Efficacy of Different Fungicides against Leaf Blight of Carrot Caused by Alternaria alternata (Fr.) Keissler

Carrot (Daucus carota L.), out of the most important vegetables root crop belonging to Apiaceae family, is cultivated worldwide. It is well distributed throughout the temperate, tropical and subtropical parts of the world (Bose and Som, 1990) and extensively cultivated in Europe, Asia, North Africa and North and South America (Thompson and Kelly, 1957). Afghanistan is the main centre of origin, from where the carrot originated for cultivation purpose, Mackevic (1929) and Banga (1976). The carrot introduced from Persia to India, according to Shoemaker (1947). The carrot is  used for medicinal purposes including stomach ulcers, abscesses, bladder, liver and kidney problems, to aid in childbirth and even as aphrodisiacs. Cultivation of roots for consumption dates back to 600 A.D. when purple root types were grown in the area currently known as Afghanistan (Sangeetha and Shanthakumar 2016). The carotene in one medium-sized carrot supplies our daily requirement of Vitamin A (Rubatzky et al., 1999). The edible part of carrot is the stored taproot. Carrot contains high amount of carotene (10 mg/100 g), thiamine (0.04 mg/100 g) and riboflavin (0.05 mg/100 g) and also serves as source of carbohydrate, protein, fat, minerals, vitamin C and calories (Yawalker, 1985). Carrot is an excellent source of alpha and beta carotene, the forerunner of vitamin A, the edible portion of carrot root (per 100 g) contains carbohydrate (10.6 g), fibre (1.2 g), moisture (86 g) and carotene (1890 mg) (Bose et al., 1986). The foliar diseases of carrot, Alternaria leaf blight is major one, which occurs worldwide. Strandberg (1992); Tulek and Dolar (2015) reported that even A. alternata, A. tenuissima and A. radicina also causes leaf blight disease of carrot. Alternaria blight of carrot was first reported in 1855 from Germany (Chupp and Sherf, 1960) and later from many countries of temperate and Mediterranean regions of the world Belgium, Holland, USA, Denmark, Israel, France and India (Farrar et al., 2004, Jensen et al., 2004). The pathogen attacks both root and seed crop but losses are more in case of seed crop in nature. The disease appears as brownish water soaked lesions on the margins and tips of older leaflets which gradually extend to become deep brown and blighted. As the spot increase in number, the inter-veinal tissue dies until the entire leaflet is killed. In moist weather disease spread rapidly. On leaf petioles, elongated dark spots appeared and the entire leaf dies without spots on the foliage. It also causes damping-off of seedlings, blight of seed stalk and black decay of roots. Under heavy infection conditions leaves are entirely destroyed and harvesting becomes difficult which results in 40-60 per cent yield losses (Vintal et al., 1999; Farrar et al., 2004; Yadav et al., 2021). The fungus A. alternata produced profuse mycelium on Potato Dextrose Agar (PDA) with an average width of 4.42 mm in diameter, conidiophores, conidia and intercalary chlamydospores measured as 42.26×4.29 mm, 47.16×13.49 mm and 7.22 mm in diameter, respectively. Initially, the mycelium was hyaline that turned to grey-brownish, multicelled, septate and irregularly branched. Conidia were born in chains upto 10 or more on conidiophores. They were light olivaceous to dark brown in colour, varied in shape from obclavate to mostly ellipsoidal, muriform having tapered apex with 1 to 3 longitudinal and 2-10 transverse septa (Nagrale et al., 2013). The productivity of carrot in Rajasthan is very less as compared to India. It may be due to several reasons. Among them, the diseases might be out of the major limiting carrot prodaction. The fungal disease, particularly leaf blight was observed as severe disease of carrot (Soyal et al., 2016).

Efficacy of fungicides were tested against Alternaria alternata both in lab as well as in cage house condition.
 
Evaluation of the efficacy of fungicides in vitro
 
Evaluation the efficacy of seven fungicides along with control (Table 1) was studied against mycelia growth of Alternaria alternata by poisoned food technique (Nene and Thapliyal, 1971) Required quantity of each fungicide (Table 1) was added aseptically to 100 ml of sterilized PDA medium in 150 ml flask separately so as to get four different concentrations (250, 500, 750 and 1000 ppm). The medium was supplemented with streptomycin sulphate @ 50 ppm to prevent bacterial contamination. The flasks were shaken to ensure proper and uniform distribution of the fungicides. The medium was poured separately in sterilized petri plates and allowed to solidify. For each treatment three replications were taken and medium without fungicides served as check. Each plate was inoculated with 5 mm diameter mycelial bit of the fungus. Inoculated plates were incubated at 25±1°C for 7 days. The linear growth of test fungus was recorded and per cent growth inhibition was calculated by Vincent’s (1947) formula.
   
Where:
I = Inhibition per cent.
C = Colony diameter (mm) in control plate.
T = Colony diameter (mm) in treated plate.
 

