarshana Somasiri1 ·
Kariyawasam Ranaweerage Ranjith Mahanama3 · Dassanayake Mudiyanselage Jayantha Bandara Senanayake4 ·
Galbada Arachchige Sirimal Premakumara1,5
Received: 23 February 2023 / Revised: 19 November 2023 / Accepted: 27 November 2023
© The Author(s) under exclusive licence to Society for Plant Research 2024
Abstract
Rice is the staple food over half of the world including Sri Lanka which has numerous rice varieties. Identification of Sri
Lankan rice varieties (RVs) at the grain level is a great challenge due to its high diversity. Further, extremely limited research
has been carried out on this topic to date. The present study aimed to characterize widely cultivating 10 traditional and 15
new improved RVs at grain level using internationally accepted physical and chemical test methods. Grain length and size
were studied as physical tests (n = 5 each). Ferrous sulphate, phenol, modified phenol, NaOH and KOH tests (n = 4 each)
were studied as chemical tests. Physical tests were able to group RVs into 4 groups as extra-long, long, medium and short
grain rice. In contrast, chemical test methods, ferrous sulphate, phenol, modified phenol, NaOH and KOH tests were able
to group RVs into 4 (no colour change, brown, strong brown and dark brown streaks), 5 (no colour change, strong brown,
dark brown, reddish yellow and black), 5 (no colour change, strong brown, dark brown, dark reddish brown and black), 5
(pale yellow, yellow, olive yellow, light red and red) and 6 (pale yellow, yellow, olive yellow, light red, red and dark red)
groups respectively. None of the physical or chemical test methods alone were able to characterize studied RVs at the grain
level. The combination of both methods was able to cluster selected RVs into two main clusters (CI and CII) and was able
to identify 3 RVs (Rathel, Suwadel and Kalu Heenati) at the grain level. It is concluded that the selected methods could be
coupled with other varietal identification methods for grain level characterization of Sri Lankan rice.
Keywords Varietal identification · Grain level characterization · Physical and chemical test methods · Traditional rice ·
New improved rice · Sri Lankan rice
Introduction
* Madara Dilrukshi Wijesekara Samaranayake
madarasamaranayake@yahoo.com
1
Modern Research and Development Complex (MRDC),
Industrial Technology Institute (ITI), Halbarawa Gardens,
Malabe and Bauddhaloka Mawatha, Colombo 07, Sri Lanka
2
Department of Agricultural Technology, Faculty
of Technology, University of Colombo, Colombo, Sri Lanka
3
Department of Chemistry, Faculty of Science, University
of Colombo, Colombo, Sri Lanka
4
Rice Research and Development Institute, Batalagoda,
Sri Lanka
5
Department of Basic Science and Social Science, Faculty
of Nursing, University of Colombo, Colombo, Sri Lanka
Rice is the staple food of half of the world’s population (Raju
et al. 2017). It is reported to provide significant quantities of
essential nutrients and numerous bio-active phytochemicals
for rice consumers (Rathna Priya et al. 2019). As a result of
the long history of cultivation and selection under diverse
environments, rice exhibits a remarkable diversity (Raju
et al. 2017; Rathna Priya et al. 2019). Further, high yielding,
nutritionally and functionally sound hybrid rice varieties are
continuously being introduced for commercial cultivation to
meet the increasing demand due to rapid population growth
(Birla et al. 2017).
The consumer preference and market value of rice
are highly varietal dependent based on grain quality
Vol.:(0123456789)
Vegetos
characteristics of rice namely physicochemical, nutritional,
functional and sensory properties (Birla et al. 2017; Rathna
Priya et al. 2019; Zhou et al. 2018). Therefore, identification of the exact rice variety at the grain level has become a
key interest among plant breeders, seed certifying authorities and rice growers (Singh et al. 2017a). Rice varietal
identification can be performed through morphological,
molecular, chemical and physical methods (Das et al. 2017;
Kumar et al. 2021; Nagendra et al. 2020; Raju et al. 2017).
Conventionally, rice varieties have been identified at the
plant level using plant morphological characters which are
tedious, time consuming (Mathat et al. 2019; Singh et al.
