Search

Diplodia ear rot (DER), caused by the fungus Stenocarpella maydis, has become a prevalent corn disease in the Midwest. The survival of S. maydis on corn kernels and stalks was evaluated in Tippecanoe, Co., Indiana, over 17 months. Infested corn residue was either left on the soil surface or buried at 10 or 20 cm. Survival of S. maydis was determined by observing the presence of pycnidia per unit of corn residue under a stereomicroscope and by assessing conidia viability by evaluating germination. Months of environmental exposure and soil depth affected S. maydis survival. Pycnidia production and conidia germination were observed up to 11 months on corn kernels and 17 months on corn stalks when left on the soil surface. Minimal or no conidia germination of S. maydis was observed on residue recovered from 10 or 20 cm after 4 months on kernels and 7 months on stalks. These results demonstrate that surface corn residue can be a long-term source of inoculum and at least two years of rotation to a nonhost crop or residue removal through tillage may be necessary to reduce potential initial inoculum.

The causal agents of Diplodia ear rot are two species of the Stenocarpella genus, S. macrospora and S. maydis. In addition to ears, both pathogens can infect leaves and stalks, and both are present in most corn-production regions around the world. It is difficult to visually distinguish between the two pathogens based on plant symptoms and fungal signs. To facilitate accurate and rapid pathogen identification, polymerase chain reaction (PCR) assays were developed for identification of each species. Species-specific primers of 18 to 20 nucleotides in length were designed, targeting a portion of the internal transcribed spacer (ITS) region of the fungal genome for conventional and real-time PCR assays. The conventional PCR method successfully amplified a single 1.7-kb and 800-bp fragment for each S. maydis and S. macrospora isolate, respectively. The real-time method was performed using SYBR green dye, and detection of each specific target pathogen was successfully obtained. In total, 82 S. maydis and 15 S. macrospora isolates were tested to evaluate the reproducibility of these primers. Both methods provide a rapid and specific tool for the detection of Stenocarpella spp.

Diplodia ear rot, a corn (Zea mays L.) disease caused by the fungus Stenocarpella maydis (Berk.) B. Sutton, has been a persistent ear rot across the United States. Management options are currently limited. Field trials conducted under inoculated and non-inoculated conditions were established at two locations in Indiana from 2011 to 2013 to test the fungicides azoxystrobin plus propiconazole and prothioconazole against Diplodia ear rot. Fungicides were applied at three individual growth stages during each year. Fungicides did not consistently reduce Diplodia ear rot compared to non-fungicide-treated controls in any year. Applications also did not consistently increase yield at any timing under inoculated and non-inoculated plots compared with the non-fungicidetreated control. Fungicides were tested in an in vitro assay to determine the effective fungicide concentration at which 50% of mycelial growth or conidial germination of S. maydis was inhibited (EC50). Propiconazole and prothioconazole EC50 values indicated efficacy in reducing fungal growth under controlled conditions; however, current fungicide application methods and plant barriers to fungicide contact with the pathogen may prevent these products from effectively reducing Diplodia ear rot in a field setting. Accepted for publication 23 August 2015. Published 1 September 2015

A produtividade e a qualidade do milho podem ser influenciadas pela ocorrência de doenças, cuja intensidade pode ser afetada por fatores ambientais e por práticas fitotécnicas. Dessa forma, o objetivo deste estudo foi avaliar o efeito do arranjo de plantas de milho e da densidade de semeadura no rendimento de grãos e na massa de mil grãos, bem como na incidência de podridões da base do colmo, grãos ardidos e de fungos associados aos grãos. O estudo foi realizado nas safras 2010/2011 e 2012/2013, em Chapecó, SC, Brasil. Os tratamentos foram constituídos por diferentes espaçamentos entre linhas (0,45 e 0,80 m) e densidades de plantas (50, 60, 70, 80 e 90 mil plantas ha-1), com delineamento de blocos casualizados em esquema de parcelas sub-subdivididas. Na parcela principal foram testados dois híbridos simples de milho de ciclo precoce (P30F53H e DKB 240H), nas subparcelas os espaçamentos e nas sub-subparcelas as populações de plantas. As unidades experimentais consistiram de seis linhas de 4 m de comprimento. O rendimento de grãos no espaçamento 0,45 m foi 29,65% superior ao obtido no espaçamento 0,80 m para os híbridos estudados. A massa de mil grãos e a incidência de grãos ardidos reduziram com o aumento da população de plantas. No entanto, a incidência de Fusarium verticillioides, Fusarium graminearum e Stenocarpella maydis não foi influenciada pelas populações de plantas nem pelos espaçamentos testados nas condições do presente estudo.

