Research Natesom266

1981

Influence of Resin Duct Size and Number on Dleoresin Flow in the Southern Pines1

I!i,

John D. Hodges, William W. Elam, and Donald R. Bluhm

SUMMARY

The number of radial resin ducts was significantly

higher in slash pines than in loblolly, longleaf, or

shortleaf. Average width of resin ducts was less

in shortleaf than in the other three species. Flow

rate of oleoresin was not correlated with size or

number of resin ducts for any of the four species.

Additional keywords: Pinus echinata, Pinus elliottii,

Pinus palustris, Pinus taeda, Dendroctonus frontalis.

INTRODUCTION

Oleoresin of conifers is a defense against attack by

bark beetles. In some tree species, resistance to attack may be related td’both chemical and physical

properties of the oleoresin (Smith 1975). But in the

southern pines resistance seems to be controlled by

physical properties such as viscosity and rate, amount,

and duration of flow (Hodges et al. 1977, 1979.).

For the southern pines, these variables for oleoresin flow differ greatly both among and within

species (Hodges et al. 1977). Oleoresin flow is the

most important variable for loblolly (Pinus taeda

L.) and shortleaf (Pinus echinata Mill.) pines in distinguishing between trees that are resistant and those

that are susceptible to southern pine beetle (Hodges

et al. 1979). In slash pine (Pinus elliottii Engelm.),

rate of oleoresin flow is strongly related to viscosity

and to number and size of radial resin ducts (Schopmeyer et al. 1954) but this relationship has not been

reported for the other southern pines. We wanted to

discover the nature of the relationship between rate

of oleoresin flow and the number and size of radial

resin ducts in all the major southern pines. A strong

correlation might permit forest managers to evaluate

tree resistance to beetle attack by measuring resin

duct size and number.

METHODS

Study trees were located on the Kisatchie National

Forest in central Louisiana. The study area is within

the natural range of longleaf, loblolly, and shortleaf

pines, but slightly west of the natural range of

slash pine. The slash pine trees we examined had

been planted; trees of the other species originated

from natural regeneration. We studied 17 loblolly,

14 longleaf, 19 slash, and 15 shortleaf trees.

Oleoresin viscosity, flow (rate, duration, and amount),

‘The work reported here was sponsored in part by the Southern

Forest Experiment Station, Forest Service-USDA.

Use of trade names is for information only and is not an endorsement by the USDA Forest Service.

Southern Forest Experiment Station/T-10210 U.S. Postal Services Bldg., 701 Loyola Avenue, New Orleans, La. 70113

Forest Service, U.S. Department of Agriculture.

Serving Alabama, Arkansas, Louisiana, Mississippi, Eastern Oklahoma. Tennessee, Eastern Texas.

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Table 1 . - Comparison of radial resin duct size and number, viscosity and flow rate of oleoresin in the major

southern pines’

Species

Resin duct width

Horizontal Vertical Average Number Viscosity Flow rate

M (cl) (I4 (stokes) (ml/hr)

Loblolly 52.6

(46.9-60.9)

56.5

(47.8-64.1)

54.6a 35.3a

(26.0-46.5)

162a

(8.3-72.2)

1.5a

(0.2-2.9)

Longleaf

Shortleaf

57.3

(47.6-67.2)

46.7

(39.0-52.2)

(48::4.3),

51.4

(44.7-58.9)

57.6a

49.0b

32.6a

(26.446.3)

35.5a

(26.547.7)

55.7b

(27.6-i 13.4)

20.9a

(9.4-38.8)

l.lb

(0.3-2.9)

0.8~

(0.1-2.2)

Slash 53.7

(47.3-59.7)

55.9

(51.4-64.4)

54.8a 43.9b

(31.7-55.2)

241 .Oc 0.6~

(63.5-547.6) (0.3-2.2)

I Means followed by the same letter in a column are not significantly different at the 0.05 probability level

(Duncan’s Multiple Range Test).

and rate of crystallization were measured (Hodges

et al. 1977). For observation and measurement of

resin ducts, we removed two xylem samples from

each tree. The samples, which measured 13x38 mm,

were removed with a chisel from opposite sides of

the tree. The samples contained xylem of the 3 most

recent years’ growth. They were immediately placed

in formalin-acetic acid-alcohol-water (FAA) fixing

and killing solution (Sass 1958).

We dehydrated xylem samples by standard methods using tertiary butyl alcohol (TBA) and then embedded them in Tissuemat (Sass 1958). Samples

were cut in half, and tangential sections, 35-38~

thick,were cut on a rotary microtome. Most sections

were taken from early wood. We made cuts parallel

to tracheid orientation to insure good cross sections

of radial resin ducts and to decrease friction on the

microtome blade. Sections were stained with 2.0

percent safranin and counterstained with 0.5 percent

fast green. Three or four slides of each sample were

prepared. From these we chose the best sections

for measurement of resin ducts.

