Discovering a New Fungus Causing Leaf Spots in Corn

Jim Crocker
16th January, 2024

Discovering a New Fungus Causing Leaf Spots in Corn

Maize (Zea mays)

Photo adapted from: Jonsense / CC BY (Source)
Leaf spot diseases pose a significant threat to maize production globally. These diseases, often caused by various Curvularia species, can lead to substantial yield losses. Identifying the specific Curvularia species responsible for outbreaks is crucial for developing effective control strategies. Recent research from ICAR-NBAIM[1] details the identification of Curvularia verruculosa as a cause of leaf spot in maize plants in Uttar Pradesh, India – a finding that expands our understanding of this plant pathogen. The study began with observations of leaf spot symptoms in a maize field in February 2017. Affected leaves displayed yellow spots, initially small but growing up to 1 cm in diameter, surrounded by a pale area called a chlorotic halo and dark borders. Researchers collected samples of the diseased leaf tissue and, using standard laboratory techniques, isolated the fungal pathogen responsible. This involved growing the fungus in a controlled environment on a nutrient-rich medium, and then purifying it to obtain a single, genetically identical culture. Initial identification relied on observing the fungus’s physical characteristics – its colour, shape, and the structure of its reproductive spores (conidia). These characteristics closely matched descriptions of Curvularia verruculosa previously documented[2]. However, visual identification can be unreliable due to similarities between different Curvularia species. Therefore, the researchers employed molecular methods to confirm their findings. Molecular identification involves analyzing the fungus’s DNA. Specifically, the team focused on two regions of DNA: the ITS rDNA region and the gpd gene. These regions contain genetic “fingerprints” unique to each species. By comparing the DNA sequences obtained from the isolated fungus with those available in genetic databases, they found a 100% match with Curvularia verruculosa strains already documented. The DNA sequences were then added to public databases for future reference. To definitively prove that Curvularia verruculosa was indeed the cause of the disease, the researchers conducted a pathogenicity test. They sprayed a suspension of fungal spores onto healthy maize plants and monitored them for disease development. Plants sprayed with the fungus developed the same leaf spot symptoms observed in the field, while control plants (sprayed with sterile water) remained healthy. Furthermore, the fungus was successfully re-isolated from the newly infected plants, confirming its role as the causative agent. This study represents the first documented report of Curvularia verruculosa causing leaf blight in maize in India. Previously, Curvularia verruculosa was known to cause leaf spot in other plants, such as cotton[3] and common beans. The findings build upon earlier work that highlighted the increasing significance of Curvularia and Bipolaris species as maize pathogens in India[2]. The earlier study[2] detailed the use of multiple gene regions to accurately identify these pathogens, a technique that supports the current study’s molecular confirmation of C. verruculosa. The ability of Curvularia verruculosa to secrete enzymes that break down plant tissues, as demonstrated in cotton[3], likely contributes to its ability to cause disease in maize. The secretion of enzymes like cellulase, xylanase, and protease weakens the plant’s defenses, allowing the fungus to colonize and spread.

AgricultureEnvironmentBiotech

References

Main Study

1) First report of leaf spot of maize caused by Curvularia verruculosa in India.

Published 13th January, 2024

https://doi.org/10.1094/PDIS-07-23-1410-PDN

Related Studies

2) Multi-Gene Phylogenetic Approach for Identification and Diversity Analysis of Bipolaris maydis and Curvularia lunata Isolates Causing Foliar Blight of Zea mays.

https://doi.org/10.3390/jof8080802

3) Incidence of leaf spot disease on cotton caused by Curvularia verruculosa and role of its hydrolytic enzymes in pathogenesis.

https://doi.org/10.1007/s12298-018-0557-9


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