Gain and variation after two generations of selection in slash pine in Georgia / by Earl R. Sluder

yl
Georgia Forestry Commission
QgS'M
Research
REPORT

Jo. 5

April, 1989

GAIN AND VARIATION

After Two Generations Of Selection

In Slash Pine In Georgia

By
Earl R. Sluder

eceived
1 1989
DOCUMENTS UGA LIBRARIES

Author
s*
Earl R. Sluder is a plant geneticists with the Regeneration and Breeding of Loblolly Pine in the Southeast Project of the Southeastern Forest Experi-
ment Station, USDA Forest Service, at
Macon, Georgia. He received his B.S., M.S. and Ph. D. degrees from North
Carolina State University at Raleigh.

GAIN
AND
VARIATION
After Two
Generations Of Selection In Slash Pine In Georgia

by Earl R. Sluder

ABSTRACT
Wind-pollinated slash pine progenies from (1 ) eight first-generation seed orchard clones, (2) bulked seed from their eight progenies in a 15year-old seedling seed orchard, and (3) 1 5 individual second-generation selections from the progenies in the seedling seed orchard were tested on an Upper Coastal Plain and a flatwoods site in Georgia. Contrasts between
progeny groups and checklots at age 5 years show that each selection
stage beyond the unrogued cloanal seed orchard produced gain in resistance to fusiform rust. Variation within groups of first- and second-
generation progenies remained high enough to afford further progress from selection, particularly in fusiform-rust resistance.
Genetic improvements in agricultural crops and domestic animals are greatly increasing profitability in agriculture and animal husbandry. The southern pines are being planted and grown as a crop, which presents both the opportunity and the need to apply genetic principles to increase prof-
itability in forestry.

In the early 1950's Georgia Forestry Commission foresters located several hundred well-formed, fastgrowing disease-free slash pines (Pinus elliottii Engelm. var. elliottii) as candidates for a tree improvement program. After further screening, 1 49 of these selected trees were propagated by grafting and used to establish two clonal seed orchards to supply seed needed for planting in
Georgia.
Trees grown from these seeds are expected to be better in growth rate and other traits than trees from seeds collected in natural stands. But the only way to find out if
they are better, and how much better, is to compare per-
formance of their progeny with that of natural-stand check lots in properly designed studies. Questions about the potential for gain in succeeding generations of selec-
tion and breeding are: (1 ) How much genetic variation in
economic traits is harbored in the selected genotypes? (2)
How much gain can be made each generation? (3) Over how many generations of selection and breeding can suc-
cessive gains be made? As soon as ramets of the seed orchard clones began
flowering, the Georgia Forestry Commission, in cooperation with the Southeastern Forest Experimetn Station,
USDA Forest Service, began controlled pollinations to
progeny test the clones. The first progeny tests, planted in 1961, included a plantation designed for conversion to a
seedling-origin seed orchard. When the conversion was
completed and the remaining seedling-origin seed
orchard trees were flowering, a study was designed to quantify gains made in this second-generation orchard, to compare them with gains made in the first generation clonal orchard, and to compare performance of progenies
from both orchards with that of natural-stand check
lots.
Materials and Methods
The progenies included in the second-generation seedling seed orchard were from controlled pollinations
of 1 7 of the clones in the first-generation clonal orchard. A mixture of pollen from 30 other clones in the orchard was
used on these 1 7. The 1 7 "polymix" progenies produced were planted in a replicated design at the Georgia Forestry Commission's Arrowhead Seed Orchard in Pulaski
County. Some 2,635 seedlings were planted. Roguing in 1967, 1969, 1971, and 1974 reduced the number to
141 trees, 5.35 percent of the original number. Trees removed were those (1) infected by the fusiform-rust fungus (Cronartium quercuum (Berk.) Miyabe ex Shirai f. sp. fusiforme), (2) with obviously slow growth, or (3) with
poor stem or branch characteristics. In the 1 974 roguing, spacing and flower production also were considered. One
progeny that consistently grew slowly and had high fusiform-rust susceptibility was eliminated in 1 974.
All cones were collected from the remaining seedling
seed orchard trees in 1975 (about 4,000 cones) and 1 976 (about 1 7,000 cones). Each year, the seeds were kept separate by individual tree. A bulk lot representing the rogued seedling seed orchard was made in each of the two years by mixing seed from each tree in proportion to that tree's contribution to total orchard yield. These two
bulk lots were overall orchard check lots. In addition, eight
family bulk lots were made from the 1 976 collection. The
three kinds of seed lots available from the seedling seed orchard, therefore, were two overall bulk lots, eight family bulk lots, and individual-tree lots, all from wind-polli-

