Euphytica 27 (1978) 397409

C H A N G E S IN M O R P H O L O G I C A L A N D P H Y S I O L O G I C A L T R A I T S A S S O C I A T E D

W I T H R E C U R R E N T S E L E C T I O N F O R G R A I N Y I E L D IN M A I Z E a

M. A. B. F A K O R E D E z and J. J. M O C K

Department of Agronomy, Iowa State University, Ames, Iowa 50011, USA

Received 16 September 1977

INDEX WORDS

Zea mays L., correlated responses, maize ideotype, reciprocal recurrent selection, recurrent selec- tion for specific combining ability.

SUMMARY

Experiments were conducted during the growing seasons of 1975 and 1976 to determine changes in morphological and physiological traits associated with recurrent selection for grain yield in maize (Zea mays L.). Four variety hybrids, BSSS(R)CO x BSCBI(R)CO, BSSS(R)C7 x BSCBI(R)C7 [from a reciprocal recurrent selection program involving Iowa Stiff Stalk Synthetic (BSSS) and Iowa Corn Borer Synthetic # 1 (BSCB1)], BS12CO x B14A, and BS12C6 x B14A [from a half-sib selection program involving the open-pollinated variety Alph (BS12) and the inbred tester B14A] were grown at 59 300 and 98 800 plants/ha near Ames, Iowa We obtained data on CO2-exchange rate (an estimate of photosynthetic rate), grain yield, grain-yield components, flowering dates, maturity traits, light interception and use, shelling percentage, harvest index, and various other

plant traits. COz-exchange rate did not change appreciably with recurrent selection for yield. Grain yield per

hectare and per plant were larger for the improved than unimproved hybrids. Grain-yield compo- nents did not change significantly with recurrent selection. Kernel weight of BSSS(R)C7 x BSCB1 (R)CT, however, was larger than that of BSSS(R)C0 x BSCB1 (R)C0. Pollen-shed-to-silking interval was shorter for the improved than the unimproved hybrids, and grain-filling duration was longer in C7 x C7 than in Co x C O of the reciprocal recurrent selection program. Furthermore, improved hybrids were characterized by smaller tassels and more upright canopies. Usually, plant traits and leaf-area-related traits were similar for all hybiids.

Although dry-matter productivity was similar for all hybrids, those that were improved by recur- rent selection produced more grain per unit leaf area and per unit light interception. Also, BS 12C6 x B14A was characterized b~¢ a higher harvest index than BS12CO x B14A.

We concluded that the source (i.e., photosynthetic capacity) was not limiting grain yield in BSSS(R) x BSCBI(R) and BS12. Increased grain yields that resulted from recurrent selection were consequences of longer grain-filling duration for BSSS(R) x BSCBI(R) and increased transloca- tion of photosynthate from source to sink for both BSSS(R) x BSCBI(R) and BSl2.

1 Journal Paper J-8953 of the Iowa Agriculture and Home Economics Exp. Stn., Ames, Iowa. Project No. 2152. 2 Present address: Department of Plant Science, University of Ire, Ile-Ife, Nigeria.

Euphytica 27 (1978) 397

I N T R O D U C T I O N

M. A. B. FAKOREDE AND J. J. MOCK

Maize (Zea mays L.) breeding programs have emphasized selection for improved grain yield per se, and incorporation of desirable agronomic traits (e.g., disease resistance, insect resistance, lodging resistance) usually is secondary. Because this approach to crop improvement is expensive and time consuming, development of efficient plant types through the use of yield components and morphological and (or) physiological traits has been suggested (DONALD, 1968; FREY, 1970). DONALD

(1968) used the term 'ideotypes' to describe these plant types. He defined ideotypes as 'plants with model characteristics known to influence photosynthesis, growth, and (in cereals) grain yield'. MOCK & PEARCE (1975) proposed an ideotype of maize that would be adapted to high-productivity environments of the U.S. Corn Belt. This ideotype should be characterized by, among other traits, efficient interception and use of solar energy, maximum photosynthetic efficiency, efficient conversion of photosynthate into grain, short pollen-shed-to-silking interval, and long grain-fil- ling period.

Breeding of crop ideotypes assumes strong genetic associations exist between grain yield and the morphological and physiological traits that are to be used either as indirect selection criteria or in combination with grain yield in a selection index. To determine relationship among several traits of maize, we evaluated changes in morphological and physiological traits that resulted from seven cycles of a reciprocal recurrent selection program for grain yield and six cycles of a recurrent half-sib family selection program. Previous studies (EBERHART et al., 1973; RUSSELL et al., 1973) have reported significant grain-yield improvements for the first five cycles of selection in both programs.

