management of seed borne pathogens of maize

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Abstract

Management of seed mycoflora was studied by different seed treatment methods viz., physical, chemical and biological methods. By physical methods, seeds treated with hot water at 45ËšC for 25 and 30 minutes and at 50ËšC for 10, 15, 20, 25 and 30 minutes reduced seed mycoflora, but adversely affected seed germination. However, maximum seed germination was recorded when seeds were treated at 40ËšC for 30 minutes and this treatment also reduced seed mycoflora effectively. In dry heat treatment, seed treatment at 50ËšC for one hour effectively reduced the seed mycoflora, but adversely affected seed germination. However, dry heat treatment at 40ËšC for one hour reduced the seed mycoflora without affecting seed germination. In solar heat treatment, seeds exposed to solar heat treatment at 12-14 h on terrace effectively reduced the seed mycoflora followed by 13-15 h, 14-16 h, 12-13 h, 13-14 h, 14-15 h and 15-16 h. Seed treatment with fungicides viz., carbendazim, thiophanate methyl, captan, mancozeb and chlorothalonil at the rate of 2 g and 3 g per kg of seed effectively eliminated seed mycoflora. The maximum seed germination of 90 per cent was recorded when seeds were treated with carbendazim @ 2 and 3 g per kg of seed. In seed treatment with bioagents viz., Trichoderma viride, T. harzianum, P. fluorescens and Bacillus subtilis, seed mycoflora was significantly reduced when maize seeds were treated with T. harzianum and T. viride at 6 g per kg of seed, where as maximum seed germination of 92 per cent was recorded when seed were treated with T. viride and P. fluorescens at 6 g per kg of seed.

INTRODUCTION

Maize (Zea mays L.) is one of the important cereal crops next only to wheat and rice in the world and utilized as food, as feed for livestock and as raw material for industry. World area under maize crop is 147.56 million hectares with a production of 701.27 million tonnes (Muhammad Akber et al., 2008) whereas, in India maize is cultivated on an area of 8.11 million/ha. Total maize production is 19.77 Mt, with an average yield of 2,435 kg/ha in 2007-08 (Anon, 2008). In Karnataka, maize occupies an area of 1.11 million hectares producing of 3.20 million tonnes with a productivity of 2894 kg/ha (Anon., 2008).

A total of 112 diseases are known to occur on maize causing economic damage to the crops (Anon, 1960) and among them more than 70 diseases are reported as seed-borne. Important seed-borne diseases of maize are leaf spot, leaf blight, Collar rot, kernel rot, scutellum rot, seedling blight, anthracnose and head smut (Richardson, 1990).

Seeds are known to carry a considerable amount of microorganisms. Some of these cause various diseases. Pathogens are associated with seeds in the form of contaminants, externally and internally as seed borne. These organisms become active under favourable condition and affect the seed germination (Christensen and Lopez, 1963) which results in lower plant population and abnormal seedlings in field, thereby causing considerable reduction in yield. Invasion by fungi in storage might result in the discoloration of the seeds, rise in temperature, mustiness, loss in weight and various changes in the seed constituents. Some of the seeds infecting fungi produce mycotoxins such as aflotoxin, patulin, citrinine and ochratoxin (Bilgrami et al., 1979).

Seed treatment occupies one of the important positions in the integrated management of any disease and has provided excellent results in reducing losses caused by diseases with increase in quality and quantity of seeds.

Material and methods

Management of seed mycoflora

Seed treatment

To control seed mycoflora highly infected seeds of the hybrid variety Nithyashree were selected and subjected to different seed treatment methods viz., 1) Physical 2) Chemical and 3) Biological methods. 400 seeds were incubated at room temperature on moist blotters as per standard blotter method. Seeds without treatment served as control. Effect of seed treatment on seed germination and per cent seed mycoflora were recorded by using steriobinocular microscope in all seed treatment methods.

Physical seed treatment methods

Hot water treatment

Maize seeds were subjected to hot water treatment at 35°C, 40°C, 45°C and 50°C with time interval of 10, 15, 20, 25 and 30 min. at each temperature level, and experiment was replicated four times. Seeds without treatment served as control. Seeds were shade dried for half an hour and incubated for seven days on moist blotters. Observations were recorded on 8th day.

Dry heat treatment

Maize seeds were subjected to different temperature levels viz., 35, 40, 45 and 50°C for an hour by keeping them in hot air oven. 400 seeds were placed on moist blotters as per the standard blotter method and incubated for seven days. Observations were recorded on 8th day.

Solar heat treatment

Maize seeds were subjected to solar heat treatment by keeping them on terrace in afternoon at time duration of 12-13 h, 13-14 h, 14-15 h, 15-16 h, 12-14 h, 13-15 h, and 14-16 h in April month. 400 seeds were placed on moist blotters as per standard blotter method and incubated for seven days. Observations were recorded on 8th day.