2017a) and do not facilitate to identification of rice varieties at grain level. Besides, it requires more area to carry
out field grow-out-tests and also those characters may be
altered by environmental factors (Mathat et al. 2019; Singh
et al. 2017a). The molecular methods are more accurate and
specific but need huge investment and thorough technical
knowledge and skills (Nagendra et al. 2020). In contrast,
physical and chemical test methods are relatively quicker,
easy to carry out, reproducible and inexpensive (Das et al.
2017; Kumar et al. 2021; Raju et al. 2017). Internationally,
physical and chemical test methods have been used by many
researchers for varietal identification at grain level for different crops (Mathad et al. 2019; Rai et al. 2020) including
rice to a certain extent (Das et. al. 2017; Kumar et al. 2021;
Nagendra et al. 2020; Singh et al. 2017a; Vijayalakshmi and
Vijay 2009).
In Sri Lanka, rice is the staple food and it has a very
long history of cultivation. The country holds more than
1000 traditional rice varieties and new improved high yielding rice varieties are also being introduced (Rambukwella
and Priyankara 2016) to cater to the increasing demand for
rice by rice consumers. The research carried out during the
last 10–12 years in the country on the nutritional and health
benefits of Sri Lankan rice were able to prove that some of
the Sri Lankan rice varieties have greater nutrient densities,
desirable physicochemical properties and functional properties (Abeysekera et al. 2017; Abeysekera and Premakumara
2016; Premakumara et al. 2013; Samaranayake et al. 2017).
However, identification and differentiation of traditional and
new improved rice varieties of Sri Lanka especially at the
grain level is a great challenge due to their high diversity.
There are number of reported studies on the use of morphological and molecular level characters (Bandara et al.
2017; Weerakoon and Somaratne 2021; Wijayawardhana
et al. 2015) to differentiate Sri Lankan rice varieties at plant
level. However, to date, none of the studies have attempted
to identify Sri Lankan rice varieties at the grain level. Thus,
the present study aimed to characterize widely cultivating
traditional and new improved rice varieties of Sri Lanka at
the grain level using a range of physical and chemical test
methods.
Materials and methods
Chemicals and reagents
Phenol, copper sulfate, ferrous sulfate, sodium hydroxide
(NaOH) and potassium hydroxide (KOH) were obtained
from Sigma Aldrich, USA and were of analytical grade.
Sample collection
Commercially important and widely cultivating ten traditional and fifteen new improved rice varieties were
collected from Rice Research and Development Institute
(RRDI), Batalagoda, Sri Lanka. The selected rice varieties were grown and harvested under experimental field
conditions at RRDI, Batalagoda. The selected traditional
rice varieties were Herath Banda (Ac 689), Kalu Heenati
(Ac 721), Kahawanu (Ac 1319), Kurulu Thuda (Ac 69),
Madathawalu (Ac 1312), Murungakayan (Ac 395), Pachchaperumal (Ac 798), Pokkali (Ac 809), Rathel (Ac 137)
and Suwadel (Ac 579) while selected new improved rice
varieties were Bg 300, Bg 352, At 362, At 311, At 307,
At 308, Bg 360, Bg 358, Bg 94–1, Bg 366, Bw 367, Bg
379–2, Bg 403, Bg 450 and Bw 272-6b.
Evaluation of grain size
The grain sizes of the paddy seeds (n = 5 each) of selected
rice varieties were determined according to the method
described by Juliano (1985) and classified according to
the Philippines National Standard (2019) for grading and
classification for paddy and milled rice.
Seed chemical properties of rice varieties
Five chemical tests namely ferrous sulfate, phenol, modified phenol, NaOH and KOH tests were carried out for
paddy of selected rice varieties of Sri Lanka and details
of each method are described below.
Ferrous sulphate test
The ferrous sulphate test was carried out according to the
method described by Vijayalakshmi and Vijay (2009).
Fifty paddy seeds in four replicates (n = 4 each) were
soaked in 1.5% (w/v) ­F eSO 4 solution for 4 h at ambient temperature (28 ± 2 °C). Then, excess moisture was
removed using a blotting paper and seeds were examined
for colour changes and grouped according to the Munsell
Vegetos
soil colour charts (Macbeth Division of Kollmorgen
Instruments Corporation 1994).
