2016-08-14T18:45:59+05:302016-08-14T18:45:38+05:302016-08-14T18:45:59+05:30Acrobat PDFMaker 11 for Worduuid:cefb11c2-9e24-46f4-9d75-f71c4de3e677uuid:fafdab96-c65c-4200-be67-ac94ce6526fc14xmlStudies on The Behavior of Proliferated Shoots and Roots of Two Fig Cultivars In Vitro gemmaAdobe PDF Library 11.0D:20160731224254Grizli777
International Journal of ChemTech Research CODEN (USA): IJCRGG, ISSN: 0974-4290, ISSN(Online):2455-9555 Vol.9, No.07 pp 73-85, 2016
Biological Soil Treatment to Control Fusarium solani and Tylenchulus semipenetrans on Sour Orange Seedlings Under Greenhouse Conditions Riad S.R. El-Mohamedy; Mostafa M. A. Hammam; Farid Abd-El-Kareem and Mahfouz M. M. Abd-Elgawad Plant Pathology Department, National Research Centre, Dokki 12622, Giza, Egypt. Abstract : Dry root rot and slow decline diseases of citrus caused by Fusarium solani and Tylenchulus semipenetrans, respectively, are serious diseases attacking many groves in Egypt. We evaluated the efficiency of soil amended with bio-agents and compost alone or in combination to control both diseases simultaneously on sour orange (Citrus aurantum) seedlings under greenhouse conditions. All tested bioagents reduced T. semipenetrans population densities and the linear growth of F. solani. Complete inhibition of the linear growth was obtained with Trichoderma viride, T. harzianum isolate no 3 and Bacillus subtilis isolate no 4. The compost with each of Bacillus subtilis, Trichoderma harzianum or T. viride could reduce the rate of nematode build-up to 0.35, 0.38, and 0.41; respectively. The most effective treatment against F. solani was compost + mixture of T. harzianum + T. viride which reduced disease incidence and severity by 87.5%. The highest reduction in total count of F. solani was obtained with compost + mixture of T. harzianum + T. viride which reduced total count by 82.1%. Treatment with compost alone could increase (P ≤ 0.05) fresh weight of sour orange roots over that treated with F. solani and/or T. semipenetrans. Other treatments were less effective. The highest increase in enzyme activities was obtained with combined treatments of compost and T. harzianum, T. viride, B. subtilis (or T. harzianum + T. viride) which increased the peroxidase, polyphenol oxidase and chitinase activities 300, 72.2 and 109.9%, respectively. Key words: Keywords: Biocontrol, compost, Fusarium solani, greenhouse, sour orange, Tylenchulus semipenetrans. Introduction Dry root rot disease of citrus caused by Fusarium solani (Mart.) is one of the most serious diseases attacking citrus trees especially in newly reclaimed lands in Egypt, it has been estimated to adversely affect 8.9% of lime trees and caused 39.6% loss in fruit yield 1. This disease was reported to attack all citrus varieties in Egypt1,2. Likewise, slow decline disease of citrus caused by the citrus nematode Tylenchulus semipenetrans (Cobb) is another important disease worldwide where nematode population levels may affect fruit yield differently under various conditions 3-,8. Both pathogens can infect and thrive on sour orange; the most common rootstock in Egypt so far. Control of the two diseases depends mainly on fungicides and nematicides application9,5. Such chemicals are not always desirable due to potential hazards to human beings and the environment. Biological control agents and soil amendments individually or in combination are among the recent recommended alternatives for controlling the nematodes and soil borne pathogens.control agents and soil amendments individually or in combination are among the recent recommended alternatives for controlling the nematodes and soil borne pathogens.control agents and soil amendments individually or in combination are among the recent recommended alternatives for controlling the nematodes and soil borne pathogens.Using agricultural and domestic food wastes or some grains as substrates for T. harzianum growth, formulation and/or direct delivery in soil for controlling phytonematodes and soil borne pathogens on economically important crops were recorded.12-17. In Egypt, such alternative control methods are needed for