The potential of sodium silicate in suppressing root pathogens and managing stalk-rot complex of maize

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Potential of sodium silicate in suppressing root pathogens

and managing stalk-rot complex of maize

By

El-Said M.El-Shabrawy, Ehab M.Taha and Elhamy M.El-Assiuty

Plant Pathology Research Institute, A.R.C., Giza

Abstract:

The utility of applying sodium silicate as a compound friendly with the environment, in managing stalk-rot complex of maize was investigated. Significant retardation of the linear growth of the target pathogens was happened in Si amended-PDA. Using as seed coating, seed soaking or soil treatment, application of Na silicate could significantly control the disease in infested-potted soil and field trials in sick plots.

Introduction:

Silicon (Si) is the second most abundant element after oxygen in soil. The hypothesized roles of silicon in plants include the positive effect on reproduction, lessening of metal toxicity, providing structural rigidity and increasing resistance to fungal diseases such as root-rots (Bẻlanger et al., 1995). Potentiality of soluble silicon in controlling fungal diseases was reported in some field and horticulture crops (Qin and Tian, 2005; Menzies et al., 1992; Bẻlanger et al., 2003). The mechanisms responsible for the protection of plants from diseases by silicon are not well understood. It may acts by eliciting biochemical defense reactions, including lignin, phenolic compounds, and pathogenesis-related proteins in infected plants as reported by Cherif et al.(1994) and Epstein (1999). Stalk-rot complex of maize is the most important soil-borne disease of maize. Several pathogens (fungal and bacterial) are involved in this complex disease. Cephalosporium maydis (the cause of late-wilt) is considered the first invader in the field that opens avenues for other pathogens to enter the infected plant roots. In addition to the late-wilt fungus, Fusarium verticillioides, Sclerotium rolfsii and Rhizoctonia solani are the most common pathogens that could be recovered from naturally infected maize stalks. The objectives of the current investigation was to assess the inhibiting effect of Na silicate on these maize-root pathogens in vitro and study the possibility of its using in managing the stalk-rot complex disease of maize in vivo.

Material and Methods

In vitro bioassay of sodium silicate against the target pathogens:

Sodium metasilicate monohydrate Na2SiO3.9H2O (Fine chem.) was used in the current study. It was added to autoclaved PDA to give the required concentrations. Petri dishes (7 cm diam.) were inoculated at the center with discs (0.8 cm diam.) from 4-day old culture of each of the maize root pathogens, namely Cephalosporium maydis, Rhizoctonia solani, Fusarium verticillioides and Sclerotium rolfsii. Plates were incubated at 280 C for 4 days. Four replicates were used and silicon free plates acted as control. After the elapse of the incubating period, diameters of the fungal radial growths were measured and percentage of reduction in the fungal colony diameters was calculated.

In vivo studies:

In greenhouse, study was done to assess the efficiency of sodium silicate against late-wilt, the most important and serious disease of maize under artificial infestation. Autoclaved sorghum grains in glass bottles were inoculated with fresh inocula of C.maydis, the late-wilt fungus, and incubated at 280 C for one month. After the elapse of the incubation period, potted soil was infested with the grown pathogen at the rate of 2.5 % (w/w) and moistened with water to permit the pathogen to establish itself in soil two weeks before planting. Na silicate was applied as seed coating, seed soaking or soil treatment. Coating was made to seed as described by Bardin et al.(2004). Seed were soaked for 15 min. in 1% methyl cellulose (MC) solution (Aldrich Chemical, Milwaukee, WI) at a concentration of 3 ml per 100 seeds. Thereafter, seed were removed and placed in plastic bags, each containing 0.8, 1.0, or 1.5 g of Na2SiO3.9H2O per 100 seed. Bags were inflated with air and shaken vigorously. Soaking was done to seed prior to planting in aqueous solution of the above mentioned concentrations of Na2SiO3.9H2O for 8 hours. Soil treatment was done by amending the infested soil with Na2SiO3.9H2O at the rate of 15, 20 & 40 g/No.25 pot. This experiment was quadruplicated and untreated pots acted as control. Seven seeds were planted in each replicate pot and emerged seedlings were recorded and thinned to five after two weeks of planting. Plants were fertilized by NPK as usual and plants were examined periodically to record any abnormality that might be happened due to application. Percentage of infection was calculated at the end of the experiment (90-100 days of planting) and results were statistically analyzed.

In the field, study was carried out in the disease nurseries of the Agricultural Experiment Research Stations of Gemmeiza and Sakha.

The four treatments described under greenhouse experiment, i.e. seed soaking, seed coating, and soil treatment were used to evaluate the efficiency of sodium silicate against stalk-rot disease of maize. A susceptible local variety was used in this experiment. Seeds were treated with Na2SiO3.9H2O at the same rates that used in greenhouse. Soil was treated by incorporating Na2SiO3.9H2O under seed beds. Treatments were arranged in a complete randomized design with four replicate plots, four rows (6M length) each and untreated plots acted as control. Cultural practices (irrigation, fertilization, borers control ….etc.) were carried out as usual. Plants were periodically inspected and disease readings were taken at the end of the experiment (after 100 days of planting) and recorded as percentage of infection for each treatment. Also, efficiency of treatments was determined as reduction in infection percent over the control.

Results and discussion

In vitro bioassay:

Alike findings of Bi et al. (2006) and Li et al. (2009) working on soil fungi, we found that sodium silicate has direct fungitoxic activity against the root-infecting pathogens of maize. Data presented in Table 1 indicate that Na silicate was efficient in reducing the colony diameter of all target pathogens, generally. The degree of sensitivity of fungal growths to Si, however, differed from pathogen to another. R.solani was highly sensitive to the poison effect of Na silicate, where it was completely suppressed at 1.2 % Na2SiO3. Whereas, F.verticillioids tolerated the silicate compound, where, its radial growth was reduced to 16.8 mm (efficiency of 76%) at 3.0% of Na silicate. Data in Table1 also indicate that the growth of S.rolfsii was completely reduced at 3.0 %. The radial growth of C.maydis was completely suppressed at the concentration of 1.6 % Na silicate (Table 1).

