Journal of the Rubber Research Institute of Sri Lanka, (1996) 77, 54-65 
WEAKENING EFFECT OF 2-FURALDEHYDE ON RIGIDOPORUS 
LIGNOSUS THE CAUSE OF WHITE ROOT DISEASE OF RUBBER 
K E Jayasuriya, J W Deacon 1 and T H P S Fernando 
(Accepted 10 September 1995) 
ABSTRACT 
Furfuraldehyde is recognized as a potential fumigant which has the ability to 
weaken Rigidoporus lignosus in artificially or naturally infected rubber root inocula. 
Addition of sulphur to soil at 100 g per 75 kg of soil, inactivated or prevented the 
formation of R. lignosus mycelial cords from artificially or naturally infected inocula. 
Drenching 2.4% aqueous solution of furfuraldehyde in to soil (1 liter/75 kg) where 
R. lignosus inocula were buried, caused weakening or inactivation of R. lignosus in 
artificially or naturally infected inocula. However, combination of two treatments 
had no synergistic effect on both types of R. lignosus inocula in soil. 
Key words: anatagonism, furfuraldehyde, mycelial cords, Rigidoporus lignosus, 
rubber 
INTRODUCTION 
White root disease caused by Rigidoporus lignosus (Kl.) Imaz. is the most 
destructive root disease in rubber plantations. Presently around 5-10% of the 
cultivated lands in Sri Lanka are affected and under bare patches due to white root 
disease (Jayasinghe et al., 1995). The pathogen spreads as mycelial strands on 
infected roots or directly as cords through soil. In Sri Lanka, the production of 
rubber is marginally economic (Pieris, 1966) so the focus of work in this 
investigation was to explore noval methods that might be as cheap as possible for 
control of the damaging white root disease. It was anticipated that such work might 
lead to exploitation of biocontrol agents either alone or in conjunction with soil 
chemical treatments to enhance the degree of control. 
1
 Institute of Cell & Molecular Biology, The University of Edinburgh, Daniel 
Rutherford Building, King's Buildings, Mayfield Road, Edinburgh EH9 3JH, 
UK. 
54 
K E Jayasuriya et al. 
Many attempts were made towards the control of R. lignosus, in which 
successful results were obtained using (a) some chemicals of the triazole group (Tran, 
1985; Tan, 1990; Ng & Yap, 1990; Chan et al., 1991; Gohet et al., 1991; Lam & 
Chin, 1993), (b) 2% Pentachlorophenol in bituminous base (Jayasinghe etal, 1995) 
(c) biological control agents (Tong-Kwee & Keng,1990; Jayasuriya & Deacon, 1995) 
(d) fumigants such as furfuraldehyde (Jayasuriya & Deacon, 1996). In studies of 
Jayasuriya & Deacon (1996), furfuraldehyde completely stopped R. lignosus mycelial 
growth on Malt extract agar (MEA) supplemented with 0.3% furfuraldehyde. 
Furthermore, 3 hour exposure to 0.2 ml furfuraldehyde caused 80% inhibition of/?. 
lignosus mycelial cord growth rate from established inocula. When applied to soil 
for fumigation, /?. lignosus mycelial cord growth was suppressed and the activities 
of resident soil fungi were enhanced causing reduction of R. lignosus mycelial cord 
growth through soil. 
In most studies the results were obtained in vitro conditions. However, 
furfuraldehyde appeared to be a potential chemical for effective control of R. lignosus 
as it reduced the growth of R. lignosus on culture media as well as in soil (Jayasuriya 
& Deacon, 1996). Therefore, experiments reported in this paper were focused on 
drenching furfuraldehyde to soil and exposing R. lignosus inocula to furfuraldehyde 
or its vapor to investigate its fumigative effect on R. lignosus i n s u l a in soil. To 
achieve our targets three rubber growing sites in three agro-climatic regions were 
selected for the investigation: site 1- Rubber Research Institute premises experimental 
fields, site 2- Matara, site 3- Kegalle. The work reported in this paper was carried 
out both in Edinburgh, UK and Sri Lanka. 
