Integrated management of chocolate spot (Botrytis fabae Sard) through host resistance and fungicide application in the highlands of Bale, Southeastern Ethiopia

Because of its nutritional value, Faba bean (Vicia faba L.) is one of the most important food legumes both as energy and protein source. It is among the most important pulse crops produced in Ethiopia in general and on the highlands of Bale in particular. Field experiment was conducted at Sinana Agricultural Research Center on-station using RCBD with three replications to study the integrated effect of fungicide (sprayed at various frequencies) and faba varieties to manage chocolate spot. The experiment consisted of fi ve (5) fungicide application frequencies and two Faba bean varieties (Gebelcho and Mosisa). Logistic model, [ln [(Y/1-Y)] was used to calculate the disease parameters such as disease progress rate (r) and AUDPC. The partial budget analysis was carried out to asses fi nancial profi tability of fungicide application for the management of chocolate spot. ANOVA showed statistically signifi cant difference (P<0.05) among the treatments for the disease parameters. The lowest chocolate spot severity (23.15%) and the best chocolate spot disease control was achieved from Gebelcho variety sprayed four times. Similarly, the lowest r (-0.00453units/day) and AUDPC (823.1 %-days) were recorded from Gebelcho variety sprayed four times. Regarding yield and yield components, ANOVA showed signifi cant differences (P<0.05) among the treatments. The highest number of pods per plant (15.28) was recorded from Gebelcho variety sprayed 2 times whereas, the highest TKW of 662.60 g was recorded from Gebelcho variety sprayed three times. In terms of grain yield, the maximum grain yield of 3515.44 kg/ha was obtained from Mosisa variety sprayed four times and four times spray of Gebelcho variety gave the second highest grain yield of 3313.70kg/ha. Partial budget analysis has shown the maximum marginal benefi t of 41044.8ETBha-1 obtained from Mosisa variety sprayed four times at weekly interval while the second marginal benefi t of 38624.4ETBha-1was obtained from Gebelcho variety sprayed four times at weekly interval. The maximum MRR of 1726.11 % was obtained from Mosisa variety sprayed once and the second highest MRR (1592.84 %) was calculated from Gebelcho variety sprayed four times. Therefore, the recommendation is made depending on the results from the biological studies and partial budget analysis. For small scale farmers, it is recommended to produce Mosisa variety by spraying mancozeb 80% WP once to maximize the fi nancial benefi t from faba bean production. But, for small scale farmers who can afford, it is recommended to produce faba bean variety Mosisa sprayed three times by a fungicide mancozeb 80%. However, for large scale farmers who are producing faba bean for export market are recommended to produce faba bean variety Gebelcho sprayed four times at 7-10 days interval. Research Article Integrated management of chocolate spot (Botrytis fabae Sard) through host resistance and fungicide application in the highlands of Bale, Southeastern Ethiopia Ermias Teshome* and Dagne Kora Sinana Agricultural Research Center, P.O.Box-208, Bale-Robe, Ethiopia Received: 31 January, 2021 Accepted: 22 February, 2021 Published: 24 February, 2021 *Corresponding author: Ermias Teshome, Sinana Agricultural Research Center, P.O.Box-208, Bale-Robe, Ethiopia, E-mail:


Introduction
Faba bean (Vicia faba L.) is among the most important pulse crops produced in Ethiopia covering about 459, 183.51 ha of land with a total annual production of 697, 798.39tyr -1 [1]. The interest of farmers to produce faba bean in Ethiopia is growing because of the fact that its demand on the export market is increasing [2]. It is also one of the most important food legumes due to its high nutritive value both in terms of energy and protein contents (24-30%) and also is an excellent nitrogen fi xer. However, its average yield under smallholder farmers is very low, ranging from 1 to 1.2tha -1 [3]. Lack of or low adoption of high yielding cultivars, diseases, weeds and insect pests together with abiotic factors are the major constraints for Faba bean production [4]. Chocolate spot (Botrytis fabae Sard.) is one of economically important diseases that damages all Citation: Teshome  seeded varieties (Gebelcho)). The fertilizer rate of 100 kg NPS/ ha was applied as non-experimental variable. The disease development was rated using 1-9 scoring scale, where, 1= No disease symptoms or very small specks; 3= few small discrete lesions; 5= some coalesced lesions with some defoliation; 7= large coalesced sporulating lesions, 50% defoliation and some dead plant; and 9= Extensive lesions on leaves, stems and pods, severe defoliation, heavy sporulation, stem girdling, blackening and death of more than 80% of plants [11]. Disease scores were converted to Percent Severity Index (PSI) [12].

