Effect of Varieties and Fungicide Rate on Chocolate Spot ( Botrytis fabae ) Disease of Faba Bean ( Vicia faba L.) at Tach Gayint District in South Gondar Zone, Amhara Region, Ethiopia

Faba bean is suffered with many biotic and abiotic factors. Chocolate spot disease, caused by Botrytis fabae is one of the biotic factors limiting yields of this crop resulting in yield losses up to 68% in Ethiopia. The experiment was conducted during 2020/2021 cropping season at Tach Gayint district, Ethiopia to determine the integration of faba bean varieties and fungicide rates on reducing chocolate spot disease. The experiment consisted of 12 treatments, viz. three faba bean varieties and four rate of Mancozeb fungicide in factorial arrangement. The experiment was laid out as randomized complete block design (RCBD) with three replications. Data was collected and analyzed. Results indicated that, disease incidence was reached at maximum percentage in all treatments on the last dates of assessment. But treatments were significantly difference in severity level. The least disease severity was recorded from varieties treated by 3.5 kg/ha of Mancozeb 80% WP with mean values Walki (12.7%), and (18.1% and 20.8%) on Gora and local variety respectively at the final dates of disease assessment. Similarly, the reduced AUDPC was also recorded from varieties treated by 3.5 kg/ha of Mancozeb 80% WP with mean values Walki (371.8% unit/day) and (539% and 686.4% days) on varieties Gora, and Local respectively. Whereas the maximum disease severity and AUDPC were obtained from unsprayed plots. Based on the results obtained, variety Walki treated with Mancozeb 80% WP at rate of 2.5 kg/ha and 3.5 kg/ha were effective to reduce the effect of chocolate spot disease for the study area.


Introduction Background and Justification
Faba bean (Vicia faba) is multi-purpose crop that plays an important role in the socio-economic life of farming communities in Ethiopia [1]. The crop is grown in the highlands (1800 -3000 m.a.s.l) of the country which receiving an annual rainfall of 700 -1000 mm where the need for cold temperature is met [2] [3].
The crop occupies the largest area in Ethiopia among other pulses [4] [5].
Despite the wide cultivation of the crop, its average yield is quite low in Ethiopia and the productivity is far below the potential because of several biotic and abiotic factors [6] [7] [8]. The production of faba bean is about 2.1 ton/ha compared with the production potential ranging from 2.3 to 3.9 tons/ha in Ethiopia [9].
Diseases are the most important factors limiting the production of faba bean.
Chocolate spot disease, caused by Botrytis fabae is one of the yields limiting factor of this crop. It is the most important disease of faba bean worldwide and it can devastate the yield of unprotected crops up to 67% [10]. The disease is highly prevalent and destructive, causing yield loss up to 61% on a susceptible and 34% on tolerant faba bean varieties in the central highlands of Ethiopia [11]. [12] also reported even higher losses of 68% in the unsprayed faba bean plots in northwest Ethiopia. The disease can be occurred across all the agro-ecological zones but it is more serious in areas of high rainfall (>900 mm) and high elevation (>2000 m.a.s.l) [7].
Various management options have been developed to reduce the yield losses of faba bean due to chocolate spot worldwide including Ethiopia. These include the use of chemical fungicides such as Mancozeb, Fungozeb, Nativo and Diprocon [3], resistant/tolerant varieties [13], use of certain cultural practices such as crop residue management and altering planting date [14] and biological control like Trichoderma harzianum; T. viride; Bacillus subtilis, Pseudomonas putida, Pseudomonas fluorescens and Ampelomyces qusisqualis [15]. As [16] reported, Integration of faba bean varieties with foliar sprays protected high chocolate spot epidemics, increased yield, yield components and maximized marginal benefit compared to a single control approach. Although, several improved faba bean varieties are released and important fungicides are recommended [17]. Farmers still depend on local varieties and raise the lack of improved seed as major problem for faba bean production [18]. There is also a gap on proper usage of the fungicide including its rate, specificity and time of application. With increasing faba bean diseases particularly chocolate spot disease farmers become obligated to shift their land from faba bean to cereal crop production. Currently, there is an urgent need to improve faba bean yield since the crop remains an important crop in the study area. One way of confronting this challenge is with sound crop protection programs that increase the productivity of the crop by refinement of integrated disease management strategies. The objectives of this study were, to evaluate the integration of faba bean varieties and fungicide application rates for

Description of the Experimental Site
The experiment was conducted at Agat farmer training center site in Tach Gayint district. Geographic location of the experimental site was 11˚34'53.9"N latitude and 38˚29'41.7"E longitude with an elevation of 2671 m.a.s.l [19].

