Assessment of physiological races of Exserohilum turcicum isolates from maize in Argentina and Brazil

Abstract

Northern corn leaf blight (NCLB) is one of the most important diseases in maize worldwide. It is caused by the fungus Exserohilum turcicum, which exhibits a high genetic variability for virulence, and hence physiological races have been reported. Disease control is based mainly on fungicide application and host resistance. Qualitative resistance has been widely used to control NCLB through the deployment of Ht genes. Known pathogen races are designated according to their virulence to the corresponding Ht gene. Knowledge about of E. turcicum race distribution in maize-producing areas is essential to develop and exploit resistant genotypes. Maize leaves showing distinct elliptical grey-green lesions were collected from maize-producing areas of Argentina and Brazil, and 184 monosporic E. turcicum isolates were obtained. A total of 66 isolates were collected from Argentina during 2015, 2018 and 2019, while 118 isolates from Brazil were collected during 2017, 2018 and 2019. All isolates were screened on maize differential lines containing Ht1, Ht2, Ht3 and Htn1 resistance genes. In greenhouse experiments, inoculated maize plants were evaluated at 14 days after inoculation. Resistance reaction was characterized by chlorosis, and susceptibility was defined by necrosis in the absence of chlorosis. The most frequent race was 0 in both Argentina (83%) and Brazil (65%). Frequencies of race 1 (6% and 24%) and race 23N (5% and 10%) were very low in Argentina and Brazil, respectively. The high frequency of race 0 isolates provides evidence that qualitative resistance based on the tested Ht genes is not being used extensively in Argentina and Brazil to control NCLB. This information may be relevant for growers and breeding programs as the incidence of NCLB is increasing in both countries.

Molecular and Morphological Characterization of Exserohilum turcicum (Passerini) Leonard and Suggs Causing Northern Corn Leaf Blight of Maize in Bihar

“…The details of the districts surveyed and the areas from which diseased isolates were collected for variability studies are given in Table 1 . Field samples were labeled, kept in cold boxes, and brought to the laboratory for further study [ 16 ].…”

“…Colonies were observed at 2–3 day intervals until full growth was attained. Small portions of fungal mycelium from fully grown culture were aseptically transferred to plates of fresh PDA culture medium in order to obtain pure cultures of E. turcicum [ 16 , 18 ].…”

Distribution, Etiology, Molecular Genetics and Management Perspectives of Northern Corn Leaf Blight of Maize (Zea mays L.)

“…The physiological race of S. turcica present in the Indian subcontinent has been determined to be Race 2 [98]. Studies have also shown that S. turcica migration is likely over long distances, which could shift virulence to new regions [99]. Selection pressure, sexual recombination within the pathogen, and the capability to migrate long distances may create more virulent populations and contribute to spatial and temporal race population shifts.…”

Guaiacol as a natural melanin biosynthesis inhibitor to control northern corn leaf blight

“…Leonard & Suggs is the causal pathogen of the highly lethal and devastating foliar disease northern corn leaf blight (NCLB), which occurs in all maize-producing regions ranging from tropical to temperate zones, seriously threatening the maize production with significant losses in both quality and quantity. 1,2 This fungus usually produces a large number of melanins in hyphae and its colony on culture medium shows dark to black-gray color. In addition to hyphae, its conidia are highly melanized and olivaceous brown to dark gray, which is associated with ellipse-or cigar-shaped gray-to tan-colored lesions on the corn leaves.…”