Chemical seed treatment

The maize seeds were treated with six fungicides viz., carbendazim, captan, chlorothalonil, mancozeb, thiophanate methyl and ridomil at the rate of 2 g, 3 g and 4 g per kg of seed at each treatment level. In each treatment were 400 seeds plated on moist blotters with four replications. Seeds without treatment served as control and incubated for seven days. Observations were recorded on 8th day.

Biological seed treatment

In this experiment maize seeds were treated with commercial formulations of Trichoderma viride, T. harzianum, Pseudomonas fluorescens and Bacillus subtilis at the rate of 2, 4, 6, and 8 g per kg of seed. After each treatment seeds were plated on moist blotter by using standard blotter method. Seeds were incubated for seven days and observations were recorded on 8th day.

RESULTS AND DISCUSSION

Hot water treatment

In the management of maize seed borne fungi, seed treatment with hot water at 50ËšC for 15, 20, 25 and 30 minutes inhibited seed germination compared to control. However, seed treatment with hot water at 40ËšC for 30 minutes significantly increased seed germination and reduced seed mycoflora effectively. Hence this appears the optimum temperature and duration combination that reduces seed mycoflora and enhances seed germination (Table 1). This is inconformity with the results of Rahman et al. (2008) who reported that seed treatment with different levels of hot water treatment viz., 48ËšC, 50ËšC and 52ËšC significantly reduced the seed borne pathogenic fungi of maize viz., Bipolaris maydis, Curvularia lunata and Fusarium spp. from 60.47, 71.07 and 76.99 % to 19.31, 29.37 and 4.01 % respectively. Seed germination was also increased after the seed treatment with hot water.

Table 1: Effect of hot water treatment for control of maize seed mycoflora

Sl.

No

Hot water

temperature

(ËšC)

Time

(min)

Seed

germination

(%)

Per cent seed mycoflora

Per cent reduction over control

Aspergillus niger

Aspergillus

flavus

Penicillium

sp.

Fusarium sp.

Rhizopus sp.

Curvularia sp.

Bipolaris sp.

Cladosporium sp.

Boryodiplodia theobromae

Alternaria sp.

Nigrospora oryzae

Mean

1.

35

10

85

70

78

100

33

48

4

2

20

5

3

6

33.5

2.6

15

85

70

77

100

33

48

2

2

20

5

2

5

33.0

4.0

20

86

68

75

100

33

47

2

2

19

4

2

4

32.3

6.1

25

87

66

74

100

32

46

1

1

18

4

2

3

31.5

8.4

30

88

63

72

100

32

43

0

1

15

4

2

2

30.3

11.9

2.

40

10

86

66

72

100

32

45

4

2

18

4

3

4

31.8

7.5

15

87

61

71

100

32

43

3

2

17

4

2

3

30.7

10.7

20

88

58

70

100

31

41

2

2

15

3

1

2

29.5

14.2

25

89

52

68

99

30

39

1

1

13

3

1

2

28.0

18.6

30

89

49

67

98

29

35

0

0

11

3

0

2

26.7

22.3

3.

45

10

87

60

70

100

30

41

3

2

14

4

2

2

29.8

13.4

15

88

58

69

99

29

39

2

2

12

3

1

2

28.7

16.5

20

89

55

68

98

27

38

1

0

10

2

0

0

27.7

19.5

25

88

52

66

98

26

36

0

0

9

2

0

0

26.2

23.8

30

86

46

65

97

24

34

0

0

7

2

0

0

25.0

27.3

4.

50

10

86

56

68

98

27

38

3

0

8

2

1

2

27.5

20.0

15

84

49

67

97

26

35

2

0

5

0

0

2

25.7

25.3

20

83

46

65

95

24

32

0

0

3

0

0

1

24.1

29.9

25

79

42

62

93

19

30

0

0

0

0

0

0

22.3

35.1

30

77

38

60

90

17

28

0

0

0

0

0

0

21.1

38.6

Control

85

74

79

100

33

49

5

2

22

5

3

6

34.4

-

Dry heat treatment

In dry heat treatment as the temperature increased from 35ËšC to 50ËšC for duration of one hour, seed mycoflora was decreased but adversely affected seed germination. Seed treatment at 50ËšC recorded minimum association of 17 per cent by Rhizopus sp. followed by Fusarium sp. (17 per cent), A. niger (28 per cent), A. flavus (45 per cent), and Penicillium sp. (93 per cent) and inhibited seed germination. However seed treatment at 40ËšC recorded 98 per cent association by Penicillium sp. followed by, A. flavus (62 per cent), Rhizopus sp. (35 per cent), Fusarium sp. (25 per cent), A. niger (57 per cent), N. oryzae (2 per cent), Cladosporiuym sp. (11 per cent), Botryodiplodia theobromae (2 per cent) and Curvularia sp. (1 per cent). Seed mycoflora was inhibited upto 22.7 per cent when seeds were treated at 40ËšC dry heat and maximum seed germination of 87 per cent was also recorded. Hence this appears the optimum temperature and duration combination that reduces seed mycoflora and enhances germination of seeds (Table 2). The present investigation also agrees with the reports of Prasanna Kumara (2004). He reported that in dry heat treatment when seeds treated at 50°C for one hour significantly decreased seed mycoflora of pigeonpea but inhibited seed germination, where as maximum seed germination was recorded when the seeds were treated at 40°C.