MATERIALS AND METHODS 
Furfuraldehyde (Sigma Co. USA) was used as a 1% or 2.4% dilution to 
drench into soil. R. lignosus (isolate RT) isolated from infected roots collected from 
Ratnapura, a rubber growing area of the wet zone of Sri Lanka, was used throughout 
the study. The fungus was stored in 2 cm3 sterilized elm wood blocks. 
Preparation of R. lignosus inocula from rubber tree roots 
Freshly cut 15 mm thick rubber tree roots were washed thoroughly under 
running tap water. Soil particles adhering to the surface were removed. Then 8 cm 
lengths were cut, soaked in distilled water for 1 hour, and autoclaved for 45 minutes 
at 121 °C in 500 ml glass beakers covered with tin foil. R. lignosus was grown on 
55 
Weakening effect of furfuraldehyde 
MEA in 9 cm Petri dishes unti l the c o l o n y m a r g i n reached the edge. About 6 c m 2 
b l o c k s of MEA c o l o n i z e d b y R. lignosus were cut f r o m the margins o f the plates and 
transferred asept ical ly to the autoclaved roots in the beakers. Then the foi l o n the 
beakers was sealed wi th m a s k i n g tape and they were incubated for 8 weeks. 
Effects of sulphur and furfuraldehyde applied to soil on R. lignosus inocula. 
Rubber root pieces (1-1.5 c m thick and 8 c m long) that were natural ly or 
ar t i f ic ia l ly infested wi th R. lignosus, were used as inocu la . Naturally infected inocula 
were cut f r o m large diseased trees o n the day o f the exper iment o r the prev ious d a y . 
An exper imental b l o c k in site 1 (site 1 - Rubber Research Institute premises 
exper imenta l f ie ld) was prepared 3 days before the establishment o f the exper iment . 
A 2 m w i d e strip o f land was cleared o f g round cover and leve l led . Ten 
bucket -shaped containers (made o f PVC) w h i c h ho ld 75 kg o f wet soi l (30% w/w) 
were sunk into the so i l up to g r o u n d level and f i l led with the same s o i l . The soi l in 
these containers represented "disturbed s o i l " . The containers had 2 holes dr i l l ed at 
the bot toms for dra inage. The so i l was a l lowed to settle for 4 days . Two types o f 
i n o c u l a were then bur ied in 5 r andomly selected containers about 15 c m b e l o w the 
sur face . Each container received 9 pieces o f inocu la w h i c h served as 9 repl icates. At 
other posi t ions in the experimental site, equivalent inocula were bur ied at 25 c m 
depth by d i g g i n g holes o f 15 c m diameter. These sites represented "undis turbed" 
s o i l . The f o l l o w i n g treatments were used: 
(1) natural inocu la in undisturbed soi l (NIUS), (2) art i f icial inocu la in undisturbed soi l 
(AIUS), (3) natural inocu la in d isturbed soi l (NIDS), (4) art i f icial inocu la in d isturbed 
soi l (AIDS), (5) natural inocu la in d isturbed soi l wi th added su lphur , 100 g/75 k g soi l 
(NIDS+S), (6) art i f icial inocu la inVl is turbed soi l wi th added su lphur , 100 g/75 kg 
soi l (AIDS+S), (7) natural inocu la in d isturbed soi l with added su lphur , 100 g/75 k g 
so i l and 1 l itre o f 1% fur fura ldehyde (NIDS + S + Fl), (8) art i f icial inocu la in 
d is turbed soi l wi th added su lphur , 100 g/75 kg soi l + 1 l itre o f 1 % fur fura ldehyde 
(AIDS + S+ Fl), (9) natural inocu la in d isturbed soi l wi th 1 l itre o f 1% 
fu r fura ldehyde (NIDS + F1), (10) art i f icial inocula in d isturbed soi l with 1 litre o f 1 % 
fur fura ldehyde (AIDS+ F1), (11) natural inocu la in d isturbed soi l with 1 litre o f 2.4% 
fu r fura ldehyde (NIDS+F2.4),"(12) art i f icial inocula in d isturbed soi l wi th 1 litre o f 
2.4% fu r fura ldehyde (AIDS+F2.4). ' 
56 
K E Jayasuriya et al. 
