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II. Seed Filling: Definition and Measurement

II. Seed Filling: Definition and Measurement

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246



D. B. EGLI



Both of these methods can be applied at all levels, but the growth curve

method requires extensive sampling and selection of the appropriate regression

model to produce acceptable estimates. The EFP avoids dealing with the nonlinear lag phases of seed growth and requires fewer samples.

Plant growth stages can also be used to estimate seed-fill duration at the

individual plant or plant community levels. The time between growth stages R5

(beginning of seed fill) and R7 (an estimate of PM, Fehr and Caviness, 1977) is

widely used in soybean [Glycine max (L.) Merr.] (Egli et al., 1984; Agudelo et al.,

1986). The period between anthesis or silking and PM is popular in many cereals

(Daynard and Kannenberg, 1976; Darrock and Baker, 1995). PM is usually

estimated from a visual appraisal of seed or plant characteristics (Egli, 1998).

Growth stage estimates may not be as precise as those based on seed growth

curves [e.g., R5 – R7 is not the same for indeterminate and determinate soybean

cultivars (Agudelo et al., 1986; Pfeiffer and Egli, 1988)], but they have the

advantage in that they are non-destructive and easy to determine.

Munier-Jolain et al. (1993) and Ney et al. (1993) used seed moisture levels,

which are closely associated with the stage of seed development (Fraser et al.,

1982), to estimate seed-fill duration in soybean and pea (Pisum sativum L.).

Comparisons of published estimates of seed-fill duration can be misleading

because of the variety of methods used to estimate it, species variation in growth

characteristics and environmental effects. However, comparisons of published

estimates of seed-fill duration provide some useful general information about the

length and variation of this important growth stage. The variation in seed-fill

duration among species, based on whole-plant growth characteristics, is

frequently less than the variation within a species in a summary of field trials

(Table I). A similar summary of EFP also found more variation within than

between species (Egli, 1981). The longer seed-fill duration of maize (Zea mays

L.) (Table I) represents an apparent exception to this pattern, however, this

advantage was not evident in comparisons of EFP (Egli, 1981), so it could be

longer simply because the anthesis to beginning seed growth period is longer in

maize than in other species. There are no obvious relationships between known

plant characteristics and seed-fill duration in Table I. The seed-fill duration of C4

crops [sorghum (Sorghum bicolor L.), pearl millet (Pennisetum glaucum (L.)

Leeke)]—discounting any advantage for maize—is not longer than C3 crops.

Species with high seed protein [soybean, groundnut (Arachis hypogea L.)] or oil

[sunflower (Helianthus annuus L.), groundnut] concentrations do not have

shorter seed-fill durations than cereals [wheat (Triticum aestivum L.), rice (Oryza

sativa L.)] that produce seeds with low protein and oil concentrations.

The seed-filling period represents less than half of the total growth cycle of

most crops. It represented only 26 –41% of the total growth cycle of a group

of soybean cultivars from Maturity Groups 00 through V (Zeiher et al., 1982;

Egli, 1994). The proportion was only 32 – 38% in pearl millet (Craufurd and

Bidinger, 1988), but it was slightly larger in maize (44% for six hybrids)



Table I

Variation in Seed-Fill Duration Within and Among Crop Species



Maize



100



Wheat



120



Barley

Rice



120

80



Sorghum

Pearl millet

Sunflower

Soybean



120

110

200

380



Chickpea

Cowpea

Groundnut



230

250

310



Seed-fill duration

(days)

Number of

experiments



Number of

genotypes



Method of

estimation



Mean



Range



Reference



4

2

3

2

2

4

1

1

2

1

2

2

3

1

1

1



8

30 –35

6

11

16

9

5

29

19

2

5

27

13

3

38d

6



Silking to PM

Silking to PM

Silking to maximum seed mass

Cubic polynomial

Anthesis to maturity

Anthesis to PM

Cubic polynominal

Broken stick-iterative regression

Flowering to PM

Flowering to maturity

First anthesis to PM

Growth stage R5–R7

Growth stage R5–R7

Sigmoid growth curve

Flowering to maturity

Curvilinear regression



58

65

51

36

37

31

35

26

35

28

41

33

41

37c

21

46



54–62

49–73

48–54

34–40

34–45

29–33

34–37

20–37

30–40

28–28

38–46

28–40

36–46b

34–39

15–30

35–53



Bolanos (1995)

Daynard and Kannenberg (1976)

Hanway and Russell (1969)

Gebeyehou et al. (1982)

Reynolds et al. (1994)

Garcia del Moral et al. (1991)

Jones et al. (1979)

Kato (1989)

Quinby (1972)

Craufurd and Bidinger (1988)

Villalobos et al. (1994)

Egli (1994)

Boerma and Ashley (1988)

Davies et al. (1999)

Dow el-madina and Hall (1986)

Witzenberger et al. (1988)



PM, physiological maturity.

