Management of Ascochyta Blight (Ascochyta rabiei) in Chickpea Using a New Fungi...

Mohammed Amin, Fufa Melkamu

  Open Access OPEN ACCESS  Peer Reviewed PEER-REVIEWED

Management of Ascochyta Blight (Ascochyta rabiei) in Chickpea Using a New Fungicide

Mohammed Amin1,, Fufa Melkamu1

1Department of Plant Science, College of Agriculture and Veterinary Science, Ambo University, Ethiopia

Abstract

Ascochyta blight is the Ethiopia's most important disease of chickpea that affects the quantitative and qualitative chickpea yield. Fungicides management is essential to control this disease. To evaluate the effect of new fungicide management on the ascochyta blight field trial was conducted in 2013 cropping season on randomized complete blocks design with three replications. Factors including: foliar sprays (Top, mancozeb and without spray as control). Statistical analysis showed significant differences among the treatments. The comparison of means showed that application of top fungicide was a suitable strategy for reduction of ascochyta blight severity, incidence and AUDPC as well as the maximum seeds per pod, pods per plant and grain yield recorded on new fungicide. Up to 244.29% marginal rates of return and 14595.5 Birr/ha net benefits were obtained by Top fungicide application. In general, as any other chemical systems, Top fungicide control of ascochyta blight should be regarded as one facet of the integrated control program rather than a method to be used alone.

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Cite this article:

  • Amin, Mohammed, and Fufa Melkamu. "Management of Ascochyta Blight (Ascochyta rabiei) in Chickpea Using a New Fungicide." Research in Plant Sciences 2.1 (2014): 27-32.
  • Amin, M. , & Melkamu, F. (2014). Management of Ascochyta Blight (Ascochyta rabiei) in Chickpea Using a New Fungicide. Research in Plant Sciences, 2(1), 27-32.
  • Amin, Mohammed, and Fufa Melkamu. "Management of Ascochyta Blight (Ascochyta rabiei) in Chickpea Using a New Fungicide." Research in Plant Sciences 2, no. 1 (2014): 27-32.

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1. Introduction

Chickpea (Cicer arietinum L.) is the third most important food legume in the world. India accounts for approximately 65% of world chickpea production, followed by Pakistan (9.5%) and Turkey (6.7%) [1]. Ethiopia is the leading chickpea producer in Africa. Despite the large area under chickpea cultivation, total production and productivity is quite low in most chickpea growing countries and there is a wide gap between potential yield (5 tons ha-1) and actual yield (0.8 tons ha-1). The primary cause of low yields in chickpea is its susceptibility to a number of biotic and abiotic stresses. Among biotic stresses, ascochyta blight is caused by Ascochyta rabiei (Pass.) Labr. is a widespread foliar disease that causes extensive crop losses (up to 100%) in most regions of the world where the crop is commonly grown [2].

Chickpea blight is the most devastating chickpea foliar disease in many countries [3]. This disease has caused considerable losses ranging from 5 to 100% around the world [4]. Ascochyta blight infection and disease progression occur from 50 to 25°C with an optimum temperature of 16-20°C, and a minimum of 6 hour leaf wetness. Disease severity increases with the increase in relative humidity [5]. Cloudiness and prolonged wet weather favor rapid development and spread of both diseases. The pathogens survives on infected or contaminated seeds, infected chickpea debris which causes ascochyta blight, produces both rain splashed conidia and windblown ascospores. As reported by [6], 2-3 foliar sprays with captan, mancozeb or chlorothalonilat 2-3 g L-1 water can effectively manage Ascochyta rabiei.

An adequate level of genetic resistance is not available in the cultivated genotypes and fungicides become ineffective under the high disease pressure. Hence, fungicides are available management an option is essential to successfully manage the disease and mitigate yield losses. Seed and soil borne nature of Ascochyta rabiei makes fungicidal seed treatments essential and useful [7]. Production of chickpea in the rainy season (main cropping) in Ethiopia could not be envisaged without fungicide application to control Ascochyta rabiei. Chlorothalonil, carbendazim and mancozeb were used to control A. rabiei disease. The application was judicious as there was no alternative to shift to new fungicides. At the same time, prices were fluctuating and up surging as the need for fungicides increase by farmers. Therefore, with the objective to alleviate the problem of price increase on fungicides, get an alternative control option for A. rabiei disease, and minimize the chance of resistance development this activity will be initiated. Hence, this study was undertaken with the following objectives: to evaluate new fungicide (Top) sprays for ascochyta blight management and yield components and seed yield and to determine the economics of fungicide application.