nated seeds.
The maternal parents of the eight seedling orchard families from which the bulk seed lots were made are still in the rogued first-generation clonal orchard. Windpollinated seeds were collected from these eight clones for use in the study. Both seed orchards are surrounded by a large area of loblolly pine-hardwood forest and farm land, so outside slash pine pollen is at a very low level.
Two other check lots were obtained from the Georgia Crop Improvement Association. One was commercial
seed from Telfair, Treutlen and Emanuel Counties, and the other a bulk lot from the unrogued first-generation clonal orchard. Both were collected in 1 965.
Four kinds of seed lots were included in the study: (1) wind-pollinated seeds from eight of the clones remaining in the rogued first-generation orchard; (2) family-bulk lots from second-generation polymix progenies of the eight clones in (1), which were in a rogued seedling seed orchard; (3) individual-tree lots from 1 5 second-generation trees selected from 6 of the progenies in (2); and (4) four check lots -- two bulk lots from the seedling seed orchard, one bulk lot from the unrogued clonal orchard, and a commercial collection. The total number of seedlots was 35 (Appendix table 1 ).
Seedlings for the study were grown in 1 978 by the Georgia Forestry Commission in the Morgan Nursery near Byron, GA., and planted as 1-0 stock in the spring of 1 979 on two test sites in Georgia. One was a flatwoods site in Ware County and the other an Upper Coastal Plain site in Houston County. At both locations each seed lot was
replicated five times in 1 6-tree plots in a randomized com-
plete block design. Spacing was 2.5m x 2. 5m (8.2' x 8.2)
in Houston County and 2.5m in bedded rows approximately 3.7m (1 2') apart in Ware County.
At ages 2, 3, and 5 years, survival, height, and fusiformrust infection were measured or assessed at both test sites. Only the fifth-year results are reported here, but the fifth-year rust data reflect all mortality from rust through age 5. Rustinfection was expressed as thenumberof cankers per seedling and as the percentage of seedlings free of rust at age 5. Prior to analysis of variance, percentages were transformed to arcsins of their square roots. Means were separated with Duncan's multiple range test (Duncan 1955). Data were analyzed for each of the two planting sites and for the two sites combined.
The various check lots and family and progeny groups in this study represent stages of selection ranging from unselected natural stands to progenies from secondgeneration selections. Six contrasts between means of these groups were contstructed and tested for significance. Also, the relative variation remaining among families within groups (1), (2), and (3) above was
determined.
RESULTS AND DISCUSSION
Trait means for the groups representing the various stages of selection, along with six contrasts and their significance tests, are shown in Table 1. The numbers
assigned to the seedlots in Table 1 represent the various stages of selection and breeding, and the contrasts were
designed to show gains made in individual stages. Only one contrast was significant on the flatwoods site but five were for the fusiform-rust and one for the height traits on

the Upper Coastal Plain site. All the significant contrasts selection stage produced an increment of gain rather than involved changes in the desired direction; that is, that loss. For cankers per tree, negative contrasts reflect the desired change, whereas positive contrasts are desired
for the other traits.
For the fusiform-rust traits, the only contrast showing an undesirable response to selection was that between the unrogued clonal orchard check and the commercial check (2 vs 1 , Table 1 ). The unrogued orchard check was more susceptible than the commercial check on both sites, though not significantly so. Apparently, selecting rust-free trees in natural stands did little to increase the proportion of rust resistance genes in the unrogued clonal
orchard relative to that in natural stands. Later roguing and selection based on progeny test results have been
effective in increasing rust resistance.

Along with the increase in rust resistance has come little change in survival and only moderate improvement in
height growth rate. However, selection after the initial stage has been primarily for rust resistance, so this result
is not surprising. Selection for survival perse was not performed so the only survival response to be expected would be one that is correlated with a trait that was selected for, such as rust resistance. Such a correlated response in survival may appear as the trees get older and more rust mortality occurs.
Contrasts between groups 1 (commercial check) and 6 (progenies from second generation selections) (Table 1 give estimates of total gains after two generations of selection. On the Upper Coastal Plain site, gain in the rustfree trait was 1 5.7 percentage points, or 53.6 percent of the check. The decrease in number of cankers per tree was 1 3.7 percent of the check. Also realized was an 1 1 .1

-- Table 1. Group means and contrasts between groups for fusj.form-rust, height,
and survival at age 5 years of f.lash pine tested on two sites.