A small piece of cardboard with a cutout area of

either 1 .O cm* or 0.5 cm* was placed over the slide

and secured with tape. All resin ducts within the

cutout area were counted. Ten resin ducts/cm* were

randomly selected for measurement of the horizontal

and vertical axes. We used an ocular micrometer at

a magnification of 100X. Two sets of measurements

were made-one included the width of the enclosed

epithelial cells and one did not.

A one-way analysis of variance was used to test

for variation in number and size of resin ducts among

species and among trees within a species. Duncan’s

Multiple Range Test (Steel and Torrie 1980), at 0.05,

was used to test for differences among species.

RESULTS AND DISCUSSION

Radial resin ducts are located in fusiform rays

with ray parenchyma cells above and below the

resin ducts. Three or four epithelial cells, either

triangular or rectangular, line each resin duct. These

cells are easily distinguished from ray parenchyma,

which are smaller and rounder. Radial resin ducts

often lie next to longitudinal resin ducts, so the

two resin canal systems may be interconnected and

thus continuous.

In cross section, resin ducts are slightly elliptical

with the vertical axis usually longer (table 1). But in

all species a few resin ducts were wider on the

horizontal axis. The elliptical shape is more pronounced for shortleaf and loblolly pine than for slash

and longleaf. The resin ducts for trees in this study

were less elliptical than those found in young slash

pines (horizontal width of 5.49 and vertical width

of 70.0~) by Schopmeyer et al. (1954).

Average diameter of resin ducts (table 1) was

significantly less in shortleaf than in loblolly, slash,

and longleaf pines, which did not differ significantly.

The’num,ber of resin ducts per cm* was significantly

J.D. Hodges is Professor of Silviculture, W.W. Elam is Plant Physiologist, and D.R. Bluhm was a graduate assistant at Mississippi State

University, Mississippi State, Mississippi.

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higher in slash pine than in the other three species.

For slash pine, Mergen et al. (1955) found a relationship between tree age (rings from pith) and

number and size of resin ducts. Number of resin

ducts decreased curvilinearly with age to age 20,

and size decreased linearly with age at least to age

30. The average age for our trees, then, was 44 years

for loblolly, 46 for longleaf, 59 for shortleaf, and 32

for slash. Slash pines were all about the same age,

but the other three species varied widely. No trees

were less than 20 years old and few were less than

30. Age and resin duct size or number did not correlate for any of the four species.

For longleaf, loblolly, and slash pines, number and

size of resin ducts were not related. For shortleaf

the correlation was low (r = 0.32) but significantly

different from zero at the 0.05 level.

Rate of oleoresin flow was not correlated with size

or number of resin ducts for any of the four species.

This lack of correlation probably reflects dependence of resin flow rate on other characteristics such

as oleoresin viscosity, volume of oleoresin in the

system, rate of crystallization, and oleoresin exudation pressure. A negative relationship between flow

rate and viscosity has been found for all speciesthe more viscous the oleoresin, the slower the rate

of flow. (Hodges et al. 1977). Schopmeyer et al.

(1954) showed that the product of three independent

variables, the reciprocal of viscosity, and number

and size of resin ducts, accounted for 63 percent of

the variation in flow rate among young slash pines.

But our study shows that differences in viscosity

alone will account for 65 percent of the variation in

slash pines, 56 percent for shortleaf, 50 percent for

longleaf, and 36 percent for loblolly.

Previous work has shown that flow rate is highly

correlated with total flow of oleoresin (r >.95) and

that how well loblolly and shortleaf trees will resist

attack can be predicted by flow measurements

(Hodges et al. 1977,1979). We hoped that measurements of radial resin ducts could be used to predict

oleoresin flow and thus resistance to beetle attack.

Results of this study show that such a relationship

does not exist.

Hodges, J.D., W.W. Elam, and W.F. Watson.

1977. Physical properties of the oleoresin system

of the four major southern pines. Can. J. For.

Res. 7:520-525.

Hodges. J.D., W.W. Elam, W.F. Watson, and

T.E. Nebeker.

1979. Oleoresin characteristics and susceptibility

of four southern pines to southern pine beetle

attack. Can. J. Entomol. 111:669-696.

Mergen, F., P.E. Hoekstra, and R.M. Echols.

1955. Genetic control of oleoresin yield and

viscosity in slash pine. For. Sci. 1:19-30.

Sass, J.E.

1956. Botanical Microtechnique. 3rd Ed. 266 p.

Iowa State Univ. Press. Ames, Iowa.

Schopmeyer, C.S., F. Mergen, and T.C. Evans.

1954. Applicability of Poiseuille’s law to exudation

of oleoresin from wounds of slash pine. Plant

Physiol. 29:62-67.

Smith, R.H.

1975. Formula for a describing effect of insect and

host-tree factors on resistance to western pine

beetle attack. J.Econ. Entomol. 66:641-644.

Steel, R.G.D., and J.H. Torrie.

1960. Principles and procedures of statistics.

461 p. McGraw-Hill, New York.

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