Maydis leaf blight (MLB) is caused by the ascomycete fungi Bipolaris maydis and is reported from most maize growing regions of the world including India. It is also known as southern corn leaf blight (SCLB). The occurrence of any specific disease depends on environmental conditions, cultural practices and the hybrid that is grown. It is most serious in warm and wet temperate and tropical areas, where yield losses close to 70% have been reported due to the disease. The production of spore is influenced by temperature (Warren, 1975). Infected tissues are extensively covered with spots and chlorosis rendering them non productive. It is found to have a higher saprophytic ability (Blanco and Nelson, 1972) and hence high primary inoculum level will be likely to be found in areas with high disease occurrence. In SCLB, Two races, race O and race T are responsible for causing this disease in Pakistan, while race C has been reported only in China (Wei et al., 1988).
SYMPTOMS
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Common lesions are elongated, tan lesions between veins on leaves
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Different isolates of this pathogen will cause lesions of different sizes
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Race O causes long, tan, lesions that have brown borders on leaves
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Lesions will develop differently on various inbreds and hybrids
PATHOGEN INVOLVED
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Cochliobolus heterostrophus (Bipolaris maydis)
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Three races known of this pathogen viz. race O, race T and race C
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Race T and race C are known to be specifically virulent to corn with cytoplasm male-sterile T and cytoplasm male-sterile C, respectively.
HABITAT
MLB favours warm and moist conditions for development. Temperature range, 70°F to 90°F is ideal for the fungus to survive and germinate. Extended moist conditions are important for fungi to be able to germinate quickly and effectively. Highly dense maize crops with minimum tillage are good for spread of disease spores can easily be blown from one plant to another.
LIFE CYCLE
Maydis leaf blight (MLB) is primarily follows an asexual disease cycle. Under the right conditions, conidia or asexual spores are released from wounds of a diseased corn plant and dispersed to surrounding plants through splashing rain or wind (Figure 1). After conidia or asexual spores are transmitted from an infected plant to a healthy one, the fungi germinate on the leaf’s tissue. Once infected, leaf tissue will turn brown and eventually the leaf will fall. In good conditions, spores can germinate and penetrate the plant in just 6 hours. Bipolaris maydis overwinters in plant debris as spores until favourable conditions return. This fungus is also capable of following a sexual disease cycle, but this has only been found in laboratory environments.
MANAGEMENT PRACTICES
Cultural Practices: The most effective way of reducing chances of infection is by planting hybrid species of maize. Hybrid species will greatly reduce chances of infection as they are bred to be resistant to the disease. Tilling fields at the end of the season is very helpful because it will break down the infected plant residue left from diseased plants, reducing chances of spores germinating next season. Crop rotation is also recommended to reduce chances of further infection when economically viable.
Chemical Control: Foliar fungicides can be a helpful deterrent in seed production fields. Before using fungicides, always check the label for cautionary advice and application guidelines.
REFERENCES
Blanco, M.H. and Nelson, R.R. (1972). Relative survival of populations of race T of H. maydis on corn hybrid in normal cytoplasm. Plant Disease Reporter. 56: 889-891.
Warren, H.L. (1975). Temperature effects on lesion development and sporulation after infection by races O and T of B. maydis. Phytopathology 65: 623-626
Wei, J., Lui, K., Chen, J., Luo, P. and Stadelmann, O.Y. Lee. (1988). Pathological and physiological identification of race C of Bipolaris maydis in China. Phytopathol. 78: 550-554.
Contributed by :
Dan Singh Jakhar
Department of Genetics and Plant Breeding, Institute of Agricultural Sciences,
Banaras Hindu University, Varanasi – 221005, UP, India
contact : dansingh410@gmail.com
