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Variation in Leaf Photosynthesis among Wild Species in Genus Oryza and among the Progeny of Selected Crosses of the Wild species with a Rice Cultivar.

Zhao Ming2,3, Renee Lafitte1, Erik Sacks1, Glenn Dimayuga1 and Xiuqin Zhao3

1International Rice Research Institute, www.irri.org.cigar Email r.lafitte@org.cigar
2
China Agricultural Academy of Science CAAS. www.caas.net.cn Email zhaomingcau@163.net
3
China Agricultural University www.cau.edu.cn

Abstract

There was a wide range in leaf photosynthetic rates (Pn) of 16 different species of Oryza measured in a tropical environment where O. sativa and O. rufipogon were identified as potential sources of enhanced photosynthetic rate. Two F1 hybrids between O.sativa O. rufipogon were significantly greater than the O.sativa parents and other F1 hybrids. Among the F2 progeny, segregants with even greater rates of photosynthesis were identified, while the F3 derived from superior F2 plants maintained the high-photosynthesis trait, with a highly significant parent-offspring regression coefficient of 0.86. The progenies with high Pn when grown in the tropics were also planted in a temperate area, and good stability of high photosynthetic capacity was found. Genetic resources in the genus Oryza could serve as a source of alleles to increase photosynthetic rate in the cultivated species.

Media summary

Genetic resources in the genus Oryza could be one source of increased rates of single leaf photosynthesis in the cultivated species.

Key words

rice, photosynthesis, Oryza ,O. sativa , O. rufipogon

Introduction

The need to improve the rate rice photosynthesis is a more important challenge in order to break the postulated yield potential barrier in rice (Peng, S., 2000). One possible way is to identify high photosynthesis rates among the genetic resources in the genus Oryza and use these materials in a wide crossing program. The objectives of this study were to assess the extent of genetic variation for high rates of single leaf photosynthesis (Pn) in wild Oryza and to measure the variation in Pn in the progeny from crosses between O.sativa O. rufipogon when grown in a tropic and temperate environment.

Materials and methods

Accessions of 16 different species and eight F1 hybrids of O.sativa O. rufipogon with relatively high individual plant yield were grown in greenhouse tanks at the International Rice Research Institute (IRRI), Philippines. For the evaluation of F2 progeny, seeds from the F1 plants were planted in an upland experimental field at IRRI. The female parent and F1 were used as controls. Seeds were collected from 16 randomly selected F2 plants and from four high-Pn F2 plants from the hybrid 20557-10. Three high Pn progenies selected from the tropical region (IRRI), their parents and four accessions of O. rufipogon were planted in pots in China Agricultural University in order to study the PN under temperate conditions. All plants were grown under well-watered aerobic conditions. Rates of Pn were measured from 10:00am to 3:00pm on clear days during the flowering stage. Leaf Pn of the F1 and F2 progeny grown in China was measured using a CAU photosynthesis measurement system (China Agricultural University). Photosynthetic active radiation (PAR) and leaf temperature was about 1500 to 1700 μmol m-2s-1 and 35 to 37 oC respectively. The Pn of the wild species and of the F3 progeny grown at IRRI was measured with a Li-Cor6400 (Li-Cor corp., USA). Leaf temperature, ambient PAR, and CO2 concentration was about 30 oC, 1200 μmol m-2s-1, and 350 ppm respectively.

Results

Photosynthetic survey of wild species

There was a wide range in photosynthetic rate (Pn) observed among species (Table 1). O. rufipogon accession 105697 achieved a rate of 37.6 μmol m-2s-1. O.australiensis also reached high levels of Pn.

Photosynthesis of F1 hybrids and parental lines

There were significant differences in Pn among the eight F1 progeny from O. sativa and O.rufipogon crosses. Photosynthesis of hybrids 20472-6 and 20557-10 exceeded the apparent mid-parent mean. The average Pn of the O.rufipogon accessions were similar to the F1’s except for Tawsan1, which tended to have a lower rate than other entries.

