Improvement of Traditional Rice Varieties by Gamma Irradiationin the Philippines
Fernando B. Aurigue1, Ana Maria S. Veluz, Arvin O. Dimaanoand Adelaida C. Barrida2
Project Leader: 1 July 2017 onwards; 2 2013-2015 (retired)Department of Science and Technology-Philippine Nuclear Research InstituteCommonwealth Avenue, 1101 Diliman, Quezon City, Metro Manila, Philippines
Abstract
Two Philippine traditional rice varieties, namely: Umangan and Native Borie, wereused to develop mutant lines that are suitable for organic farming or sustainableagricultural practices of rice production.
Seeds were subjected to acute gamma ray treatment and grown as M 1 generation
together with the non-irradiated materials as control. Comparisons were made between
plants treated with 200 Gy and 300 Gy, and also with the non-irradiated plants. Early
flowering plants with reduced height, more tillers, and higher number of filled grains
per panicle were observed from the segregating M 2 generation but no selection was made.
M 3 generation was grown from bulked seeds and putative mutant plants with thedesired agronomic characteristics were selected based on the results of statisticalanalysis. The M 4 generation did not show any line that is better than the control in anyof the parameters measured.
Apparently, plants with desirable mutated traits were noticed but not isolated earlyenough. Continuous bulking of seeds and late selection for the desired characteristics
showed the importance of following the prescribed methodology. Failure to develop
putative mutant lines during the given period (2013-2017) is attributed to the stalling of
the project for 1½ years due to lack of personnel, change of workforce, leadership, andpriorities in the Philippine government, and seasonal cultivation of rice in theexperimental area. With the lessons learned, the current Director of the Institute andProject Leader on mutation breeding of rice have strengthened their partnership orcollaboration with the Philippine Rice Research Institute and state universities andcolleges that conduct rice improvement programs to use the gamma irradiation facility
for developing mutant varieties of rice and other crop plants.
Keywords: gamma irradiation, mutant, rice, traditional rice variety, varietal
improvement
66

Introduction
Rice (Oryza sativa L.) is the Philippines’ most important staple crop. Rice productionis also the main source of livelihood of more than 2.5 million households or about 2.1
million farmers (FAO, 2018). It is very important to the food supply and economy ofFilipinos. The country is the eight largest rice producer in the world, accounting to 2.8%of global rice production (FAO, 2018) but the Philippines is the third largest rice importerin 2015, having imported 1.8 million metric tons that year, and continues to be one of
the largest importer of rice in the world market to satisfy the domestic demand (Exconde,2018). The major reason for this imbalance is that the population of the Philippines hasgone up to 104.9 million in 2017 and Filipinos have been consuming more milled ricethan what is being produced domestically. Per-capita rice consumption was 109.875 kg
in 2015 to 2016 (Ordinario & Arcalas, 2018). Domestic consumption of milled rice ranged
from 12.85 metric tons in 2013 to 13.25 metric tons in 2017 (USDA, 2019).
According to Crop Statistics of the Philippines, during the period of 2014 to 2018,rice production in the country grew at an average annual rate of 0.3%, from 18.97 million
metric tons in 2014 to 19.28 million metric tons in 2017. Likewise, the total area
harvested increased from 4.74 million hectares in 2014 to 4.81 million hectares in 2017
or at an average annual rate of 0.4% (PSA, 2018). However, the national average yield
for all ecosystems remains low at about 3.87 metric tons per hectare at a relatively highproduction cost of US$0.24 (PhP12.00) per Kg.
To sustain rice production, other means of increasing productivity must be employed.
Organic farming is becoming popular in the Philippines, especially with the organic ricethat has increasing demand and commands higher selling price. Additionally, healthconscious-Filipinos are looking into options of consuming organically-grown rice andtraditional rice varieties (TRVs). Growing number of farmers are planting TRVs mainly
because they are more adapted to the ecosystem and do not need much agrochemical
inputs as compared to hybrid rice which are highly dependent on agricultural chemicals
such as synthetic fertilizers and pesticides (herbicides, fungicides and insecticides).
Another means is to develop mutant lines from TRVs that are highly adapted toexisting ecosystems but do not require as much inputs as the more popular and highly
promoted hybrid rice varieties. Mutant varieties that are suited to organic agricultural
practices are more sustainable for year-round production. The objective of the project isto develop mutant lines with improved agronomic characteristics through gamma
irradiation of seeds of two select TRVs.