Group and Contrast

Rust- free

Trait Cankers/tree Height

Survival

Upp;r Coastal Plain Site

1 Commercial check

29-3

2 Clonal orchard check

20.4

3 First-generation families

32.8

4 Seedling S.O. bulk (1976)

59-2

5 Second-generation bulk fami; .ies 42.6

6 Second-generation selections;

45.0

4.38 5-03 4.47 2.56 3.22 3-78

2 vs 1 3 vs 2 4 vs 3 5 vs 3 5+6 mean vs 3 6 vs 5

- 8.9 12.4 26.4 9.8** 11.0*
2.4

0.65 -O.56 -1.91* -1.25* -0.97**
O.56

Flatwoods Site

1 Commerical check

94.4

2 Clonal orchard check

86.0

3 First-generation families

90.0

4 Seedling S.O. bulk (1976)

100.0

5 Second-generation bulk famil ies 91.8

6 Second-generation selections

92.5

0.10 .66
.12 .00 .10 .10

2 vs 1
3 vs 2 4 vs 3 5 vs 3 5+6 mean vs 3 6 vs 5

-8.4 4.0
10.0 1.8 2.1 0.7

O.56 -0.54* -0.12 -0.02 -0.02
0.00

#*( Significant at the 0.01 level h Significant at the 0.05 level

3.23 3.60 3-55 3.76 3-56 3-59
0.37 -0.05
0.21** 0.01 0.02 0.03

80.0 82.5 78.0 88.4 77-9 80.5
2.5 -4.5 10.4 -0.1
1.2 2.6

2.34 2.13 2.41 2.16 2.41 2.39
-0.21 0.28
-0.25 0.00
-0.01 -0.02

62.5 46.2 55-4 46.2 53-7 58.9
-16. 9-2
-9.2 -1.7
0.9 5-2

percent gain in height. In the plantation on the flatwoods
site, the only gain was 2.1 percent of the check in
height.
Considerable variation in rust resistance still exists
among first- and second generation families and among
second-generation selections (table 2). Further gains

should be possible with further selection and testing, especially in the plantation on the Upper Coastal Plain site where rust incidence has been quite high. Since very low rates of infection have occurred on the flatwoods site (Appendix tables 2-5), little opportunity for selection for rust resistance is expected in that plantation.

Table 2. --The standard deviation among families within groups expressed as a percentage of the mean of the group for four traits at age 5 years.

Family
Families of firstgeneration clones
Second-generation bulk families
Families from secondgeneration selections

Trait

Plantation site

Upper Coastal Plain

Flatwoods

-percent

Rust- free Cankers/tree Height Survival

36.8 41.0
9-0 7-8

77-8 7-3
12.2 32.4

Rust- free Cankers/tree Height Survival

23.0
*
33-0
4.8
6.7

166.7 13.8 27.1 35-8

Rust- free Cankers/tree Height Survival

52.2 60.2
7-8 9-1

121.9 9-2
24.7 52.5

LITERATURE CITED
Duncan, D B. 1 955. Multiple range and multiple F tests.
Biometrics 1 1 :1-42.

-- Appendix table 1. Description of progenies and check lots of slash pine.

Progeny : or Check :
GO^XW
(60XP)XW,B (60XP)XW,S (60XP)XW,S (60XP)XW,S (60XP)XW,S
119XW (119XP)XW,B (ii9XP)xw,s (H9XP)xw,s (H9XP)xw,s

Description
60 x wind (5-ramet mix) - First-generation family (60 x polymix) x wind (15-tree mix) - Second-generation bulk (60 x polymix) x wind - Second-generation selection (60 x polymix) x wind - Second-generation selection (60 x polymix) x wind - Second-generation selection (60 x polymix) x wind - Second-generation selection
119 x wind (5-ramet mix) - First-generation family (119 x polymix) x wind (5 - tree mix) - Second-generation bulk (119 x polymix) x wind - Second-generation selection (119 x polymix) x wind - Second-generation selection (119 x polymix) x wind - Second-generation selection