MATERIALS A N D METHODS

We grew the variety hybrids t, BSSS(R)CO x BSCBI(R~CO BSSS(R)C7 x BSCBI(R]C7, BS12CO x B14A, and BSt2C6 x B14A at the Iowa State University Hind's Farm, near Ames, Iowa, during the 1975 and 1976 growing seasons. The first two hybrids were obtained from a reciprocal recurrent selection program involving Iowa Stiff Stalk Synthetic (BSSS) and Iowa Corn Borer Synthetic ~1 (BSCBI) (PEN- r,nc & EBERHART, 1972; EBERHART et al., 1973). The second two hybrids were from a half-sib recurrent selection program in the open-pollinated variety Alph (BS 12) with inbred B14A as the tester variety (RUSSELL et al., 1973). Both programs were initiated in 1949 by Dr G. F. SPRAGUE, and grain yield was the primary selection criterion. Previous studies ( E B E R H A R T et al., 1973; RUSSELL et al., 1973) have shown significant grain-yield improvements for the first five cycles of selection in both programs.

Our experiments were grown in split-plot arrangements with three replications each year. Plant densities [59300 (low density) and 98 800 (high density) plants/ha] were the main plots, and hybrids were randomized to subplots. Six- and eight-row (rows 5.3 m long and spaced 76 cm apart) subplots were used in 1975 and 1976, re- spectively. Each subplot was overplanted and thinned to desired plant densities.

1 Hereinafter variety hybrids will be referred to as hybrids.

398 Euphytica 27 (1978)

R E C U R R E N T S E L E C T I O N I N M A I Z E

Each year, 112 kg N/ha were applied before planting, and 56 kg N/ha were side-dres- sed at approximately five weeks after planting. Also, 2.5 and 10.2 cm water were ap- plied from an overhead sprinkler irrigation system on July 15, 1975, and July 9, 1976, respectively. The following data were obtained for each subplot.

Photosynthetic rates of ear leaves. CO2-exchange rates (CER) of excised ear-leaf sections were measured as described by PEARCE et al. (1976). We measured CER of one leaf section from each of four (in 1975) or five (in 1976) competitive plants during grain filling [i.e., approximately HANWAY'S (1971) growth stage 6.0]. This growth stage corresponds to CER 2 of CROSBIE et al. (1977). Procedures for CER measure- ment were similar to those reported by CROSBn~ et al. (1977). We used CER per plant [CERPLA = (CER x leaf area/plant)/1000] and CER per hectare (CERPHA = CER x leaf area index) as estimates of canopy photosynthesis.

Light interception. Amounts of light intercepted by the canopies at the ear (ELI) and at the soil (SLI) levels were determined as described by FAKOREDE & MOCK (1976).

Flowering dates. Dates when 50~o of plants in each subplot attained anthesis (DPS) and incipient silk extrusion (DSE) were expressed as days from July 1. Pollen-shed- to-silking interval was obtained by substracting DPS from DSE.

Plant traits. Ear and plant heights, numbers of green leaves per plant, tassel branch number (i.e., including the central tassel branch), and tassel dry weights were obtained for five competitive plants per subplot during grain filling.

Leaf area. We determined areas of leaves subtending top ears (ELA) of five randomly chosen plants per subplot by the formula (MONTGOMERY, 1911) ELA = 0.75 x length x maximum width (i.e., ELA = 0.751w). Also, we estimated leaf area per plant as ELA × 9.39 (PEARCE et al., 1975). Additionally, leaf area per plant was converted to leaf area index by the formula, EAI = leaf area per plant x number of plants per unit land area.

Leaf-orientation values (LOV). Measurements necessary to calculate leaf-orienta- tion values for the leaf above (ALOV) and below (BLOV) the top ear were obtained during grain filling, and LOV was calculated by the formula (PEPPER, 1974):

n

LOV = E [O(Lfp/Lt)]/n i - 1

where 0 = leaf angle (degrees from horizontal), Lfp = length (cm) of each leaf from its collar to the point where it became parallel to the soil surface or 'flagged' (i.e., 'flagging point'), L t = total length (cm) of each leaf, and n = number of leaves measured per subplot (i.e., 5).

