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Growth, Development and Yield Determination in Barley

M. R. Jalal Kamali and W. J. R. Boyd

Department of Plant Sciences, University of W. Australia, Nedlands, W. A., 6907.

Introduction

In a typical spring barley the accumulation of dry mass (growth) commences slowly with the emergence of the coleptile and increases exponentially until physiological maturity (Fig. 1). During that interval crop growth is characterized by an orderly sequence of ontogenic events (development), such as coleoptile emergence, floral initiation and anthesis (Fig. 2). These events precipitate the coordinated initiation, appearance and growth of tissue structures (such as leaves, stems, spikes and grain) characteristic of the mature plant. The timing of developmental events, together with rates of tissue structure initiation and appearance, determines the manner in which accumulating dry mass is partitioned into those structures and, to the proportion stored as grain (Figs. 1 & 2). Cultivar and growing season conditions impact on developmental progress, on growth and the manner of its partitioning. From an analysis of the latter the determination of yield involves three component steps. These are:

  • The development a vegetative foundation for future yield determination over the vegetative phase.
  • The translation of that vegetative foundation, over the pre-anthesis stage of the reproductive phase, to actual yield potential at the time of anthesis.
  • The realization of yield potential over the post-anthesis stage of the reproductive phase.

This paper quantifies the numerous factors contributing to the accumulation and partitioning of dry matter among commercially available barley cultivars differing substantially in their phenology and in their agro-ecological regions of adaptation in Western Australia.

Materials and Methods

Plant growth and developmental progress were examined by frequent sampling from five replicated field trials over four growing seasons. All trials were sown in the interval of late May/early June under conditions of high soil fertility and at a density of 100 plants m-2. At a wheatbelt location in 1994 and 1995 heavy opening rainfall ensured a fully charged soil profile at the time of sowing. With limited winter rainfall in 1994 soil moisture deficiency intensified from the time cv. Stirling was approaching anthesis. The 1995 season was very different. Persistent winter rainfall resulted in saturated soils until shortly before anthesis in cv. Stirling. With ample soil moisture reserves, and below average temperatures thereafter, physiological maturity occurred a month later. To overcome the confounding of soil moisture related problems, the 1996 and 1997 trials were located on the UWA Field Station in Perth (a costal location) where, on a free draining soil with the availability of irrigation and higher but less extreme temperatures, the inherent potential of cultivars was more fully expressed.

Results

a. Development of vegetative foundation for future yield

During the vegetative phase, from sowing (S) to coleoptile emergence (CE) and CE to floral initiation (FI), the barley plant initiates its total complement of leaves and primary tillers (Fig. 2). The mean duration of this phase varied with cultivar and to a greater extent with season (Table 1). Variation in temperature and radiation, together with cultivar differences in the timing of FI and leaf sizes, were considered the primary factors responsible for mean cultivar differences recorded for canopy development (LAI), shoot numbers and dry mass at FI.

b. Translation of vegetative foundation to actual yield potential at anthesis

The interval from FI to anthesis comprises two sub-stages. During the first (FI to MPN = maximum primordia number) spikes are formed and, during the second (MPN to Anthesis), those spikes grow in size concurrently with the elongation of the stem internodes subtending them (Fig. 2). Mean cultivar differences in the duration to FI (vegetative phase) expanded over the interval from FI – Anthesis and, unlike seasonal differences, were significantly correlated with one another (Table 2). Mean leaf area indices, shoot numbers and dry masses increased slowly during spike formation but exponentially thereafter (Fig. 1), with variation due to seasons greater than variation among cultivars. Similar comments apply to the rates of stem elongation and tiller appearance but not, spikelet primordia number. The imbalance between the exponential increases in LAI (= assimilate supply) and growth (= assimilate demand) generated competition between and within plants and tillers, restricting the number of fertile spikes and spikelets at anthesis to about 60% of the maximum formed; irrespective of dry mass (Fig. 1 and Table 2). Seasonal, but particularly, cultivar differences in dry mass at FI were reflected in dry mass at anthesis; indicating dominant influences of cultivar, temperature and radiation on dry matter accumulation over the pre-anthesis stage.

Table 1 : Season and cultivar means for measures of thermal durations (Cd), leaves, shoot and dry mass over the vegetative phase (S – FI). It is over this interval that the vegetative foundation for future yield is established. Temp = mean for temperature, PTQ = photo-thermal quotient, S = sowing, CE = coleoptile emergence, FI = floral initiation, LN = leaf number on the main stem, LAI = leaf area index, DM = dry mass.

Variation

Temp

PTQ

Duration (Cd)

LN

LAI

Shoot/ plant

DM

due to:

oC

MJ/ m2.oC

S - CE

CE - FI

S - FI

FI

FI

FI

g/m2

Seasons

                 

1994

12.2

0.8

102

358

460

5.0

0.68

4.9

36.0

1995

10.7

0.7

110

276

387

4.0

0.38

3.7

18.0

1996

13.6

0.6

120

306

426

4.2

0.49

3.3

22.3

1997a

15.6

0.6

117

390

506

4.6

-

4.5

30.1

1997b

15.5

0.6

108

406

514

5.2

-

5.3

57.9

Cultivars

                 

Unicorn

13.9

0.6

113

307

420

4.0

0.28

3.4

23.4

Stirling

13.5

0.7

111

338

450

4.7

0.50

4.0

28.6

Harrington

13.0

0.7

111

350

460

4.8

0.74

4.6

42.3

Skiff

13.4

0.7

110

393

503

4.9

0.38

5.3

40.8

Table 2: Season and cultivar means for measures of thermal durations (Cd), leaves, shoot and spikelet, and dry mass over the spike formation stage (FI - MPN) and spike/stem growth (MPN – Anth) sub-stages. It is over these intervals that the vegetative foundation at FI is translated into actual yield potential at anthesis. Temp = mean for temperature, PTQ = photo-thermal quotient, S = sowing, FI = floral initiation, MPN = maximum primordia number, Anth = anthesis, LN = leaf number on the main stem, LAI = leaf area index, RCE = rate of canopy expansion (LAI/Cd), TI = tiller interval (Cd/tiller), TS = tiller survival (%), DM = dry mass.