In treatments where sulphur was used, it was sprinkled on the soil at 100 g/75 
kg soil in each container, and thoroughly mixed with the soil before the inocula were 
added. In treatments where furfuraldehyde was used, it was drenched into soil as 1 
litre of 1% or 2.4% aqueous solutions per container, after burial of inocula. 
Theoretically, these two concentrations may provide furfuraldehyde concentration in 
the soil water sblution of approximately 0.08% or 0.2% respectively (soil moisture 
content was 30%, w/w). 
After 5 weeks, root pieces were retrieved for examination and for isolation 
of fungi that had invaded the inocula. By visual observations, records were made on 
the presence of mycelial cords on the inocula, number of mycelial cords formed and 
their length, status of epiphytic mycelia on the inocula and degree of decay of the 
root pieces. Soon after root pieces were brought to the laboratory, and cleaned 
carefully without damaging the existing mycelia on them. Then, three lengths of 
mycelial cords (approximately 5 mm long) were cut from the surface of each 
inoculum, surface-sterilized with 70% ethanol in sterilized distilled water and 
transferred to MEA supplemented with streptomycin and chlortetracycline (30 iig ml"1 
of each), to see if R. lignosus could grow from them. Using a cork borer, (9 mm in 
diameter) plugs were removed from bark and wood of each inoculum piece and 
transferred on to PDA supplemented with antibiotics at the above rate. Plates were 
then incubated for 2-3 days. Fungal colonies growing out were transferred onto fresh 
PDA for purification. Each fungus isolated was later opposed to R. lignosus on dual 
membered plates as described by Dennis & Webster'(1971) to assess its antagonistic 
properties. All fungi that suppressed R. lignosus were stored and maintained on 
PDA. 
Survival of weakened R. lignosus inocula in different soils in different 
agro-climatic zones of Sri Lanka 
Artificially and naturally infested root inocula were prepared as described 
earlier. Two experimental plots (1.5 m x 5 m) were selected at each of the sites, 
Kegalle (site 3) and Matara (site 2), on land where rubber had grown for a 
considerable period. White root disease incidence is negligible in site 2 compared to 
site 3. Holes', 20 cm deep and 15 cm diameter, were dug at a distance of 50 cm from 
each other within and between rows. Soil from each hole was bulked and pH was 
measured. Both types of inocula were fumigated in sealed glass desiccators by 
placing a cotton wool plug soaked with 0.2 ml furfuraldehyde on the base of the 
desiccator without touching the inocula. After two hours of exposure, the inocula 
were placed in the holes. Two pieces of inocula were placed in each hole on a 
randomized design. One inoculum piece was considered as one replicate and six 
replicates were employed for each treatment. Inocula were buried for 5 weeks about 
57 
Weakening effect of furfuraldehyde 
20 cm below the ground surface. This level was selected for burial, as Pearce & 
Malajczuk (1990) indicated that significantly (P< 0.001) more rhizomorphs (mycelial 
cords) were produced by Armillaria luteobubalina at 12 cm depth than at 28 cm depth 
in soil. Then the holes were filled with same soil and the area was demarcated with 
wooden pegs. The experiment consisted of the following treatments: 
(1) Healthy freshly cut root piece.(control), (2) Naturally infested inoculum (NI), (3) 
Artificially infested inoculum (Al). (4) Naturally infested inoculum fumigated with 
0.2 ml furfuraldehyde for 2 hours (NI-FUM), (5) Artificially infested inoculum 
fumigated with 0.2 ml furfuraldehyde for 2 hours (AI-FUM). 