managing these pathogens. The application of biological control using antagonistic microorganisms i.e., Trichoderma harzianum, T. viride and Bacillus subtilis, proved to be successful for controlling various phytonematodes and soil-borne plant diseases on different crops18-24. Many soil-borne pathogens can be reduced by application of composts made of different raw materials25. Currently it is believed that a combination of antagonistic microorganisms with mature compost may be more efficient in inhibiting diseases than using single antagonistic microbial strain or compost alone25-27. The purpose of this research is to evaluate the efficiency of soil amended with bio-agents and compost alone or in combination to control the fusarium dry root rot and slow decline diseases under greenhouse conditions. Activities of three enzymes, that may be involved in inducing resistance of plants to the attacking pathogens, were measured. Materials and Methods Source of pathogenic fungus and bio-agents: Pathogenic isolate of F. solani the causal agent of dry root rot disease of citrus plants and antagonistic strains of Trichoderma harzianum, T. viride and B. subtilis were obtained from Plant Pathology Dept. at the National Research Centre. Source of plant compost: Chemical analysis and properties of the plant compost obtained from El-Nile Company, Egypt were as follows: total nitrogen 1.53%, total phosphorus 0.29%, total potassium 1.13%, total iron (1368 ppm), total zinc (70 ppm), total copper (12 ppm), total organic matter (31%), organic carbon 33.4%, carbon / nitrogen ratio 12:1, pH (1:100) 8.1, EC 1:100, and humidity (8.54%). Laboratory experiment: Evaluation of antagonistic effect of some rhizospheric fungi on the linear growth of F. solani: Four antagonistic isolates of T. harzianum, T. viride and B. subtilis were tested to study their inhibitory effect against F. solani in vitro. Each of the obtained fungal antagonists, and pathogenic fungus were grown on Potato Dextrose Agar (PDA) medium for 7 days at 25 ± 2°C. Disk of individual antagonistic fungi and disk of F. solani were placed on opposite sides of Petri plates containing PDA medium 28. Inoculated plates were incubated for 7 days at 25 ± 2°C. Five plates for each particular treatment/isolate were used as replicates. The plates were then examined and growth area of F. solani was measured. The reduction percent in linear growth of F. solani was calculated. Evaluation of antagonistic effect of B. subtilis on the linear growth of F. solani : Four isolates of B. subtilis were tested to study their inhibitory effect against F. solani in vitro. Antagonistic isolates were grown individually on nutrient agar medium (NA) for 48 h at 30 ± 2°C. Using dual culture plate assay, 6-mm-diameter disk of F. solani was placed near the edge of Petri plate containing PDA medium. Loop of bacterial isolate was placed as individual streak in the opposite of F. solani 29. Inoculated plates were incubated for 7 days at 25 ± 2°C. Five plates for each particular treatment were used as replicates. The plates were then examined and linear growth of F. solani was measured and the reduction percent in linear growth was calculated. Greenhouse experiment: 1) Evaluating the efficiency of soil amended with bio-agents and compost alone or in combination on dry rot and slow decline diseases of citrus seedlings. Inoculum Preparation of biocontrol agents: T. harzianum and T. viride were grown on PDA medium at 25 ± 1°C for 10 days; afterwards the mycelium with the spores was scraped from Petri plate and mixed with sterilized distilled water (20 ml/plate) in a blender. The suspension was adjusted by hemocytometer slide to 3 × 106 colony forming units (cfu)/ml as described by30. Also, one loop of B. subtilis isolate was inoculated into Nutrient Broth medium (g/l): peptone 5 g, beef extract 3 g, sodium chloride 5 g, glucose 20 g, pH 7; and incubated on a shaker incubator (125 rpm) at 28 ± 1°C. Antagonistic bacterial cells were then harvested after 48 hours of growth in culture medium by centrifugation at 6,000 rpm for 15 min and re-suspended in a phosphate buffer (0.01 M, pH 7.0). The concentration was adjusted by plate count technique to an approximately 3 × 107 cfu/ ml as mentioned by 30. Soil infestation with F. solani Sandy-loam soil was autoclaved at 120°C for 1 h. Plastic pots (30 cm diameter, 5 kg soil) containing sterilized sandy-loam soil were artificially infested with the inoculum of F. solani at the rate of 50 ml (106 cfu/ ml) / kg soil 31. One 2-year-old healthy seedling of the most widespread commercial rootstocks in Egypt, i.e., Sour orange (Citrus aurantum L.) was transplanted to each pot. The seedlings were obtained from Citrus Research Division, Agriculture Reseach Center, Giza, Egypt. Preparation and inoculation of Tylenchulus semipenetrans Soil and root subsamples were obtained from ‘Baladi’ mandarin (Citrus reticulata Blanco) orchard 32 with a hand trowel (ca 6 cm diam X 30 cm deep) beneath the tree canopy at 1.25 m from the trunk and mixed. The subsamples were composited into a single sample of about 1000 cm3 representing a random tree. Samples were bagged, labeled and taken to the laboratory for nematode extraction and count. Ninety samples were thoroughly mixed from which ten 250-cm3 soil samples were processed for extraction of citrus nematode juveniles (J2) and males while the fibrous roots were washed from the soil to recover females of the citrus nematode33. Key reference of 34 was consulted to identify T. semipenetrans via examining several mounted adult females in glycerin. All counted live T. semipenetrans J2 and males were retuned back to the bulk soil which was caliberated so that each 1 kg soil contained 3000 T. semipenetrans J2 and males. Five days after the addition of F. solani, 1 kg soil with 3000 T. semipenetrans individuals was added per pot. Preparation of bio-compost Inocula of antagonistic fungi isolates, i.e. T. harzianum or T. viride (1012 cfu/ml) in addition to the antagonistic bacteria, i.e. B. subtilis, (1016 cfu/ ml) were prepared as mentioned before. Plant compost was autoclaved at 120oC for 60 min. Fungal and bacterial suspensions were added individually to sterilized plant compost at the rate of 2:1 (Plant compost: suspension, W:V), then mixed thoroughly to ensure equal distribution of microorganism suspension through the plant compost. The prepared mixture was placed on paper sheet and left for air dry 4-6 hrs at room temperature (22-25 oC) in laminar flow under sterilized conditions. Soil treatment with compost and/or bioagents: Soil infested with F. solani and T. semipenetrans was treated with bio-agent fungi or bacteria at the rate of 50 ml (106 cfu/ ml)/ kg soil of each antagonistic fungi or bacteria. Plant compost or bio-compost (compost + bio agents) was added to soil infested with F. solani and T. semipenetrans at the rate of 50 g/ kg soil. The compost and/or bioagent (s) were added 5 days after nematode inoculation. Treatments The treatments can be summarized as follows: 1) Non infested soil, 2) soil infested with F. solani, 3) soil infested with T. semipenetrans, 4) Soil infested with F. solani ( FS) + T. semipenetrans( TS), 5) soil infested with (FS + TS) + plant compost ( PC), 6) soil infested with (FS + TS) + T. harzianum, 7) soil infested with (FS + TS) + T. viride, 8) soil infested with (FS + TS) + B. subtilis, 9) soil infested with (FS + TS) + PC + T. harzianum, 10) soil infested with (FS + TS) + PC + T. viride, 11) soil infested with (FS + TS) + PC + B. subtilis, and 12) soil infested with (FS + TS) + PC+ T. harzianum+ T. viride. Ten replicates/seedlings were used for each treatment. Disease assessment: Ninety days after treating sour orange pots with compost and/or bioagents in the greenhouse, the development of disease severity of Fusarium root rot disease on seedlings of each treatment was estimated on 0-4 scale (0 = healthy plant and 4 = died plant ) according to35. Percentages of disease infection and severity of each treatment were calculated. Count of Fusarium solani in rhizosphere soil Plate count technique using Peptone-pentachloronitrobenzene (PCNB) agar medium and PDA medium supplement with 250 ppm chloromycetin was used according to 6 to determine