Maturity traits. ApproximateJy 40 days after DSE in 1975, we sampled five or more kernels per ear from five randomly chosen plants per subplot to determine black- layer formation (BLF). This was done every other day until all plots attained black

Euphytica 27 (1978) 399

M. A. B. F A K O R E D E A N D J. J. M O C K

layer. Effective grain-filling duration (GFD) was obtained by subtracting DSE from BLF.

Productivity traits. At approximately BLF, six competitive plants were cut near the soil surface, dried to constant moisture, and weighed. Weights were divided by 6.0 to give dry matter per plant, which was multiplied by number of plants per plot and divided by plot area to give total dry-matter productivity. Grain yield and grain-yield components (ear number, kernel row number, ear length, ear diameter, cob diameter, kernel depth, 300-kernel weight, and grain weight per plant) were obtained for 10 competitive plants in 1975 and for plants from a bordered row in 1976. Ears were weighed at harvest (Fw,), dried, and reweighed (Dw,) each year. Percentage ear moisture at time of harvest was estimated as [(Fwt-Dw,)/Fwt] × 100. Also, weights of shelled grain were multiplied by 100, and the product was divided by Dwt to obtain shelling percentage. Kernel moisture percentage at harvest was estimated as the product of shelling percentage and ear-moisture percentage. Grain per plant was divided by dry matter per plant to give harvest index.

Analysis of variance (subplot means~ was performed for each trait (hybrids and densities were fixed effects and years were random effects), and means of main effects and interaction effects that showed significant F-values were tested further by ap- propriate LSD values.

Usually, year effects were not significant in our study; consequently, plant-density and hybrid effects will be emphasized in our discussion.

RESULTS AND DISCUSSION

Significant differences between unimproved and improved hybrids indicated that recurrent selection was effective for improving grain yields of BSSS(R~ x BSCBI(R~ and BS12 (Table D. Average difference between the CO x CO and C7 x C7 of the reciprocal recurrent selection program was 2.54 q/ha (or 5.51~o) per cycle; a total gain of 17.76 q/ha in seven cycles of selection. Similar values for the half-sib program were 3.05 q/ha (or 8.48~) per cycle and a total gain of 18.28 q/ha in six cycles of selection.

Contrary to results obtained in other studies (FAKOREDE, 1977~, differences be- tween unimproved and improved hybrids for number of ears/100 plants were not significant, a manifestation of the large C.V. (25 .5~ associated with this trait. Usually, grain-yield components of unimproved and improved hybrids from the same selection program did not differ appreciably. BSSS(R~C7 x BSCBI(R~C7, however, produced heavier kernels than BSSS(R~C0 x BSCBI(POC0. Usually, the low density was more favorable for the expression of grain yield and grain-yield components than the high density (Table D.

Except for CERPHA, photosynthesis traits were higher at the low than the high plant density (Table 2~. Differences for these traits between unimproved and im- proved hybrids were not significant. Because significant differences were observed for grain yields of these hybrids, we concluded that the source (i.e., photosynthetic ac- tivity) was not the primary factor limiting grain yield in BSSS, BSCB1, and BS12. CROSBIE et al. (1978) reached a similar conclusion for 64 random inbreds of maize

400 Euphytica 27 (1978)

Tab

le 1

. E

ffec

ts o

f pl

ant

dens

itie

s an

d hy

brid

s on

gra

in y

ield

and

gra

in-y

ield

com

pone

nts

of f

our

mai

ze v

arie

ty h

ybri

ds.

~a

Tra

its

Den

siti

es

Hyb

rids

plan

ts/h

a B

SS

S(R

) x

BS

CB

I(R

) B

S12

x B

14A

5930

0 98

800

LS

D 0

.05

CO

x

CO

C

7 x

C7

Co

C6

LS

D 0

.05

Tot

al g

rain

yi

eld

(q/h

a)

54.0

1 45

.98

5.65

46

.05

63.8

1 35

.92

54.2

0 14

.75

Gra

in y

ield

/ pl

ant

(g)

94.0

2 49

.28

10.7

4 65

.96

91.6

8 51

.03

77.9

5 21

.04

Num

ber

of e

ars/

10

0 pl

ants

87

.92

70.4

2 11

.33

78.3

3 89

.17

71.6

7 77

.50

NS

x

Ear

len

gth

(cm

) 16

.96

14.3

3 1.

40

14.1

2 15

.06

16.1

9 17

.22

1.51

E

ar d

iam

eter

(cm

) 4.