Table 2: Effect of dry heat treatment for control of maize seed mycoflora

Sl.

No

Dry heat temperature

(ËšC)

for 60 min.

Seed

germination

(%)

Per cent seed mycoflora

Per cent reduction over control

Aspergillus niger

Aspergillus

flavus

Penicillium

sp.

Fusarium sp.

Rhizopus sp.

Curvularia sp.

Alternaria sp.

Cladosporium

sp.

Nigrospora oryzae

Bortyodiplodia theobromae

Bipolaris sp.

Mean

1.

35

86

70

73

100

29

49

2

2

19

3

4

2

32

6.9

2.

40

87

57

62

98

25

35

1

0

11

2

2

0

26.6

22.7

3.

45

86

43

51

95

21

23

0

0

5

1

0

0

21.7

36.9

4.

50

84

28

45

93

17

17

0

0

0

0

0

0

18.1

47.4

Control

85

75

80

100

32

50

5

3

22

5

5

2

34.4

-

Solar treatment

Studies on solar heat treatment for the management of maize seed mycoflora revealed that minimum association of 92 per cent by Penicillium sp. followed by Fusarium sp. (61 per cent), A. flavus (45 per cent), A. niger (30 per cent), and Rhizopus sp. (3 per cent). The maximum reduction of 19.4 per cent by seed mycoflora was recorded when seeds were exposed to 12-14 hr solar heat and maximum seed germination of 89 per cent was also observed (Table 3). Similarly Rai et al. (2001) treated maize seeds with UV radiation and observed reduction of fungal species with increased duration of exposure.

Table 3: Effect of solar heat treatment for control of maize seed mycoflora

Sl.

No

Time

(h)

Seed

germination

(%)

Per cent seed mycoflora

Per cent reduction over control

Aspergillus niger

Aspergillus

flavus

Penicillium

sp.

Fusarium sp.

Rhizopus sp.

Alternaria sp.

Nigrospora oryzae

Bipolaris sp.

Curvularia sp.

Cladosporium

sp.

Botryodiplodia theobromae

Mean

1.

12-13

87

68

72

98

30

45

1

3

1

4

16

4

31.0

10.1

2.

13-14

86

68

73

100

31

46

2

3

2

5

16

5

31.9

7.53

3.

14-15

86

69

74

100

31

47

2

4

2

5

18

5

32.4

6.00

4.

15-16

86

70

74

100

32

47

2

4

2

5

19

5

32.7

5.21

5.

12-14

89

58

67

92

28

42

0

1

0

2

14

2

27.8

19.4

6.

13-15

88

60

68

95

29

43

0

2

1

3

15

3

29.0

15.9

7.

14-16

87

67

70

97

30

45

1

3

1

4

16

4

30.7

11.0

Control

85

75

80

100

33

50

3

5

2

6

21

5

34.5

-

Chemical seed treatment

The results of the chemical seed treatment revealed that seed treatment with carbendazim, thiophanate methyl and captan at rate of 3 g per kg of seed completely eliminated A. niger, A. flavus, Curvularia sp., Trichoderma sp., N. oryzae, B. theobromae, Alternaria sp., Cladosporium sp. and Bipolaris sp. without affecting seed germination, where as chlorothalonil decreased total seed mycoflora upto 94.11 per cent. Minimum reduction of 37.05 per cent seed mycoflora was recorded when maize seeds were treated with metalaxyl 8%+ mancozeb 64 wp @ 2 g per kg of seed. The maximum seed germination of 90 per cent was recorded when seeds were treated with carbendazim (Table 4). Similarly Manoj Kumar and Agarwal (1998) also reported that seed treatment with fungicides viz., thiram, rovral, dithane M-45, dithane Z-78, and bavistin + thiram (1:1), considerably reduced seed borne pathogen especially B. maydis, B. theobromae and F. moniliforme. Thiram and bavistin were significantly superior to other fungicides in improving seedling vigour of discolored maize seed.

Table 4: Effect of chemical seed treatment for control of maize seed mycoflora

Sl.

No

Fungicides

Chemical concentration

@ g/kg

Seed

germination

(%)

Per cent seed mycoflora

Per cent reduction over control

Aspergillus niger

Aspergillus flavus

Penicillium sp.