67

Materials and Methods
Seeds of two TRVs were obtained from the Philippine Rice Research Institute(PhilRice), Department of Agriculture (DA) in the Science City of Muñoz, Nueva Ecija,Central Luzon. These two rice varieties, namely: 1.) Umangan; and 2.) Native Borie wereselected according to their popularity or extent of use in Luzon island, Philippines.
Based on results of previous studies on radio-sensitivity of rice seeds to acute gamma
radiation, the seeds were treated with 200 Gy and 300 Gy of gamma rays as therecommended dose levels, while non-irradiated seeds served as the control. Irradiatedand control seeds were sown in beds and protected from birds and rodents. Soil samples
were collected and analyzed for elemental analysis prior to land preparation. Dependingon the results for nitrogen, phosphorus and potassium, the recommended amount oforganic fertilizer was incorporated evenly in the soil 3 days before transplanting.
Seedlings were soaked in biofertilizer for 30 minutes before transplanting. A
Randomized Complete Block Design (RCBD) with at least three replicates was followed
every cropping season. During the second year or at M 2 , radiation-modified kappacarrageenan (RMKC) solution, which has been developed as a plant growth promoter atPNRI from another project, was applied as foliar spray at 100 ppm. Foliar application
was done every week for 1 month. On the third year or at M 3 , the use of RMKC wasmodified by increasing the concentration to 200 ppm but applying only three times: 14days after transplanting (DAT), 35 DAT, and 60 DAT. At M 4 , the recommended
application rate followed was 200 ppm at 15 DAT, 30 DAT, and 45 DAT.
Proper cultural management was employed during the whole cropping season in all
generations of planting. The activities included the maintenance of proper water level at
different stages of plant growth, manual control of golden apple snail, installation of nets
to prevent birds from eating the grains and trapping of field rats. The same
methodologies were followed throughout the conduct of the project (up to M 4 only).
Sowing of seeds of putative mutant plants selected from M 3 generation was delayedfor 1½ years. This is largely attributed to a chain of unprecedented events starting off
with health trepidation leading to an early retirement in December 2015 for Ms. Barrida
as Project Leader. By June 2016, a new President of the Philippines was installed,bringing new national and institutional priorities, and a status quo in the organizational
set-up of some projects. Finally, by July 2017, Mr. Aurigue received his designation as
the new Project Leader, thereafter resuming the planting, evaluation and selection ofputative mutant lines as planned for the project.
Seeds from selected M 3 plants were sown on paddy soil placed in black polyethylene
plastic (PEP) bags on July 31, 2017 for M 4 generation plants. The seedlings were68

transplanted into two rice paddies on August 17 and 18, 2017 following RCBD with three
replications. Data for vegetative traits were gathered on November 6, 2017. Necessary
cultural practices were employed until harvesting on November 28, 2017. Data gatheringon yield parameters were conducted afterwards when the intact seeds have been sundried properly with less than 12% moisture content.
Results and Discussion
The M 1 generation of both Umangan and Native Borie flowered earlier (80 DAT)
than the control plants. For Umangan, high number of grains per panicle was obtained
from 200 Gy with 184.5, followed by 300 Gy with 133.0 (Table 1). For Native Borie, hightillering was observed at 200 Gy with 25.7 followed by the control with 21.3 (Table 2).
Table 1. Agronomic characteristics of non-irradiated and irradiated Umangan at M 1
generation
DosePlantheight(cm)*Numberof tillers
per
Plant*

