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.

The use of matrix assisted laser desorption ionization time-oflight mass spectrometry, Fourier transform infrared spectroscopy, and other analytical means of identifying and differentiating microorganisms hold much promise. These analytical tools have been extensively assessed for their ability to differentiate bacteria and fungi. Most of this research has been coordinated in medically relevant microorganisms, but the technology can work just as well with agriculturally important microorganisms. In this thesis, these technologies were reviewed and then subsequently studied for their ability to differentiate Aspergillus species (that devastate corn and other crops yearly with aflatoxin contamination), as well as Macrophomina phaseolina and Thielaviopsis basicola which limit yields on soybean and other crops yearly. With the use of these technologies, harmful plant pathogens could be identified and subsequently treated to improve crop yields and also help to protect our nation and state’s food supply.

Microbial-root associations are important to help plants cope with abiotic and biotic stressors. Managing these interactions offers an opportunity for improving the efficiency and sustainability of agricultural production. By characterizing the bacterial and archaeal community (via 16S rRNA sequencing) associated with the bulk and rhizosphere soil of sixteen strawberry cultivars in two controlled field studies, we explored the relationships between the soil microbiome and plant resistance to two soilborne fungal pathogens of strawberry (Verticillium dahliae and Macrophomina phaseolina). Overall, the plants had a distinctive rhizosphere microbiome relative to the bulk soil, with higher abundances of known beneficial bacteria such as Pseudomonads and Rhizobium. Plant genotype, biomass, leaf nutrient content and mortality were influenced differently by the rhizosphere microbiome in each of the two trials. In the V. dahliae trial, the rhizosphere microbiome was associated with plant biomass and leaf nutrient content and only indirectly to the disease resistance. In the M. phaseolina trial, the rhizosphere microbiome was associated to plant biomass, but not nutrient content; furthermore, resistant cultivars had larger abundances of Pseudomonas and Arthrobacter in their rhizosphere relative to susceptible cultivars. The mechanisms involved in these beneficial plant-microbial interactions and their plasticity in different environments should be studied further for the design of low-input disease management strategies.

Effects of nitrogen management and cultivar on strawberry production under disease pressure Kamille Garcia-Brucher California strawberry growers face increasing regulatory pressures to manage nitrogen (N) applications in their production system. Standard practice in the California strawberry industry is to apply a synthetic pre-plant controlled release fertilizer (CRF) to ensure the crop has sufficient N during winter establishment. Some research from the UC Cooperative Extension suggests this practice is not efficient at delivering N to the crop since most of the N is released from CRF before strawberry crop N uptake is significant. Another concern for California strawberry growers is loss of their crop to a myriad of soilborne pathogens. Compost is commonly applied as a soil amendment in California strawberry fields as it offers both agronomic and environmental benefits including the potential for disease suppression. In light of legislation restricting N in some California cropping systems, Ag Order 4.0, and incentives programs established to promote soil conservation practices, compost may be a viable substitute for synthetic pre-plant CRF N. In this study, we investigated the effects of pre-plant fertilizer and strawberry cultivar on fruit yield, disease incidence, soil and plant N dynamics and soil carbon (C) at the Cal Poly Strawberry Center, San Luis Obispo, CA in a field infested with Macrophomina phaseolina. Pre-plant fertilizer treatments included 100 lb N/ac Cal Poly certified organic compost, 100 lb N/ac synthetic CRF and a control treatment (0 lb N/ac). Strawberry cultivars included three UC varieties, ‘Monterey,’ ‘Albion,’ and ‘San Andreas,’ and one Driscoll’s proprietary cultivar. Fruit yield and plant mortality data were collected throughout the growing season. Soil C was measured from soil samples collected in the root zone (6 in) while soil nitrate was measured from pore water samples collected in and below the root zone (6 and 12 in, respectively). Strawberry crop N uptake was determined using destructive plant samples while fruit N concentration was determined from subsamples of harvested fruit taken in April, May, June, and July each year. Although compost application did not significantly affect C sequestration and did not reduce disease incidence, there was no significant difference in total yield between compost and CRF treatments suggesting that compost can substitute for synthetic CRF without negatively affecting yield. There was significantly less plant mortality in control treatments compared with compost and CRF treatments suggesting excessive pre-plant N impacts disease incidence by M. phaseolina but more research is needed to better understand the mechanisms of infection by this soilborne pathogen. Total yield in this experiment was lower compared with statewide averages and crop N concentration was lower compared with the literature which is likely a result of disease pressure. Fruit N concentrations for the cultivars in this study were lower than the conversion coefficient defined by the Ag Order which means growers are removing less N through harvest allowing them more room in their N budget. Based on our results, compost may be substituted for synthetic CRF without negatively affecting yield and perhaps even make desirable soil improvements in this production system. And in fields with significant levels of M. phaseolina in the soil, N applications should be considered as it was seen to impact disease incidence. Keywords: compost, controlled release fertilizer, M. phaseolina, nitrogen uptake, Ag Order 4.0