Phenol test
The phenol test was carried out as per the methods described
by Singh et al. (2017b) and Vijayalakshmi and Vijay (2009).
Briefly, four replicates (n = 4 each) of 50 paddy seeds were
pre-soaked in distilled water for 18 h at room temperature
(28 ± 2 °C). Then, seeds were transferred to Petri dishes containing 2 layers of filter papers moistened with 4 ml of 2%
(w/v) phenol solution. Petri dishes were covered and kept at
room temperature (28 ± 2 °C), examined for colour change
after 24 h and classified according to Munsell soil colour
charts (Macbeth Division of Kollmorgen Instruments Corporation 1994) based on the intensity of seed coat colour.
Modified phenol test
The modified phenol test was carried out similar to the phenol test according to the methods of Singh et al. (2017b)
and Vijayalakshmi and Vijay (2009) except paddy seeds
(n = 4 each) were pre-soaked in 0.5% (w/v) C
­ uSO4 solution
instead of distilled water. Then, based on the degree of staining of seed coat, rice varieties were grouped according to the
Munsell soil colour charts (Macbeth Division of Kollmorgen
Instruments Corporation 1994).
KOH test
The KOH test was carried out according to the methods
described by Das et al. (2017), Singh et al. (2017b) and
Vijayalakshmi and Vijay (2009). Four replications (n = 4
each) of 50 paddy seeds were soaked in 5% (w/v) KOH solution for 3 h at room temperature (28 ± 2 °C). Then, rice varieties were grouped according to Munsell soil colour charts
(Macbeth Division of Kollmorgen Instruments Corporation
1994) based on the colour intensities of the soak solution.
NaOH test
The NaOH test was carried out as per the procedures
described by Das et al. (2017); Singh et al. (2017b) and
Vijayalakshmi and Vijay (2009). Fifty seeds were soaked in
5% (w/v) NaOH solution in four replications (n = 4 each) at
room temperature (28 ± 2 °C) for 3 h and based on the colour
intensity of the soak solution rice varieties were classified
according to Munsell soil colour charts (Macbeth Division
of Kollmorgen Instruments Corporation 1994).
Statistical analysis
The grain lengths of paddy samples were expressed as
mean ± standard deviation (SD) of five replicates (n = 5
each). The physical and chemical characteristics of selected
rice varieties were statistically analyzed by hierarchical cluster analysis using SPSS version 20 to examine the dissimilarities of the selected rice varieties. The clustering method
used was Ward’s linkage and the measure of dissimilarity
was based on Euclidean distance. Data were converted to
unique type i.e., nominal data, prior to analysis.
Results and discussion
The present study attempted to distinguish selected twentyfive (25) Sri Lankan rice varieties at the grain level based on
their physical and chemical characteristics. The selected rice
varieties are commercially important and widely cultivating varieties in the country (Socio Economics and Planning
Centre, Department of Agriculture 2019).
As for physical characteristics, grain length and grain size
were used. Grain size is one of the most stable properties
of a rice variety (Juliano 1985) and one of the parameters
that could be used to identify rice varieties at the grain level
(Kumar et al. 2021). The results of grain lengths and sizes
of the studied rice varieties of are presented in Table 1. Seed
lengths of studied rice varieties varied from 5.8 to 10.1 mm.
According to the grading and classification of paddy and
milled rice by Philippines National Standard (2019), lengths
of full size paddy seeds ≥ 9.9 mm, 9.8–8.8 mm, 8.7–8.0 mm
and < 8.0 mm are classified as extra-long, long, medium and
short grains respectively. Results of the present study clearly
showed that most of the tested rice varieties were short grain
rice varieties. Further, the studied rice varieties were able
to group into four as extra-long, long, medium and short
grain rice varieties. In a recent study by Kumar et al. 2021
has used grain size to characterize some of the rice varieties
and was able to classify the rice varieties into two groups as
medium and long.