Photosynthetic Characteristics of F2 populations and parents in the field

Photosynthesis was measured in the F2 progeny derived from the two F1 hybrids 20472-6 (n=48) and 20557-10 (n=154). Both populations showed a normal distribution of Pn (Figure 1). On average, the F2 populations did not differ from the female parent from which they were derived, but exceptional F2 individuals greatly exceeded the female parent (Table 2). The five plants with the greatest maximum photosynthesis were identified from the hybrid 20557-10. These plants were measured again on different days using the Li-Cor photosynthesis system, and rates greater than 30 μmol m-2 s-1 were again recorded.

Inheritance of photosynthetic rate in F3 progeny

The correlation between Pn of the F2 clones and F3 plants was 0.86 (P<0.01), indicating high realized heritability of this trait (Figure 2). Thirteen of the F2 clones had a significantly greater Pn than the F1 clone. Among the F3 families, one had a significantly greater mean Pn than Azucena. There was still considerable segregation within each F3 family, indicating that further selection is needed to genetically fix the high-photosynthesis trait.

Stability of high photosynthetic rate when grown in a tropical and temperate area

The progenies also presented higher Pn with 34-35.5 μmol m-2s-1, compared with other all cultivated and wild rice when grown in the temperate area (Table3). The Pn of SHP-8 was 61.54,23.53 percentage higher than the female and male parents.

Figure1. Distribution of photosynthetic rate (μmol m-2s-1) in populations of field-grown F2 plants derived from two inter-specific hybrids. For hybrids 20557-10(left), n=154; for 20472-6(right), n=48. Arrows indicate photosynthetic rate measured for the O.sativa parent in the same experiment.

Figure 2. Photosynthetic rates (μmol m-2s-1) of twenty F2 clones versus photosynthetic rates of populations of F3 derived from each F2 plant. Error bars reflect the LSD at P<0.05.

Table 1. Characteristics of Oryza accessions evaluated for photosynthetic rate (Pn). Values followed by the same letter do not differ at p<0.05.

Species

IRGC#

Genome

Habitata
A/P S/Sh

Pn (μmol m-2s-1)

Species

IRGC#

Genome

Habitata
A/P S/Sh

Pn (μmol m-2s-1)

O. alta

105685

CCDD

P

Sh

24.2b

O. longistaminata

101741

AA

P

S

34.4d

O. australiensis

101397

EE

P

S

33.8d

O.longistaminata

103904

AA

P

S

28.8c

O.australiensis

103303

EE

P

S

35.6de

O. meridionalis

101148

AA

A/P

S

34.0d

O. australiensis

104090

EE

P

S

36.7e

O. minuta

101099

BBCC

P

S

29.9c

O. australiensis

105272

EE

P

S

34.8d

O. minuta

101081

BBCC

P

S

31.2c

O. barthii

104983

AA

A

S

27.2c

O. minuta

80683

BBCC

P

S

24.5b

O. barthii

106300

AA

A

S

31.5c

O. officinalis

104707

CC

P

Sh

23.5b

O. eichingeri

100881

CC

A

S

21.1b

O. punctata

101330

BB

A

Sh

22.8b

O. glaberrima

102665

AA

A

S

27.2c

O. rufipogon

104640

AA

P

S

25.6bc

O.glumaepatula

100971

AA

P

S

14.3a

O. rufipogon

105697

AA

P

S

37.6e

O. grandiglumis

105671

CCDD

P

Sh

25.3bc

O. rufipogon

(Rampur 6)

AA

P

S

34.4d

O. latifolia

100172

CCDD

P

Sh

23.4bc

O. sativa

(Azucena)

AA

A

S

27.6b

a Habitat: A/P = annual / perennial, S/Sh= sun / shade.

Table 2. Rates of photosynthesis recorded in the greenhouse for the tillers near flowering in the O. rufipogon and F1 hybrids, Photosynthesis was measured using CAU photosynthesis system.