94xW (9itXP)XW,B (94XP)XW,S (94xp)xw,s (94XP)XW,S
50XW (50XP)XW,B (50XP)XW,S (50XP)XW,S

94 x wind (2-ramet mix) - First-generation family (9^4 x polymix) x wind (6-tree mix) - Second-generation bulk (94 x polymix) x wind - Second-generation selection (9^ x polymix) x wind - Second-generation selection (9^ x polymix) x wind - Second-generation selection
50 x wind (4-ramet mix) - First-generation family (50 x polymix) x wind (6-tree mix) - Second-generation bulk (50 x polymix) x wind - Second-generation selection (50 x polymix) x wind - Second-generation selection

20XW (20XP)XW,B (20XP)XW,S (20XP)XW,S

20 x wind (5-ramet mix) - First-generation family (20 x polymix) x wind (3~tree mix) - Second-generation bulk (20 x polymix) x wind - Second-generation selection (20 x polymix) x wind - Second-generation selection

71XW (71XP)XW,B (71XP)XW,S
6xw (6XP)XW,B
76XW (76XP)XW,B
Check 1 Check 2 Check 3 Check 4

71 x wind (3-ramet mix) - First-generation family (71 x polymix) x wind (3~tree mix) - Second-generation bulk (71 x polymix) x wind - Second-generation selection
6 x wind (5-ramet mix) - First-generation family (6 x polymix) x wind (4-tree mix) - Second-generation bulk
76 x wind (4-ramet mix) - First-generation family (76 x polymix) x wind (4-tree mix) - Second-generation bulk
Seedling seed orchard bulk - 1975 Seedling seed orchard bulk - 1976 Commercial seed collection (Georgia Crop Improvement Assoc.) Seed orchard collection (Georgia Crop Improvement Assoc.)

1/
Georgia Forestry Commission serial numbers for the first-generation selections.

-- Appendix table 2. Significance tests for the various sources of variation in
four traits at age 5 years in two slash pine test plantings analyzed separately and combined.

Source of variation

Trait Rust-free Cankers/tree Height Survival

Upper Coastal Plain Site

Replication Seed lot (all) First-generation families Second-generation families Second-generation selections

Flatwoods Site

Replication Seed lot (all) First-generation families Second-generation families Second-generation selections

Two sites combined

Site

**

Replication in site

**

Seed lot (all)

*

First-generation families



Second-generation families

Second-generation selections

#

Site x seed lot

*

# Significant at the 0.01 level Significant at the 0.05 level

**

#

*#

##

*

**

#

*

#

Appendix table 3"--Means for rust, height and survival traits at age 5 years for wind-]pollinated families from f irst generation orchard clones of slash pine tested on two sites

Family

Rust- free Percent

Trait Cankers /tree
Number

Height
m

Survival Percent

Upper Coastal Plain Site

60XW 6xw
50XW 119XW
76XW 94xw 7ixw 20XW

54. 2a 4l.2ab 39-7ab 33-8ab 27.3ab 26.4ab 25.8ab 14. 2b

2.00a 5-50ab 4.44ab 5 . 58ab 4 . 22ab 3.l8ab 3 . 80ab 7.02b

3.91a 3.62ab 3.45b 3.46b 3.51b 3.38b 3.53b 3.54b

78.8a 75-Oa 79.9a 75-Oa 81.1a 80. 0a 78.1a 76.0a

Mean

32.8

4.47

3.55

78.0

Flatwoods Site

6oxw 76XW
94xw 71.2a
20XW 6XW
50XW 119XW
71XW

98.6a 92.7a
92.3a
89.6a 89.3a 88.1a 88.0a 84.3a

0.02a .07a .09a
.16a .14a .18a .14a .16a

2.46a 2.45a
2.30a
2.54a 2.26a 2.26a 2.62a 2.37a

56.2a 63.5a
44.4a 56.2a 34.6a 61. 2a 56.2a

Mean

90.3

0.12

2.41

55-4

1/
Means followed tjy a common letter do not differ sign:Lficantly at the 0.05

level accordingI to Duncan s Multiple range test.