total counts of Fusarium solani in rhizosphere soil of each treatment. Five plates were used as replicates for each treatment. Total count of fungus was expressed as cell forming units per gram dry soil. Assessing parameters of Tylenchulus semipenetrans population and plant growth: Ninety days after treating sour orange seedlings with compost and/or bioagents in the greenhouse, the plants were carefully removed from soil, the shoot systems of the tested plants were cut off and the roots gently washed from the soil. Tylenchulus semipenetrans counts as number of J2 and males in 250 g soil and number of females and eggs in 5 g roots per plant were recorded. The rate of T. semipenetrans build-up and the nematicidal activity, if any, of each treatment on T. semipenetrans population were reported. Also, after removing plants from soil, lengths and fresh weights of the shoots and lengths and fresh weights of roots were recorded. 2) Evaluating the efficiency of soil amended with bio-agents and compost alone or in combination on enzyme activities of sour orange seedlings. Extraction of enzymes: Sour orange root samples (2g/pot) were taken soon after plant removal and ground in a mortar in the presence of purified sand plus 4 ml of 0.1 M sodium phosphate buffer (pH 7.1) 37. The homogenate was strained through four layers of cheesecloth then the filtrates were centrifuged at 3000 rpm for 20 min. at 6°C. The obtained supernatant fluids (crude enzyme extracts) were used for assaying activities of peroxidase, polyphenol-oxidase (PPO) and chitinase enzymes at 425, 420 and 540nm, respectively using Spectrophotometer (Spectronic 20-D). Enzyme extract was replaced by distilled water in control blank cuvette. Peroxidase assay: Peroxidase activity was determined according to the method described by 38. The cuvette contained 0.5 ml. 0.1 M potassium phosphate buffer at pH 7.0 + 0.3 ml of enzyme extract + 0.3 ml 0.05 M pyrogallol + 0.1 ml 1.0% H2O2 and distilled water to bring cuvette contents to 3.0 ml. The reaction mixture was incubated at 25°C for 15 min. Peroxidase activity was expressed as the increase in absorbance at 425 nm/g fresh weigh. Polyphenol-oxidase assay: The polyphenol-oxidase activity was determined according to the method described by 39. The reaction mixture contained 0.2 ml enzyme extract, 1.0 ml of 0.2 M sodium phosphate buffer at pH 7.0 and 1.0 ml 10-3 M catechol and complete with distilled water up to 6.0 ml. The reaction mixture was incubated for 30 min at 30°C. Polyphenol-oxidase activity was expressed as the increase in absorbance at 420 nm/g fresh weigh. Chitinase assay: Chitinase activity was spectrophotometrically measured (at optical density 540 nm/g fresh wight/60 min) according to the method of 40. Statistical analysis: Data were subjected to analysis of variance (ANOVA) and averages of shoot and root weights and lengths as well as numbers of each nematode developmental stage were compared using Duncan's New Multiple Range Test. Nematode counts were log-transformed before ANOVA since T. semipenetranshas showed contagious distribution.41. Results Evaluation of antagonistic effect of some bioagents on the linear growth of Fusarium solani: Four antagonistic isolates of Trichoderma harzianum, T. viride and B. subtilis were tested to study their inhibitory effect against F. solani in vitro. Results in Table (1) indicate that all tested bioagents significantly reduced the linear growth of F. solani. Complete inhibition of linear growth was obtained with T. harzianum (isolate no. 3), T. viride and B. subtilis ( isolate no. 4). The highest reduction was obtained with T. viride (isolate numbers 2 and 3) which reduced the linear growth by 78.8 %. Other isolates showed moderate effect. Greenhouse experiment: This experiment was carried out to evaluate the efficacy of bio-agents and compost alone or in combination for controlling Fusarium dry root rot disease and citrus slow decline under greenhouse conditions. Effect on root rot disease of sour orange: Results in Table (2) revealed that the most effective treatment was compost + mixture of T. harzianum + T. viride which