Annals of Sri Lanka Department of Agriculture. 2007.9:199-208.
EFFECT OF DIFFERENT SOIL AMENDMENT PRACTICES ON SIGATOKA LEAF SPOT DISEASE EPIDEMIC IN BANANA GROWN IN NORTH CENTRAL PROVINCE OF SRI LANKA L.C. WIJETILAKA and W.R.A.C.D. RANASINGHE Regional Agricultural Research and Development Center, Makandura, Gonawila
ABSTRACT A field experiment was laid out to find suitable management practices for banana Sigatoka leaf spot (SLS) disease at the Regional Agricultural Research and Development Centre, Makandura in yala 2006 and maha 2006/07 season. Septoria leaf spot appeared at the early stages of the crop and later SLS caused by the fungus Mycosphaerella spp became predominant. The DOA recommendation of fertilizer and cowdung application were compared with organic fertilizer application which consisted of cowdung and paddy husk ash applied (2kg/plant/month) as main plots. Three banana varieties namely Seeni kesel, Ambun and Embul were also established as sub plots in split plot design with four replicates. Disease severity percentage was recorded fortnightly and disease epidemic computed. Growth and yield parameters were also measured. Application of paddy husk ash showed (r=0.45) lowest rate of average apparent infection rate of SLS disease followed by DOA fertilizer recommendation (r=0.49) and cowdung application (r=0.51). Of the varieties, Ambul showed the highest average apparent infection rate (r=0.63) followed by Ambun (r=0.43) and Seni kesel (r=0.40). However, yield parameters did not change with different management practices, which implied that soil amendment of Embul with cowdung or paddy husk ash and mixed cropping with Ambun and Seeni kesel reduced the disease. The high labor cost involved in soil amendments may be compensated by the long term effects of reduced environment pollution. KEYWORDS: Cultural control, Musa spp, Sigatoka leaf spot.
INTRODUCTION Banana is an important staple food in many countries in the humid tropics (Mobambo, 2002) and in Sri Lanka it is the most demanding fruit crop. It is grown all over the country mainly by small scale farmers and in home gardens. Several fungal diseases are reported in banana growing in Sri Lanka. Among these, leaf spot diseases such as Septoria, Cordona and Yellow Sigatoka were of minor importance earlier. Yellow Sigatoka disease, caused by Mycosphaerella musicola was common in Sri Lanka. However, recently the Sigatoka diseases became a potential threat due to the occurrence of Black Sigatoka with the evolution of Mycosphaerella fijiensis Merelet. (Udugama, 2002).
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Worldwide, the leaf spot disease caused by species of Mycosphaerella resulted in moderate to severe damage whenever significant rainfall occurs (Jacome et al., 2003). The disease is prevalent throughout the humid tropics and has a wide host range. It was reported that there is a 50% yield losts due to Yellow sigatoka disease (Burt et al., 1991) and 76% loss due to Black sigatoka disease (Mobambo et al., 1996). Management of both sigatoka diseases is difficult when the pathogen develops genetic resistance to fungicides. However, the disease can be managed using fungicides but this is a costly operation for the medium and small producers who are most affected (Maciel Cordero et al., 1998). Sigatoka leaf spot disease (SLS) is spread by wind or soil. The propergules of the disease are conidia and ascospores. Organic amendments could help to reduce the soil-borne inoculation of the disease and also increase plant resistance. The objective of this field experiment was to compare field performance in relation to initiation and spreading of SLS and monitor yield of different banana varieties with the use of different types of soil amendments which can be easily adopted in sustainable agricultural systems of the North Central Province in Sri Lanka. MATERIALS AND METHODS The experiment was conducted at the Regional Agricultural Research and Development Centre, Makandura during yala 2006 and maha 2006/2007. Average rainfall at the site is 932.3mm and maximum and minimum temperatures are 24.6째C and 32.7째C respectively. Three varieties of banana were established in a split-plot design as sub plots and three levels of management practices were arranged in the main plots with four replicates. Three varieties of banana which are widely grown in Sri Lanka were used in this study namely Embul, Amban and Seeni kesel and the different fertilizer management practices adopted are given in Table 1. Table 1. Description of different fertilizer treatments. Treatment Dosage/pit 1. DOA recommendation Cowdung Urea TSP MOP 2. Cowdung 3. Ash from paddy husk
2 kg 40.0 g 26.7 g 83.3 g 2.0 g 2.0 g
Application interval (Months) 4
1 1
BANANA SIGATOKA LEAF SPOT EPIDEMICS 201
Assessment of Sigatoka leaf spot disease epidemics All varieties in each main plot were screened against initiation and spreading of SLS disease throughout the experimental period. Spacing between banana plants was 3m x 3m. Three plants of each variety were considered as a main plot and there were three main plots per replicate. This was replicated four times and the SLS disease incidence recorded fortnightly from the field establishment in each treatment separately. The climatic parameters during the cropping season are given in Table 2. Table 2. Weather parameters in the cropping season of banana. Parameter Value Total rain fall (mm) Average maximum temperature (°C) Average minimum temperature (°C) Relative humidity (%)
1588.7 33.9 23.0 88.4
The experiment was established in a fallow land where there was no previous banana cultivation. The apical leaf of the plant was considered as the first leaf and the percentage area of disease spread was assessed in each leaf separately. Leaves of the plant were categorized according to area affected by the disease as 0-6 grades (Anon., 1998). 0 = No symptoms 1 = less than one percent of lamina with symptoms 2 = 1 to 5% of lamina with symptoms 3 = 6 to 15% of lamina with symptoms 4 = 16 to 33% of lamina with symptoms 5 = 34 to 50% of lamina with symptoms 6 = 51 to 100% of lamina with symptoms Disease severity index was calculated in each plant using the following formula; Σ nb Infection index = ------------(N-1) T Where, n = Number of leaves in each grade b = Grade N = Number of grades used in the scale T = Total number of leaves scored Epidemic level was calculated using the disease severity.