Allelopathy occurs when one organism releases a compound into the environment that affects the functioning of another organism. Scientists have long suspected that alleopathic plant compounds could offer novel, softer chemistries to the ongoing battle of controlling pests in agricultural fields. Strawberry growers rely on toxic fumigants to kill soilborne fungal pests, weeds, nematodes, and insects. Increased regulations have reduced the use of fumigants (including methyl bromide), and strawberry growers need new sustainable pest control solutions. We selected four putative allelochemicals with known fungicidal and herbicidal activity (ferulic acid, gallic acid, juglone, and p-Coumaric acid). We assessed the pesticidal activity of these plant compounds both in agar and in soil on two emerging soilborne fungal pathogens (Macrophomina phaseolina and Fusarium oxysporum f.sp. fragariae), and four annual weeds commonly found in strawberry production fields (Malva parviflora, Melilotus officinalis, Poa annua, and Senecio vulgaris). We also assayed lettuce (Lactuca sativa ‘Inferno’), which served as a positive control plant species due to its sensitivity to phytotoxic compounds. Fitted sigmoidal dose-response curves predicted EC50 and EC75 values for each combination of plant compound and pest. All plant compounds inhibited the in vitro radial mycelial growth of the two soilborne fungal pathogens in a dose-dependent manner. Fusarium oxysporum f.sp. fragariae was more sensitive to the plant compounds than Macrophomina phaseolina. Average EC50 values for the radial mycelial growth of two F. oxysporum f.sp. fragariae isolates were 75.1 parts per million by weight (ppmw) juglone, 469 ppmw p-Coumaric acid, and 687 ppmw ferulic acid. Average EC50 values for the radial mycelial growth of two M. phaseolina isolates were 196 ppmw juglone, 2869 ppmw p-Coumaric acid, and 5716 ppmw ferulic acid. The three compounds we assayed in vitro also reduced M. phaseolina colony forming unit counts in soil and the EC50 values were 476 ppmw ferulic acid, 612 ppmw juglone, and 827 ppmw p-Coumaric acid. Metconazole, the conventional fungicide control, did not inhibit M. phaseolina colony forming unit counts in soil at its label high rate. The plant compounds required similar or lower rates to inhibit colony forming units that grew from M. phaseolina overwintering structures (microsclerotia) in soil as to inhibit radial mycelial growth in vitro. Based on the EC50 value in soil assays, ferulic acid was the least expensive plant compound to apply on a per acre basis to inhibit M. phaseolina ($74,226). In F.oxysporum f.sp. fragariae soil assays, the compounds induced hormesis at lower rates and may be germination stimulant candidates. Metconazole and the high rates of every compound effectively or completely inhibited F. oxysporum f.sp. fragariae colony forming units in soil. The plant compounds were more herbicidal than fungicidal in vitro. When combining the in vitro seedling length results for L. sativa, M. parviflora, P. annua, and S. vulgaris the EC50 values differed significantly (p < .0001) and were: 47 ppmw juglone, 120 ppmw p-Coumaric acid, 189 ppmw ferulic acid, and 297 ppmw gallic acid. At least one rate of ferulic acid, juglone, and p-Coumaric acid inhibited the germination of all plant species, while gallic acid only inhibited the germination of P. annua at 1000 ppmw (p < .05). In soil, visible microbial contamination in individual wells of 24-well plates and seed dormancy made it difficult to fit curves to weed seedling length data. The soil assay L. sativa seedling length EC50 values 11 days after initial treatment were slightly higher than in vitro, although plant compounds were in the same order of phytotoxicity: 129 ppmw juglone, 616 ppmw p-Coumaric acid, 644 ppmw ferulic acid, and 1584 ppmw gallic acid. Based on the EC50 value in soil assays, the least expensive compound to inhibit L. sativa seedling length on a per acre basis was gallic acid ($21,676). Germination 26 days after initial soil treatment generally declined in a dose-dependent manner for each compound. There was a direct relationship between plant compound rate and seedling damage in soil with the higher rates of all compounds, except p-Coumaric acid, inducing damage comparable to a conventional herbicide (pendimethalin or oxyfluorfen). Contaminated treatments appeared to be due to an interaction between plant compounds and microorganisms because herbicide and water controls had almost no microbial growth 11 days after initial treatment. Further, there was a significant positive linear relationship between level of contamination in phenolic acid-treated wells (ferulic acid, gallic acid, and p-Coumaric acid, p < .0001) and the in soil rate. This relationship was slightly negative in juglone soil treatments (p = .0167), which may be due to its greater antimicrobial activity than the phenolic acids. We propose that herbicidal effects in soil were due to the joint effect of the plant compounds themselves, and the microbial growth in wells. Microbial growth was either antagonistic or additive to the inhibitory action of the plant compounds. The plant compounds we assayed were inhibitory of emerging fungal pathogens in strawberry production and common annual strawberry field weeds. Evidence presented in this thesis correlates well with past research that not only found plant compounds to be herbicidal and fungicidal, but also described their modes-of-action (such as the production of reactive oxygen species that causes necrotic lesions on roots, and inhibition of glycolytic enzyme activity that prevents germination), and implicate plant compounds as carbon sources for a variety of microorganisms. Compound prices are currently exorbitant, but may decline as demand increases. Whether or not they provide effective pest control may depend on soil texture, organic matter, microbial diversity, and other edaphic factors.