reduced disease incidence and severity by 87.5%. The highest reduction was obtained with compost + T. harzianum or T. viride which reduced disease incidence and severity by 75%. Other treatments were less effective. Effect of bioagents and/or compost on total count of Fusarium solani in sour orange rhizospheric soil: Results in Table (3) indicated that all treatments significantly reduced the total count of F. solani in rhizospheric soil of sour orange seedlings. The highest reduction in total count of F. solani was obtained with compost + mixture of T. harzianum + T. viride which reduced total count by 82.1. This was followed by infested soil treated with compost + T. harzianum or T. viride in a descending order of efficiency. Other treatments were less effective. Effect of bioagents and/or compost on parameters of T. semipenetrans populations and plant growth: Nematode development and reproduction were reduced by all treatments (Table 4). This was quite clear since the rate of nematode build up was < 1; that is, nematode final population is less than nematode initial population in all treatments. The data suggest that the treatments delayed nematode development or did not allow the nematode to complete its life cycle by the end of the experiment. The greatest reduction in total numbers of T. semipenetrans was caused in the treatment of compost + B. subtilis + F. solani, followed by compost + T. harzianum + F. solani, compost + T. viride + F. solani, and B. subtilis + F. solani in a descending order. Other treatments were less effective. Treatment with compost alone could increase (P ≤ 0.05) fresh weight of sour orange roots over that treated with F. solani and/or T. semipenetrans (Table 5). Effect of bioagents and/or compost on other plant growth parameters were only numerically different. Impact of soil amended with bio-agents and compost alone or in combination on enzyme activities of sour orange seedlings: Results in Table (6) revealed that all tested treatments significantly increased the tested enzyme activities. The most effective treatments were compost combined with T. harzianum and/or T. viride, or combined with B. subtilis which increased the peroxidase, polyphenol oxidase and chitinase activities. Single treatments were less effective. Table 1. Effect of bio-agents on linear growth of Fusarium solani (n = 5)*.
Bio agent
Isolate number
Fusarium solani
Linear growth
Reduction %
Trichoderma harzianum
1
34 c
62.4
2
27 d
70
3
0.0 f
100
4
15 e
83.3
Trichoderma viride
1
40 b
55.2
2
19 e
78.8
3
19.0 e
78.8
4
0.0 f
100
Bacillus subtilis
1
0.0 f
100
2
46 b
48.8
3
32 cd
64.4
4
0.0 f
100
Control
90.0 a
0
*Means in a column followed by the same letter are not significantly (P ≤ 0.05) different according to Duncan’s New Multiple Range Test. Discussion Fusarium root rot disease caused by F. solani and citrus slow decline incited by T. semipenetrans are two of the most serious diseases attacking citrus trees especially those cultivated in newly reclaimed lands of Egyptian desert1,5,32. All tested treatments (Tables 1-6) were effective and could serve as environmentally friendly products that can replace hazardous chemical fungicides and nematicides. The application of biological control using antagonistic microorganisms i.e., Trichoderma harzianum, T.viride and Bacillus subtilis, proved to be successful for controlling various soil-borne plant diseases in many countries11,21-24. In the present study, all tested bioagents significantly reduced the linear growth of F. solani. Complete inhibition of linear growth was obtained with T. harzianum (isolate no 3), T. viride and B. subtilis (isolate no 4). The highest reduction was obtained with T. viride (isolate numbers 2 and 3) which reduced the linear growth by 78.8%. Moreover, under greenhouse experiment results revealed that the most effective treatment was compost + mixture of T. harzianum + T. viride which reduced disease incidence and severity by 87.5% (Table 2). Table 2. Effect of biological soil treatments on root rot complex of sour orange caused by F. solani and T. semipenetrans under greenhouse conditions (n = 10)*.
