Stenocarpella Maydis: Identification, Management, and Population Diversity
Abstract
Diplodia ear rot (DER) has been a persistent corn disease across the Midwest, and in recent years it has become an annual problem. The objectives of this study were to i) develop a molecular assay for the identification of Stenocarpella maydis, causal agent of DER, ii) evaluate the effect of crop rotation and tillage on DER severity, iii) determine the survival period of S. maydis in corn residue at different soil depths in a corn field, and iv) identify genetic diversity among S. maydis isolates collected from the Midwestern and Southern United States. The genus Stenocarpella contains two species, S. maydis and S. macrospora, both able to infect corn plants. Previously, identification of the two species was based only on time consuming morphological methods. An accurate molecular assay was developed that can be performed under conventional or real-time PCR, and both are able to distinguish between S. maydis and S. macrospora from pure culture or infected tissue. Field experiments were conducted at the Agronomy Center for Research and Education (ACRE) in Tippecanoe County, Indiana. From 2013 to 2014, four corn production systems were evaluated for DER control under non-inoculated and inoculated conditions. Stenocarpella maydis survival was assessed over 12 months at the soil surface, and at 10 and 20 cm burial depths. Results indicate that crop rotation with soybean and tillage practices did not eliminate Diplodia ear rot, and in certain years did not reduce DER severity. Stenocarpella maydis was able to survive on the soil surface in corn residue for at least 11 months. However, S. maydis conidia recovered from samples were not able to infect corn ears under controlled conditions after 7 months. These results indicate that at least a one year rotation away from corn is necessary in order to eliminate inoculum. Tillage operations must reduce surface residue to a minimal percentage to reduce inoculum. High genotypic diversity was observed among S. maydis isolates in the US. Genotypic diversity was higher within sample regions and similar between the Midwestern and Southern US S. maydis populations. This indicates that recombination occurs among S. maydis isolates. Although no sexual reproduction has been reported, both mating type genes, Mat1-1 and Mat1-2 were identified and amplified across 60 selected isolates.
Degree
Ph.D.
Advisors
Wise, Purdue University.
Subject Area
Plant Pathology
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