Charcoal rot of soybean is an important disease affecting soybean. Charcoal rot is caused by the ubiquitous soilborne fungus Macrophomina phaseolina (Tassi) Goid. The fungus infects over 500 plant species. Although charcoal rot occurs primarily under drought-like conditions, it has also been reported in high-yield irrigated soybean environments. Symptoms of charcoal rot on soybean include wilting, stunting, and premature death. Management options to reduce charcoal rot-associated losses are limited. The objective of this research was to reduce M. phaseolina colonization of soybean by supplementing with secondary nutrients, specifically calcium and magnesium; therefore, reducing the concentration of the associated toxin, and determine if isolates of M. phaseolina from non-soybean hosts are pathogenic on soybean and rotational hosts. Between 2014 and 2016, non-irrigated, M. phaseolina-inoculated field and field replicate greenhouse experiments evaluated applications of 1,120 kg/ha of Ca and Mg alone and in combination at pre-plant, at-plant, and pre-plant followed by at-plant compared with an inoculated and non-inoculated. Disease ratings were visually assessed from roots collected at R3, R5, R7, and R8. Colony forming units (CFU) were used to quantify fungal colonization in root tissue. Gas chromatography mass spectrometry was used to quantify the concentration of botryodiplodin, a toxin previously associated with charcoal rot from root tissue. An application of calcium applied pre-plant provided the greatest numerical reduction, 39.7%, in toxin concentration and also reduced disease severity by 1.0% and CFUs by 15.4% when compared to the inoculated control in a moderately resistant cultivar. Although numerical benefits were observed, these data do not support applications of Ca and Mg as a charcoal rot management option. Numerical differences were observed between rotational hosts and isolates in pathogenicity studies. The greatest numerical reduction of 34% in soybean dry plant weight was observed with the corn isolate when compared to the non-inoculated control. Macrophomina isolates from corn had up to an 8% greater colonization in soybean than corn or cotton plants. Although no significance was observed between isolates with regard to dry plant weight and colonization, colonization occurred regardless of treatment; suggesting crop rotation should not be a stand-alone charcoal rot management option.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Thesis (doctoral)--Universität, Göttingen, 1999.

Macrophomina phaseolina is a generalist ascomycetic fungal pathogen, capable of infecting over 500 genera of plants and limiting yield in crops grown in Mississippi. Recent documentation of M. phaseolina on Impatiens × hybrida, a newfound host, has merited multiple experiments to quantify the exact nature of this relationship. Despite M. phaseolina being a soil-borne pathogen, disease symptoms were only reported in aboveground tissue. Mode of infection experiments revealed both above and belowground tissues are susceptible to infection. In vitro experiments identified the optimal temperature for the growth of M. phaseolina to be 26°C, where more than 10x the accumulated biomass resulted compared to samples grown at 37°C. Impatiens × hybrida hosts were particularly prone to infection at temperatures above 27°C. In vitro fungicide assays revealed Banrot and T-Bird to be suitable chemical control agents for limiting M. phaseolina growth.

No description available.

Master of Science / Department of Plant Pathology / Christopher R. Little / Christopher R. Little / Charcoal rot, caused by Macrophomina phaseolina, is the most important soybean disease in Kansas. Several strategies have been recommended to control this disease including crop rotation, lower plant densities, biological control, plant resistance and tolerance, and fungicide application. However, those techniques have not been completely effective and the information concerning soil texture, irrigation and micronutrient fertility (particularly manganese) upon charcoal rot disease severity and the pathogen population is limited. The objective of this study was to determine key factors that affect the biology of M. phaseolina and charcoal rot processes under laboratory, greenhouse and field conditions. M. phaseolina microsclerotia were produced from PDA pure isolate and infested Japanese millet in the laboratory and characterized by different techniques such as serial dilutions in semi selective media with the aim to produce quality inoculum to reliably infect soybean seedling roots under greenhouse conditions; production of inoculum by infesting Japanese millet was the most efficient method. Root colonization and root infection of soybean seedlings was assessed through the use of M. phaseolina inoculum under controlled conditions in the greenhouse. Root infection by M. phaseolina and microsclerotia longevity in soil is determined by environmental factors such as soil moisture content, soil texture and source of inoculum. The objective of the greenhouse study was to determine the impact of these variables on seedling root infection at the V1 and V2 development stages. Artificial soils with different textures were infested; M. phaseolina microsclerotia and soybean seedlings were exposed to different soil moisture contents including pot saturation, pot (field) capacity, and permanent wilting point. Soil populations and levels of root colonization for the stages were assessed by estimating CFUs and root length. Results indicate that soil texture has a significant impact upon root morphology and root length. Root populations of M. phaseolina were significantly higher in sandy soil textures and lower in the fine-textured soils, suggesting an impact of soil water holding capacity in the root infection process. The effect of water stress on seedling root colonization by M. phaseolina indicates that early infection may be more important than previously thought. A field study was also conducted to determine the effect of the aforementioned variables in a 2-year field experiment conducted at two Kansas locations. Pathogen colonization was iii assessed by measuring colony-forming units (CFUs) from ground root tissue at R2-R4 (post-flowering/early pod development) and R8 (maturity) stages. Soil populations (pre-planting and post-harvest) of M. phaseolina, yield parameters, and plant characteristics were obtained. Results indicated that there are complex relationships between soil physiochemical properties (pH, NPK content, exchangeable cations, and organic matter) and soil texture (sand, soil, and clay composition), which may mitigate disease severity and pathogen levels in host tissue. Results also indicated that in natural M. phaseolina-infested soils, cropping history and soil texture play an important role in charcoal rot processes and influence the levels of pathogen soil populations, root colonization at maturity and, more importantly, soybean yield.