2. Materials And Methods

2.1. Description of the Study Area

Experimental trail was conducted at Ambo University Research Station during the 2013 cropping season. The altitude of the study areas was between 1900 and 3100 m. a. s. l, geographical positions of N 08° 43.423-N 10° 12.082 and E 037° 28.902-040° 62.590. Heavy rain observed from onset of July to the end of October. The annual rainfall ranges from 1000-1588.06 mm and the temperature of the district ranged between 9.44°C and 21.86°C with average of 15.65°C. The soil of the experimental site is clay loam in texture and pH value of 6.8.

Table 1. Variety of chickpea used for experiment with its agronomic characteristics

2.2. Experimental Design and Treatments

The experiment was arranged in randomized complete block design with three replications. Three fungicide treatments (Top, mancozeb and no treatment) were used. In this experiment, mancozeb was used as a standard check. Likewise, Top was a new fungicide chemical which have not been used before for the controls of ascochyta blight disease in Ethiopia. As described on Table 1, seeds of improved chickpea local variety (Desi type) which is susceptible to ascochyta blight were planted into each plot size of 0.8 × 1.5 m. Spacing between plants and rows were maintained as 10 cm and 30 cm, respectively. There were 8 plants per row and the three central rows were harvested for determining seed yield. Each chickpea plots consisted of a total five rows. Each plot and blocks were separated by a buffer zone of 1 and 1.5 m, respectively to prevent fungicide drift or cross contamination. First spray of fungicides were started soon after the initial appearance of disease symptoms using knap-sack sprayer. The Top and mancozeb fungicides were applied at the rate of 1 L/ha and 2kg/ha, respectively at an interval of eight days. All agronomic practices such as weeding, cultivation were kept uniform for all treatments in each plot.

2.3. Disease Scoring

Natural inoculation was relied upon in all experimental plots. Beginning at 62 days after planting, assessment for ascochyta blight severity and incidence were conducted at weekly intervals. Incidence of ascochyta blight as assessed by counting the number of plants on the middle three rows, 15 pre tagged plants, were expressed as percentage of total plants. Since ascochyta blight affects all aerial parts of the plant, the disease reaction of individual treatments were recorded on whole plant basis 62 days after planting on 15 randomly selected plants per plot using a 1‒9 rating scale similar to those utilized by [2, 9, 10, 11]. where 1, no visible symptoms; 2, minute lesions prominent on the apical stems; 3, lesions up to 5‒10 mm in size and slight drooping of apical stems; 4,lesions obvious on all plant parts and clear drooping of apical stems; 5, lesions on all plants parts, defoliation initiated, breaking and drying of branches slight to moderate; 6, lesions as in 5, defoliation, broken, dry branches common, some plants killed; 7, lesions as in 5, defoliation, broken, dry branches very common, up to 25% of plants killed; 8, symptoms as in 7 but up to 50% of the plants killed and 9, symptoms as in 7 but up to 100% of the plants killed. To evaluate treatment costs, benefits, and economic analysis, data on costs of fungicide applications (fungicide costs, labor for fungicides application, and costs associated with sprayer equipment hire; planting, weeding, cultivation, harvesting and threshing costs for grain seed) were recorded. The per cent incidence was calculated as:

Rating scales were converted into percentage severity index (PSI) for the analysis of disease severity using the following formula:

2.4. Disease Progression Analysis

Area under the disease progress curve (AUDPC) and growth curve models were developed for the disease progress data. AUDPC values were calculated for each plot using the following equation [12].

Where, Xi is the cumulative disease severity expressed as a proportion at the ith observation, tiis the time (days after planting) at the ith observation and n is total number of observations.

2.5. Agronomic Data Recorded

Data of yield and yield components and other agronomic parameters were collected as follows:

Plant height (cm): average height of 15pre tagged plants of each plot measured from ground level to the tip at maturity.

Number of pods per plant: were determined as the average number of pods of 15 randomly pre-tagged plants from the three central rows.

Number of seeds per pod: were determined as the average number of seeds of 10 randomly selected pods from pre-tagged plants.

Seed yield (Kg/ha): was obtained from the three central rows of each experimental plot; it was converted into kilogram per hectare (after adjusting to 10% seed moisture content using moisture meter).

Hundred seeds weight (g): the weight of hundred seed obtained at random sample from the total seed harvested of each experimental plot was recorded.