Chemical characterization of selected rice varieties based
on color responses to 5 chemical tests namely ferrous sulfate, phenol, modified phenol, NaOH and KOH tests were
used in this study. These chemical tests have been used in a
number of research studies for varietal characterization of
crops such as pigeon pea and mustard (Mathad et al. 2019;
Rai et al. 2020). In addition, these tests have been used in
the varietal characterization of different rice varieties the
world over (Das et al. 2017; Kumar et al. 2021; Nagendra
et al. 2020; Singh et al. 2017a, 2017b; Vijayalakshmi and
Vijay 2009). Further, these chemical tests are recommended
by the Association of Official Seed Analysts (AOSA) for
Vegetos
Table 1 Paddy seed length and size of selected rice varieties of Sri
Lanka
Rice variety
Paddy seed length
(mm)
Paddy seed size
Rathel
Bw 367
Bg 358
Bg 450
Suwadel
Kahawanu
Bg 360
Bw 272-6b
At 307
Madathawalu
Bg 379–2
Pachchaperumal
Bg 352
Bg 366
Kalu Heenati
Bg 403
Bg 300
Herath Banda
Murungakayan
At 362
Pokkali
At 308
Kurulu Thuda
Bg 94–1
At 311
5.8 ± 0.1
5.9 ± 0.1
6.0 ± 0.0
6.0 ± 0.1
6.1 ± 0.1
6.3 ± 0.1
6.3 ± 0.1
6.7 ± 0.1
7.1 ± 0.1
7.3 ± 0.1
7.4 ± 0.1
7.5 ± 0.1
7.6 ± 0.0
7.7 ± 0.1
7.8 ± 0.1
7.8 ± 0.1
7.9 ± 0.1
8.0 ± 0.1
8.8 ± 0.2
8.9 ± 0.1
8.9 ± 0.1
9.1 ± 0.1
9.1 ± 0.0
9.3 ± 0.2
10.1 ± 0.2
Short
Short
Short
Short
Short
Short
Short
Short
Short
Short
Short
Short
Short
Short
Short
Short
Short
Medium
Long
Long
Long
Long
Long
Long
Extra long
Paddy seed lengths were expressed as mean ± standard deviation of
five replicates (n = 5 each); Extra-long: ≥ 9.9 mm, long: 9.8–8.8 mm,
medium: 8.7–8.0 mm, short: < 8.0 mm
cultivar purity testing of seeds of different crops including
rice (Copeland and McDonald 2001).
The individual color responses of each rice variety for
ferrous sulfate, phenol, modified phenol, NaOH and KOH
tests used in the present study are given in Fig. 1, 2, 3, 4a,
b, respectively. Further, the summary of colour responses
obtained for all the chemical tests used in the present study
are given in Table 2. The ferrous sulfate test is a simple test
which is used to differentiate genotypes based on the presence of secondary metabolites (Sripunitha and Sivasubramaniam 2014). The colour responses of studied rice varieties
for the ferrous sulfate test are presented in Fig. 1. Only the
traditional red rice variety, Kalu Heenati has shown “no colour change” to the ferrous sulfate test while the rest of the
rice varieties have shown different color responses. Based
on the colour responses, the selected rice varieties were able
to be differentiated into four groups as rice varieties with
no colour change, brown streaks, strong brown streaks and
dark brown streaks (Table 2). According to the findings by
Kumar et al. 2021, seventeen genotypes of rice they have
studied were able to group into two using the ferrous sulfate
test. Similarly, Vijayalakshmi and Vijay (2009) had grouped
twenty-three rice varieties into three groups based on the
ferrous sulfate test.
The phenol test is based on a genetically controlled
enzyme-based reaction (Kumar et al. 2021; Singh et al.
2017b; Sripunitha and Sivasubramaniam 2014) and therefore, unaffected by the environmental conditions (Kumar
et al. 2021; Raju et al. 2017). In the phenol test, the aromatic
ring of phenol gets oxidized into a pigmented compound
known as melanin primarily by the catalytic activity of the
tyrosinase enzyme present in the seed coat (Das et al. 2017;
Singh et al. 2017a, b; Vijayalakshmi and Vijay 2009). The
intensity of the colour reaction depends on the quality and
quantity of the tyrosinase enzyme and therefore could be
utilized as an index to distinguish crop varieties including
rice (Das et al. 2017; Raju et al. 2017; Singh et al. 2017b).