Approximate concentrations from Sinclair and de Wit (1975), Hulse et al. (1980), Langer and Hill (1991) and Bewley and Black (1994).

b

Range based on cultivar means.

c

Irrigated.

d

Diverse genotypes from four countries grown in California.



SEED-FILL DURATION



Species



Protein

concentrationa

(g kg21)



a



247



248



D. B. EGLI



(Hanway and Russell, 1969). The preliminary events in the yield production

process (vegetative growth, flowering and seed set), take up to twice as much

time as the production of the seeds that make up economic yield. All crops do not

suffer from such a limited yield production period—tuber growth in potato

(Solanum tuberosum spp. tuberosum) continues for up to 120 days (Moorby and

Milthorpe, 1975; Spitters, 1987; Vos and Groenwold, 1987; Burton, 1989).

Storage root growth in sugar beet (Beta vulgaris L.) covers 90– 110 days (Milford

and Watson, 1971; Fick et al., 1975) and cassava (Manihot esculenta Crantz)

roots accumulate dry matter for up to 300 days (Howeler and Cadavid, 1983;

Aleves, 2002). Compared to these root and tuber crops, the time allocated to yield

production in grain crops is not long, which puts much more emphasis on the rate

of growth when producing exceptionally high yields.



III. VARIATION IN SEED-FILL DURATION

Seed-fill duration, like most plant growth processes, has both an environmental and a genetic component. The length of the seed-filling period of a crop in

a specific environment is determined by the genetic potential of the genotype and

the environment. Environmental conditions during vegetative growth, flowering

or seed set could indirectly affect seed-fill duration by altering other aspects

of plant growth, but many environmental effects are a direct response to the

environment during seed filling. We will focus on direct effects of the

environment during seed filling.



A. TEMPERATURE

Seed-fill duration generally increases as temperatures decrease below 308C in

many crops (Fig. 1) including maize (Tollenaar and Bruulsema, 1988; Muchow,

1990; Wilhem et al., 1999), spring and winter wheat (Spiertz, 1978; Vos, 1981;

Al-Khatib and Paulsen, 1984; Wardlaw and Moncur, 1995; Gibson and Paulsen,

1999), sunflower (Chimenti et al., 2001), lentil (Lens culinais) (Summerfield

et al., 1989) and oat (Avena sativa L.) (Hellewell et al., 1996). There may be

exceptions to this general trend, for example, there was little effect of

temperatures between 20 and 308C on seed-fill duration in soybean (Egli and

Wardlaw, 1980) or rice (Chowdhury and Wardlaw, 1978). The seed-fill duration

of rice and wheat was the same at 36/318C (day/night temperature), but the

duration of wheat was longer at temperatures below 33/288C (Tashiro and

Wardlaw, 1989). The seed-fill duration of a japonica rice cultivar did not change

between 33/28 and 21/168C while that of sorghum more than doubled over the

same range (Chowdhury and Wardlaw, 1978). The effect of shorter seed-fill



SEED-FILL DURATION



249



Figure 1 The relationship between temperature and seed-fill duration for several crop species.

Seed-fill duration was estimated by the effective filling period and data from each source was averaged

across genotypes, years or experiments where appropriate. The regression was significant at

P , 0:001: Maize—Tollenaar and Bruulsema (1988) and Wilhem et al. (1999); wheat—Vos (1981),

Tashiro and Wardlaw (1989), Hunt et al. (1991) and Wardlaw and Moncur (1995); rice—Fujita et al.

(1984) and Tashiro and Wardlaw (1989); sunflower—Chimenti et al. (2001).



durations at higher temperatures may be mitigated by an increase in seed growth

rate (Chowdhury and Wardlaw, 1978; Spiertz, 1978; Wardlaw and Moncur,

1995) that reduces or prevents changes in final seed size. Comparisons of relative

temperature effects among experiments may be misleading because of variation

in techniques, but comparisons in the same experiment suggest that species

differences exist and are important.

The response to temperature during seed filling may not be the same as during

other reproductive growth stages. The simulation model CROPGRO uses a flat

temperature response between 25 and 358C for all reproductive growth stages

in soybean, but the response to temperatures below 258C is less during seed

filling than during early reproductive growth (Boote et al., 1998). The rate of

development at 108C, relative to the maximum rate at 308C, was 0.2 during

early reproductive development compared with 0.8 during seed filling. Including

this differential response greatly improved the model’s predictive ability in

cooler climates.



B. WATER STRESS

Water stress during seed development shortens the filling period and reduces

yield of many crop species, including wheat (Gallagher et al., 1976; Brooks et al.,

1982; Nicolas et al., 1984; Yang et al., 2000; Ahmadi and Baker, 2001), rice



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