30

4.06

0.

15

4.19

4.

29

4.03

4.

21

NS

C

ob d

iam

eter

2.

57

2.48

N

S

2.48

2.

57

2.48

2.

56

NS

K

erne

l de

pth

(cm

) 0.

87

0.79

N

S

0.86

0.

86

0.78

0.

83

NS

K

erne

l ro

w n

umbe

r 15

.77

15.2

6 0.

32

15.8

3 16

.43

14.4

0 15

.38

1.08

30

0-ke

rnel

wei

ght

(g)

74.9

1 71

.32

2.49

66

.76

72.2

0 76

.99

76.5

1 5.

08

Her

eina

fter

, N

S w

ill b

e us

ed t

o in

dica

te n

onsi

gnif

ican

t di

ffer

ence

s at

0.0

5 le

vel o

f pro

babi

lity

.

M. A. B. FAKOREDE AND J. J. MOCK

obtained from BSSS, and EVANS (1974) reported that primitive, poor-yielding wheats had higher photosynthetic rates than present-day, high-yielding varieties. Evidently, superior yields of crop plants do not result from high photosynthetic rates per se. Although CER values in our study were similar to values for CER 2 reported by CROSBIE et al. 0977), the variety hybrids we studied demonstrated somewhat lower CER than previously observed for conventional maize hybrids (HEICHEL & MUS- GRAVE, 1969).

Both unimproved and improved hybrids attained 50~ pollen shed on approx- imately the same day, but the improved hybrids displayed incipient silk extrusion earlier than their unimproved counterparts (Table 2). Pollen-shed-to-silking in- terval, therefore, was shorter for the improved hybrids. Differences between hybrids from the half-sib program for days to black-layer formation, grain-filling duration, and percentage ear and grain moisture at harvest were not significant. Date of black-layer formation was later, and length of grain-filling duration was longer for BSSS(R)C7 × BSCBl(R)C7 than for BSS(R)C0 x BSCBI(R)C0 (Table 2). These results, plus the data obtained for percentage grain moisture (Table 2), indicated that BSSS(R)C7 × BSCBl(R)C7 reached maturity later than its unimproved counterpart.

More days were required for the hybrids to attain 50~ pollen shed and 50~, silk emergence at the high than at the low plant density (Table 2). Furthermore, pollen- shed-to-silking interval was longer at the high plant density. Number of days to black-layer formation, grain-filling duration, and percentage ear and grain moisture at harvest were not affected significantly by plant densities.

Differences between plant densities for tassel branch number were not significant, but tassel weight was heavier at the low than the high density (Table 3). Results ob- tained for the two traits indicated that tassel size of improved hybrids was smaller than that of unimproved hybrids. These results, and those obtained for pollen-shed- to-silking interval, further substantiated earlier conclusions (MOCK & BUREN, 1972; BUREN et al., 1974; MOCK & PEARCE, 1975) that negative associations exist between grain yield and these traits.

Ear height and plant height were not affected significantly by plant densities or hybrids, and differences between plant densities for ear height:plant height ratio were not significant (Table 3). This ratio, however, was lower for the improved than the unimproved variety hybrids.

Numbers of leaves per plant were similar across plant densities (Table 3), but LAI was larger at the high than low plant density. Furthermore, LAI at the high density was larger in 1975 than 1976 [6.12 vs. 5.37; LSD(0.05) for density x year interaction was 0.24]. FAKOREDE et al. (1977) found that 9.39 x 0.751w overestimated leaf areas in 1975 but not in 1976; probably, this overestimation caused these differences. Ear- leaf-area, leaf area per plant, and dry-matter (DMPLA) and grain (GRPLA) produc- tion per unit leaf area were greater at the low density.

Hybrids displayed similar values for numbers of leaves per plant, ear-leaf area, leaf area per plant, and LAI (Table 3). Leaf areas of unimproved hybrids were as efficient as those of their improved counterparts in producing dry matter, but improved hybrids produced more grain per unit leaf area. Because photosynthetic rates (Table 2), leaf areas, and DMPLA (Table 3) were similar for all hybrids, we propose that improved hybrids demonstrated greater abilities to translocate photosynthate from leaves to developing grain.

402 Euphytica 27 (1978)

Tab

le

2.

Eff

ects

of

plan

t de

nsit

ies

and

hybr

ids

on p

hoto

synt

hesi

s tr

aits

, fl

ower

ing

date

s, a

nd m

atur

ity

trai

ts o

f fo

ur m

aize

var

iety

hyb

rids

.