Research that focused on maize production on the central Highveld of South Africa was traditionally, since the early twentieth century, dealt with by the Department of Agriculture at Potchefstroom. During the 1970s the Highveld Region at Potchefstroom assigned a group of researchers with an interest in maize to a unit termed the Summer Grain Centre that in 1992 became part of the Agricultural Research Council’s Grain Crops Institute. Members of this group in particular gave research attention to various aspects of crop protection in maize, including the soil insect complex, the maize stem borer complex, maize streak disease, the ear rot complex and various leaf diseases. This paper deals with research progress on the African stem borer, Busseola fusca, and ear rot caused by Stenocarpella maydis. The emphasis is on research with a practical application rather than that of an academic nature.

In an attempt to obtain superior levels of resistance to Stenocarpella maydis ear rot, three elite maize inbred lines (DO620Y, E739 and B37) from different genetic backgrounds that had previously been shown to have useful levels of resistance were crossed in all combinations. Additionally, two susceptible experimental maize populations were crossed to a resistant experimental inbred line as donor parent. Progeny in each of the five populations was selfed and selected for resistance over five successive generations, following artificial inoculation of plants at the localities Potchefstroom, Cedara and Hazyview. The five populations progressed from the S1 during 1997/98 to the S5 during 2000/01. A progressive improvement in resistance occurred over seasons in all progenies. After three cycles of selection, approximately 50% of the selections showed less than 10% infected ears, with a total of 84 selections showing no infection. Selections displaying the lowest disease incidence at any one locality were not ...

The objective of this study was to provide a better understanding of the interrelationship between methods of screening for resistance to ear rot, caused by Stenocarpella maydis. The inheritance of resistance as well as genetic and phenotypic correlation of various selection criteria were investigated. A complete diallel cross of 10 inbred lines, ranging from resistant to susceptible, was evaluated at each of three localities, representative of different environments within the South African maize production area. Plants were artificially inoculated twice during the vegetative stages of plant development. Resistance to ear rot was found to be controlled by additive gene effects, with low dominance and interaction effects. Significant genetic correlations existed between various characteristics relating to disease incidence, with high heritability and highly correlated responses. The incidence of rotted ears was the most practical and reliable method to select for resistance. However, the simultaneous use ...

Fifteen maize inbred lines were evaluated for resistance to ear rot, using artificial inoculation of plants with isolates of Stenocarpella maydis from 13 localities in the South African maize production area. Five inbreds and four isolates were common to the four seasons of evaluation. The inbreds B37, D0620Y and E739 showed levels of resistance superior to that of the standard Hill. Isolates provided inconsistent infection levels in different years. All interactions were significant, with seasonal effects predominating over the genotype x isolate interaction.

The optimum inoculation position on the maize plant, and optimum time of inoculation with Stenocarpella maydis for artificial induction of ear rot were determined in field trials. The placement of a conidial suspension on the shank at silking resulted in the highest incidence of S. maydis ear rot.

Survival of and pycnidium production by Stenocarpella maydis in artificially infected maize stalk stubble placed on, half buried into, and buried in the soil were determined in field trials over a nine month period. Survival was higher in stubble which remained on the soil surface than in buried stubble. Pycnidial development increased on surface and buried stubble from September onwards, but subsequently decreased on buried stubble. Conidia retrieved from the variously positioned stubble segments did not vary in viability. More pycnidia were produced over an eleven month period on naturally infected stubble retrieved from the soil surface than from in soil. Reisolation and conidium viability of S. maydis from the surface stubble were higher than from buried stubble. Zusammenfassung Der Zusammenhang zwischen der Lage des Maisstoppels im Boden und dem Uberleben von Stenocarpella maydis (Diplodia maydis) Uber einen Zeitraum von 9 Monaten wurde das Uberleben und die Pyknidienproduktion von Stenocarpella maydis in kunstlich inokulierten Maisstoppeln unter Feldbedingungen beobachtet. Die inokulierten Stoppeln wurden auf dem Boden, zur Halfte oder ganz im Boden plaziert. Die hochste Uberlebensrate wurde in den Stoppeln, die auf der Bodenoberflache lagen, festgestellt. Die Entwicklung von Pyknidien erhohte sich an den Stoppeln ab September, unabhangig von der Lagerung, bei den begrabenen Stoppeln wurde jedoch ein Ruckgang der Pykinidienentwicklung zu einem spateren Zeitpunkt beobachtet. Die Viabilitat der Konidien alier Stoppeln war gleich. Mit naturlich befallenen Stoppeln wurde eine hohere Anzahl von Pyknidien uber eine 11monatige Periode von den Stoppelstucken gewonnen, die von der Bodenoberflache aufgelesen worden waren, als von denen, die in der Erde begraben waren. Auserdem war die Reisolierung und Konidienviabilitat bei den von der Oberflache stammenden Stoppelstucken hoher als von den begrabenen.