Fusarium sp.

Rhizopus sp.

Curvularia sp.

Alternaria sp.

Nigrospora oryzae

Bipolaris sp.

Cladosporium sp.

Botryodiplodia theobromae

Mean

1.

Carbendazim

2

90

0

0

20

0

46

1

0

0

1

0

0

6.1

82.02

3

90

0

0

12

0

44

0

0

0

0

0

0

5.0

85.29

4

88

0

0

8

0

41

0

0

0

0

0

0

4.4

86.91

2.

Thiophanate methyl

2

89

0

0

0

0

48

0

0

0

0

0

0

4.3

87.35

3

87

0

0

0

0

46

0

0

0

0

0

0

4.1

87.94

4

85

0

0

0

0

40

0

0

0

0

0

0

3.6

89.41

3.

Captan

2

89

0

14

0

11

45

0

0

0

0

0

0

6.3

81.47

3

89

0

0

0

0

43

0

0

0

0

0

0

3.9

88.52

4

88

0

0

0

0

38

0

0

0

0

0

0

3.4

90.00

4.

Mancozeb

2

87

15

22

0

9

46

0

0

0

0

0

0

8.3

75.58

3

88

7

14

0

7

42

0

0

0

0

0

0

6.3

81.47

4

88

0

8

0

5

31

0

0

0

0

0

0

4.0

88.23

5.

Metalaxyl 8%+mancozeb 64%wp

2

86

35

57

67

28

38

0

0

0

0

8

3

21.4

37.05

3

87

19

55

58

24

35

0

0

0

0

3

1

17.7

47.94

4

87

10

51

45

21

26

0

0

0

0

0

0

13.0

61.76

6.

Chlorothalonil

2

88

11

18

0

7

22

0

0

0

0

12

2

6.5

80.88

3

88

0

12

0

5

17

0

0

0

0

5

0

3.5

89.70

4

87

0

8

0

0

15

0

0

0

0

0

0

2.0

94.11

Control

84

75

78

100

31

48

5

3

3

3

23

5

34.0

-

Biological seed treatment

In seed treatment with bioagents viz., T. viride, T. harzianum P. fluorescens and B. subtilis, seed mycoflora was significantly reduced when maize seeds were treated with T. harzianum and T. viride at 6 g per kg of seed, where as maximum seed germination of 92 per cent was recorded when seed were treated with T. viride and P. fluorescens at 6 g per kg of seed (Table 5). Manjunatha and Rao (2002) also reported that seed treatment with P. fluorescens, T. viride and T. harzianum effectively reduced A. alternata, F. moniliforme, A. flavus, A. niger, R. stolonifer, C. lunata and C. globosum infection from wheat seeds.

Table 5: Effect of bio agents on maize seed mycoflora

Sl.

No.

Bioagent

Concentration

g/kg

Seed

germination

(%)

Per cent seed mycoflora

Per cent reduction over control

Aspergillus niger

Aspergillus

flavus

Penicillium

sp.

Fusarium sp.

Rhizopus sp.

Cladosporiumsp.

Botryodiplodia theobromae

Curvularia sp.

Alternaria sp.

Bipolaris sp.

Nigrospora oryzae

Mean

1.

Trichoderma viride

2

88

18

17

32

8

18

12

2

0

0

0

0

9.7

71.47

4

90

7

13

26

4

15

8

0

0

0

0

0

6.6

80.58

6

92

0

6

20

0

13

0

0

0

0

0

0

3.5

89.70

8

92

0

2

19

0

11

0

0

0

0

0

0

2.9

91.47

2.

Trichoderma

harzianum

2

87

15

15

18

10

12

13

0

0

0

0

0

7.5

77.94

4

89

10

8

12

7

10

7

0

0

0

0

0

4.9

85.58

6

91

0

0

7

5

6

3

0

0

0

0

0

1.9

94.41

8

91

0

0

5

4

5

0

0

0

0

0

0

1.3

96.17

3.

Bacillus subtilis

2

86

69

56

45

25

36

18

3

0

0

0

0

22.9

32.64

4

88

63

50

41

21

29

15

1

0

0

0

0

20.0

41.17

6

89

57

45

35

18

26

13

0

0

0

0

0

17.6

48.23

8

89

52

43

28

15

20

10

0

0

0

0

0

15.2

55.29

4.

Pseudomonas fluorescens

2

87

66

55

63

17

45

15

3

0

0

0

0

24.0

29.41

4

89

61

49

50

13

40

11

0

0

0

0

0

20.3

40.29

6

92

52

38

46

11

39

8

0

0

0

0

0

17.6

48.23

8

92

47

32

41

8

38

5

0

0

0

0

0

15.5

54.41

Control

85

75

80

100

33

48

22

5

2

3

3

3

34.0

-

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