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Computation of disease epidemics The following formulae were used to compute disease epidemic in different management systems, where the rate of disease progress depends on the effective contact per unit of time and on the correction factor; d Xt / dt = r * ( 1-Xt ) r = Apparent infection rate By integration adding Integration constant = C Xt = 1 + C*er*t When Xt=0 at t=0 the integration constant should have the value C=-1. Equation becomes Xt= 1- er*t The log equation is, loge Xt / (1 - Xt ) = r * t ( Vanderplank, 1960 ) loge Xt / (1 - Xt ) was plotted against time (days) and r values estimated from the regression graphs. Estimation of growth parameters Date of planting, date of flower initiation, date of removing the bract, maturity period and date of harvesting were recorded. At harvesting, plant girth, height and the functional leaf number were recorded. Estimation of yield parameters At harvest, the total weight of the bunch and the average weight of the hands were recorded. Results were analyzed using SAS program (1982). RESULTS AND DISCUSSION Disease epidemics progress curves Disease epidemics of SLS disease did not show significant change with crop management practices in Embul and Ambun varieties (Fig. 1 and 2).
BANANA SIGATOKA LEAF SPOT EPIDEMICS 203 8 6
y = 0.6493x - 4.6646 R2 = 0.9596
4
y = 0.6023x - 4.2227 R2 = 0.943 y = 0.657x - 4.574 R2 = 0.9731
Loge 1/ 1-Xt
2 0 -2 -4 -6 140
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DOA Reccomended level Linear (DOAEpidemic Reccomended)
Ash
Cowdung
of sigatoka in variety Ambul against treatments. Linear (Cowdung) Linear (Ash)
Figure 1. Progress of disease epidemic of Sigatoka leaf spot disease in variety Embul under different management practices.
Variety Ambun expressed initial disease symptoms in 224 days after planting whereas both Embul and Seenikesel varieties initiated symptoms in140 days after planting. 2 y = 0.4849x - 6.4976 R2 = 0.9567
y = 0.4928x - 6.8694 R2 = 0.9826
0 y = 0.3111x - 5.39 R2 = 0.9562
Loge
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Days after planting DOA Reccomended
Ash
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Linear (Cowdung)
Linear (DOA Reccomended)
Linear (Ash)
Figure 2. Progress of disease epidemics of Sigatoka leaf spot disease in variety Ambun with different management practices.
204 WIJETILAKA AND RANASINGHE 2 y = 0.4849x - 6.4976 R2 = 0.9567
y = 0.4928x - 6.8694 R2 = 0.9826
0 y = 0.3111x - 5.39 R2 = 0.9562
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Figure 3.
DOA Reccomended
Ash
Cowdung
Linear (Cowdung)
Linear (DOA Reccomended)
Linear (Ash)
Progress of disease epidemics of Sigatoka leaf spot disease in variety Seenikesel with different management practices.
