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 Southern Forest

Research Note

SO-276

Experiment Statlon October 1961

Some Growth Aspects of Seymeria cassioicies

Charles M. Stangle and Lytton J. Musselman

SUMMARY

The root parasite, Seymeria cassioides, will not initiate

height growth without attachment to a host root when

grown under normal fertility conditions, although the

seedling may remain alive for 40 days or more without a

host. Durirrg this time the roots elongate markedly. Fresh

pine root segments do not influence the direction of root

growth. Although S. cassioides is always root parasitic in

nature, it apparently produces most of its own food, as

plants that are vigorously parasitizing pines die when

placed in the dark even though the host plant is exposed

to light.

Additional keywords: root parasite, hemiparasite,

Scrophulariaceae.

INTRODUCTION

The discovery in the late 1960’s that Seymeria

cassioides [J. F. Gmel. (Blake)], or senna seymeria,

could cause serious growth reduction and mortality of

slash pine (Pinus elliotfii Engelm.) led to a number of

studies on various aspects of the biology of this and

related root parasites (Musselman and Mann 1976). In

the course of these studies, we observed the extent and

nature of early root growth and evaluated the necessity of

light for survival.

MATERIALS AND METHODS

In order to determine plant development without the

influence of a host, waxed cartons, measuring 7 x 7 x 23

cm, were fiilled with a 5050 mixture (by volume) of sandy

loam topsoil and vermiculite. This mixture permitted easy

recovery of delicate roots. Thirty-six containers were

sown with about 10 senna seymeria seeds each in the

center of the container; after germination only one plant

was allowed to remain in each carton. Cartons were

watered regularly.

To determine if pine root segments affected root

orientation, 18 additional cartons were sown with senna

seymeria seeds placed in one corner. In nine, fresh segments of lateral pine roots were inserted into the growing

media from the bottom; in the other nine, the pieces were

inserted from the top. All pine roots were placed in the

opposite corner from the seeds and were replaced weekly with fresh pieces. They were taken from lateral roots of

2- and 3-year-old loblolly (P. taeda L) pine and measured

about 0.64 cm in diameter and 10 cm long.

All cartons were placed in a greenhouse with temperatures maintained at 26” to 30” C. Seeds failed to germinate in some containers; so the number of replicates was

not uniform among treatments. Ten, 20,30, and 40 days

after an individual seed germinated, stem development

was evaluated and cartons were carefully emptied for

observation of root orientation and measurement of

length.

For the light studies, seeds were sown in plastic pots

with a horticultural mix of one part peat to two parts

vermiculite and containing a l-month-old slash pine

seedling. After the senna seymeria plants reached about

2 cm, they were thinned to one per pot. A water-soluble

fertilizer (Peters’@ 20-19-18 NPK) was applied at a low

level every 2 weeks because no nutrients were available

in the media. The study was begun when the parasites

were 4 months old and had a mean height of 15.5 cm. The

plants were actively parasitizing the pine seedlings at this

time. Ten pots with both pine hosts and parasitic plants

were placed in a growth chamber a 12-hour light photoperiod. Another 10 were placed in a growth chamber with

complete darkness. The temperature of the growth

chambers was maintained at a constant 22’ C. The pots

Southern Forest Experiment Station/T-l 0210 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.

1
Figure 1-Seymeria roots 10 days after germination (Jeff). At 40 days (right), the long tap had two distinct laterals and

another just developing.

were watered on the third and seventh days using a green

safelight and the tests were ended after 12 days.

In a variation of the preceding test, a greenhouse test

was conducted where five pots had both pine and parasite receiving light and five pots had only the pine host

receiving light. Black plastic tubes were used to cover the

parasites. Tubes were about 6.4 cm in diameter and 46

cm long and were covered with aluminum foil to prevent

the black plastic from absorbing heat. The bottom of the

tube fit snugly against the soil. Plants were watered regularly.

RESULTS

All senna seymeria plants without host material remained in the cotyledon stage with only two small green

leaves appearing in the entire 40 days. Senna seymeria

root growth was rapid, considering the size of the seed,

which number about 22,000 per gram. Roots averaged

5.4,7.9,10.5,and 155cmlongat 10,20,30,and40days

after germination, respectively (fig. 1). There were no

lateral roots at 10 days, but in most cases laterals were

found at 20 days and thereafter. No haustoria were

observed on any of the roots, but root hairs and root caps

were present.