After 5 weeks, the inocula were retrieved. Then the inocula were cleaned of 
adhered soil particles. Visual observations were made on the degree of decay, 
number of mycelial cords formed and their lengths, and the presence or absence of 
epiphytic mycelia of R. lignosus on the inocula. Inocula were then brought to the 
laboratory in sealed polyethylene bags. Then fungi were isolated from bark and 
wood as described earlier. All the cultures of potential antagonists were preserved 
and maintained on PDA. 
Isolation of fungi antagonistic against R. lignosus from buried inocula in soil 
The isolation of antagonistic fungi that could possibly colonize R. lignosus 
inocula was carried out as a part of the experiments. Isolation was carried out from 
all types of inocula buried under soil treated differently (i.e. soil acidified with 
sulphur, from inocula weakened and buried in different soils in different agro-climatic 
zones of Sri Lanka). Bark and woody plugs (0.5 cm in diameter) were punched from 
buried inocula and transferred onto PDA supplemented with antibiotics (streptomycin 
30 jug ml"1 and chlortetracycline 30 /xg ml"1). The mycelia growing out from the 
plugs were transferred onto fresh PDA plates and opposed against R. lignosus on dual 
membered plates as described by Dennis & Webster (1971) to assess the antagonistic 
properties. 
RESULTS 
The separate and combined effects of addition of furfuraldehyde and sulphur to 
soil on R. lignosus inocula 
The experiment was designed to study the effects of furfuraldehyde drenched 
into soil and the addition of sulphur to soil, on the survival of R. lignosus in its food 
base. Sulphur was added to soil at 100 g per pot containing 75 kg of soil (30% water 
58 
K E Jayasuriya et al. 
capacity) and furfuraldehyde was drenched as 1% and 2.4% solutions to soil after 
burial of inocula. Inocula buried in the pots after soil treatment were excavated and 
examined after 5 weeks. . •  ., 
In all the treatments where sulphur was used, no mycelial cords were formed 
from the inocula and the pre-existing cords on the inoculum surfaces seemed to be 
non-viable (Table 1). In all the treatments involving artificial inocula, the 
pre-existing mycelial cords on the inocula were weakened or inactivated during 
burial, whereas at least in some treatments involving naturally infested inocula the 
pre-existing cords on the inocula were able to produce viable mycelia on agar after 
burial. Apart from the sulphur treatment, the only other treatment that seemed to kill 
R. lignosus in the inocula (and prevent its growth into soil as mycelial cords) was the 
treatment (11) involving naturally infested inocula under soil drenched with 2.4% 
furfuraldehyde. Even though Trichoderma was not added as an experimental 
treatment, Trichoderma spp. most commonly were isolated from buried inocula. 
Effect of furfuraldehyde vapour on naturally and artificially infested R. lignosus 
inocula in soils of different sites of Sri Lanka 
The incidence of white root disease of Hevea brasiliensis is- comparatively 
higher in some regions of Sri Lanka, such as Kalutara, Ratnapura and Kegalle, than 
in others such as Galle and Matara. This variation may be due to soil or 
agro-climatic factors such as precipitation of particular regions or due to different 
levels of antagonist in the soil microflora. This experiment was designed to 
investigate the mycelial cord formation from weakened inocula buried in different 
soils in Sri Lanka. Inocula were exposed to 0.2 ml of furfuraldehyde for 2 hours in 
air-tight glass containers (12 pieces of inocula were exposed to 0.2 ml of 
furfuraldehyde). Then the inocula were examined and analyzed after 5 weeks. 
Subsequently, antagonistic fungi that had been invaded on to R. lignosus were also 
isolated and tested on dual culture plates as described by Dennis & Webster (1971) 
for their in vitro antagonism against R. lignosus. 
As shown in Table 2, new mycelial cords had formed from all types of 
inoculum in the two soils tested, but in the soils from site 3 (Kegalle) there were 
generally fewer new cords formed from fumigated inocula than in the soils from site 
2 (Matara). However, as shown in Table 3, only Trichoderma spp. were isolated 
from the inocula buried in site 2 whereas different fungi including Aspergillus niger, 
Trichoderma sp. and unknown fungi were isolated from inocula buried in site 3.-Pre­
existing cords of inocula buried in site 2 were generally killed or weakened whereas 
those inocula buried in site 3 were viable. 