Different colour responses obtained for the phenol test of
the studied rice varieties are shown in Fig. 2. Based on the
color responses, 25 tested rice varieties were able to differentiated into five groups namely no colour change, strong
brown, dark brown, reddish yellow and black (Table 2).
The rice varieties that didn’t respond to the phenol test were
Kahawanu and Suwadel, and those are traditional white rice
varieties of Sri Lanka. The reason may be due to the inability
of oxidizing the phenol ring due to a shortage of electron
donors or hydroxylating enzyme in those varieties (Singh
et al. 2017b). Similar results have been observed by Das
et al. (2017), Singh et al. (2017b), Vijayalakshmi and Vijay
(2009) for some of the rice varieties tested in their studies for
varietal characterization using the same test method.
The colour reaction of modified phenol test is based on
the same principle as discussed in the phenol test method.
Besides, ­Cu2+ ions used in the test may act as a co-factor
in the reaction and enhance the colour reaction (Vijayalakshmi and Vijay 2009). In the present study, rice varieties
were differentiated into five groups as no colour change,
strong brown, dark brown, dark reddish brown and black
(Table 2). The individual color responses of each variety to
the modified phenol test are given in Fig. 3. Additionally, it
is observed that the seed coat colour of some rice varieties
has been enhanced due to the addition of ­Cu2SO4. Suwadel
was the only rice variety which did not respond to the modified phenol test. The rice variety, Kahawanu which didn’t
respond to the phenol test showed a dark brown colour in
the modified phenol test. Similar kinds of results have been
observed for different varieties of rice by Das et al. (2017),
Singh et al. (2017a), Vijayalakshmi and Vijay (2009) in their
studies. Therefore, our findings are in agreement with the
previous research findings.
The NaOH and KOH tests are also two common test
methods that have been used in previous research studies
Vegetos
Fig. 1 Colour responses for the ferrous sulfate test of selected rice
varieties of Sri Lanka. No colour change: Kalu Heenati; Brown
Streaks (7.5YR 5/4:
): Kahawanu, Herath Banda, Murungakayan, At 307, At 308, Bg 94–1, At 362; Strong brown streaks
(7.5YR 5/8:):
Bw 272-6b, Bw 367, Bg 358, Bg 450, Bg 360,
Bg 379–2, Bg 352, Bg 366, Bg 403, Bg 300; Dark brown Streaks
(7.5YR 3/4:
): Madathawalu, Pachchaperumal, Suwadel, Pokkali, Kurulu Thuda, At 311
Vegetos
Fig. 2 Colour responses for the phenol test of selected rice varieties
of Sri Lanka. No colour change: Suwadel, Kahawanu; Strong Brown
(7.5YR 5/6:
): Pachchaperumal, Herath Banda, Murungakayan,
Kurulu Thuda, Bw 367, Bg 358, Bg 450, Bg 360, Bg 379–2, Bg
352, Bg 366, Bg 403, Bg 300, At 307, At 308, Bg 94–1; Dark brown
(7.5YR 3/4:
): Rathel, Madathawalu, Pokkali; Reddish Yellow
(5YR 6/6:
): Bw 272-6b, At 362, At 311; Black (7.5YR 2.5/1:
): Kalu Heenati
Vegetos
Fig. 3 Colour responses for the modified phenol test of selected rice
varieties of Sri Lanka. No colour change: Suwadel; Strong Brown
(7.5YR 5/6:
): Herath Banda; Dark brown (7.5YR 3/4:
):
Kahawanu, Pachchaperumal, Murungakayan, Kurulu Thuda,
Madathawalu, Pokkali, Bw 367, Bg 358, Bg 450, Bg 360, Bg 379–2,
Bg 352, Bg 366, Bg 403, Bg 300, At 307, At 308, Bg 94–1; Dark
Reddish Brown (5YR 3/4:
): Bw 272-6b, At 362, At 311; Black
(7.5YR 2.5/1:
): Rathel, Kalu Heenati
Vegetos
to characterize rice varieties at grain level (Das et al. 2017;
Kumar et al. 2021; Singh et al. 2017a; Sripunitha and Sivasubramaniam 2014; Vijayalakshmi and Vijay 2009). Both
these test methods have been mainly used in distinguishing
red seed varieties from white seed varieties (Kumar et al.