Soil treatment
Root rot incidence
Disease infection
Reduction %
Disease severity
Reduction %
Fusarium solani (FS)
60 b
ـــــــ
40 a
ـــــــ
Tylenchulus semipenetrans (TS)
ـــــــ
ـــــــ
ـــــــ
FS + TS
80 a
0.0
40 a
0.0
Trichoderma harzianum (Th) + ( FS + TS)
40 c
50
10 d
75.0
Trichoderma viride (Tv) + ( FS + TS)
40 c
50
10 d
75.0
Bacillus subtilis (Bs) + ( FS + TS)
40 c
50
30 b
25
Compost +Th + ( FS + TS)
20 d
75
10 d
75.0
Compost +Tv + ( FS + TS)
20 d
75
10 d
75.0
Compost +Bs + ( FS + TS)
20 d
75
20 c
50
Compost +Tv + Th + ( FS + TS)
10 e
87.5
5 de
87.5
Compost + ( FS + TS)
40 c
50
30 b
25
Control
0.0 f
0.0
0.0 e
0.0
*Means in a column followed by the same letter are not significantly (P ≤ 0.05) different according to Duncan’s New Multiple Range Test. Table 3. Effect of biological soil treatments on F. solani population density in sour orange rhizosphere soil inoculated with F. solani and T. semipenetrans under greenhouse conditions*.
Soil treatment
Average propagules of F. solani ( cfu X 105/ g dry soil)
Total count
Reduction %
F. solani (FS)
47.8 a
T. semipenetrans (TS)
ــــــــ
ــــــــ
FS + TS
52.4 a
0.0
T. harzianum (Th) + FS + TS
20.2 d
61.5
T. viride (Tv) + (FS + TS)
23.2 d
55.5
Bacillus subtilis (Bs) + (FS + TS)
30.4 c
42.0
Compost +Th +( FS + TS)
12.8 ef
75.6
Compost +Tv + (FS + TS)
14.6 e
72.1
Compost +Bs + ( FS + TS)
18.8 d
64.1
Compost +Tv + Th +( FS + TS)
9.4 f
82.1
Compost +( FS + TS)
36.8 b
29.8
*Means in a column followed by the same letter are not significantly (P ≤ 0.05) different according to Duncan’s New Multiple Range Test (n = 10). Table (4): Effect of bio-control agents on T. semipenetrans population parameters on sour orange under greenhouse conditions after 3 months of treatments*.
Soil treatment
Nematode parameters
Final population
Rate of nematode build up
J2 + males in 250 g soil
Roots
Females and Eggs (total) in 5 g roots
Count
Reduction (%)
Count
Reduction (%)
Count
Efficacy (%)
F. solani (FS)
ــــــ
ــــــ
ــــــ
ـــــــ
ـــــــ
ـــــــ
T. semipenetrans (TS)
481 a(3)
----
3555 a
----
4036
----
1.35
FS + TS
366 b
23.9
2363 a
33.5
2729
32.4
0.91
T.h + TS + FS
340 b
29.3
1863 a
47.6
2203
45.4
0.73
T.v TS + FS
400 ab
16.8
1994 a
43.9
2394
40.7
0.80
B.s + TS + FS
389 ab
19.1
950 b
73.3
1339
66.8
0.45
Compost +T.v + TS + FS
351 b
27.0
880 b
75.2
1231
69.5
0.41
Compost +T.h + TS + FS
283 b
41.2
843 b
76.3
1126
72.1
0.38
Compost + B.s + TS + FS
330 b
17.9
730 b
79.5
1060
73.7
0.35
Compost +Tv + Th + (FS + TS)
283 b
41.2
730 b
79.5
1060
73.7
0.35
Means in a column followed by the same letter are not significantly (P ≤ 0.05) different according to Duncan’s New Multiple Range Test (n = 10). *Nematode-initial population = 3000 J2 + males.+T.h = Trichoderma harzianum, T.v = T. viride, and B.s = Bacillus subtilis.Table (5) Effect of bio-control agents on some growth parameters of sour orange seedlings artificially infected with T. semipenetrans and F. solani under greenhouse conditions; 3 months after treatment (n = 10)*.
Bio-control agents+
Growth parameters
Shoots
Roots
Length (cm.)
Increase (%)
Fresh weight (g)
Increase (%)
Length (cm.)