No description available.

An evaluation was made of soil solarization to control Macrophomina phaseolina and Sclerotium rolfsii under the climatic conditions of the Sonoran Desert region of Arizona. Tarping of moist soil with clear polyethylene in the summer was most effective in raising soil temperatures, while tarping during the fall and spring were less efficient. In one summer trial, the maximum temperatures achieved were 7-8 C higher than control plots at 1, 15, and 30 cm depths. In none of the tests was the application of tarp effective in reducing M. phaseolina populations to non-detectable levels. After a six-week summer solarization treatment, S. rolfsii was controlled at the 15-cm but not the 30-cm depth. During a fall treatment control of S. rolfsii was achieved only at the 1-cm depth. After solarization, seeds of Euphorbia lathyris were planted in solarized and control plots. The incidence of M. phaseolina-associated mortality among seedlings planted in solarized plots was always the same as the control plot with the highest disease incidence. The utility of this technique may be limited by the heat tolerance of the target organisms. Studies of bacterial antagonists were initiated to determine their utility in enhancing pathogen control after the solarization treatment. Screening 43 bacterial isolates showed that seven of Pseudomonas fluorescens and one of Serratia marcescens exhibited some form of antagonism toward M. phaseolina, S. rolfsii and Verticillium dahliae in vitro. Antagonism was manifested as a complete inhibition of fungal development or reduced hyphal development coupled with suppression of sclerotial development. The action of the antagonists was found to be fungitoxic or fungistatic rather than fungicidal. None of the four P. fluorescens isolates tested were effective in preventing M. phaseolina infection of E. lathyris seedlings. The ability of these bacteria to prevent sclerotial formation while still permitting hyphal growth may be a useful technique for studying the two phases of the fungal life cycle separately.