Variation

Temp

PTQ

Duration (Cd)

LN

Canopy

Shoot/plant

RSE

Spikelet

DM g/m2

due to

C

MJ/m2. C

FI - MPN

MPN - Anth

S - Anth

MPN

LAI

RCE x 102

TI

No.

TS

mm /Cd

No.

SS

MPN

Anth

Seasons

                               

1994

12.7

1.3

294

374

1128

8.3

2.8

1.02

84

7.2

56

-

 

-

223

709

1995

11.0

1.0

292

466

1144

7.3

1.6

0.37

100

5.0

75

-

 

-

123

427

1996

13.7

0.7

428

559

1414

8.7

4.8

1.35

36

8.7

64

1.8

45

65

261

782

1997a

13.2

1.0

413

519

1439

8.7

-

-

54

9.0

59

1.6

43

61

260

830

1997b

12.4

0.9

396

527

1380

9.2

-

-

45

9.6

55

1.4

46

64

439

1013

Cultivars

                               

Unicorn

12.3

0.9

318

460

1198

7.7

2.6

0.95

63

7.5

63

1.9

46

62

208

623

Stirling

12.5

0.9

364

490

1290

8.7

2.8

0.84

67

7.4

67

1.6

41

63

249

750

Harrington

12.6

1.0

399

467

1305

8.9

4.0

1.40

70

7.1

61

1.5

50

67

338

840

Skiff

12.6

1.1

368

543

1395

8.4

2.0

0.59

59

9.5

57

1.2

45

61

263

781

c. Realization of actual yield potential at the time of maturity

In the interval from anthesis to maturity grains form and grow in size (Figs. 1 and 2). The duration of this interval varied minimally with cultivar but greatly with season. Plant dry mass doubled, with contributions from current photosynthesis supplemented by the translocation of stored reserves as canopy senescence increased (Fig. 1 and Table 3). Seasonal and cultivar differences in dry mass at maturity was strongly correlated with dry masses at anthesis but not, with either grain yield or harvest index. This reflex the influence of temperature, evaporative demand and soil moisture availability on the realisation of potential yield.

Table 3: Season and cultivar means for measures of thermal durations (Cd), leaves, shoot and spikelet, and dry mass over the post-anthesis innterval (Anth – PM). It is over this intervals that the potential yield at the time of anthesis is translated into realizeable yield at maturity. Temp = mean for temperature, PTQ = photo-thermal quotient, S = sowing, AA = awn appearance, Anth = anthesis, LN = leaf number on the main stem, MLAI = maximum leaf area index, RCS = rate of canopy senescence (LAI/Cd), MShn = maximum shoot number, PT = primary tiller, FShn = fertile shoot number, DM = dry mass, GY = grain yield, HI = harvest index.

Variation

Temp

PTQ

Duration (oCd)

LN

Canopy

Shoot number/plant

DM

GY

HI

due to

oC

MJ/m2.oC

S - PM

Anth - PM

AA

MLAI

RCS x 102

MShn

PT

FShn

(g/m2)

(g/m2)

(%)

Seasons

   

-

-

-

-

-

-

-

-

-

-

-

1994

21.6

1.50

1657

528

12.0

5.36

0.91

10.2

4.0

5.5

1234

472

38

1995

14.2

1.48

1826

683

11.0

2.49

0.30

5.5

3.2

4.2

1050

503

48

1996

15.0

1.27

1983

569

12.3

7.24

0.83

9.8

4.7

6.2

1433

653

43

1997a

15.9

1.27

2117

679

11.8

-

-

10.3

4.0

6.0

1653

615

38

1997b

15.9

1.28

2020

640

12.0

-

-

11.6

-

6.5

1718

670

39

Cultivars

                         

Unicorn

14.1

1.25

1812

614

11.3

4.91

0.60

9.0

4.0

5.5

1335

582

45

Stirling

16.8

1.38

1925

635

12.0

4.83

0.64

9.3

3.9

5.9

1410

559

40

Harrington

17.0

1.40

1938

634

11.8

5.49

0.75

8.3

3.9

5.0

1466

604

40

Skiff

17.5

1.40

2007

612

11.8

3.48

0.52

11.0

3.8

6.0

1445

594

43

Conclusions

  • Relative to growing season duration the timing of anthesis is a major factor determining the adaptation of cultivars and their classification into developmental groupings. Although correlated with the duration to FI, cultivar differences in the timing of anthesis were significantly greater due to subtle variation in the duration of sub-stages over the interval from FI to Anthesis.
  • Developmental differences within cultivar groupings were inconsistently expressed due to interactions with transient and unpredictable variations in seasonal weather conditions. Such differences are of value in retrospectively explaining cultivar differences in performance but, of limited value as selection criteria or for predictive purposes.
  • With results of any single trial reflecting specific adaptation to the seasonal weather conditions experienced, selection in early generations is therefore opportunistic, with recommendations unreliable unless replicated over a realistic number of seasons.

References

1. Boyd, W. J. R. (1996): In: Barley genetics VII. Proc. 7th Int. Barley Genet. Symp., Saskatoon, Canada. pp. 276-283

2. Jalal Kamali, M. R. (1999): Ph. D. Thesis (submitted), The University of Western Australia. pp. 380.

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