Soybean (Glycine max L. Merrill) is the world’s most important seed legume, often called the “miracle crop.” It is the most versatile of the world’s major crops. It can be grown in a wider variety of soil and climatic conditions than any other major world crop. Currently, soybeans account for about 35% of total harvested area devoted to annual and perennial oilseed crops. The global production of soybean for the year 2019-2020 recorded 336.563 million metric tons. Brazil tops global soybean production 123 million metric tons and productivity 3333 kg per hectare, followed by America and Argentina. India is far behind and having the opportunity to improve its productivity [7].  Soybean expansion is occurring much faster than with other significant grains or oilseeds crops. It is susceptible to many diseases that cause significant yield loss each year.  Disease threat consistent causes attributing to low yield, diseases occupy the prime position concerning yield loss. Some of the essential fungal foliar diseases of soybean were Alternaria leaf spot (Alternaria tenuissima), Cercospora frog eye leaf spot (Cercospora sojina), Rust (Phakopsora pachyrizi), Myrothecium leaf spot (Myrothecium roridum), Target leaf spot (Corynospora cassicola) and Colletotrichum blight (Colletotrichum dematium). Leaf spot incited by Alternaria tenuissima reported being the most prevalent and comprehensive spread disease in soybean [8] reported 10 to 20% reduction in yield due to Alternaria leaf spot as resulted on account of premature defoliation, pod and seed decay [4] reported that among the different foliar diseases, leaf blight Alternaria spp., is one of the most dominant ones that causes average yield loss in the range of 32-57%. Frogeye leaf spot of soybean caused by Cercospora sojina is an economically important foliar disease. Monoculture and favourable environmental conditions cause severe economic loss [5, 2, 11, 10]. Since the last few years, Alternaria and Frog eye leaf spot is considered a minor disease in Vidarbha but now-a-days, leaf spot symptoms on soybean are being observed in severe proportion from various places Vidarbha region on existing cultivated varieties of soybean that becoming potentially threat for soybean cultivation. It was considering the importance of soybean yield losses due to Alternaria and Frog eye leaf spot the present investigation was carried out under field conditions to compare the efficacy of the newer fungicide with available fungicide against both Alternaria tenuissima andCercospora sojina.

Materials and Methods

Field evaluation

The field experiment was carried out on the Regional Research Centre, Amravati (Dr Panjabrao Deshmukh Krishi Vidyapeeth, Akola) during Kharif, 2017 Randomized Block Design with nine treatments in three replications. Soybean variety, JS-335, was used in field experiments as it contributes most of the area of soybean cultivation. It was sown at 45 x 05 cm spacing in plot size 3.6m x 6 m (8 lines of 6-metre length). The crop was raised as per recommended package of practices, and protective irrigation was given as and when required. New combination of fungicide Azoxystrobin 5.6% w/v + Tebuconazole 10% w/v + Prochloraz 20% w/v EC was tested against Alternaria tenuissima andCercospora sojina with three different concentrations 2.0 ml/lit, 2.5ml/lit and 3ml/lit  to standardize dose with other recommended fungicides.  A newer fungicide and five recommended fungicides along with control were evaluated under field condition. Two sprayings of all the treatments were undertaken at 55 and 70 days after sowing of the crops. One plot/replication was maintained as the control without spraying any fungicides. Observations on foliage Alternariaand Frog eyeleaf spot disease were recorded after each spraying. For recording percent, disease index 0-9 scale was used [1]. Rating scale is as 0-No lesions/spots/discolouration, 1-1% area covered with lesions / spots / discolouration, 3-1.1–10% area covered with lesions/spots/discolouration, 5-10.1–25% area covered with lesions / spots / discolouration, 7-25.1 –50% area covered with lesions / spots / discolouration, 9-More than 50% area covered with lesions/spots/ discolouration. Five plants per treatment per replication were selected randomly and tagged for recording the observations. Three trifoliate leaves (bottom, middle and top) from the main branch on each observed plant were selected for recording observations and the percent disease index of Alternariaand Frog eyeleaf spot was worked out as per the procedure [9]. At harvest of the crops, an observation on seed yield was recorded in all the treatments and yield data was presented on per plot and per hectare basis.

Calculation of Percent Disease Index (PDI)

The above rating scales or grades are utilized to calculate PDI using the following formula [14] and yield of soybean (q/ha) was recorded and analysis was done using standard statistical methods.