Length ofpanicle
(cm)*

Total
number ofgrains per
panicleNumberof filled
grains per
panicle*Numberof unfilled
grains per
panicle*Control

97.55

18.4

22.23

116.7 b

82.6

34.1

200 Gy101.46

17.5

22.76

184.5 a

101.1

83.4

300 Gy101.40

19.7

23.43

133.0 ab

102.3

30.3

* not significant
Means followed by similar letter within the same column are not significantly differentat 5% level DMRT
Table 2. Agronomic characteristics of non-irradiated and irradiated Native Borie at M 1generation
DosePlantheight(cm)*Numberof tillers
per plant

Length ofpanicle
(cm)*

Total
number ofgrains per
panicle*Numberof filled
grains per
panicle*Numberof unfilled
grains per
panicle*Control

122.3321.3 b

23.00

188.3

142.7

45.6

200 Gy121.6125.7 a

26.86

184.3

123.3

61.0

300 Gy121.0517.3 c

25.05

174.3

122.0

52.3

* not significant
Means followed by similar letter within the same column are not significantly different
at 5% level DMRT69

In the M 2 generation, results for Umangan also showed early flowering at 200 Gy
with 70 DAT followed by 300 Gy with 77 DAT. At 200 Gy, there was 7.15% reduction inplant height. Increase in the number of grains per panicle was noted at 300 Gy (Table 3and Figure 1). Meanwhile, for Native Borie, early flowering at 85 DAT was observed forboth 200 Gy and 300 Gy. The control plants took 100 DAT to flower. There was anincrease in number of tillers per plant as 16 tillers were counted for 200 Gy and 17 tillersfor 300 Gy (Table 4).
Table 3. Agronomic characteristics of non-irradiated and irradiated Umangan at M 2
generation
NumberofUnfilled
GrainsperPanicle

100seedWeight(g)Dose

Numberof Days
toFlowerPlantheight(cm)Numberof Tillers
perPlant

LengthofPanicle(cm)

Numberof Filled
Grainsper
PanicleControl

80

82.93

17.0

22.16

86.0

24

4.24

200 Gy

70

77.00

15.0

21.46

93.0

18

4.51

300 Gy

77

80.26

18.0

21.53

99.0

214.47

Table 4. Agronomic characteristics of non-irradiated and irradiated Native Borie at M 2
generation
Plantheight(cm)Numberof Tillers
perPlant

LengthofPanicle(cm)

Numberof Filled
Grainsper
PanicleNumberofUnfilled
Grainsper
Panicle100seedWeight(g)100106.33

11.0

25.66

121.0

45

4.11

200 Gy85106.66

16.0

26.66

119.0

48

3.91

300 Gy85

97.53

17.0

25.33

112.0

47

3.70

Dose

Numberof Days
toFlowerControl

70Figure 1. Control and M 2 plants derived from Umangan irradiated with 300 Gy of acute
gamma radiation.
In the M 3 generation, the number of days to flowering, number of tillers per plant,
and the total number of filled grains per panicle were significantly affected by thetreatments for Umangan (Table 5). At 200 Gy, plants flowered 14 days earlier than thecontrol, whereas at 300 Gy plants flowered 11 days earlier than the control. Meanwhile,the number of tillers per plant increased from 11 to 14 for plants derived from both 200
Gy and 300 Gy. The number of grains per panicle obtained at 200 Gy (152 seeds) and at
300 Gy (132 seeds) is comparable to those of the control plants (147 seeds).
In Native Borie, the plant height, number of days to flower, and number of tillers
per plant were significantly affected by the treatments at M 3 (Table 6). Plants derived
from 200 Gy and 300 Gy flowered 7 days earlier than the control. Reduction in plantheight was about 10.46% and 6.46% less than the control at 300 Gy and 200 Gy,
respectively. The number of tillers per plant increased by four at 300 Gy (18 tillers) andby two at 200 Gy (16 tillers) compared to the control (14 tillers). Figure 2 shows foliar
application of RMKC solution during tillering stage.