Increase (%)
Fresh weight (g)
increase (%)
Untreated check
44.5 a
-
28.6 a
-
56.2 a
-
20.3 ab
-
F. solani (FS)
37.0 a
-
12.2 a
-
30.7 a
-
12.1 b
-
T. semipenetrans (TS)
40.7 a
-
13.8 a
-
36.7 a
-
11.0 b
-
N + F
44.5 a
-
13.0 a
-
33.2 a
-
10.6 b
-
T.h + TS + FS
41.2 a
-
17.3 a
-
42.7 a
-
16.1 ab
-
T.v TS + FS
39.7 a
-
24.1 a
-
33.5 a
-
14.7 ab
-
B.s + TS + FS
36.5 a
-
23.8 a
-
54.5 a
-
19.9 ab
-
Compost +T.v + TS + FS
51.5 a
15.7
19.1 a
-
41.0 a
-
15.7 ab
-
Compost +T.h + TS + FS
44.0 a
-
19.0 a
-
44.2 a
-
15.7 ab
-
Compost + B.s + TS + FS
43.2 a
-
16.9 a
-
38.7 a
-
24.6 ab
21.2
Compost +Tv + Th + ( FS + TS)
44.0 a
-
19.1 a
-
54.5 a
-
19.9 ab
-
Compost + TS + FS
48.5 a
9.0
26.7 a
-
42.7 a
-
28.6 a
40.9
Means in a column followed by the same letter are not significantly (P ≤ 0.05) different according to Duncan’s New Multiple Range Test (n = 10). *Nematode-initial population = 3000 J2 + males.+T.h = Trichoderma harzianum, T.v = T. viride, and B.s = Bacillus subtilis. (-) means no increase. The highest reduction was obtained with compost + T. harzianum or T. viride which reduced disease incidence and severity by 75%. All treatments significantly reduced the total count of F. solani in rhizospheric soil. The highest reduction in total count of F. solani was obtained with compost + mixture of T. harzianum + T. viride which reduced total count by 82.1% (Table 3). The highest increase in enzyme activities was obtained with combined treatments of compost and T. harzianum, T. viride, B. subtilis or (T. harzianum + T. viride ) which increased the peroxidase, polyphenol oxidase and chitinase activities more than 300.0, 72.2 and 109.9 % respectively (Table 6). These results are in partial or full agreement others 13,42,43,44. In this respect, 44 found that the mechanisms of the antagonism of T. harzainum against different pathogens may be due to mycoparasitism, competition and antibiosis. Utilization of composts to minimize organic waste pollution and to reduce the addition of chemical fertilizers, nematicides and fungicides in crop production is a promising strategy for both the present and the future and so can serve for sustainable agriculture raw materials 15,27 and mature composts can sustain biological control agents 8. Furthermore, many soil-borne pathogens can be reduced by application of composts made of different 45. In the present work, results revealed that the most effective treatment was compost + mixture of T. harzianum + T. viride which reduced disease incidence and severity on sour orange by 87.5%. Table (6) Enzyme activities of sour orange seedlings in response to different treatments (n = 10)*.
