Page 24 - Volume 4, Issue 1, January 2011

Anastasiadis

et al.

22

(14) and stored in 1 l flasks filled with tap wa-

ter at 4

o

C (approximately for 5-7 days) until

further use. For the trials with live infective

juveniles (IJ) and prior to the soil inocula-

tion, the nematodes were left for 30-60 min

at room temperature in order to recover. For

the trials with dead IJ, the nematodes were

heat-killed prior to soil inoculation on a heat

block at 70

o

C for 15 min.

Diallyl disulfide (purity 70%) was pur-

chased from Across Organics (New Jersey,

USA). Laboratory-based gas chromatogra-

phy analysis revealed two other main com-

ponents: diallyl sulfide (15%) and diallyl

trisulfide (12%).

Tomato seedlings (cv. ‘Belladona’) with

three pairs of leaves were transplanted in

250 cm

3

plastic transparent pots containing

commercial compost soil. After two days,

groups of five egg masses (about 2,000

eggs, as estimated after dissolving the egg

masses with sodium chloride) were added

to the pots. All EPN treatments were added

simultaneously with

Mj

at a rate of 7,000 live

S. carpocapsae

(Sc) or 7,000 heat-killed. Each

pot received 20 ml of 2 μl/ml diallyl disulfide

solution (Dd) in a single or a double appli-

cation, i.e. concurrent with

Mj

inoculation

(single application) or concurrent with and

one week after

Mj

inoculation (double appli-

cation). Control pots received 20 ml of dis-

tilled water.

The experiment consisted of eight treat-

ments (plus control) and each treatment

was replicated five times in a completely

randomized experimental design.

Experimental plants were incubated in a

growth chamber at 25

o

C. After 28 days, the

roots were submerged in water to gently

rinse away the soil. The roots were dried off

on tissue paper and their fresh weight was

measured. Subsequently, the roots were cut

into 1-2 cm pieces and females of

Mj

were

teased from the roots and counted at 17.5x

magnification. Statistical analysis was per-

formed with SAS software (SAS Institute,

Cary, NC) and mean separation was con-

ducted using the Tukey’s test (12).

Thenumber of female

Mj

counted in roots

treated with live or dead Sc and/or Dd was

significantly lower than that in the untreated

control (P<0.001). The greatest disparity was

observed when Dd was applied in a double

application (at 0 and 7 days post-

Mj

inocula-

tion) to soil previously treated with dead or

live Sc. No statistically significant (P<0.001)

differences were noted between the treat-

ments with live and dead Sc. However, in

both treatments, the number of

Mj

females

was reduced by 32% and 45%, respectively,

compared to the control. The total numbers

of

Mj

females counted in tomato roots treat-

ed with Dd in a single or a double applica-

tion, were significantly (P<0.001) lower than

those in the control. In treatments with dead

Sc + Dd, the number of

Mj

females that de-

veloped from egg masses in the Dd double

application was significantly (P<0.001) lower

than that in the single application. In treat-

ments with live Sc + Dd, the number of

Mj

females developed from egg masses in the

Dd double application was not significant-

ly (P<0.001) different to that of the single ap-

plication (Table 1). No statistically significant

differences were noted with regard to root

weight (P>0.05). The results of the present

study showed that both live and dead IJ of

Sc suppressed

Mj

on tomato plants, which is

in accordance with the findings of Lewis

et

al.

(9). In contrast to these results, Grewal

et

al.

(6) found no effect of live IJ, which may in-

dicate that these nematodes act by a slower

release of the intestinal bacterial agents in-

duced by their natural death. Bird and Bird

(3) also suggested that PPN suppression

may be due to a competition for habitat and

space. These factors may influence the ef-

fectiveness of live IJ, depending on the en-

vironmental conditions, the plant parasitic

and entomopathogenic nematode species,

the soil type and the host plant or the pres-

ence/absence of insect hosts. The results

of the present study are in agreement with

previous research on nematode suppres-

sion by garlic seeds and bulbs, garlic essen-

tial oil and garlic essential oil components (1,

6). Diallyl disulfide was more effective when

it was used in two applications, one concur-

rent with

Mj

inoculation and a second one

7 days later. It is likely that some eggs that