CONTROL OF SOIL-BORN PATHOGENS IN TOBACCO AND TOMATO
SEEDBEDS WITH ALTERNATIVE TO METHYL BROMIDE METHODS
Preliminary note
K.Tzavella-Klonari
Lab. of Plant Pathology, School of Agriculture, Aristotle University of Thessaloniki, GR
Abstract The use of methyl bromide in soil desinfestation is a common practice in tobacco and tomato seedbeds, as well as in tomato crops grown in greenhouses of Northern Greece, because of its effectiveness against Rhizoctonia solani, Sclerotinia sclerotiorum and Pythium sp. soil-born pathogens causing damping-off diseases.
In a research program for the evaluation of alternative to methyl bromide methods, two chemicals and one biological agent were tested. The experimental field seedbeds established from July to November 1999,were artificially inoculated with Rhizoctonia solani and Sclerotinia sclerotiorum .The four treatments examined were methyl bromide (69gr/m*), metham sodium (200 ml/m*), quintozene+etridiazole as Terrachlor Super-X (2-3 applications with 0,3 gr/lit of water /m*), and Trichoderma koningii (incorporated in the soil at 15 gr solid six days old culture /1,25 kgr of soil. There were six replications for each treatment in a randomized complete block design.
The efficacy of the treatments was evaluated at 10 days intervals by counting healthy plants good for transplanting. The experiment was repeated two times. At the same time, all treatments were also examined on pot-seedbeds placed in growth chamber at 25 C and 16 /8 hours light /darkness.
The results obtained show that methyl bromide gave the highest number of healthy plants, followed by that of metham sodium. Terrachlor applications provided good control of the diseases studied only for a short time after treatment. The biological agent gave the lowest number of healthy plants compared with those of the other treatments, but these plants had better growth.
Introduction Methyl bromide is used for the control of soil-born pathogens in sedbeds as well as in greenhouses of Northern Greece. The fungi Rhizoctonia solani, Sclerotinia sclerotiorum, and species of the genus Pythium are the most important pathogens that cause damping-off diseases in tobacco seed-beds of the area as it was cited in a research survey carried out in 21 seedbeds in Langada area in the villages Profitis, Polidendri, Chrisafgi, Scholari, and Nymphopetra (unpublished data), during the spring 1997 and spring 1998. Besides, the same fungi are the causes of damping-off diseases in tomato seedbeds, and also the causes of root and collar rots of seedlings in the first stages of their development after the transplantation in the greenhouse.
This work is a part of a research program funded by the Greek Ministry of Agriculture in order to evaluate alternatives to methyl bromide methods for the control of rootnot nematodes, soil-born pathogens and weeds.
The cases of the fungi Rhizoctonia solani and Sclerotinia sclerotiorum were studied separately in tobacco and tomato seedbeds, artificially inoculated and treated with three chemicals and a biological agent.
MATERIALS AND METHODS
Experimental seedbeds in the field. Seedbeds in special plastic boxes 32,5X43,5cm were prepared in the field. A soil mixture made of a "Grass land" peat pH 5,2-6,3 and perlite at a rate 4/1 was used.
Inoculum. In the case of Rhizoctonia solani, cultures of the fungus were prepared in a medium made of peat, cornmeal and water 1/1/1.Petri dishes containing 30gr. of this medium were inoculated and kept for 10days at 21 °C. One petri dish of this culture was added to 1,25 kgr of the soil.
In the case of Sclerotinia sclerotiorum, cultures of the fungus were prepared on carrot slices 40gr in flasks (Erlenmeyer) and kept for 10 days at 21 °C. The contain of each flask was blended with 200ml of water and it was poured on the soil (one flask for 1,25 kgr of the soil mixture).
The seedbeds after been inoculated were irrigated for 11days in order to allow the establishment of the fungi.
Treatments
1.Methyl bromide used for soil desinfection.
2.Metham sodium used for soil desinfection.
3.Soil irrigation with the fungicides quintozene-etridiazole (Terrachlor Super-X).
4.Application of the biological agent Trichoderma koningii
5.Control ( soil inoculated for each case without being treated rather by chemical or biological treatment).
1. Methyl bromide desinfection
Soil mixture infested by each fungi, as it was descriped above, was covered by polyethylene trasparent sheets 18μ thick (french type) and was fumigated by methyl bromide 68g/m2
The soil remained covered for three days. The seeds were sown 18 days after the plastic removal. In the mean while the soil was stired and irrigated.
2. Metham sodium (Vapan) desinfection
Soil mixture was irrigated with 200ml of metham sodium /1lt water/m2 and then it was covered for three days. The sowing was done 18 days later, in the mean while the soil was irrigated.
3. Soil irrigation by Terrachlor Super-X.
a. The soil was irrigated with 0,3g/1lt water/m2 at the same day of the removal of the cover in the treatments 1 and 2.
b. The soil irrigated again with the same rate of the fungicide just after the sowing.
c. A third application was done 10 days after the sowing.
4.Application of the biological agent
Cultures of the fungus Trichoderma koningii grown on wheat brans (15gr/50ml water)
for 6 days at 21 C in darkness were blended and added to the soil mixture 15gr /1,25kgr
at the sowing day.
5. Control
Seedbeds artificially inoculated in the above mentioned way were sown with no chemical or biological treatment.
Sowing
Tobacco seedbeds Three replications of every treatment were prepared. Each replication was seeded with 0,3 gr of tobacco seed (local variety Basmas) giving rise to 3000 plants (appoximately) per replication.
Tomato seedbeds Three replications of every treatment were prepared. Each replication was seeded with 280 seeds of tomato variety Ace 55 (8 rows X 35 plants).