Amaranthus retroflexus L. (redroot pigweed) is a major weed of many crops in North America including corn, soybean, and potato. It can be readily controlled by chemical and cultural methods. However, some populations of A. retroflexus have developed resistance against the application of triazine herbicides. Biololical control could be an alternative method to control this weed species. In 1990, a Macrophoma sp. causing foliar lesions was isolated from redroot pigweed and the potential of this plant pathogenic fungus as a mycoherbicide was evaluated. Large numbers of infective propagules were produced in solid substrate fermentation with chickpeas. When inoculated with 10$ sp8$ or 10$ sp9$ conidia m$ sp{-2}$, plants at the cotyledon to 2-leaf stage showed the most severe damage. Disease developed over a wide range of dew period durations (6 hr to 24 hr) and temperature regimes (14 C to 26 C), and the most rapid and destructive disease development occurred following a 24-hr dew period at 18 C. In controlled environment studies, this Macrophoma sp. was pathogenic to the genus Amaranthus and the closely related genus Celosia.

Thesis (Ph.D.) - University of Queensland, 2004. / Includes bibliography.

Resumo: Objetivou-se o ajuste de metodologia e seleção de genótipos de guandu para resistência a Macrophomina phaseolina a partir de material obtido pela Embrapa Pecuária Sudeste, e verificar o desenvolvimento micelial e esporulação do fungo em meios de cultura. O trabalho foi conduzido em casa de vegetação na UNESP/Jaboticabal no período de agosto de 2004 a dezembro de 2005. Para o ajuste de metodologia e seleção de genótipos resistentes ao fungo as sementes foram submetidas a escarificação com lixa d'água e inoculação artificial através do método de exposição das mesmas ao patógeno por diferentes períodos, que variaram de O a 72 horas. Foram avaliadas porcentagem de plantas sobreviventes e massa fresca. Já para o crescimento micelial e esporulação do fungo foi utilizado o método de sobreposição de discos de diferentes hospedeiros no meio de cultura. A escarificação das sementes contribuiu para a penetração do fungo nas mesmas o período de 24h de exposição das sementes ao fungo são suficientes para detectar diferenças no grau de resistência dos genótipos. Os genótipos mais resistentes são g167-97, g124-95, g27-94, g40-95, g154-95, g127-97 e g9m-97, e os mais suscetíveis são g48-95, g123-95, g8-95, g168-99 e g1m-95. A sobreposição de discos foliares de guandu em meio BDA e folha de papel de filtro em meio sojinha proporcionam um incremento na esporulação de M. phaseolina. / Abstract: This work had the objective of determining the best schedule for artificial inoculation and select pigeon pea genotypes resistant to Macrophomina phaseolina in material obtained by Embrapa Pecuária Sudeste, and verify the mycelial growth and sporulation of the fungi in middle of culture. The work were carried in greenhouse at the UNESP/Jaboticabal, from August 2004 to December 2005. For the methodology and selection adjustment of resistant genotypes to the fungi the seeds were submitted scarified with water sandpaper and artificial inoculation the seeds were the contact method to fungi for different periods, which varied from O to 72 hours. They were evaluated percentage of surviving plants and fresh mass. For the mycelial growth and sporulation of the fungi was used the superposition of disks method of different hosts in the middle of culture. The scarified of the seeds contributed for penetration of the fungi at the seeds; the period of 24h of contact of the seeds to the fungi enough to detect differences in the resistance degree ofthe genotypes. The genotypes g167-97, g124-95, 927-94, g40-95, g154-95, g127-97 and g9m-97 were found to be the most resistant and most susceptible were g48-95, g123-95, g8-95, g168-99 and g1m-95. The treatment with superposition of the leaf disks of pigeon pea in BDA and disks of filter paper in middle of soybean extract were the treatments that provided better sporulation levei in the conditions of that experiment were half. / Orientador: Rita de Cássia Panizzi / Coorientador: Rodolfo Godoy / Banca: Antonio de Goes / Banca: Patrícia Menezes Santos / Mestre

No description available.