Table (1): Growth of target pathogens on Na2SiO3 amended-PDA.

Treatments

PDA amended withNa2SiO3 /at

R.solani

F. verticillioides

S. rolfsii

C.maydis

C.D.*

R**

C.D.*

R**

C.D.*

R**

C.D.*

R**

3.0%

0.0

100

16.8

76.0

0.0

100

0.0

100

1.6%

0.0

100

32.3

53.9

17.3

75.3

0.0

100

1.2%

0.0

100

39.5

43.6

23.0

67.1

12

82.9

Cont.

70

-

70

-

70.0

-

70.0

-

LSD (0.05)

0.080

3.022

2.593

2.240

Current results showed that Si has poison effect on target pathogens as reported by previous investigators. Bi (2006) stated that Si resulted in a collapse and shrinkage of fungal hyphae and spores, which consequently causing the loose of sporulation. Li (2009) observed that ultastrucural alterations were happened by using transmission electron microscopy, including thickening of the hyphal cell walls. We may also, hypothesized that the inhibitory effect of Na silicate may, also, be regarded to shifting the pH to alkalinity due to releasing of free Na in the growing medium, the unsuitable milieu for the fungal growth.

In vivo experiments:

Data (Table 2) indicate that all treatments, whether in the greenhouse or the field significantly reduced the disease infection comparable to the control. Efficiency in decreasing the disease incidence was increased by increasing the compound concentration as shown in Table2. Results obtained throughout this study led to the hypothesis that Si would act as a modulator influencing the plant defense response in maize plants. Fawe et al. (2001) suggested that Si act as a secondary messenger of systemic acquired resistance (SAR). Induction of biochemical defense response by Si treatment as a result of accumulating oxidative enzymes at the infection site as suggested by Qin and Tian (2005) may support the success of Na silicate in managing the root-infecting diseases of maize obtained throughout this investigation.

Table (2): Effect of Na2SiO3 on late-wilt (greenhouse,2010) and stalk-rot

( field,2011) of maize.

Treatment

Greenhouse

Field of Gemmeiza

Field of Sakha

% inf.

E*

% inf.

E

% inf.

E

Seed soaking in aqueous solution

3.0%

20

69.2

23.3

45.1

25

46.5

1.6%

35

46.2

33.3

23

35

25.1

1.2%

55

15.4

41.7

3.8

40

14.3

Control

65

43.3

46.7

LSD (0.05)

0.243

0.268

0.268

Seed coating (g/100seed)

3.0%

15

76.9

25

42.3

26.7

42.9

1.6%

20

69.2

28.3

34.7

30

35.8

1.2%

30

53.9

36.7

15.3

35

25.1

Control

65

43.3

46.7

LSD (0.05)

0.324

0.268

0.167

Soil treatment (g/hill)

40

25

61.5

38.3

11.5

40

14.3

20

35

46.2

41.7

3.8

43.3

7.2

15

45

30.7

43.3

0.0

45

3.6

Control (0)

65

43.3

46.7

LSD (0.05)

0.282

0.509

0.328

* efficiency of treatment

Present study threw the light on silicon compounds as abiotic agents, friendly with the environment that can be used to control plant diseases rather than the hazardous pesticides which pollute the surrounding environment.

References:

Bẻlanger, R.R.; Benhamou, N. and Menzies, J.G. 2003. Cytological evidence of an active role of silicon in wheat resistance to powdery mildew (Blumeria graminis f.sp.tritici). Phytopathology, 93: 402-412.

Bẻlanger, R.R.; Bowen, P.A.; Ehret, D.L. and Menzies, J.G. 1995. Soluble silicon: Its role in crop and disease management of greenhouse crops. Plant Disease, 79: 329-336.

Bi, Y.; Tian, S.P.; Gue, Y.R.; Ge, Y.H. and Qin, G.Z. 2006. Sodium silicate reduces postharvest decay on homi melons: Induced resistance and fungistatic effects. Plant Disease, Vol.90 No.4: 279-283.

Chẻrif, M.; Asselin, A. and Bẻlanger, R.R. 1994. Defense responses induced by soluble silicon in cucumber roots infected by Pythium spp. Phytopathology, 84: 236-242.

Epstein, E. 1999. Silicon. Annu.Rev.Plant Physiol. Plant Mol.Biol., 50:641-664.

Fawe, A.; Menzies, J.G.; , M. and Be'lenger, R.R. 2001. Silicon and disease resistance in dicotyledons. In: Silicon in Agriculture (Dantoff, L.E., Snyder, G.H. and Krondofer G.H., Eds.), pp. 159-170.

Li, Y.C.; Bi, Y.; Ge,Y.H.; Sun, X.J. and Wang,Y.J. 2009. Antifungal activity of sodium silicate on Fusarium sulphureum and its effect on dry rot of potato tubers. J.Food Sci., 74 (5): M213-M218.

Menzies, J.G.; Bowen, P.; Ehret, D. and Glass, A.D.M. 1992. Foliar applications of potassium silicate reduce severity of powdery mildew on cucumber, muskmelon, and zucchini squash. J.Am.Soc.Hortic. Sci., 117: 902-905.

Qin, G.Z.and Tian, Shi P. (2005). Enhancement of biocontrol activity of Cryptococcus laurentii by silicon and the possible mechanisms involved. Phytopathology, 95 (1): 69-75.

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