2021; Singh et al. 2017a; Sripunitha and Sivasubramaniam
Vegetos
◂Fig. 4 a Colour responses for the NaOH test of selected rice varie-
ties of Sri Lanka. Pale Yellow (5Y 8/4:
): 1—4; Yellow (5Y 8/8:
): 5—13; Olive Yellow (2.5Y 6/8:
): 14 and 15; Light Red
(2.5YR 6/8:
): 16—19; Red (10R 4/8:
): 20 – 25. b Colour responses for the KOH test of selected rice varieties of Sri Lanka.
Pale Yellow (5Y 4/8:
): 1—6; Yellow (5Y 8/8:
): 7—13;
Olive Yellow (2.5Y 6/8:
): 14 and 15; Light Red (2.5YR 6/8:
): 20; Red (10R 4/8:
): 16—19, 21—23; Dark Red (10R
3/6:
): 24 and 25. Rice varieties named from 1 to 25 as follows;
1- Bg 450; 2- Bg 360; 3- Bg 352; 4- Bg 300; 5- At 307; 6- At 308;
7- Kahawanu; 8- Bw 367; 9- Bg 358; 10- Bg 379–2; 11- Bg 366; 12Bg 403; 13- Bg 94–1; 14- Rathel; 15- Suwadel; 16- Madathawalu;
17- Kalu Heenati; 18- Murungakayan; 19- Hearth Banda; 20- At 362;
21- Pachchaperumal; 22- Bw 272-6b; 23- At 311; 24- Pokkali; 25Kurulu Thuda
2014). The reason for the colour reactions in NaOH and
KOH tests is still not well understood (Nagendra et al.
2020). However, it is reported that variations in colour
may be due to inherent chemical differences, the genetic
makeup of enzyme systems or the reaction of secondary
metabolites present in the seeds of different crops (Kumar
et al. 2021; Singh et al. 2017a, b; Sripunitha and Sivasubramaniam 2014). The colour responses of studied rice varieties for NaOH and KOH tests are presented in Fig. 4a, b
respectively. Based on the colour intensities in NaOH test,
25 selected rice varieties were able to be distinctly categorized into five as pale yellow, yellow, olive yellow, light red
and red (Table 2). On the other hand, the colour intensities
obtained for the KOH test for selected rice varieties were
able to group the rice varieties into six as pale yellow, yellow, olive yellow, light red, red and dark red. Similar findings have been observed by a number of researchers for their
tested rice varieties (Das et al. 2017; Kumar et al. 2021;
Singh et al. 2017a; Sripunitha and Sivasubramaniam 2014;
Vijayalakshmi and Vijay 2009). Thus, our findings are in
agreement with the previous research findings.
As none of the physical and chemical test methods alone
were able to characterize selected rice varieties at grain
level, the suitability of a combination of physical and chemical test methods were tested in hierarchical cluster analysis
and results are presented in Fig. 5. Results showed two main
clusters (C I and C II) at 15 rescaled distance units [Line
PQ in Fig. 5]. Cluster I comprised of 14 rice varieties (Bw
367, Bg 358, Bg 360, Bg 450, Kahawanu, At 307, Bg 300,
Bg 352, Bg 403, Bg 366, Bg 379–2, At 308, Bg 94-1and
Suwadel) which have been clustered into three groups of rice
having similar characteristics (Group 1, 2 and 3 in Fig. 5)
and one rice variety (Suwadel) identified at grain level. All
the rice varieties in Cluster I were non-pigmented (white)
rice varieties and 85% of them were short grain varieties.