                                                                Sum of numerical rating

Percent Diseases Index=   —————————————————————————— × 100

                                       Total number of plant x Maximum ratting scale observed

Percent disease control (PDC) was worked out by applying the formula

   PDI in control plot – PDI in treatment plot

Percent Disease Control=    —————————————————– × 100

    PDI in control plot

Treatments

Table 1: Efficacy of fungicides against Leaf spot Alternaria tenuissima in Soybean

Table 2: Efficacy of fungicides against Leaf spot Cercospora sojina in Soybean

*Figures in parentheses are Square root transformed value

Table 3: Effect of fungicide on seed yield of soybean

Results                                                                                  

Field evaluation

Data presented in Table 1, indicates that, the percent disease incidence of Alternaria tenuissimawas in the range of 8.45 to 15.22 at 55 DAS.  Sprays of fungicide in treatment T3 Azoxystrobin 5.6% w/v + Tebuconazole 10% w/v + Prochloraz 20% w/v EC (0.2%) 3ml/lit resulted in least disease index 8.45 and it was at par with treatment  T2 i.e. Azoxystrobin 5.6% w/v + Tebuconazole 10% w/v + Prochloraz 20% w/v EC (0.2%) 2.5ml/lit resulted in disease index 8.52. Maximun disease index found in untreated control i.e. 15.22. After the first spray percent disease control achieved in the range of 38.96 to 44.48 at 55 DAS.  The highest per cent disease control recorded in treatment T3 i.e. 44.58 followed by treatment T2 44.02. Similar treand was observed in 70 DAS the percent disease incidence of Alternaria tenuissimawas in the range of 9.80 to 18.75 at 70 DAS. Sprays of fungicide in treatment T3 Azoxystrobin 5.6% w/v + Tebuconazole 10% w/v + Prochloraz 20% w/v EC (0.2%) 3ml/lit resulted in least disease index 9.80 and it was at par with T2 i.e. Azoxystrobin 5.6% w/v + Tebuconazole 10% w/v + Prochloraz 20% w/v EC (0.2%) 2.5ml/lit resulted in disease index 9.88. 70 DAS the highest per cent disease control recorded in treatment T3 Azoxystrobin 5.6% w/v + Tebuconazole 10% w/v + Prochloraz 20% w/v EC (0.2%) 3ml/lit i.e. 47.73 followed by treatment T2 Azoxystrobin 5.6% w/v + Tebuconazole 10% w/v + Prochloraz 20% w/v EC (0.2%) 2.5ml/lit 47.31.

Data presented in Table 2, indicates that, the percent disease incidence of Cercospora sojina was in the range of 6.90 to 16.71 at 55 DAS.  Sprays of fungicide in treatment T3 Azoxystrobin 5.6% w/v + Tebuconazole 10% w/v + Prochloraz 20% w/v EC (0.2%) 3ml/lit resulted in least percent disease index (6.90) and it was at par with treatment  T2 i.e. Azoxystrobin 5.6% w/v + Tebuconazole 10% w/v + Prochloraz 20% w/v EC (0.2%) 2.5ml/lit resulted in percent disease index 6.96. Maximun percent disease index found in untreated control i.e. 16.71. After the first spray percent disease control achieved in the range of 51.83 to 58.71at 55 DAS.  The highest per cent disease control recorded in treatment T3 i.e. 58.71 followed by treatment T2 58.35. Similar treand was observed in 70 DAS the percent disease incidence of Alternaria tenuissimawas in the range of 8.10 to 21.74 at 70DAS sprays of fungicide in treatment T3 Azoxystrobin 5.6% w/v + Tebuconazole 10% w/v + Prochloraz 20% w/v EC (0.2%) 3ml/lit resulted in least percent disease index (8.10) and it was at par with treatment T2 i.e. Azoxystrobin 5.6% w/v + Tebuconazole 10% w/v + Prochloraz 20% w/v EC (0.2%) 2.5ml/lit resulted in disease index (8.14). After 70 DAS the highest per cent disease control recorded in T3 Azoxystrobin 5.6% w/v + Tebuconazole 10% w/v + Prochloraz 20% w/v EC (0.2%) 3ml/lit i.e. 62.74 followed by treatment T2 Azoxystrobin 5.6% w/v + Tebuconazole 10% w/v + Prochloraz 20% w/v EC (0.2%) 2.5ml/lit 62.56. The trend in reduction of disease has reflected in the yield (Table 3). Maximum yield (1184 kg/ha) was recorded in treatment T3 Azoxystrobin 5.6% w/v + Tebuconazole 10% w/v + Prochloraz 20% w/v EC (0.2%) 3ml/lit sprayed plots it was at par with treatment 2 Azoxystrobin 5.6% w/v + Tebuconazole 10% w/v + Prochloraz 20% w/v EC (0.2%) 2.5ml/lit  i.e. (1146kg/ha). Minimum yield was obtained in untreated control (638kg/ha). Expermental results with respect to disease management of soybean Leaf Spot under field condition by the use of fungicides were well endorsed [12] by testing the effect of tebuconazole and reported that the fungicides could be used effectively for the management of foliar disease. Propiconazole @ 0.1%, carbendazim @ 0.1% and hexaconazole @ 0.1% found effective in the management of anthracnose of soybean [6]. These results are well corroborated with the earlier findings [13, 3].