2.6. Data Analysis

Data on disease parameters (incidence, severity, PSI, AUDPC) and data on yield and components (plant height, pods/plant, seeds/pod, hundred seed weight and seed yield) were subjected to analysis of variance (ANOVA) using Statistical Analysis System (SAS) version 9.2 software. Fisher’s protected Least Significant Difference (LSD) values were used to separate differences among treatment means (P < 0.05) for the field evaluation of ascochyta blight disease.

2.7. Yield Loss Estimation

The relative losses in yield of each treatment were determined as percentage of that of protected plots of the experiment. Losses were calculated separately for each of the treatment and yield component of the chickpea was determined as a percentage of that of the protected plots and yield losses was calculated based on the formula of:

Where, RL – relative loss, Y1 mean of the respective parameter on protected plots (plots with maximum protection) and Y2-mean of the respective parameter in unprotected plots (i.e. untreated plots or treated plots).

2.8. Economic Benefits Assessment

Price of chickpea seeds (Birr/kg) was assessed from the local market and total price of the commodity obtained was computed on hectare basis. Input costs like fungicides and also labor costs/ha were recorded. The price of fungicides were calculated based on their frequencies used on plot basis and were converted into a hectare. The total amount of these materials used for the experiment was computed and their price was converted into hectare basis. Cost of labor for spraying these fungicides application from the first day to final were calculated and then converted on hectare basis. The net return for each fungicide treatment was obtained by deducting total cost of fungicide protection from total return. Increase in net return (net benefit) due to fungicide application was assessed by deducting the net return from the unsprayed plot. The rate of return to investment was computed by dividing the net benefit by net variable cost. The fungicide that yielded the highest rate of return was generally recommended for the use by farmers.

3. Results and Discussion

3.1. Ascochyta Blight Severity and Incidence

Chickpea ascochyta blight severity was first observed on 54 days after planting (DAP). However, diseases assessment was started at 62 DAP. The two fungicides were significantly (p < 0.05) different in terms of their respective reaction to the disease (P < 0.05).

The plots showed significantly (p < 0.05) different levels of ascochyta blight severity at all dates of assessment (62, 70, 78 and 86 DAP). On the first date of severity assessment, the lowest average severity level of ascochyta blight was recorded on Top (28.6%) and followed by mancozeb (30.8%) fungicide sprayed plots while the maximum level of severity was scored on control plot (35.9%). Moreover, the maximum (45.4%) and minimum (33.8%) severity were recorded on ‘Top’ and control respectively on the last date of severity assessment (Figure 1). This might be due to the fact that “Top” fungicide has ability to reduce primary infection and at the same time it is able to manage spreading of ascochyta blight secondary inoculum between neighboring plants. Based on a study conducted in Canada, [13], states that although genetic resistance is available in some cultivars, it is only partial and starts to break down at flowering. Lack of resistance in chickpea cultivars helps fungicide to play an important role in the management of disease. Foliar application with protectant fungicides such as Bordeaux mixture (a.i. copper sulphate + hydrated lime), wettable sulphur (a.i. sulphur), maneb and captan can result in reduced disease levels [14]. Chlorothalonil (BravoR), a contact fungicide was effective against A. rabiei, [15].

Figure 1. Severity of ascochyta blight as influenced fungicide sprays on chickpea during 2013

There was significant (p < 0.05) ascochyta blight incidence difference between plots treated with Top, mancozeb fungicide and no spray until the third date of disease assessment. The difference between the levels of disease incidence remained statistically (p < 0.05) non-significant on fourth (86 DAP) date of disease assessment. Plot sprayed with Top showed significantly lower disease incidence than the unsprayed plot after a week when it was first treated with the fungicide. The unsprayed plot had the maximum disease incidence levels consistently for the last four assessment dates. On the third date of disease assessment i.e. on the 78th DAP, the mean incidence level of the disease on unsprayed plot was 99.3% whereas plots sprayed with Top and mancozeb fungicide were 95.7 and 98.9%, respectively (Figure 2).Treatment of seed with Crown fungicide can greatly help in reducing the initial inoculum level and preventing the spread of the disease or races into new areas [16]. Similarly, [17], reported that Thiabendazole reduced the incidence of seed borne Ascochyta rabiei from 45% in the untreated control to 0% in treated seed. Ascochyta blight is seed-borne and infected seed is an important source of primary inoculum in the field [18, 19]. As a result, seedlings emerging from infected seeds show severe disease development [7]. Under the condition when disease-free seed is not available, foliar spray is preferable to prevent spread of the disease.

