Survey and in vitro efficacy of fungicides and bioproducts against Turcicum leaf blight disease of maize caused by exserohilum turcicum

Introduction

Maize (Zea mays L.) is the third most important cereal crop after wheat and rice in India. It is one of the most versatile emerging crops, having wider adaptability under varied agroclimatic conditions. It is known as the 'Queen of cereal' and staple food crop for human beings and basic raw material for food, feed and industrial products such as oil, protein, starch, beverages, food sweeteners, pharmaceuticals, cosmetics, etc. This crop is being grown throughout the season, i.e. in spring, kharif and Rabi seasons. Due to continuous cultivation of maize, the pressure of insect pests and disease is also increasing due to the continuous availability of the host plant. It can be grown in various agro-climatic conditions in many parts of India. In India, it occupies the 5 th rank in area and 3 rd in production and productivity among cereal crops. It is cultivated in an area of 10.04 million ha, with a total annual production of 33.62 million tonnes, giving an average yield of 3.19 tonnes/ha (Agristat, 2022) [17] . The growing of maize is totally rainfed in the North-east region of India for its food security. It is used for direct consumption, and used as feed, fodder for livestock and for industrial purposes also. In the NER region, the production and production is very low as compared to other states of India; it needs expansion in area, dependent on rainfall, as well as adoption of new hybrids which is resistant or tolerant to pests and diseases. Diseases are one of the major constraints for the reduction in yield. Amongst the diseases such as Turcicum Leaf blight, Maydis Leaf blight, Banded Leaf and Sheath Blight, and Common rust. The Turcicum Leaf Blight of Maize, which is also known as Northern corn leaf blight, caused by Exserohilum turcicum, is a major disease of maize that affects the production and productivity of maize (Nongmaithem et al.). It can reduce the yield up to 90% under conducive environmental conditions. Therefore, a survey and in vitro evaluation of fungicides and a bioproduct study were conducted for sustainable management and for incorporation in the Integrated disease management of Turcicum Leaf Blight diseases of Maize.

Materials and Methods Survey for Incidence and Severity of Turcicum Leaf Blight Disease of Maize

A random survey was conducted in five districts of Manipur, namely Imphal East, Imphal West, Senapati, Bishnupur and Kangpokpi districts to identify the major diseases occurring in the state of Manipur. Before conducting the survey, preliminary information was gathered from the Krishi Vigyan Kendra about the major maze-growing district in Manipur. And the survey was conducted for three consecutive years during the kharif season from 2021-2023. The survey was conducted randomly by selecting the field at an interval of 10 km in all the districts. In each district, 3 villages were selected and identified, and five fields were surveyed by selecting 100 plants randomly, varying the stage of crop from knee high to gain filling stage. The incidence of the disease was calculated by using the formula given by Nawanosike et. al. (2015).

Disease incidence =

𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑑𝑖𝑠𝑒𝑎𝑠𝑒𝑑 𝑝𝑙𝑎𝑛𝑡 𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝𝑙𝑎𝑛𝑡 𝑒𝑥𝑎𝑚𝑖𝑛𝑒𝑑 × 100

The disease severity was calculated by using a 1 to 9 disease rating scale, given by Chung et al. (2010) [3] ; Mitiku et al. (2014) [14] (Table 1). The Percent Disease Index (PDI) was calculated by using the formula given by Wheeler (1969). The individual scoring of each plant was converted into PDI as described by Hooda et al. (2018) [8] .

Isolation and purification of the pathogen

The isolation of the plant pathogen was done by using the method described by Manamgoda et al. (2012) [12] . Initially, the leaf samples were cut in into small pieces of 0.5x0.5cm in diameter containing both healthy and infected-looking tissues and sterilized in 1% sodium hypochlorite solution, followed by washing in three changes of sterile distilled water. After removing the excess water, the cut portions were aspectically transferred to sterile petriplates containing 20 ml of solidified potato dextrose agar and kept in an incubator at 25±1 O C for 5 days. After 5 days, a bit of mycelium from the actively growing portion was transferred aseptically to new, fresh PDA petridishes. After purifying, the culture was transferred to a PDA test tube for further use.

In-vitro evaluation of fungicides and bioproducts

The in vitro efficacy of fungicides and bioproducts was performed by using the poisoned food technique on Potato agar medium described by Vincent (1947) [15] . For Trichoderma asperellum, the in vitro evaluation was conducted by the dual culture method described by Dennis and Webster (1971) [5] . The efficacy was evaluated by calculating the percent inhibition of mycelial growth over the control.