59 
Weakening effect of furfuraldehyde 
Table 1. Effect of sulphur and furfuraldehyde in soil on inocula o/R. lignosus 
Treatments* Degree of Status of Number 
decay of mycelial of 
inocula cords on the mycelial 
inocula** cords 
formed*** 
1. NIUS fresh active 1-3 
2. AIUS 50% weakened 1-3 
3. NIDS 50% active 4-6 
4. AIDS 50% weakened 1-3 
5. NIDS + Sulphur fresh inactive none 
6. AIDS + Sulphur 50% inactive none 
7. NIDS + Sulphur+1% fresh inactive none 
Furfuraldehyde 
8. AIDS + Sulphur+1% 50% inactive none 
Furfuraldehyde 
9. NIDS + 1 % Furfuraldehyde fresh active 1-3 
10. AIDS + 2.4% Furfuraldehyde fresh weakened 1-3 
11. NIDS + 2.4% Furfuraldehyde 50% inactive none 
12. AIDS + 2.4% Furfuraldehyde 50% inactive 1-3 
* NI= natural (root) inoculum; AI= artificially colonized inoculum; DS= disturbed 
soil; S= sulphur addition; furfuraldehyde = drenched to soil; US= undisturbed soil; 
DS= disturbed soil,**active, inactive or weakened: when mycelial cord fragments 
were surface sterilized and transferred to MEA, active cords produced active mycelia 
on agar, weakened cords produced active mycelia from less than 50% of the 
fragments, inactive cords did not produced active mycelia at all, ****number of cords 
formed from the edges of inocula. 
60 
K E Jayasuriya et al. 
Inoculum type* Degree of Status of mycelial cords No. of mycelial 
decay** on. surfaces of cords formed from 
• inoculum*** each inoculum+ 
Site 2 - Matara 
control (fresh root) 
NI- unfumigated 
NI- fumigated 
Al- fumigated 
Al- fumigated 
50% 
Al-unfumigated >75% 
50% 
50% 
Site 3 - Kegalle 
control (fresh root) fresh 
NI- unfumigated fresh 
Al- unfumigated 50% 
NI- fumigated 50% 
50% 
Pre-existing cords not 1-3 
viable 
Pre-existing cords not 2-4 
viable 
Pre-existing cords not 2-3 
viable 
Pre-existing cords not 2-3 
viable 
Pre-existing cords 1-3 
viable, new cords 
formed 
Pre-existing cords viable 4-6 
Pre-existing cords 1-3 
viable, new cords 
formed 
Pre-existing cords not 
viable 
1-2 or none 
* NI= naturally infested rubber tree root inocula; AI= artificially infested rubber 
tree root inocula, **Degree of decay was observed visually by examining the status 
of bark and the wood, *** pre-existing cords were visually identified as they were 
discoloured and the newly formed once were clearly distinguishable as they were 
white coloured, + number of mycelial cords formed from edges of each inoculum 
was counted. 
61 
Table 2. Effect of fumigation of rubber tree root inocula of R. lignosus with 
furfuraldehyde before burial in soil in two agro-climatic regions of 
Sri Lanka. 
Weakening effect of furfuraldehyde 
DISCUSSION 
The results of the experiments have showed that furfuraldehyde has a lethal 
or sub-lethal effect on R. lignosus in soil. A concentration of 0.1% in media was 
adequate for 50% inhibition of R. lignosus (Jayasuriya & Deacon, 1996). 