Soil treatment+
Enzyme activities
Peroxidase
Polyphenol oxidase
Chitinase
Activity
Increase %
Activity
Increase %
Activity
Activity
Fusarium solani (FS)
0.5 d
ــــــ
1.5 d
1.2
Tylenchulus semipenetrans (TS)
0.7 d
1.7 d
1.0 d
FS + TS
0.7 d
0.0
1.8 d
0.0
1.1 d
0.0
Trichoderma harzianum (Th)+FS+TS
2.5 b
226.8
2.8 b
55.5
2.4 b
118.2
Trichoderma viride (Tv) + (FS +TS)
2.4 b
242.9
2.8 b
55.5
2.6 b
136.4
Bacillus subtilis (Bs) + (FS + TS)
2.3 b
228.5
2.2 c
22.2
2.0 c
81.8
Compost +Th + (FS + TS)
2.8 a
300.0
3.4 a
88.8
3.4 a
209.1
Compost +Tv + (FS + TS)
2.9 a
314.3
3.4 a
88.8
3.2 a
190.9
Compost +Bs + (FS + TS)
2.8 a
300.0
3.1 a
72.2
3.2 a
190.9
Compost +Tv + Th + (FS + TS)
2.9 a
314.3
3.5 a
94.4
3.6 a
227.3
Compost + (FS + TS)
1.4 c
100.0
2.4 c
2.7 b
100.0
Means in a column followed by the same letter are not significantly (P ≤ 0.05) different according to Duncan’s New Multiple Range Test (n = 10). *Nematode-initial population = 3000 J2 + males.+T.h = Trichoderma harzianum, T.v = T. viride, and B.s = Bacillus subtilis. The incidence of several soil-borne plant pathogens, including phytonematodes, has also been reduced by using composts made of different raw materials 11,46,47,48. In this respect, 25 reported that Trichoderma sp. in combination with composts from agricultural wastes, was used to suppress Rhizoctonia solani in cucumber seedlings. Also, Trichoderma asperellum with compost were used to suppress Fusarium wilt of tomato 47. Our study documented the beneficial effects of biocontrol agents such as Trichoderma harzianum, T. viride, and Bacillus subtilis as well as organic amendments on suppressing Tylenchulus semipenetrans population densities and enhancing growth parameters of citrus seedlings 49,50. Mature composts are known to sustain biological control agents, whereas immature composts do not. Immature composts also can negatively affect the growth of crop plants if they introduce pathogens to the soil or growing medium 3,4,43,45,49,50. Currently, it is believed that a combination of antagonistic microbes with mature compost may be more efficient in inhibiting diseases than using single antagonistic microbial strain or compost alone 11,25,26,47.
Control of T. semipenetrans and F. solani through soil amended by organic materials or agricultural wastes alone or in combined with bio-control agents may be attributed to: 1-increasing the activity of the indigenous microflora resulting in suppressing pathogen populations through competition or specific inhibition, 2-releasing degradation compounds such carbon dioxide, ammonia, nitrites, saponins or enzymes which are generally toxic to the pathogens, 3-inducing plant defense mechanisms, 4- enhancing cellulase and glucanase to high concentration as a result of the breakdown of cellulase and lignin by microorganisms in the soil 51,52. The reduction in F. solani infection and severity as well as T. semipenetrans rate of build-up on seedlings may be attributed to their decreased population densities in the soil and plant roots (Tables 2-4). The inhibitory effect of biocontrol agents might be related mainly to the antagonistic properties, which involve parasitism and lysis of pathogenic fungi and nematodes and/or competition for limiting factors in the rhizosphere, mainly iron and carbon 53,54. Recently however, another possible mechanism has been suggested by 55 namely, induced resistance in plants to the attacking pathogens. Such a mechanism was supported in the present study by increasing enzyme activities in the infested plants treated with these bioagents and/or compost (Table 6). 18,56 reported that Bacillus subtilis isolates exhibited strong antagonistic activity against M. phaseolina and other phytopathogens including F. oxysporum and R. solani. 57 recorded that 38% of B. subtilis isolates showed competitive activity against Fusarium oxysporum. On the other hand, 6,11,19,58 reported that T. viride, T. harzianum, T. hamatum had ability to suppress growth of several plant-parasitic nematode species; e.g. Meloidogyne spp., and T. semipenetrans and fungal plant pathogens including M. phaseolina, F. oxysporum and R. solani on several economically important crops. Our main goal was to document that the tested bioagents and/or compost can suppress these two pathogens simultaneously after such a relatively short period of time; 90 days. Yet, for more extended time, it is likely that other plant growth parameters, in addition to the increased fresh weight of roots (Table 5), would have benefited from such suppressions for both pathogens. Further investigations are necessary to confirm the effectiveness of the bioagents and/or compost we tested on Fusarium solani and Tylenchulus semipenetrans under field conditions. Controlling of plant diseases depends mainly on fungicides and nematicides application such chemicals are not always desirable due to potential hazards to human beings and the environment. . Alternative approaches to fungicides and nematicides are needed for controlling plant diseases 59, 60,61,62,63,64,65. Acknowledgement: This work was supported in part by In-House project No. 10120604 and US-Egypt Science and Technology Joint Fund (project No. 338). References
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