Figure 2. Incidence of ascochyta blight as influenced by fungicide treatments on chickpea during 2013
3.2. Diseases Progress: Area Under Diseases Progress Curve

The area under disease progress curve (AUDPC) is a very convenient summary of plant disease epidemics that incorporates initial intensity, the rate parameter, and the duration [20] of the epidemic which determines final disease intensity. Effect of Top and mancozeb foliar sprays were significantly (P < 0.01) different in terms of reducing AUDPC. Lower value of AUDPC was calculated from top spray (1330.08%-day) and followed by mancozeb (1435.53%-day) while the maximum AUDPC was recorded from control plot (1722.87%-day) (Figure 3). [21], claim that the benefits of using seed treatments to control ascochyta infection on field pea are inconclusive, possibly because airborne inoculum has a greater influence on the ascochyta diseases on this crop, than seed borne inoculum.

Figure 3. Progress of ascochyta blight as influenced by fungicide treatments on chickpea during 2013
3.3. Effect of Fungicide Spray on Yield Components, Grain Yield and Loss of Chickpea in 2013

[22], state that various agronomic characters like pod/plant, seeds/pod, hundred seed weight, days to flowering, and days to maturity play an important role in the severity of ascochyta blight in chickpea. In current experiment, data on grain yield, seeds per pod, plant height, pods per plant and hundred seed weight were collected. Grain yield was significantly (P < 0.05) increased by fungicide sprays. Top fungicide treatment significantly increased grain yield (4.79 tons/ha) and followed by mancozeb (4.43 tons/ha). Nonetheless, the lowest grain yield was recorded on control plot (2.92 tons/ha). [23] prove that fungicide applications in chickpea have had a substantial impact on seed yield at one site; yield in the untreated check is less than 5% of the best fungicide treatment.

Relative yield losses due to ascochyta blight reached 41.3% on control and 10.9% on mancozeb treated plot, respectively. Seeds per pod of the chickpea were significantly increased by fungicide treatments. Maximum Seeds per pod of 1.67 and 1.61 were recorded on sprayed plots by Top and mancozeb, respectively. While, the minimum seeds per pod was scored on plot without fungicide treatment (Table 1).

Table 2. Effect of foliar spray of fungicides on yield components and grain yield of chickpea

Effect of Top and mancozeb foliar sprays was significantly (P < 0.05) different in terms of enhancing pods per plant. Plots treated with Top and mancozeb showed pods per plant 117.9 and 128.96, respectively. Whereas, the lowest pods per plant 112.7 was recorded on control plot (Table 2).The increased seed yield with high plant population is attributable to the production of more pods [24] and more seeds per unit area [25], despite more disease on individual plants [26].

3.4. Cost Benefit Analysis

Partial budget analysis indicated that the new fungicide, top had the highest total return but the unsprayed plots had the lowest total return (Table 3). On the other hand partial budget analysis indicated that Top and mancozeb fungicides spray schedules used gave high Net benefit and rate of return. [27] indicated that when assessing a crop for risk, it is also necessary to asses it for the potential to cover the cost of application which depends on the potential yield. Fungicides are used because they provide effective and reliable disease control, deliver production in the form of crop yield and quality at an economic price and can be used safely [28]. In Canada, the timely and efficient use of fungicides has remained a major factor in the successful management of ascochyta blight nd the economic viability of pulse crops.

Table 3. cost and benefit analysis (B/ha) of fungicides spray for ascochyta of chickpea

4. Conclusions

Top fungicide treatments significantly reduced the ascochyta blight severity, incidence and AUDPC, and increased pods per plant, seeds per pod and grain yield of chickpea as compared with mancozeb treatment and the untreated control at Ambo, Ethiopia. This is an indication of the potential as well as the exhibition of the great potential of the Top to effective control of the ascochyta blight in the specified area. Therefore, due to judicious reduction in disease epidemics, cost effective made Top higher in controlling ascochyta blight. Based on the results of the this location test carried out at Ambo, Ethiopia on the effectiveness of the test fungicide, Top, and consideration of the wide range of ascochyta blight disease in chickpea controlled, the use of Top by both individually and or private sector will no doubt improve chickpea production in in similar agro-ecology as well. This is because of excellent in ascochyta blight control and reasonable and acceptable price to be invested in fungicides control. In general, as any other chemicals systems, Top fungicide control of ascochyta blight should be regarded as one facet of the integrated control program rather than a method to be used alone.

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