Furthermore, R. lignosus on culture media was exposed to furfuraldehyde vapour, the 
lethal effect of this volatile chemical was confirmed: growth of R. lignosus was 
reduced 80% by 3 hour exposure to the chemical, at concentrations that would be 
achievable by drenching the chemical around the collar of an infested tree. However, 
the effect of furfuraldehyde in field conditions need further study. For example, it 
is not known whether the chemical could penetrate into the tissues of infected plants 
or into plant residues to weaken the pathogen and enhance its susceptibility to 
biocontrol [A similar study was carried out by Lim et al. (1990), using fungicides of 
the triazole group by adding them to soils and assessing their persistence in soil and 
their vapour phase effect on R. lignosus growth. Tridemorph was found to be the 
most persistent, maintaining a level of inhibition of 60-70% at 100 ug a.i. kg"1 soil 
and 77-90% at 200 /xg a.i. kg"1 soil]. Even partial weakening of surviving inoculum 
of R. lignosus by furfuraldehyde could be beneficial if the chemical also enables 
antagonistic fungi such as Trichoderma to grow and antagonize, the residual inoculum 
of R. lignosus. Such an alteration of the soil microflora by furfuraldehyde was 
reported by Canullo et al. (1992). 
Despite the substantial degree of control of mycelial cord growth by some soil 
treatments with Trichoderma, bran or furfuraldehyde (Jayasuriya & Deacon, 1996), 
the results of one comparison of sulphur with furfuraldehyde in soil (Table 1) showed 
clearly that sulphur treatment was highly effective in suppressing mycelial cord 
growth by R. lignosus, presumably due to its marked effect in lowering the soil pH. 
This experiment was done in field conditions and using in some treatments, natural 
inocula (infected root materials) of the pathogen. Because of the completely 
suppressive effect of sulphur alone, it was impossible to see if sulphur combined with 
a furfuraldehyde treatment would enhance the degree of control, but this possibility 
might be further explored, especially with larger pieces of host residue as inoculum 
units. 
In a separate experiment in which R. lignosus inocula were buried in different 
sites, it was noted that all the epiphytic mycelial cords were inactive after burial for 
5 weeks in site 2 (Matara). It was also important to note that only Trichoderma spp. 
could be isolated from the bark surfaces of buried inocula. However, new mycelial 
strands were formed from buried inocula in both sites. 
62 
K E Jayasuriya et al. 
63 
From the results obtained herein, it may be difficult to predict that drenching 
2.4% furfuraldehyde may totally kill the pathogen on buried inocula as it formed 
mycelial cords through soil. However, according to Table 1, it seems that the 
pathogen on the surface was weakened or killed. Therefore, it may be benifitial to 
supplement an antagonist to prevent forming mycelial cords. Apart from this, 
sulphur seemed to be highly effective on reducing and killing the mycelial cords. 
Results from the Table 2 showed that all pre-existing mycelial cords were 
killed on inocula buried in site 2 which can presumably be due to the fact that 
weakened mycelia were more sensitive for an attack by antagonistic organisms in soil 
microflora. This can be proved by the fact that, from all the inocula buried in site 
2, only Trichoderma spp. such as T. harzianum and T. koningii were isolated whereas 
from inocula buried in site 3, different fungi were isolated. As Jayasuriya & Deacon 
(1996) reported in their results obtained in soil studies, proliferation of Trichoderma 
in soil may be suppressed by other competitive soil fungi. This was demonstrated 
well in treatments in which soil was fumigated with furfuraldehyde, where T. 
harzianum (strain TV 12b) sporulated abundantly. 
CONCLUSIONS 
The results obtained from the experiments reported here indicate that 
furfuraldehyde has a potential to control R. lignosus in vitro. Sulphur amendments 
to soil can cause detrimental effects on formation of R. lignosus mycelial cords 
presumably by altering the soil microflora in favour of acidophylic fungi such as 
Trichoderma spp. As there is no additive effect of furfuraldehyde and sulphur in soil, 
sulphur may be effective on reducing the mycelial cord growth by R. lignosus. It 
may be possible to suggest that furfuraldehyde can be used as a fumigant to weaken 
the R. lignosus pathogen and consequently amend an antagonistic organism such as 
Trichoderma sp. for a complete control.. 
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