P~

b,a

"-.1

Den

siti

es

Hyb

rids

plan

ts/h

a B

SS

S(R

) x

BS

CB

I(R

) B

S12

× B

12A

5930

0 98

800

LS

D0.

05

Co

× C

o "l

× C

7 C

o C

6 L

SD

0.0

5

Pho

tosy

nthe

sis

trai

ts

CE

R (

mg

CO

2 dm

-2

h-1)

27

.48

CE

RP

LA

(g

CO

z pl

ant

- 1

h-

1)

1.84

C

ER

PH

A (

kg C

O2

ha-

1

h-

1)

1.07

Flo

wer

ing

and

mat

urit

y tr

aits

5

0~

pol

len

shed

(da

ys

from

Jul

y 1)

21

.04

50

~ s

ilk

emer

genc

e (d

ays

from

Jul

y 1)

24

.67

Pol

len-

shed

-to-

silk

ing

inte

rval

(da

ys)

3.63

B

lack

-lay

er f

orm

atio

n (d

ays

from

Jul

y 1)

81

.17

Gra

in-f

illi

ng

dura

tion

(da

ys)

52.2

5 E

ar m

oist

ure

~ 28

.85

Gra

in m

oist

ure

~ 22

.08

22.6

4 3.

73

23.8

0 22

.21

25.9

9 28

.23

NS

1.33

0.

31

1.40

1.

45

1.66

1.

83

NS

1.29

N

S

1.04

1.

09

1.24

1.

35

NS

22.8

8 0.

88

22.4

2 22

.25

21.3

3 21

.83

NS

28.5

4 1.

41

27.1

7 25

.50

28.1

7 25

.58

1.43

5.67

1.

64

4.75

3.

25

6.83

3.

75

1.02

82.5

8 N

S

80.0

0 84

.33

81.0

0 82

.17

3.25

50.3

3 N

S

48.0

0 54

.83

49.5

0 52

.83

3.56

31

.81

NS

30

.53

34.1

2 28

.12

28.5

4 4.

02

23.4

2 N

S

22.7

5 26

.55

19.9

3 21

.78

3.76

4~

ta~

-~

Tab

le 3

. E

ffec

ts o

f pl

ant

dens

itie

s an

d hy

brid

s on

pla

nt a

nd l

eaf

trai

ts o

f fo

ur m

aize

var

iety

hyb

rids

.

Den

siti

es

Hyb

rids

pl

ants

/ha

BS

SS

(R)

× B

SC

BI(

R)

5930

0 98

800

LS

D 0

.05

Co

× C

o C

7 ×

C7

Pla

nt t

rait

s N

umbe

r of

tass

el b

ranc

hes

17.9

8 T

asse

l w

eigh

t (g

) 25

.34

Ear

hei

ght

(cm

) 10

7.33

P

lant

hei

ght

(cm

) 22

5.78

E

ar h

eigh

t: p

lant

hei

ght

rati

o 0.

48

BS1

2 x

BI4

A

Lea

f tra

its

Num

ber

of le

aves

/pla

nt

12.3

5 E

ar-l

eaf

area

(cm

2)

714.

65

Lea

f ar

ea/p

lant

(m

2)

0.67

L

eaf

area

ind

ex

3.88

D

MP

LA

(m

g/cm

2)

42.2

6 G

RP

LA

(m

g/cm

2)

14.2

1

Co

C6

LS

D 0

.05

17.3

5 N

S

20.5

2 17

.70

17.4

0 15

.03

2.33

18

.12

5.08

22

.43

19.2

9 24

.79

20.4

0 2.

05

110.

03

NS

10

7.90

10

5.48

11

2.37

10

8.95

N

S

222.

61

NS

21

5.12

22

2.72

22

3.68

23

3.25

N

S

0.49

N

S

0.50

0.

47

0.50

0.

47

0.03

11.4

6 N

S

11.7

8 11

.68

12.1

0 12

.06

NS

65

7.92

47

.75

645.

08

700.

49

696.

18

703.

38

NS

0.

59

0.04

0.

58

0.65

0.

64

0.65

N

S

5.74

0.

17

4.42

5.

02

4.90

4.

91

NS

31

.31

6.84

37

.06

38.2

0 33

.90

37.9

7 N

S

8.37

2.