F1

Pn (μmol m-2s-1)

O.sativa

Pn (μmol m-2s-1)

O. rufipogon

Pn (μmol m-2s-1)

20342-3

28.7

   

Tawsan 11

38.3

20472-6

45.5

IR63371-38

20.4

Ulanpur 7

36.7

20485-3

27.1

WAB56-50

28.2

Kyant-1

33.8

20495-1

38.4

IRAT216

28.5

Tawsan 1

37.4

20515-12

34.1

Azucena

22.7

Ulanpur 18

35.5

20537-12

24.2

   

Rampur 11

19.8

20552-10

25.4

   

Nagesa 18

34.8

20557-10

43.3

   

Rampur 6

30.0

Average

35.7

 

23.8

 

33.6

LSD0.05

9.6

 

6.9

 

12.5

a LSD to compare entries within a group.

Table3.Rates of photosynthesis recorded at three different development stages in the wild rice and F2, F3 hybrids with high photosynthesis rate, and some cultivated cultivars.

Type

Name

40-day seedling
Pn (μmol m-2s-1)

70-day plant
Pn (μmol m-2s-1)

flowering Pn
Pn(μmol m-2s-1)

Average
Pn (μmol m-2s-1)

IRRI
Pn (μmol m-2s-1)

Cultivars

Azucena

34.61.2

23.01.6

28.71.8

28.7b

19.1*

Wild rice

Rampur6

22.21.6

16.12.3

27.61.5

22.0c

26.8*

Hybrids from cultivated
and wild rice

SHP1(F2

35.61.6

34.01.3

32.61.9

34.0a

42.2*

SHP1-6(F3

36.41.5

35.11.5

32.61.5

34.7a

 

SHP1-8(F3

38.22.1

34.92.1

33.32.4

35.5a

 

* mean value measured in tropic area in IRRI.

Discussion

Wild Oryza species are considered to be a rich source of agronomic traits, including insect and disease resistance and increased biomass, and even yield and its components (Moncada P et al.2001, X..Li et al., 1998) Variation in light-saturated assimilation rate and phosphoenolpyruvate (PEP) carboxylase activity has been reported in a set of Oryza species, and the O.rufipogon accessions evaluated had photorespiration rates significantly lower than the O.sativa genotypes tested (Yeo et al., 1994). We also found significant variation in photosynthetic rates among different accessions, cultivars, and inter-specific hybrids. The rates of photosynthesis reported here were measured under realistic levels of temperature and radiation for tropical rice, and are substantially greater than those previously reported. Species with very high levels of Pn were O. australiensis and O.rufipogon. O.australiensis is an EE genome species, and interspecific hybrids show rather limited levels of introgression of the wild genome. This species is adapted to high light environments in seasonally dry areas of Australia. In contrast, O.rufipogon is an AA genome species, like rice, and inter-specific hybrids have significant introgression from the wild species. This species is adapted to a wide range of environments, mostly semi-aquatic. Both of these species were capable of maintaining high rates of photosynthesis when grown in well-watered, aerobic soil conditions.

For the inter-specific hybrids showing high photosynthesis in the F1, photosynthesis in the F2 showed a normal distribution, indicating that this trait is quantitatively inherited. Photosynthesis of F2 plants was highly correlated with average photosynthesis of their F3 progeny, and normal distributions of photosynthetic rate were observed in the F3 populations. These results are again consistent with a multi-gene trait. And we also found that progenies with high photosynthetic rates in the tropic also had high photosynthetic capacity when in a temperate area.

References

A.R.Yeo and T.J.Flowers.(1994). Photosynthesis and photorespiration in the genus oryza. Journal of Experimental Botany. Vol. 45. No. 274, 553-560.

Moncada P., Martinez C. P., Borrero J., Chatel M., Gauch H., Guimaraes E., Tohme J. & McCouch S. R. (2001) Quantitative trait loci for yield and yield components in an Oryza sativa x Oryza rufipogon BC2F2 population evaluated in an upland environment. Theoretical and Applied Genetics, 102, 41-45.

Peng S., Laza R.C., Visperas R.M., Sanico A.L., Cassman K.G. & Khush G.S. (2000) Grain yield of rice cultivars and lines developed in the Philippines since 1966. Crop Science, 40, 307-314.

Xiao J.H., Li J.M., Grandillo S., Ahn S.N., Yuan L.P., Tanksley S. D. & McCouch S.R. (1998) Identification of trait-improving quantitative trait loci alleles from a wild rice relative, Oryza rufipogon. Genetics, 150, 899-909.

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