Seedbeds in growth chamber
Seedbeds prepared in plastic boxes 21X16cm according to the same treatments and replications of the seedbeds in the field, and they were kept in growth chamber at 25 °C and 16 hours light / 8 hours darkness.
Taking samples
The first samples were taken 20 days after the sowing, and we continue to take samples every 10 days. Plants were examined macroscopicaly for damping-off symptoms. Plants with obvious symptoms were separated, while plants suspected for disease were examined in microscopical observation. Treatments evaluation was done by counting the healthy plants good enough to be transplanted. In tobacco seedbed each sample consisted of 1000 plants from each replication (3 replications per treatment), while for tomato seedbeds 70 (2 rowsX35) plants of each replication ( 3 replications per treatment) were sampled.
All the experiments were repeated twice from June 23, to November 16, the year 1999 and the third repetition is still gowing on.
RESULTS
Some of the results, we have got till now, are shown in Tables 1, 2, for tomato seedbeds in the field. Results of tomato seedlings grown in the growth chamber are in Table 3. Tobacco seedlings yielded from tobacco seedbeds in the field are shown in the Tables 4,and 5. There is not statistical evaluation of the results because there are still repetitions of experiments in progress.
Table 1 Tomato seedbeds in the open fieldInoculum: Rhizoctonia solani
Plant yield from 3 repeats
Treatments / First
Sampling
27 - 10 - 99 / Second
Sampling
6 – 11 - 99 / Third
Sampling
16 - 11- 99 / In total
Methyl Bromide /
Expected: 210
Counted: 201Healthy: 196
Diseased: 5 / 210
202
200
2 / 210
184
164
20 / 560
Metham Sodium
(Vapam) / 210
191
187
4 / 210
192
192
0 / 210
178
161
17 / 540
Terrachlor
Super - X / 210
151
92
59 / 210
158
75
83 / 210
139
25
114 / 192
Trichoderma koningii / 210
127
73
52 / 210
141
66
75 / 210
134
52
82 / 191
Control / 210
153
84
69 / 210
147
42
105 / 210
118
29
89 / 155
* Sowing: 2 - 10 – 99
** Each sample consists of 2 rows x 35 plants x 3 repeats / seedbed = 210 plants
Table 2 Tomato seedbeds in the open field
Inoculum: Sclerotinia sclerotiorum
Healthy plants at the second sampling 5 - 11 - 99
Treatments / Repeats / Intotal
First / Second / Third
Methyl Bromide / 1st: row 33/35
8th: row 33/35 / 1st: 35/35
7th: 34/35 / 1st: 32/35
8th: 29/35 / 196
Metham Sodium
(Vapam) / 4th: 32/35
5th: 35/35 / 1st: 33/35
5th: 35/35 / 3rd: 33/35
8th: 33/35 / 201
Terrachlor
Super - X / 4th: 35/35
6th: 35/35 / 3rd: 32/35
5th: 29/35 / 3rd: 32/35
6th: 29/35 / 192
Trichoderma koningii / 2nd: 32/35
5th: 34/35 / 3rd: 35/35
7th: 32/35 / 1st: 33/35
6th: 34/35 / 200
Control / 3rd: 28/35
5th: 31/35 / 2nd: 30/35
5th: 34/35 / 2rd: 30/35
7th: 34/35 / 187
* Sowing: 1 - 10 – 99
** Plants from 2 rows of each repeat/seedbed were taking
Table. 3 * Tomato seedbeds in plant growth chamber
Inoculum: Rhizoctonia solani
Treatments / Expected* / Germinated / Healthy / Diseased
Methyl Bromide / 160* / 146 / 145 / 1
Metham Sodium (Vapam) / 160 / 155 / 155 / 0
Terrachlor Super – X / 160 / 125 / 106 / 19
Trichoderma koningii
/ 160 / 143 / 121 / 23Control / 160 / 152 / 113 / 39
*Sowing 19 - 10 - 99, taking of samples 20 days after sowing
** 160 plants from two repeats (80 x 2)
Table. 4 * Tobacco seedbeds in plant growth chamber
Inoculum: Rhizoctonia solani
Treatments / Expected* / Germinated / Healthy / Diseased
Methyl Bromide / 160** / 146 / 145 / 1
Metham
Sodium (Vapam) / 160 / 155 / 155 / 0
Terrachlor Super - X / 160 / 125 / 106 / 19
Trichoderma koningii
/ 160 / 143 / 121 / 23Control / 160 / 152 / 113 / 39
*Sowing 19 - 10 - 99, taking of samples 20 days after sowing
** 160 plants from two repeats (80 x 2)
Table 4. Tobacco seedbeds in the open field
Inoculum: Rhizoctonia solani
Plants healthy at the first sampling 20 -10 - 99
Teatments / Intotal 3 repeats
Methyl Bromide / 2486/3000
Metham Sodium (Vapam) / 2307/3000
Terrachlor Super - X / 1689/3000
Trichoderma koningii / 2240/3000
Control / 1859/3000
*Sowing: 30 -9- 99
** Plants from the 2/6 each replication area were taking as sampls (randomised)
Table. 5 *Tobacco seedbeds in the open field
Inoculum: Sclerotinia sclerotiorum
Healthy plants at first sampling 23-10-99
Treatments / 3 repeats in total
Methyl Bromide / 2486/3000**
Metham Sodium (Vapam) / 2307/3000
Terrachlor Super - X / 1689/3000
Trichoderma koningii / 2240/3000
Control / 1859/3000
* Sowing: 30 - 9 - 99
** Plants from the 2/6 each replication area were taking as samples (randomized)