Experimental Materials
In the experiment three faba bean varieties viz. Gora (EK01024-1-2), Walki (improved variety) and one Local variety were used. Varieties were selected based on their resistance level to chocolate spot. Walki is highly resistance, Gora (EK010241-2) moderately resistant [20] and local susceptible to chocolate spot was taken. [7] reported that in most cases local varieties are low yielding and highly susceptible to both biotic and abiotic stresses.
Seeds of the two varieties (Gora and Walki) were obtained from Adet and Gondar Agricultural Research Centers and local cultivar from farmer saved seeds. Fungicide (Mancozeb 80% WP) was used in this study and it was obtained from legal and authorized local market, since it is available in the area. As [17] Pulse crop manual, it is indicated, Mancozeb 80% WP is the best fungicide to manage chocolate spot of faba bean and also based on the research of [16] on management of chocolate spot the highest grain yield was recorded from plots sprayed with Mancozeb 80% WP.

Experimental Design and Procedures
The treatments were arranged in a randomized complete block design (RCBD) with factorial combination of four application rates of Mancozeb fungicide (unsprayed, 1.5 kg/ha, 2.5 kg/ha and 3.5 kg/ha) and three varieties (Local, Gora and Walki) in three replications (

Data Collection
All disease data were recorded since disease on set observed on the field and M. Abera, M. Semagn

2) Disease Severity
The disease severity was recorded from ten pre-tagged plants in each plot. It was recorded as the percentage of the total leaf surface covered with chocolate spot lesions on each expanded leaflet separately at regular intervals using a 0 -9 scale ( Table 2).
The severity grades were converted into percentage severity index (PSI) according to the formula by [22].
Sum of numerical rating PSI 100 No. of plant scored max max score on scale = × ×

3) Area under Disease Progress Curve (AUDPC)
The area under the disease progress curve (AUDPC) was calculated for each plot from PSI according to [23].
where, x i represents the cumulative disease severity expressed as a proportion at the ith observation, t i the time of the ith assessment, and n the total number of observations. AUDPC values were expressed in %-days.

Statistical Data Analysis
Data was subjected to analysis of variance (ANOVA) to determine the effects of varieties and fungicide rate combination. ANOVA in the significant of their effect, means will separated using Fisher's protected least significance difference (LSD) test at 0.05 level of probability [26]. The data was analyzed using Statistical Analysis System (SAS) software version 9.2 [27].  Table 3).

Results and Discussion
The disease was more rapid on local variety, which reached at higher level of final disease incidence (100%) followed by Gora (96.7%) 112 DAS. Lower disease incidence (85%) was recorded on variety Walki, (   Means within the same column followed by the same letter(s) are not significantly different; DAS = Days after Sowing, LSD (0.05) = Least significant Difference at P ≤ 0.05; M = Mancozeb; CV = Coefficient of Variations; WP = Wettable powder. and 12.7%) respectively at the final date of disease assessment (112DAS) ( Table   4). This finding was similar with [29] who reported that highest mean disease severity (47%) was recorded from unsprayed plot compared with highly protected plots with mean value (2%). Similarly, [30] showed that, applications of fungicide integrated with resistance varieties of faba bean increases the potential of reducing the severity of chocolate spot diseases than susceptible varieties.

3) Area under disease progress curve (AUDPC)
The analysis of variance showed that there was a significant difference (P ≤ 0.05) among main effect of varieties, fungicide rates and the interaction effects of varieties and fungicide rates for AUDPC (Table 5).
Based on the interaction effect of varieties and fungicide rate the local variety of faba bean sprayed with 1.5 kg/ha, 2.5 kg/ha and 3.5 kg/ha of Mancozeb 80% 2.5 kg/ha). These results indicated that the disease has progressed at faster rate on the unsprayed plot than plots which were sprayed with Mancozeb fungicide. This result is in agreement with [35] who showed that plots sprayed with Mancozeb retarded the apparent infection rate than unsprayed plots. Similarly, [16] reported that varieties sprayed with Mancozeb 80% WP were effective to reduce the apparent infection rate of chocolate spot disease than unsprayed varieties.
Maximum apparent infection rate was recorded from Local unsprayed (0.028318 units/day) and the minimum was from Walki sprayed with 3.5 kg/ha (0.008941 units/day). This finding becomes in agreement with [31] who showed that integrated use of resistance varieties with fungicide effectively reduced apparent infection rate of chocolate spot disease. Application of Mancozeb 80% WP at 2.5 and 3.5 kg/ha of on different faba bean varieties was effective to minimize the yield loss of faba bean and could be recommended to manage chocolate spot of faba bean. However, the experiment should be repeated across different environments over years in order to give the right recommendations and its rate may need to be well refined.