Discussion

In this study, the efficacy of newer fungicide was tested, and the dose standardized relied on natural inoculums and infection for the establishment of disease. The data indicate the severe grain yield losses resulted when soybean cultivars were infected by both Alternaria tenuissima and Colletotrichum sojina. The overall study demonstrated that the two spray of Azoxystrobin 5.6% w/v + Tebuconazole 10% w/v + Prochloraz 20% w/v EC (0.2%) 2.5ml/lit, first after initiation of disease and need base second spray 15 days interval has been advocated for effective management of Alternaria tenuissima and Colletotrichum sojina leaf spot of soybean. The newer fungicide found an excellent player in the management of both foliar diseases it’s going to be an excellent option for growers battling late-season foliar diseases.

Declarations

Research facilities were provided by university funds and no conflicts of interest/competing interests. The availability of data and material is original. The corresponding author is the principal investigator and the remaining two authors are co investigators.

Acknowledgments

We wish to thank Dr. N.D. Parlawar, Associate Dean, Dr Panjabrao Deshmukh Krishi Vidyapeeth, Akola,

Maharashtra, India for financial, support valuable encouragement and kind assistances.

Reference

1. Anonymous (2015) Proceeding and Technical Programme of 44^th Annual Group Meeting of AICRP on Soybean. IISR, Indore (MP), Annexure-I.
2. Carmona MA, Scandiani MM and Luque A. (2009) Severe Outbreaks of Soybean Frogeye Leaf Spot Caused by Cercospora sojina in the Pampean region, Argentina. Plant Dis. 93(9):966. 
3. Chrysantus NA (1995) The effect of timing of fungicide applications on control of frogeye leaf spot and grain yield of soybeans. European Journal of Plant Pathology 101:183–187.
4. Conn KL, Tewari JP (1990) Survey of Alternaria blackspot and Sclerotinia stem rot in central Alberta in 1989. Can. Plant Dis. Survey 70:66-67.
5. Dashiell KE and Akem C N (1991) Yield losses in soybeans from frogeye leaf spot caused by Cercospora sojina  Crop Protection 10(6):465-468
6. FAO, (2020) http://www.fao.org/faostat/en/#search/soybean
7. Gawade DB, Suryawanshi AP, Pawar AK, Apet KT, Devgire SS. Field evaluation of fungicides, botanicals and bioagents against anthracnose of soybean. Agricultural Science Digest. 2009;29(3):174-7.
8.  Gupta GK and Chauhan GS (2005) Symptoms, Identification and Management of Soybean Diseases. Technical Bulletin no. 10. Pub. IISR, Indore (MP)
9. Mayee CD, Datar VV (1986) Phytopathometry. Marathwada Agricultural University, Parbhani, Technical bulletin No. 3:110
10. [10]. Mengistu A, Kelly HM,  Bellaloui N,  Arelli PR,  Reddy KN and   Wrather AJ (2014) Tillage, Fungicide, and Cultivar Effects on Frogeye Leaf Spot Severity and Yield in Soybean. Plant Dis. 98(11):1476-1484 https://doi.org/10.1094/PDIS-12-13-1268-RE
11. [11]. Scandiani M, Ferri M, Ferrari B, Formento N, Carmona M, Luque A, Balatti P (2012) First report of races 11 and 12 of Cercospora sojina, the causal agent of soybean frogeye leaf spot, in Argentina. Plant Dis. 2012 Jul;96(7):1067. doi: 10.1094/PDIS-02-12-0154-PDN. PMID: 30727242.
12. [12]. Sharma S, Singh R and Kumar A (2020) Field Evaluation of Selected Botanicals and Fungicides for the Management of Alternaria Blight of Cluster Bean. Int. J. Curr. Microbiol. App.Sci 9(7): 1045-1053
13. [13]. Soto-Arias, JP, Munkvold, GP (2011) Impacts of foliar fungicides on infection of soybean by Phomopsis spp. in Iowa, USA. Crop Protection, 30(5), 577 580. https://doi.org/10.1016/j.cropro.2010.11.018.
14. [14]. Wheeler BEJ (1969) An introduction to plant diseases, John Wiley and Sons Ltd., London, p. 301.