Data collected
The fi eld data such as disease (severity and incidence) data, number of pods per plant, number seeds per pod, number of seeds per plant and data from laboratory which are TKW and grain yield were collected at an optimal time for collection.
The disease severity data collected based on scoring scale was converted to percent severity index for analysis. All the collected data were fed to computer, cleaned and subjected to SAS statistical package for analysis.

Data management and statistical analysis
Logistic, [ln [(Y/1-Y) [5] and Gompertz, -ln[-ln(Y)] [13], models were compared to estimate the disease parameters from each treatment. The logistic model was chosen based on the test of Goodness of the fi t of the models using coeffi cient of determination (R 2 ). Therefore, variables for fi eld experiment data under different treatments were analyzed using logistic model, ln[y/ (1-y)] with the SAS Procedure [14]. Mean separation was made based on List Signifi cance Difference (LSD) technique at 5% probability level. AUDPC [15] and disease progress rate (r) values were calculated for each plot using the formula indicated below. ANOVA was performed for disease severity index [12], AUDPC [15] and rate of disease progress (r). The association of disease parameters with yield and yield related parameters was assessed using correlation and regression analysis.

Sum of Numerical Ratings X 100 PSI
Number of Plants Scored X Maximum Score on Scale Where, X i = the PSI of disease at the i th assessment t i = is the time of the i th assessment in days from the fi rst assessment date n= total number of disease assessments

Cost-Benefi t analysis
The partial budget analysis was performed following the standard methodology, taking the variable costs in each treatment in to account ( Table 1). The Marginal Rate of Return (MRR) was computed for each treatment ( Table 2). The total income from each treatment was obtained as Sale Revenue (SR) parts of the crop and reduces faba bean production globally [5].
Similarly, it is one of the major faba bean yield limiting biotic factors for faba bean production in Ethiopia. Yield losses of up to 61% on a susceptible cultivar, and 34% on a tolerant cultivar were recorded in Ethiopia [6,7]. For its management, there are a number of possible options such as the use of moderately resistant/tolerant varieties, application of fungicides, biological control, induced resistance and cultural practices [3].
Host resistance is one of the most acceptable and economically profi and their integration with different cultural practices [9].
Indicated an option of early planting for the management of the disease. However, early planting may not be practical in regions where unreliable and erratic rainfall occurs frequently.
Besides the importance of chocolate spot on Bale highlands, the effort towards the management of this disease is very minimal.

Objective
The study was conducted to study the integrated effect of fungicide (sprayed at various frequencies) and faba varieties to manage chocolate spot.

Materials and methods
The fi eld experiment was conducted during "bona" (main) The production cost and benefi t from each treatment was analyzed using partial budget analysis. Similarly, the Marginal Rate of Return (MRR) was computed by considering the total variable costs incurred in each treatment. In this experiment the sum cost of fungicide, water, sprayer rental, labor for spraying, labor for water supply and labor for cleaning equipment were considered as variable costs. The MRR was used as major criteria which measures the effect of additional investment on net returns [16]. MRR provides the benefi t value obtained as a function of the additional investment for the management of Chocolate spot in percentage.