Further, 85% of the rice varieties showed strong brown colour for the phenol test, 93% showed dark brown colour for
the modified phenol test, 64% showed strong brown streaks
for the ferrous sulphate test and 93% showed pale yellow/
yellow colour for the KOH and NaOH tests. Cluster II comprised of 11 rice varieties (Rathel, Kalu Heenati, Herath
Banda, Murungakayan, Pokkali, Kurulu Thuda, At 362, At
311, Madathawalu, Pachchaperumal, Bw 272-6b, Rathel and
Kalu Heenati) which have been clustered into four groups
of rice having similar characteristics (Group 4, 5, 6 and 7
in Fig. 5) and two rice varieties (Rathel and Kalu Heenati)
identified at grain level. Results showed that 91% of the rice
varieties in Cluster II were pigmented rice varieties and 55%
of them were medium to long/extra-long rice varieties. For
the KOH test, 91% of the rice varieties showed light red/
red/dark red colour while 91% of the rice varieties showed
light red/red colour for the NaOH test. Moreover, 55% of
the rice varieties showed dark brown streaks for the ferrous
sulphate test.
In the comparison of traditional and new improved rice
varieties, no drastically different features were observed
among the varieties for the studied physical and chemical
tests. Among the studied traditional rice varieties, 80% of
the rice varieties belonged to Cluster II. Further, 70% of the
rice varieties were pigmented rice varieties. Furthermore,
60%, 10% and 30% were small, medium and long grain rice
varieties respectively. For the KOH test, 70% of the rice
varieties showed red/dark red colour. Similarly, 70% of the
rice varieties showed light red/ red colour for the NaOH test.
Further, 90% of the rice varieties showed brown/ dark brown
streaks for the ferrous sulphate test. In contrast, among the
studied new improved rice varieties, 86% of the rice varieties
belonged to Cluster I and mainly resemble the characteristic
features belonging to Cluster I. Further, 80% of the studied
new improved rice varieties were non-pigmented and 73%
were small grain varieties while 27% of the rice varieties
were long/extra-long grains. Additionally, 80% of the rice
varieties showed strong brown colour for the phenol test,
80% showed dark brown colour for the modified phenol test,
67% showed strong brown streaks for the ferrous sulfate test
and 80% showed pale yellow/ yellow colour for the KOH
and NaOH tests.
Considering all, it’s very clear that when the diversity
of crops is high, individual or combination of physical
and chemical test methods could be combined with other
advanced varietal identification methods for grain level characterization of rice.
Conclusion
None of the chemical (ferrous sulphate, phenol, modified
phenol, NaOH, and KOH tests) or physical test (grain length
and size) methods alone used in the present study could be
used to identify the studied Sri Lankan rice varieties at the
grain level. The combination of chemical and physical test
methods allowed characterizing three rice varieties namely
DBS
SBS
SBS
SBS
DBS
BS
SBS
SBS
BS
DBS
SBS
DBS
SBS
SBS
NCC
SBS
SBS
BS
BS