I=(C-T/C) x100

Where I = Fungal growth inhibition in per cent C=Colony diameter in control plates in cm T=Colony diameter in Treatment plates in cm Mancozeb 75 WP@ 0.25% 2.

Azoxystrobin 18.2w/w + Difenoconozole11.4% w/w SC@ 0.10% 3.

Azadirachta indica (Neem) leaves @ 10% 4.

Allium sativum (Garlic) bulb@ 10%@ 5.

Trichoderma asperellum @ 1% 8.

Poisoned Food Technique

To obtain the required concentration of fungicides and bioproduct, the required quantity of fungicides and bioproduct was added to molten, lukewarm potato dextrose agar medium. After that, 20 ml of poisoned medium was poured into sterile petri dishes and allowed it solidify. with the help of a sterile 6mm corkborer, a mycelial disc was cut from the periphery of culture plates of the fungus and then kept in the centre of 90mm Petri plates. Plates with no fungicides or bioproducts act as control plates. Three replications were maintained for each treatment. And kept at an incubator at a temperature of 28±1 o C. The radial growth of each treatment was recoded when the control plates were fully grown.

Results and Discussion Survey for Incidence and Severity of Trurcicum Leaf Blight Diseases of Maize

A random survey was conducted in five major maizegrowing districts of Manipur to know the incidence and severity of Turcicum leaf blight disease of maize, namely Imphal East, Imphal West, Senapati, Bishnupur and Kankpokpi districts of Manipur for three consecutive years during the kharif season from 2021-2023.

During the survey, a total of 50 maize fields were surveyed, 10 from each district. The results of the study indicated that Turcicum leaf blight diseases were widespread in all the districts surveyed. The mean highest disease incidence (77%) and severity (70%) were found in the Senapti district. The disease incidence was followed by Bishnupur (56%), Imphal East (51%), and Kangpokpi district with 44%. The lowest mean disease incidence was recorded in Imphal West district, with 40%. Similarly, the disease severity by Imphal East (56%), Bishnupur (52%), and Kangpokpi with 47%.

The lowest mean disease incidence was found in Imphal West District with 44% disease severity (Graph 1).

Graph 1: Showing the mean disease incidence and severity of Turcicum leaf blight disease of maize in five surveyed districts.

In-vitro Screening of Fungicides and Bioproducts

The in vitro Screening of Fungicides and Bioproducts was Done by the Poison Food Technique. The efficacy was evaluated by calculating the percentage inhibition of the mycelial growth over the control. The results showing the percentage inhibition of growth of Exserohilum turcicum by fungicides and bioproducts are shown in Table 2. Among the fungicides and bioproducts tested, Azoxystrobin 18.2 w/w + Difenoconozole11.4% w/w SC @ 0.1% was found to be the most effective and recorded 100% radial growth inhibition of the test pathogen. Allium sativum (Garlic) bulb @ 10% was also recorded highly promising with 75.80% inhibition of mycelial growth of test pathogen, i.e Exserohilum turcicum, followed by Azadirachta indica (Neem) leaves @ 10% (70.86%) and Trichoderma asperellum (62.59%). The Lowest inhibition of mycelial growth was recorded in Lantana camara @10% (55.85%). These findings are in corroboration with Manu et al. (2017) [11] , who studied that under in-vitro efficacy against Exserohilum turcicum, the mean highest per cent inhibition of mycelial growth was recorded in Garlic bulb extract, with 79.63% growth inhibition. Bhatt and Kumar (2019) [2] reported that 8 fungicides were tested under in vitro conditions against Exserohilum turcicum of Maize and found that Azoxystrobin 23%, showed the highest inhibition of 92.22% mycelial growth at a 5.0 ppm concentration.

Conclusion

The survey confirmed the widespread occurrence of Turcicum leaf blight across Manipur, with the highest incidence and severity in the Senapati district. In vitro studies revealed that Azoxystrobin + Difenoconazole was the most promising fungicide, which found 100 per cent mycelial growth inhibition of E. turcicum, causing Turcicum leaf blight disease of maize. Among bioproducts, garlic and neem extracts exhibited strong antifungal activity and can be incorporated into integrated disease management strategies to reduce chemical dependence. Further field evaluation of these promising treatments is warranted to validate their effectiveness under natural conditions.

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