71

Table 5. Agronomic characteristics of non-irradiated and irradiated Umangan at M 3generation
Plantheight(cm)*Numberof tillers
perplant

Lengthofpanicle(cm)*

Numberof filled
grainsperpanicle

Numberofunfilled
grainsperpanicle*

100-seedweight(g)*

92 b

94.66

11.0 b

23.43

121.0 ab26

4.37

200 Gy

78 a

95.20

14.0 a23.05

128.0 a24

4.44

300 Gy

81 a

96.43

14.0 a23.10

111.0 b

21

4.49

Dose

Numberof days
toflowerControl* not significant
Means followed by similar letter within the same column are not significantly different
at 5% level DMRT
Table 6. Agronomic characteristics of non-irradiated and irradiated Native Borie at M 3
generation
Plantheight(cm)NumberofTillers
perPlant

LengthofPanicle(cm)*

Numberof Filled
GrainsperPanicle*

NumberofUnfilled
GrainsperPanicle*

100-seed
Weight(g)*106 b109.06 a

14.0 b

27.27

122.33

36.33

3.99

200 Gy99 a105.11 ab

16.0 ab26.93

122.67

49.66

3.84

300 Gy99 a98.73 b18.0 a26.76

112.67

32.66

4.16

Dose

Numberof days
toFlowerControl* not significant
Means followed by similar letter within the same column are not significantly different
at 5% level DMRT72Figure 2.

UmanganNative Borie
Spraying of radiation-modified kappa-carrageenan solution on two
traditional rice varieties at M 3 generation during tillering stage.

In the M 4 generation, there was no significant differences between means for eachparameter observed (Table 7). The selected putative mutant lines were similar to theirrespective control parent. Likewise, results of statistical analysis imply that the yield of
selected putative mutant lines was not different from their respective control parent(Table 8). Some of the putative mutant lines growing in the field are shown in Figure 3.

Figure 3. Different putative mutant lines at M 4 generation.

73

Table 7.

Vegetative characteristics of non-irradiated and putative mutant lines of

traditional rice varieties at M 4 generation
Plant
Total
HeightNumberLine(cm)of
80 DAT
Tillers

Numberof
Productive
Tillers

Numberof
Unproductive
Tillers

Percent
Productive
Tillers

Umangan (Control)

104.50

10.4

9.2

1.2

88.5

Umangan (300 Gy) 4

101.60

9.9

7.9

2.0

79.8

Umangan (200 Gy) 8

97.40

8.0

7.5

0.5

93.8

Umangan (300 Gy) 23

103.00

9.6

8.5

1.1

88.5

Umangan (300 Gy) 28

98.40

8.6

7.3

1.3

84.9

Umangan (200 Gy) 39

103.73

10.2

9.0

1.2

88.2

Native Borie (Control)

122.60

8.1

7.0

1.1

86.4

Native Borie

111.97

10.9

8.0

2.9

73.4

130.80

8.8

8.4

0.4

95.4

112.43

12.5

12.3

0.2

98.4

110.10

11.5

11.5

0.0

100.0

111.03

10.2

10.2

0.0

100.0

(300 Gy) 27-1
Native Borie(300 Gy) 27-2
Native Borie(300 Gy) 34
Native Borie(300 Gy) JF-1
Native Borie(200 Gy) JF-2
Table 8. Yield parameters of non-irradiated and putative mutant lines of traditionalrice varieties at M 4 generation*Line

PanicleLength(cm)Numberof
Branches
perPanicle

Numberof
FilledGrainsNumberof
Unfilled
Grains100-Seed
Weight(g)Yield(g)Umangan (Control)

21.88 ab5.87 ab45.03 bc

71.93

2.17 b54.90 abcd

Umangan (300 Gy) 4

21.21 b5.80 ab38.03 bc

69.87

2.13 b51.07 bcd

Umangan (200 Gy) 8

21.34 b5.83 ab42.10 bc

69.87

2.17 b

51.63 bcd

Umangan (300 Gy) 23

21.03 b5.70 ab36.40 bc

69.50

2.13 b

42.30 cd

Umangan (300 Gy) 28

20.58 b5.23 b

24.93 c59.90

2.10 b25.70 dUmangan (200 Gy) 39

22.88

6.00 ab57.13 abc

74.23

2.67 b

67.20 abcab74

Native Borie (Control)