However, the lowest disease epidemic was observed in seni kesel variety under the DOA cultural practices compared to ash and cowdung treatments (Fig. 3). Apparent infection rate (r) The apparent infection rate or rate of SLS disease spread (r) in different management practices and varieties are given in Table 3. Of the management systems, ash application showed the lowest r value of 0.45 followed by DOA recommendation (r=0.49) and cowdung (r=0.51) treatments. Embul variety showed highest average rate of SLS disease spread (r=0.63) compared to Seeni kesel and Ambun varieties. Resistance to Mycosphaerella leaf spot exists among banana land races in Africa (Randy ploetz, 2004). Varietal resistance has also been found in Sri Lanka (Udugama, 2002). Table 3. Rates of Sigatoka leaf disease spread (r) in three banana varieties under differen systems. Management system Embul Seeni Ambu Mea kesel n n DOA recommendation Paddy husk ash Cow dung Mean
0.65 0.60 0.64 0.63
0.34 0.44 0.42 0.40
0.49 0.31 0.48 0.43
0.49 0.45 0.51
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Growth and yield parameters There were no significant differences in growth and yield parameters under different management systems (Tables 4 and 5). Similar observations were recorded in organic vs inorganic fertilization of plantain in Colombia (Echeverry Navarro, 2001). Table 4. Growth parameters under three management systems *. Management Plant Pseudostem Leaves at No. of Day to system height girth harvest hands flowerin (cm) (cm) (No.) g
Days to harvest
DOA 2.79 a 0.60 a 8.3 a 10.9 a 102.6 a 197.6 a recommendation Paddy husk ash 2.79 a 0.62 a 7.6 a 10.0 a 100.3 a 204.6 a Cowdung 2.8 a 0.59 a 7.7 a 10.1 a 98.9 a 203.8 a * Each figure is the mean of four replicates Means followed by the same letter in a column are not significantly different at p=0.05 according to Duncan’s multiple range test. Table 5. Yield parameters with three management systems *. Management system Average weight of Bunch hands (kg) weight (kg) DOA recommendation 1.37 a 20.32 a Paddy husk ash 1.83 a 16.29 a Cowdung 1.78 a 16.85 a * Each figure is the mean of four replicates Means followed by the same letter in a column are not significantly different at p=0.05 according to Duncan’s multiple range test.
However, there were significant differences in growth parameters among the cultivars at p=0.05. Plant height, number of hands, days to flowering and days to harvest were significantly lowest in cv. Embul (Table 6). Yield parameters also showed significant differences among the varieties (Table 7). Table 6. Growth parameters of three banana varieties*. Variety Plant Pseudoste Leaves at No. of height m girth harvest hands (cm) (cm) (No.)
Days to flower
Days to harvest
Embul 2.63 b 0.62 a 7.9 a 11.50 b 98.5 b 174.6 b Seeni kesel 2.83 a 0.58 a 8.7 a 12.38 a 116.4 a 214.7 a Ambun 2.93 a 0.61 a 7.1 a 7.64 c 91.6 a 222.3 a * Each figure is the mean of four replicates Means followed by the same letter in a column are not significantly different at p=0.05 according to Duncan’s multiple range test.
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Table 7. Yield parameters of three banana varieties *. Variety Average weight of hands (kg)
Average bunch weigh (t kg)
Embul 1.86 b 19.91 a Seeni kesel 1.24 c 15.24 b Ambun 2.27 a 17.65 ab * Each figure is the mean of four replicates Means followed by the same letter in a column are not significantly different at p=0.05 according to Duncan’s multiple range test.
Economic analysis Cost comparison showed high labor cost involvement in ash and cowdung treatments (Table 8). However, the advantages of organic fertilizer application on the environment would offset labor cost. CONCLUSIONS Results showed that there was no significant difference among application of DOA recommended fertilizer, Paddy husk ash and cow dung on disease severity in Ambun, Embul and Seeni kesel varieties. Embul showed higher apparent infection rate than Ambun and Seeni kesel. Hence, latter varieties could be cultivated in areas experiencing high sigatoka disease severity or in mixed cropping with Embul. No significant growth and yield parameters were observed among the soil amendments showing that cowdung and ash application could be used in the organic farming systems. Although input cost was lower, high labor cost could be overcome by possible longterm environmental benefits. Further, Ambun and Seeni keselwhich are resistant to the disease could be cultivated in conjunction with amendments or as mix crop with Embul.
BANANA SIGATOKA LEAF SPOT EPIDEMICS 207
Treatment
Source of fertilizer
DOA Recommendation
Cowdung Urea TSP MOP Ash Cowdung
Paddy husk ash Cowdung
Dose/plant/ kg* 2.000 0.390 0.120 0.900 24.00 24.00
kg/ha
1111.00 433.29 133.32 999.90 26664.00 26664.00
Cost of fertilizer/ha (Rs.)
Cost of labour/ha (Rs.**)
6666.00 12998.00 4666.20 33996.60 26664.00 79992.00
4800.00 14400.00 14400.00
Total cost/ha with labor (Rs.)
63126.80 41064.00 94392.00
Table 8. Comparison of annual cost of different fertilization practices in banana per year.
*Urea = Rs. 30.00 TSP=Rs. 35.00 MOP= Rs. 34.00 Cowdung = Rs. 3.00 Ash= Rs. 1.00 ** Labor /day = Rs. 300.00.
Total cost without labour/ha (Rs.)
58326.80 26664.00 79992.00
208 WIJETILAKA AND RANASINGHE
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