Regardless of the presence of a segment of pine root,

senna seymeria roots grew straight down. There was no

indication that the direction of root growth was influenced

by pine root segments. More sophisticated methods

could have been used to evaluate orientation of root

growth, but this method was chosen since it has been

observed numerous times that moist segments of pine

roots will serve for haustorial attachment, even several

months after they are severed’.

In both the growth chamber and greenhouse tests,

senna seymeria plants quickly died when they were

placed in darkness. After 4-7 days in the dark, mortality of

the parasites had started and those still living wilted.

Mortality was complete after 12 days. The rate of mortality

was about the same if host plants were in light or dark

environments. All senna seymeria plants given 12 hours

of light in the growth chamber appeared healthy and

made normal height growth. Pine hosts showed no obvious effect of continuous darkness over this 1Pday

period.

‘Mann, W. F., Jr. [n.d.] Data on file Southern For. Exp. Stn., Pineville,

La.

Stangle is Forestry Technician, Southern Forest Experiment Station, Forest Service-USDA, Pineville, Louisiana. Musselman is Associate Professor,

Department of Biological Sciences, Old Dominion University, Norfolk, Virginia.

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Previous observations on root growth in hemiparasites

of Scrophulariaceae are apparently limited to Oesau

(1973, 1975) on Melampyrum, Fitzgerald et al. (1975) on

Seymeria, and Musselman (1969) on Aureolaria. Our

results indicate that the primary root of senna seymeria is

well adapted for rapid growth into the root zones where

pine roots would be available for parasitism. Musselman

(1969) reported a seedling of Aureolaria grandiflora

[Benth. (Penn.)] surviving for 9 months without attachment to a host. Oesau (1973) grew Melampyrum arvense

[L. (Beitr.)] for about 4 months without a host and recorded a length of 47 cm when the plant died. Although

the data in these two cases are limited, it does indicate

that rapid and extended development of the primary root

may be an important adaptation for root parasites at the

seedling stage, allowing them to come in contact with

host roots.

In this study, severed segments of pine roots did not

affect the direction of growth of the parasite root. This

indicates that contact with host roots is random, similar to

the findings recorded by Oesau (1975) in a careful study

of root development in Melampyrum.

The biology of hemiparasites remains unclear. Our

limited data indicate that senna seymeria plants will not

survive without light, evidence that the plants are not

completely dependent on their hosts for food. They usually must form haustoria on roots in order to begin stem

development, however, other studies have shown that

plants without hosts will develop to maturity if high levels

of fertility are provided (Mann and Musselman 1981).

Sfriga asiatica (witchweed) is in the same family as

Seymeria and is a well-known pathogen of several grain

crops. Rogers and Nelson (1962) report growing a witchweed plant to maturity in total darkness while the host’

was maintained in light. Our work, involving vigorous,

growing plants, indicates that light is necessary for survival of senna seymeria. Witchweed and Seymeria are quite

different in their biology, however. Senna seymeria is

always green while witchweed germinates beneath the

soil and lives without light, being totally dependent on its

host for seedling development.

LITERATURE CITED

Fitzgerald, C. H., M. Reines, S. Terrell, and F! P Kormanik.

1975. Early root development and anatomical parasitehost relationships of black senna and slash pine.

Forest Sci. 21:239-242.

Mann, W. F, Jr., and L. J. Musselman.

1981. Autotrophic growth of southern root parasites.

Amer. Midl. Nat. (In press).

Musselman, L. J.

1969. Observations on the life history of Aureolaria

grandiflora and Aureolaria pedicularia (Scrophulariaceae). Amer. Midl. Nat. 82:307-311.

Musselman, L. J., and W. F. Mann, Jr.

1978. Root parasites of southern forests. U.S. Dep.

Agric. For. Serv. Gen. Tech. Bull. SO-20,76 p. South.

For. Exp. Stn., New Orleans, La.

Oesau, A.

1973. Keimung und wurzelwachstum von Melampyrurn arvense L. Beitr. Biol. Pflanzen 49:73-100.

Oesau, A.

1975. Untersuchungen zur Keimung und Entwicklung

des Wurzelsystems in der Gattung Melampyrum L.

(Scrophulariaceae). Beitr. Biol. Pflanzen 51:121-147.

Rogers, W. E., and R. R. Nelson.

1962. Penetration and nutrition of Striga asiatica. Phytopath. 52:1064-1070.

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*U.S. GOVERNMENT PRINTING OFFICE: 1981-771-081/6