BS
DBS
BS
DBS
BS
DBS
7.5YR 3/4
7.5YR 5/8
7.5YR 5/8
7.5YR 5/8
7.5YR 3/4
7.5YR 5/4
7.5YR 5/8
7.5YR 5/8
7.5YR 5/4
7.5YR 3/4
7.5YR 5/8
7.5YR 3/4
7.5YR 5/8
7.5YR 5/8
7.5YR 5/8
7.5YR 5/8
7.5YR 5/4
7.5YR 5/4
7.5YR 5/4
7.5YR 3/4
7.5YR 5/4
7.5YR 3/4
7.5YR 5/4
7.5YR 3/4
DB
SB
SB
SB
NCC
NCC
SB
SB
SB
DB
SB
SB
SB
SB
B
SB
SB
SB
SB
RY
DB
SB
SB
SB
RY
Colour Response
Colour Response
Munsell value
Phenol test
Ferrous sulfate test
7.5YR 3/4
7.5YR 5/6
7.5YR 5/6
7.5YR 5/6
–
–
7.5YR 5/6
5YR 6/6
7.5YR 5/6
7.5YR 3/4
7.5YR 5/6
7.5YR 5/6
7.5YR 5/6
7.5YR 5/6
7.5YR 2.5/1
7.5YR 5/6
7.5YR 5/6
7.5YR 5/6
7.5YR 5/6
5YR 6/6
7.5YR 3/4
7.5YR 5/6
7.5YR 5/6
7.5YR 5/6
5YR 6/6
Munsell value
B
DB
DB
DB
NCC
DB
DB
DRB
DB
DB
DB
DB
DB
DB
B
DB
DB
SB
DB
DRB
DB
DB
DB
DB
DRB
Colour Response
7.5YR 2.5/1
7.5YR 3/4
7.5YR 3/4
7.5YR 3/4
–
7.5YR 3/4
7.5YR 3/4
5YR 3/4
7.5YR 3/4
7.5YR 3/4
7.5YR 3/4
7.5YR 3/4
7.5YR 3/4
7.5YR 3/4
10YR 2/1
7.5YR 3/4
7.5YR 3/4
7.5YR 5/6
7.5YR 3/4
5YR 3/4
7.5YR 3/4
7.5YR 3/4
7.5YR 3/4
7.5YR 3/4
5YR 3/4
Munsell value
Modified phenol test
OY
Y
Y
PY
OY
Y
PY
R
Y
LR
Y
R
PY
Y
LR
Y
PY
LR
LR
R
R
Y
R
Y
R
Colour
Response
NaOH test
2.5Y 6/8
5Y 8/6
5Y 8/6
5Y 8/4
2.5Y 6/8
5Y 8/6
5Y 8/4
10R 4/8
5Y 8/6
2.5YR 6/8
5Y 8/6
10R 4/8
5Y 8/4
5Y 8/6
2.5YR 6/8
5Y 8/6
5Y 8/4
2.5YR 6/8
2.5YR 6/8
10R 4/8
10R 4/8
5Y 8/6
10R 4/8
5Y 8/6
10R 4/8
Munsell value
OY
Y
Y
PY
OY
Y
PY
R
PY
R
Y
R
PY
Y
R
Y
PY
R
R
LR
DR
PY
DR
Y
R
Colour
Response
KOH test
2.5Y 6/8
5Y 8/6
5Y 8/6
5Y 8/4
2.5Y 6/8
5Y 8/6
5Y 8/4
10R 4/8
5Y 8/4
10R 4/8
5Y 8/6
10R 4/8
5Y 8/4
5Y 8/6
10R 4/8
5Y 8/6
5Y 8/4
10R 4/8
10R 4/8
2.5YR 6/8
10R 3/6
5Y 8/4
10R 3/6
5Y 8/6
10R 4/8
Munsell value
DBS, Dark Brown Streaks; SBS: Strong Brown Streaks; BS, Brown Streaks; NCC, No Colour Change; B, Black; RY, Reddish Yellow; DB, Dark Brown; SB, Strong Brown; DRB, Dark Reddish
Brown; PY, Pale Yellow; Y, Yellow; OY, Olive Yellow; LR, Light Red; R, Red; DR, Dark Red
Rathel
Bw 367
Bg 358
Bg 450
Suwadel
Kahawanu
Bg 360
Bw 272-6b
At 307
Madathawalu
Bg 379–2
Pachchaperumal
Bg 352
Bg 366
Kalu Heenati
Bg 403
Bg 300
Herath Banda
Murungakayan
At 362
Pokkali
At 308
Kurulu Thuda
Bg 94–1
At 311
Rice variety
Table 2 Colour responses of selected rice varieties of Sri Lanka for studied chemical test methods
Vegetos
Vegetos
Fig. 5 Dendrogram for tested physical and chemical properties of selected rice varieties of Sri Lanka using hierarchical cluster analysis
Rathel, Suwadel and Kalu Heenati at the grain level. Other
selected rice varieties were able to categorize into seven
groups of rice having similar characteristics. Thus, selected
physical and chemical tests need to be coupled with other
varietal identification methods for grain level characterization of Sri Lankan rice varieties.
Acknowledgements The authors gratefully acknowledge the financial
support given by the Treasury, Sri Lanka (Grant No.TG 18/146).
Data availability The data generated in this study are available from
the corresponding author on reasonable request.
Declarations
Conflict of interest The authors declare no conflict of interest.
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