23

11.0

6 14

.05

7.88

12

.15

3.38

RECURRENT SELECTION IN MAIZE

Orientation of the upper canopy (ALOV) of BS12 was not changed significantly by half-sib recurrent selection for grain yield (Table 4). Conversely, leaf angle (AANG), length to 'flagging' point (ALfp), and ALOV increased significantly with selection in the reciprocal recurrent selection program. For the lower canopy, leaf angle (BANG), length to 'flagging' point (BLfp), and BLOV were greater for BSSS(R)C7 × BSCBI(R)C7 than BSSS(R)C0 x BSCBI(R)C0. Similarly, BLfp and BLOV were larger for BS12C6 x B14A than BS12C0 × B14A. Angle of lower leaves (BANG) did not change in the half-sib program, and total leaf lengths at both canopy positions did not change in either program. Differences between plant densities for canopy-orientation traits (except ALfp) were not significant. Although increased erectness of canopies was associated with recurrent selection for grain yield, the 'idoptype' with upright-leaf orientation above and horizontal-leaf orientation below the ear (PENDLETON et al., 1968; DUNCAN, 1971 ; WINTER • OHLROGGE, 1973; PEPPER, 1974; MOCK & PEARCE, 1975) was not obtained.

The high plant density intercepted more incident solar radiation than the low density, but the low density produced more dry matter and more grain per unit light interception at both ear and soil levels (Table 5). C7 × C7 of the reciprocal recurrent selection program intercepted more light at the ear level than CO x CO, and hybrids from the half-sib program intercepted similar amounts of light at the ear level. Also, amounts of light intercepted by the total canopy (SLI) and amounts of dry matter produced per unit of light intercepted at ear (DM/ELI) and soil (DM/SLD levels were similar for all hybrids. BS12C6 × B14A, however, displayed greater DM/ELI at the low density than BS12C0 × B14A [2.72 and 3.64 g for the two hybrids, re- spectively; LSD(0.05) = 0.87g]. Improved hybrids produced larger amounts of grain per unit of light intercepted at both canopy levels (Table 5).

Although dry matter per plant decreased with increased plant density, difference between the two densities for total dry-matter productivity was not significant (Table 6). Shelling percentage and harvest index were greater at the low than at the high plant density (Table 6). Evidently, high grain yield at the low density resulted from large photosynthetic-surface area (Table 3), high photosynthetic rate (Table 2), large sink size (Table 1), and efficient translocation of photosynthate from the source to the sink (Table 6).

Hybrid differences for production of dry matter (per plant and per hectarO were not significant (Table 6). Also, differences between hybrids from the same selection program for shelling percentage were not significant. Harvest index of BS12C6 × B14A was much larger than that of BS12C0 x B14A. Similar trends were observed for the reciprocal recurrent selection program, but differences were not significant, probably because of the high C.V. (32 .7~ associated with harvest index in this study. Harvest indices obtained in other studies (FAKOREDE, 1977) indicated an advantage for BSSS(R)C7 x BSCBI(R)C7 over BSSS(R~C0 x BSCBI(R)C0.

Results of the study reported herein indicated that the sink, rather than the source, was limiting grain yields of BSSS(R) × BSCBl(R) and BS12. Selection for larger sink size (i.e., increased grain yield) did not alter the rate at which the source (i.e., photosynthetic rate) functioned. Evidently, changes in the pattern of photosynthate distribution were induced by the attempt to increase sink size. The improved version orBS 12 translocated more dry matter to grain than to other plant parts, but BSSS(R)C7

Euphytica 27 (1978) 405

-~

Tab

le 4

. E

ffec

ts o

f pl

ant

dens

itie

s an

d hy

brid

s on

can

op

y-o

rien

tati

on

tra

its

of f

our

mai

ze v

arie

ty h

ybri

ds.

Tra

its

Den

siti

es

Hyb

rids

plan

ts/h

a

59 3

00

98 8

00

LS

D 0

.05

BS

SS

(R)

× B

SC

BI(

R)

Co

× C

o C

7 x

C7

BS

12

x B

14A

Co

C6

LS

D 0

.05

Upp

er c

anop

y L

eaf

angl

e 1

60.3

0 59

.86

N S

58

.48

63.1

8 58

.30

60.3

5 2.

82

Lfp

(cm

) 49

.07

45.4

9 3.

52

44.6

8 53

.78

42.7

8 47

.87

6.79

L

eaf

leng

th (

cm)

89.6

8 88

.07

NS

84

.58

86.8

5 91

.17

92.9

0 3.