Para o controle integrado de doenças, o tratamento químico das sementes de milho (Zea mays) torna-se indispensável, sendo a sua eficácia e influenciada por vários fatores, entre eles o tamanho das sementes. O objetivo do trabalho foi avaliar a relação do tamanho da semente e doses do fungicida thiabendazole no controle de Stenocarpella maydis, considerando-se diferentes tamanhos de sementes e doses do fungicida. As sementes classificadas nas peneiras 19, 22 e 24 foram inoculadas com S. maydis e tratadas com o fungicida thiabendazole em três doses, sendo avaliadas a incidência do patógeno e desempenho das sementes por meio de testes de qualidade fisiológica. Constatou-se com o tratamento fungicida, aumento na germinação, maior peso de plântulas e redução de tombamento provocado por S. maydis, havendo comportamento diferenciado do tratamento químico em relação ao tamanho de sementes e doses do produto. To prevent disease dissemination chemical treatment of maize (Zea mays) seeds becomes indispensable. However, the efficacy of this treatment may be influenced by a number of factors, such as seed size. Thus, the objective of this work was to evaluate the efficacy of the fungicide thiabendazole in treatment of maize seed to control S. maydis, taking into account different seed sizes. The seeds classified according to sieves 19, 22 and 24 were inoculated with S. maydis and treated with the fungicide thiabendazole in three doses. To evaluate the effect of seed treatment, test of germination on paper roll substrate, health test, (blotter method), and the dry weight of seedlings were considered. Seed treatment with fungicide provided conditions for increased germination and weight of seedlings, and reduced damping-off, caused by S. maydis. The efficacy of the fungicide seed treatment varied according to seed size and doses of the fungicide used.

Four Stenocarpella maydis (Berk.) Sutton inoculation techniques were compared over two seasons at Potchefstroom and Bethlehem on six maize cultivars differing in ear rot susceptibility. The techniques showed differentiation between cultivar susceptibility. Application of a conidial suspension behind the ear resulted in significant correlation with the disease potentials over two seasons. Similarly, the technique of placing ground-infected kernels in the leaf whorl at three growth stages is recommended for evaluation of maize genotypes for resistance to maize ear rot.

The influence of Busseola fusca incidence and damage on Fusarium moniliforme and Stenocarpella maydis ear rots was studied in the field using artificial infestation with B. fusca, mechanical damage and pathogen inoculation. B. fusca infestation increased the incidence of F. moniliforme infected maize ears irrespective of artificial or natural F. moniliforme infection. Mechanical damage plus F. moniliforme inoculum also resulted in a high incidence of F. moniliforme-infected ears suggesting that physical damage to the ear will increase F. moniliforme-infected ears. Fungus-infected rotten kernel percentages of B. fusca-damaged treatments did not differ significantly from the control. The insignificant correlation (r = −0.206; P = 0.695) between F. moniliforme- infected ears and per cent rotten kernels indicates that in the case of the former, when used as a disease criterion, damage was localized and did not result in significant grain quality reductions. Neither B. fusca nor physical damage significantly a...

Sporulation and vegetative growth of Stenocarpella maydis and S. macrospora were evaluated by growing the organisms in basal mineral salts medium amended with sucrose (0-30 g/L) and biotin (0-50 mg/L) for 28 days at 23 C under constant illumination. Sucrose at 5 or 10 g/L and biotin at 6 or 8 mg/L yielded the largest quantity of pycnidiospores of each organism. Sporulation of S. maydis, however, was higher than that of S. macrospora at all concentrations of biotin, although 6 mg/L gave the largest number of spores compared with biotin-less medium. Pycnidiospore concentrations of S. maydis and S. macrospora in media amended with 10 g/L of sucrose and 6 mg/L of biotin were 0.73×10 6 and 0 per milliliter, respectively (.)

Four techniques for inoculating corn (Zea mays) ears with Stenocarpella maydis were evaluated on six inbreds and four hybrids. Depositing a spore suspension into the sheath cavity or placing infected popcorn into the whorl resulted in low levels of infection. Spraying a conidial suspension on the silks resulted in an intermediate level of infection, and injecting a conidial suspension directly into the ear resulted in very high levels of infection. The silk spray method was selected as the best technique because of the level of infection, the ability to distinguish between resistant and susceptible inbred lines, and ease of application