Doctor of Philosophy / Department of Agronomy / Tesfaye Tesso / Fusarium stalk rot and charcoal rot caused by Fusarium thapsinum and Macrophomina phaseolina respectively are devastating global diseases in sorghum that lead to severe quality and yield loss each year. In this study, three sets of interrelated experiments were conducted that will potentially lead to the development of resistance based control option to these diseases. The first experiment was aimed at identifying sources of resistance to infection by M. phaseolina and F. thapsinum in a diverse panel of 300 sorghum genotypes. The genotypes were evaluated in three environments following artificial inoculation. Out of a total of 300 genotypes evaluated, 95 genotypes were found to have resistance to M. phaseolina and 77 to F. thapsinum of which 53 genotypes were resistant to both pathogens. In the second experiment, a set of 79,132 single nucleotide polymorphisms (SNPs) markers were used in an association study to identify genomic regions underlying stalk rot resistance using a multi-locus mixed model association mapping approach. We identified 14 loci associated with stalk rot and a set of candidate genes that appear to be involved in connected functions controlling plant defense response to stalk rot resistance. The associated SNPs accounted for 19-30% of phenotypic variation observed within and across environments. An analysis of associated allele frequencies within the major sorghum subpopulations revealed enrichment for resistant alleles in the durra and caudatum subpopulations compared with other subpopulations. The findings suggest a complicated molecular mechanism of resistance to stalk rots. The objective of the third experiment was to determine the functional relationship between stay-green trait, leaf dhurrin and soluble sugar levels and resistance to stalk rot diseases. Fourteen genotypic groups derived from a Tx642 × Tx7000 RIL population carrying combinations of stay-green quantitative trait loci were evaluated under three environments in four replications. The stg QTL had variable effects on stalk rot disease. Genotypes carrying stg1, stg3, stg1,3 and stg1,2,3,4 expressed good levels of resistance to M. phaseolina but the combination of stg1 and stg3 was required to express the same level of resistance to F. thapsinum. Other stg QTL blocks such as stg2 and stg4 did not have any impact on stalk rot resistance caused by both pathogens. There were no significant correlations between leaf dhurrin, soluble sugar concentration, and resistance to any of the pathogens.

Made available in DSpace on 2014-06-11T19:28:28Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-02-27Bitstream added on 2014-06-13T19:16:23Z : No. of bitstreams: 1 frigeri_t_me_jabo.pdf: 214550 bytes, checksum: a1c65c9e88fd5fc622a8f30d3f3a9e22 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / O objetivo dessa pesquisa foi verificar a influência de Macrophomina phaseolina, Colletotrichum dematium f. truncata e Colletotrichum lindemuthianum na qualidade fisiológica de sementes de feijoeiro, em especial nos resultados do teste de condutividade elétrica. Foram utilizadas sementes das cultivares Carioca e FT Nobre. As sementes foram infectadas com os fungos em meio de cultura BDA sem e com restrição hídrica (acrescido de manitol a -1,0 MPa). Nos tratamentos testemunhas foram utilizados os mesmos meio de cultura, porém, sem a presença dos fungos. Para cada tratamento as sementes foram sobrepostas nos meios de cultura por 16 horas para M. phaseolina e por 48 horas para o caso de C. dematium f. truncata e C. lindemuthianum. Após secagem natural foram realizados testes de sanidade, germinação em areia e de vigor, como, índice de velocidade de emergência, peso da matéria seca da plântula, teste de frio, teste de envelhecimento acelerado e condutividade elétrica. Também foram realizadas análises na água de embebição das sementes no teste de condutividade elétrica, determinando-se as concentrações de potássio, cálcio e magnésio, assim como nos meios de cultura utilizados com e sem a sobreposição de sementes, para verificação da hipótese de consumo de nutrientes das sementes pelos fungos... / The aim of this research was to verify the influence of Macrophomina phaseolina, Colletotrichum dematium f. truncata and Colletotrichum lindemuthianum in the physiological quality of bean seeds, special in the results of electrical conductivity test. There were used seeds from Carioca and FT Nobre cultivars. The seeds were artificially inoculated with fungi M. phaseolina, C. dematium f. truncata and C. lindemuthianum in BDA medium culture with and without hydric restriction (it was added -1,0 MPa manitol). In the control treatment there was used the same medium culture without the presence of the fungi. For each treatment the seeds were placed on the medium culture for 16 hours for M. phaseolina and 48 hours for C. dematium f. truncata and C. lindemuthianum. After a nature dry, seeds were evaluated, by the blotter test, sand germination and vigor tests: speed of emergence index, seedlings dry weigh, cold, accelerated aging and electrical conductivity tests. Analyses from the imbibition water of the seeds in the electrical conductivity test, were also done a measuring of concentrations of potassium, calcium and magnesium, as well as in the medium culture used with and without the seeds, to verify the hypothesis of seeds nutrients consumption by the fungi...(Complete abstract, click electronic address below)

Made available in DSpace on 2014-06-11T19:28:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-05-15Bitstream added on 2014-06-13T20:58:17Z : No. of bitstreams: 1 rosa_j_me_jabo.pdf: 154567 bytes, checksum: 0d2897a42007e37a9a5f314b75f0f0f0 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA) / 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. / 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.