 
Evaluation of the efficacy of fungicides in vivo
 
The management of Alternaria alternata in cage house condition was studied with fungicides found effective in in-vitro studies. Five treatments including control were evaluated for their efficacy by foliar spray against A. alternata. Experiment was conducted in the cage house during Rabi season 2020 - 2021. The seeds of K-4 cultivar were sown with three replications in earthen pots 9"×12". The fungicides were tested by applying as foliar spray on 60 days old plants after 10 days of inoculation of the pathogen. For comparison inoculated control was maintained without fungicidal application. Observations of the disease intensity were recorded 10 days after foliar spray. Observations on disease intensity were recorded on 5 plant selected in each pot by using disease rating scale given by Jaiman et al., (2013) with slight modifications and per cent disease intensity was calculated. The percent disease intensity (PDI) was calculated by using the formula of Wheeler, 1969. 
 

Management of alternaria leaf blight of carrot through fungicides under in vitro condition
 
A total of seven fungicides using four different concentrations (250, 500, 750 and 1000 ppm) along with control were tested in vitro against A. alternata, applying poisoned food technique (Nene and Thapliyal, 1971) and using Potato Dextrose Agar (PDA) as basal medium. The observations on per cent growth inhibition (PGI) were recorded and the results are presented in Table 2 and Plate 1a, 1b, 1c and 1d.
 

 

 

 

 

       
All the fungicides tested were found significantly superior in inhibiting the mycelial growth of A. alternata over control. Among the fungicides difenoconazole 25% was inhibited the 100% mycelial growth at all the concentrations and was found significantly superior over rest of the treatments. The next best treatment was tebuconazole 50% +trifloxystrobin 25% (96.11, 100, 100 and100%) at 250, 500, 750 and 1000 ppm concentrations, respectively. Minimum mycelial growth inhibition was observed in mancozeb 75% WP (41.61, 57.64, 69.66 and 77.43%) followed by carbendazim 12%+mancozeb 63% (73.93, 76.11, 78.69 and 82.34 %) at 250, 500, 750 and 1000 ppm concentrations, respectively; along with control plate was showed 100% mycelium growth. The superior treatments under in vitro carry forward in vivo condition. Fungicides such as hexaconazole 4%+zineb 68%, pyraclostrobin 133 G/L+ epoxiconazole 50 G/L SE, difenoconazole 25 EC, trifloxystrobin 25%+tebuconazole 50% have been shown to significantly inhibit Alternaria solani and A. alternata (Choudhary et al., 2021; Dhaka and Choudhary 2022; Dhaka et al., 2022; Nagaraj et al., 2023; Choudhary et al., 2024).
 
Management of Alternaria leaf blight of carrot through fungicides under in vivo condition
 
Five fungicides along with control were evaluated in field condition and the results presented in Table 3.
 

       
The data depicted in Table 3 showed that the disease incidence percentage of all fungicide treatments were significantly lower than untreated control. The disease incidence ranged between 11.17% to 55.20%. Lowest disease incidence was noted in difenoconazole 25EC (11.17%) followed by trifloxystrobin 25%+tebuconazole 50% (14.42%), respectively.
       
The effective fungicides under in vitro condition were farther tested under in vivo condition. Among the treatments the lowest disease incidence was noted in difenoconazole 25EC (11.17%) followed by trifloxystrobin 25%+ tebuconazole 50% (14.42%) respectively. The maximum per cent disease incidence was observed in kresoxim methyl 44.3 SC @ 0.044% (32.18%) whereas, 55.20% disease incidence was recorded in control pot. Pyraclostrobin 133 G/L+Epoxiconazole 50 G/L SE and Captan 70%+ Hexaconazole 5% are at par.
       
Almost similar result recorded by even in the results of the experiment of Alkseeva (2009) difenconazole was quite effective for controlling Alternaria blight of carrot. Badri et al., (2013) proved that the hexaconazole was most superior in inhibiting Alternaria alternata causing umbel blight of kala zeera. Ginoya and Gohel (2015) recorded the tebuconazole (50%)+trifloxystrobin (25%) (0.20%) the disease intensity was 11.23% in in vivo condition against Alternaria alternata causing fruit rot disease of chilli. The results of fungicides (in vivo) are comparable with that of the Reshma et al., (2018) where in the field evaluation the difenconazole (0.1%) effectively reduced the leaf blight of chrysanthemum. Gayithri (2020) the difenconazole (0.1%) the disease intensity was 16.05% in in vivo condition against Alternaria alternata causing Alternaria leaf blight of carrot. Similar results were observed by many workers viz., Mazumder et al., (2016); Jangid et al., (2022) and Tadelo et al., (2024).

Among the seven fungicides screened were found difenoconazole 25% inhibited the 100% mycelial growth at all the concentrations and was found significantly superior over rest of the treatments. The next best treatment was tebuconazole 50%+trifloxystrobin 25% (96.11, 100, 100 and100%) and pyraclostrobin 133 G/L+epoxiconazole 50 G/L SE (92.36, 100, 100 and 100%), followed by kresoxim methyl 44.3 SC @ 0.044% (91.72, 95.94, 100 and 100%) and captan 70%+hexaconazole 5% (88.37, 88.07, 100, 100) at 250, 500, 750 and 1000 ppm concentrations. In case of application fungicide under in vivo condition among the all treatments lowest disease incidence was noted in in foliar spray with difenoconazole 25 EC at 0.5 ml (11.17%) followed by trifloxystrobin 25% +tebuconazole 50% at 0.5 g. (14.42%) whereas, 55.20% disease incidence was recorded.

The authors are sincerely thankful to the Dean College of Agriculture Jodhpur, Rajasthan for providing necessary facilities and guidance to conduct the different experiments.

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.