83

Lea

f-or

ient

atio

n va

lue

33.0

8 30

.81

NS

31

.11

38.3

1 27

.48

30.8

8 4.

65

Low

er c

anop

y L

eaf

angl

e ~

60.9

4 61

.53

NS

57

.43

64.5

8 60

.48

62.4

3 3.

04

l_¢p

(cm

) 52

.36

49.9

8 N

S

48.9

7 57

.23

45.7

8 52

.68

5.03

L

eaf

leng

th (

cm)

96.0

3 96

.62

NS

92

.05

94.1

0 98

.45

100.

70

3.73

L

eaf-

orie

ntat

ion

valu

e 33

.75

32.3

3 N

S

31.0

3 39

.73

28.2

5 32

.95

4.38

0 >

Deg

ree

from

the

hor

izon

tal.

t,a

-,q

Tab

le 5

. E

ffec

ts o

f pl

ant

dens

itie

s an

d hy

brid

s on

lig

ht i

nter

cept

ion

and

use

by f

our

mai

ze v

arie

ty h

ybri

ds.

Den

siti

es

Hyb

rids

t,,a

-,q

plan

ts/h

a B

SS

S(R

) x

BS

CB

I(R

) B

S12

× B

14A

5930

0 9

88

00

L

SD

0.0

5 C

o x

Co

C7

× C

7 C

o C

6 L

SD

0.0

5

EL

I (~

) 78

.70

90.0

8 2.

01

78.0

8 88

.48

87.0

1 83

.99

6.02

D

M/E

LI

(g)

3.61

2.

05

0.42

2.

90

2.92

2.

55

2.94

N

S

GR

/EL

I (g

) 1.

19

0.55

0.

15

0.86

1.

05

0.60

0.

96

0.23

S

LI

(~)

90.8

1 95

.81

1.97

91

.91

92.0

3 93

.74

95.5

8 N

S

DM

/SL

I (g

) 3.

08

1.93

0.

39

2.38

2.

76

2.34

2.

54

NS

G

R/S

LI

1.03

0.

51

0.12

0.

72

1.00

0.

55

0.82

0.

22

Tab

le 6

. E

ffec

ts o

f pl

ant

dens

itie

s an

d hy

brid

s on

pro

duct

ivit

y tr

aits

of

four

mai

ze v

arie

ty h

ybri

ds.

Tra

its

Den

siti

es

Hyb

rids

plan

ts/h

a B

SS

S(R

) ×

BS

CB

I(R

) B

S12

x B

14A

5930

0 98

800

LS

D 0

.05

Co

× C

o C

7 ×

C7

Tot

al d

ry m

atte

r (m

t/ha

) 16

.03

17.5

9 N

S

15.2

9 17

.61

Dry

mat

ter/

plan

t (g

) 27

8.12

18

4.59

34

.57

213.

89

251.

15

She

llin

g pe

rcen

tage

76

.10

72.2

1 1.

99

73.8

6 77

.58

Har

vest

ind

ex (

~)

35.0

3 28

.17

3.88

31

.79

38.7

3

Co

C6

16.6

0 17

.75

218.

94

241.

43

70.5

9 74

.60

23.7

7 32

.10

LS

D 0

.05

NS

N

S

4.04

8.

70

4~

,--1

M. A. B. FAKOREDE AND J. J. MOCK

x B S C B I ( R ) C 7 increased its p roduc t iv i ty via a p ro longed grain-f i l l ing per iod and delayed matur i ty . Resul ts ob ta ined f rom growth analysis (FAKOREDE, 1977~ revealed that leaf-area du ra t i on o f BSSS(R]C7 x BSCBI (R)C7 was longer than that of BSSS(R)C0 x B S C B I ( R ) C 0 , and this difference occurred largely dur ing gra in filling. Resul ts of our s tudy, and those repor ted by MOLL & KAMPRATH (1977), therefore , in- dicate tha t increased gra in yield of maize may be achieved th rough changes in var ious phys io logica l mechanisms .

REFERENCES

BUREN, L. L., J. J. MOCK & I. C. ANDERSON, 1974. Morphological and physiological traits in maize associated with tolerance to high plant density. Crop Sci. 14: 426-429.

CROSBIE, T. M., J. J. MOCK & R. B. PEARCE, 1977. Variability and selection advance for photosyn- thesis in Iowa Stiff Stalk Synthetic maize population. Crop Sci. 17 : 511-514.