Appendix

table

4.---Means

for

rust ,

height

and

survival

traits

at

age

5

years

for seconds-generation bulk families of slash pine tested on

two sites '

Family

Rust- free Percent

Trait Cankers/tree
Number

Upper Coastal Plain Site

Height
m

Survival Percent

(60XP)XW,B (71XP)XW,B (20XP)XW,B (6XP)XW,B (76XP)XW,B (119XP)XW,B (50XP)XW,B (94xp)xw,b

51.6a

50.4a

49.5a

*

46.4a

40. 8a

36.2a

35.3a

30.4a

2.92a 2.74a 2.51a 2.11a 3.54a 3.10a 2.42a 6.44b

3.63a 3.58a 3.62a 3.63a 3.54a 3.6la 3.44a 3.40a

77.5a 81. 2a 77.5a 78.7a 81. 2a 82.5a 78.1a 66.2a

Mean

42.6

3.22 Flatwoods Site

3.56

77-9

(50XP)XW,B (71XP)XW,B (119XP)XW,B (60XP)XW,B (20XP)XW,B (6XP)XW,B (94xp)xw,b (76XP)XW,B
Mean

98.7a 95.6a 95.3a 95.0a 94.6a 93-5ab 85.1bc 76. 9c
91.8

0.01a .04a .05a .05a .05a .08ab .21bc
.29c
.10

2.19b 2.35b 2.09b 2.35b 2.40b 3.01a 2.62ab 2.28b
2.41

38.5a 57.5a 42.5a 42.5a 48.8a 69.5a 68.8a 61. 2a
53-7

1/
Means followed t)y a common letter do not differ at tile 0.05 level, according
to Duncan's Mullsiple range test

3 BIDS D3Tlb 73b2

Appendix table 5-"--Means for rust, height and survival traits at age 5 years for progenies from the second-generation selections o f slash pine
tested on two sites

Family

Rust-free Percent

Trait Cankers/tree
Number

Height
m

Survival Percent

Uppe>r Coastal Plain Site

(60XP)XW,S (71XP)XW,S (60XP)XW,S (119XP)XW,S (20XP)XW,S (60XP)XW,S (50XP)XW,S (94XP)XW,S (20XP)XW,S (H9XP)xw,s (94xp)xw,S (H9XP)xw,s (60XP)XW,S (94XP)XW,S (50XP)XW,S
Mean

?4. 8a 70. lab 68.1a-c 64.6a-d 52.5a-e 48.5b-f 48-5c-g 44.2d-g 42.4d-g 36.3e-g 31.3e-g 27-9e-g 26.5fg 25.0gh 17. 5h
45.0

1.52ab 1 . 26ab 1.25a 1.29ab 4.69a-d 2.54a-c 2.36a-c 4.92a-d 3-75a-d 7.86d 6.l6cd 4.99b-d 7.88d 2.97a-d 3-23a-d
3-78

3- 55a 3.65a 3.65a 3.51a 3.67a 3.73a 3.43a 3.30a 3.68a 3.76a 3.46a 3.69a 3.69a 3.66a 3.44a
3-59

77.5a .
96.5a 78.7a 82.5a 82.5a 75.4a 79.2a 86.2a 76.2a 75-Oa 80.0a 81. 4a 81. 2a 74.9a 80.0a
80.5

Flatwoods Site

(60XP)XW,S (20XP)XW,S (60XP)XW,S (71XP)XW,S (50XP)XW,S (20XP)XW,S
(H9XP)xw,s
(60XP)XW,S (94xp)xw,S (60XP)XW,S (50XP)XW,S (H9XP)xw,s (H9XP)xw,s (94xp)xw,s (94xp)xw,S
Mean

100.00a 98.2a 97.8a 96.4a 94.4a 94.1a 94.0a 93.3a 92.3a 91.5a 90.0a 88.8a 88.6a 85.6a 82.7a
92.5

0.00a .04a .04a .04a .06a .10a .14a .13a .09a .09a .10a .16a .11a .14a 30a
10

3.06a 2.12bc 2.42bc 2.05c 2.26bc 2.28bc 2.15bc 2.63a-c 2.24bc 2.73ab 2.19bc 2.4lbc 2.37bc 2.54ac 2 38bc
.
2.39

69.6a 37.5b 71.2a 58.6ab 39.6b 52.5ab 48.8ab 72.3a 56.2ab 56.2ab 32.9b 52.3ab 58.8ab 6l.5ab 40. 0b
58.9

1/
Means followed by a common lett< to Duncan's Multiple range test.

te 0.05 level, according

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