Results and discussion
There was statistically signifi cant difference (P<0.05) among treatments for all the disease parameters, Chocolate spot Disease Severity (%), AUDPC (%-days) and Disease Progress Rate (r) (units per day) ( Table 3). On both varieties, there was not statistical difference between treatments for chocolate spot severity during the fi rst two scoring periods. Similar the work of [17] and [18] justifi es this result and they reported that there is not statistically justifi able difference between treatments regardless of the resistant level of faba bean varieties during the early stage of disease development. The maximum chocolate spot severity of 50 % was recorded from unsprayed susceptible variety Mosisa. The second highest chocolate spot disease severity of 48.15 % was recorded from Gebelcho variety with no fungicide spray whereas lower chocolate spot severity of 23.15% and 29.32 % were recorded from Gebelcho variety sprayed four times and three times, respectively. Its agreed with similarly reported work that recorded the highest disease severity from unsprayed susceptible local variety while the lowest disease severity was recorded from moderately resistant Degaga variety sprayed at seven days interval [19]. Considering variety Mosisa, the lowest disease severity recorded was 29.63% after spraying the fungicide four times while the highest severity of 50% was recorded from unsprayed plot (Table 3). Again, this result is supported by [19] as they found that application of fungicide radically reduced disease severity and they observed high disease pressure on unsprayed plots. Chocolate spot severity showed an increasing trend with time as fungicide application frequency was decreasing (Figure 1). This trend was similarly reported by [17,19] when they found the increasing trend of diseases severity and other disease parameters with  the decreasing in fungicide application. Similarly [20] have also reported the reduction of disease severity as the fungicide application was reducing.
ANOVA for chocolate spot disease progress rate (r) has shown statistically signifi cant difference (P<0.05) between treatments. Higher disease progress rates (r) of 0.23360 units/ day and 0.21370 units/day were recorded from unsprayed plots of Mosisa and Gebelcho varieties, respectively. On the other hand, lower disease progress rates of -0.00453 units/day and -0.00262 units/day were recorded from Gebelcho variety sprayed three times and four times, respectively. The same result was reported from the work of [21]. They reported the suppression of the apparent disease infection rate in sprayed plots by about six (6) times over unsprayed plots.
Regarding AUDPC, statistically signifi cant difference was observed between treatments (P<0.05). The highest AUDP (1730.6%-days) was recorded from unsprayed plot of Mosisa (susceptible) variety whereas the lowest AUDPC (823.1%days) was recorded from Gebelcho (moderately resistant) variety sprayed four times (Table 4). Similarly [22] reported the highest AUDPC of 1817%-days from susceptible faba bean variety which has not received any fungicide spray and the lowest AUDPC of 595%-days from moderately resistant variety which has received fungicide spray at seven (7) [20,23]. Similarly [23,24], have also reported the reduction trend of faba bean TKW as the fungicide spray is decreasing.
Regarding grain yield, the highest grain yield of 3515.44kg/ ha was recorded from variety Mosisa sprayed four times whereas the lowest grain yield of 1705.5kg/ha was recorded from Gebelcho variety with no fungicide spray ( Table 2). The fungicide application frequency infl uences faba bean yield as faba bean grain yield shows a decreasing trend with decreasing  fungicide application frequency [21]. Similarly [23,24] and [22] have found that faba bean grain yield has decreased when the fungicide application decreases and they found the highest grain yield from plots which have received the highest frequency fungicide application. Host plant resistance is also one of the varietal factor which infl uences fungicide application frequency and faba bean grain yield. This study has revealed the effect of host plant resistance on faba bean yield. Mosisa variety is found to be susceptible and tolerant to chocolate spot disease while Gebelcho variety is moderately resistant to chocolate spot. At all level of fungicide spray, the highest chocolate spot disease severity was recorded from Mosisa variety. But, regardless of the disease severity scores of Mosisa variety, the highest grain yield was recorded from Mosisa variety at all frequencies of fungicide spray. This is because of the tolerance of the Mosisa variety to chocolate spot.

Partial budget analysis
Partial budget analysis has depicted the highest marginal benefi t of 41044.8ETB ha -1 from Mosisa variety sprayed with Mancozeb 80% WP four times at weekly interval and the second highest marginal benefi t of 38624.4ETB -1 was recorded from Gebelcho variety sprayed four times. The lowest marginal benefi t of 20466ETBha -1 was obtained from unsprayed Gebelcho variety with no fungicide spray (Table 2). Similarly, the highest marginal rate of return (1726.11%) was obtained from Mosisa variety sprayed once and the second highest marginal benefi t of 1592.84% was recorded from Gebelcho variety sprayed four times using a fungicide mancozeb 80% WP. This indicates that for every 1.00 ETB invested to spray Mancozeb 80% WP to produce faba bean, it gives a return of 17.26ETB and 15.93ETB from Mosisa variety sprayed once and Gebelcho variety sprayed four times, respectively. Therefore, partial budget analysis has depicted that production of Faba bean variety Mosisa sprayed once with Mancozeb 80% WP for the management of chocolate spot optimizes the profi tability from faba bean production under small scale agriculture/small holder farmers' condition and production of faba bean variety Mosisa with four times application of fungicide also gives high marginal rate of return (1419%) and the highest marginal benefi t of 41044.8ETB ha -1 .
For those farmers who produces faba bean for export market, production of Gebelcho variety sprayed four times with a fungicide Mancozeb 80% WP maximizes the benefi t from faba bean production.