25.60 a6.90 a86.27 a107.839.20 a94.40 aNative Borie

25.32 a6.40 ab69.27 ab104.203.03 b86.27 ab22.72 ab5.90 ab55.33 abc

72.07

2.30 b57.83 abcd

Native Borie

24.31

6.37 ab62.20 abc

88.10

2.80 b80.93 abc

(300 Gy) 34

ab

Native Borie

23.95

6.20 ab61.20 abc

86.27

2.77 b

76.60 abc

(300 Gy) JF-1ab

Native Borie

23.52

6.00 ab59.97 abc82.20

2.70 b

72.47 abc

(200 Gy) JF-2

abF-test

****

**ns*

**

(300 Gy) 27-1
Native Borie(300 Gy) 27-2

*Mean of 10 samples
Means followed by the same and/or sharing the same letters within a column do notdiffer significantly at p≤0.01 (**) or p≤0.05 (*)
ns = not significant
With such findings, no desirable mutant line was developed by gamma irradiation.
After reviewing the data generated from M 1 to M 3 , and upon investigation of theprocedures done in handling the generation advancement, it was found out that seeds
derived from the same gamma irradiation dose level were apparently bulked for eachvariety and no selection of putative mutant plants was conducted prior to M 3 generation.
Summary and Conclusion
The potential to develop mutant lines from two Philippine TRVs, namely: Umanganand Native Borie, that are suitable for organic farming or sustainable agricultural
practices of rice production was not tapped at the right time or generation.
Plants derived from seeds subjected to 200 Gy and 300 Gy of acute gamma ray
showed desirable characteristics at M 1 and M 2 generations but selection of putative
mutant plants was done at M 3 generation which was grown from bulked seeds. The M 4generation did not show any line that is better than the control in any of the parameters
measured.
Due to unforeseen or unexpected events from 2013 to 2017, the project was stalledfor 1½ years following the early retirement of the Project Leader without immediate
replacement, change in national and institutional leadership and priorities in the75

Philippine government, and planting of rice limited to just once a year. Now that no
mutant line was obtained for this particular project, partnership or collaboration withPhilRice and state universities and colleges was strengthened to ensure that riceimprovement programs through mutation induction by gamma irradiation will becontinued until new mutant varieties of rice and other crop plants are developed,
registered, and utilized by farmers.
Acknowledgment
The authors are grateful to PhilRice-DA for providing seeds of TRVs. The staff ofPNRI Cobalt-60 Multi-purpose Irradiation Facility are acknowledged for treating theseeds with gamma radiation. Science Aides who prepared the paddy, sowed the seeds
and transplanted the seedlings, maintained the experimental field, harvested the grains,
and assisted in data gathering are all appreciated. They are Mr. Eduardo C. Costimiano,Ms. Rosalie M. Semana, Ms. Dolores M. Lazo (2015), and Mr. John Faustus C. Vidal(2017). Ms. Mary Jane C. Manrique, who assisted in the conduct of the experiments in2013-2014, is also acknowledged.
References
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[FAO] Food and Agriculture Organization of the United Nations Regional Rice Initiative.
www.fao.org accessed on 19 January 2020.
Ordinario, C. U. and Arcalas, J. E. Y.

2018.

Snapshot of rice – consumption dataremains grainy as Pinoys grapple with supply, prices.

The Broader Look.

Business Mirror. 30 August 2018.
[PSA] Philippine Statistics Authority. 2019. Accessed on 19 January 2020.
Simeon, L. M. 2019. PhilRice seeks competitive rice yield. The Philippine Star.
[USDA] United States Department of Agriculture. 2019. indexmundi.com accessed on19 January 2020.

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