CROSBIE, T. M., R. B. PEARCE & J. J. MOCK, 1978. Relationship between CO2-exchange rate and plant traits in Iowa Stiff Stalk Synthetic maize population. Crop Sci. 18 (in press).

DONALD, C. M., 1968. The breeding of crop ideotypes. Euphytica 17: 385-403. DUNCAN, W. G., 1971. Leaf angle, leaf area, and canopy photosynthesis. Crop Sci. 11 : 482-485. EBERHART, S. A., S. DEBELA ~,~ A. R. HALLAUER, 1973. Reciprocal recurrent selection in the BSSS

and BSCBI maize populations and half-sib selection in BSSS. Crop Sci. 13:451-456. EVANS, L. T., 1974. The physiological basis of crop yield, p. 32~355. In: L. T. EVANS (Ed.), Crop

physiology. Cambridge Univ. Press. FAKOREDE, M. A. B., 1977. Direct and correlated responses to recurrent selection for grain yield in

maize breeding populations. Ph.D. dissertation. Iowa State Univ., Ames, Iowa. FAKOREDE, M. A. B. & J. J. MOCK, 1976. Leaf orientation and efficient utilization of solar energy

by maize (Zea mays L.). WMO Symposium on Agrometeorology of the Maize Crop. Proceedings (in press).

FAKOREDE, M. A. B., N. N. MULAMBA & J. J. MOCK, 1977. A comparative study of methods used for estimating leaf area of maize (Zea mays L.) from nondestructive measurements. Maydica 22: 37-46.

FREY, K. J., 1970. Improving yields through plant breeding, p. 15-58. In: R. MUNSON (Ed.), Moving offthe yield plateau. Am. Soc. Agron. Spec. Publ. 20.

HANWAY, J. J., 1971. How a corn plant develops. Iowa Coop, Ext. Serv. Spec. Rep. 48 (rev.). HEICHEL, G. H. & R. B. MUSGRAVE, 1969. Varietal differences in net photosynthesis in Zea mays L.

Crop Sci. 9: 483-486. MOCK, J. J. & L. L. BUREN, 1972. Classification of maize (Zea mays L.) inbreds for population

tolerance by general combining ability. Iowa State J. Sci. 46: 395-404. MocK, J. J. & R. B. pEARCE, 1975. An ideotype of maize. Euphytica 24: 6134523. MOLL, R. H. & E. J. KAMPRATH, 1977. Effects of population density upon agronomic traits associat-

ed with genetic increases in yield ofZea mays L. Agron. J. 69:81 84. MONTGOMERY, E. G., 1911. Correlation studies in corn. Nebraska Agric. Exp. Stn Annu. Rep. 24:

108-159. PEARCE, R. B., J. J. MOCK & T. B. BAILEY, 1975. Rapid method for estimating leaf area per plant in

maize. Crop Sci. 15: 691-694. PEARCE, R. B., T. M. CROSBm & J. J. MOCK, 1976. A rapid method for measuring net photosynthesis

of excised leaves by using air-sealed chambers. Iowa State J. Res. 55 : 25-33. PENDLETON, J. W., G. E. SMITH, R. S. WINTER & T. J. JOHNSON, 1968. Field investigation of the

relationships of leaf angle in corn (Zea mays L.) to grain yield and apparent photosynthesis. Agron. J. 60: 422-424.

PENNY, L. H. t~ S. A. EBERHART, 1972. Twenty years of reciprocal recurrent selection with two synthetic varieties of maize (Zea mays L.). Crop Sci. 12: 900-903.

PEPPER, G. E., 1974. The effects of leaf orientation and plant density on the yield of maize (Zea mays L.). Ph.D. dissertation. Iowa State Univ. (Libr. Cong. Card No. Mic. 75-10, 500). University Microfilms. Ann Arbor, Mich. (Diss. Abstr. 35 : 5234-B).

408 Euphytica 27 (1978)

RECURRENT SELECTION IN MAIZE

RUSSELL, W. A., S. A. EBERHART & U. A. VEGA, 1973. Recurrent selection for specific combining ability for yield in two maize populations. Crop Sci. 13: 257-261.

WINTER, S. R. & A. J. OHLROGGE, 1973. Leaf angle, leaf area, and corn (Zea mays L.) yields. Agron. J. 65 : 395-397.

Euphytica 27 (1978) 409