Two endemic late-season grape rot diseases, ripe rot and sour rot continue to pose a significant challenge to grape growers in Virginia and similar climates. Managing these diseases in the vineyard is challenging due to concerns over the increased risk of resistance against traditional single-site mode of action pesticides. This study evaluated the efficacy of different biopesticides and novel chemical options with a series of field trials across four vineyards in northern Virginia in 2021 and 2022. Among the tested products, a potassium-based nutrient formulation resulted in consistent ripe rot suppression in two of the three trials, showing around 46% and 83% less mean disease severity at the AHS AREC trial in 2022 and 2021, respectively, and 63% and 19% less mean disease incidence at the South Loudoun trial in 2021 and AHS AREC trial in 2022. For sour rot, zeta-cypermethrin with cyprodinil + fludioxonil or hydrogen peroxide + peroxyacetic acid resulted in effective control in two of the five trials, with a high of 71% and 73% less mean disease incidence compared to the untreated check in the Frederick trial in 2021 and 2022, respectively. In general, treatments with spinosad were less effective and resulted in lower disease control compared to those with zeta-cypermethrin and its fungicides/antimicrobials counterpart. The results suggest that integrating these biopesticides and novel chemicals into a spray program could offer a more sustainable solution for sour rot and ripe rot disease management without compromising the level of disease control. / Master of Science in Life Sciences / Ripe rot and sour rot are two diseases of concern for growers in Virginia and many other grape-growing regions due to significant losses in fresh cluster yield and the risk of contamination during the winemaking process. Traditional pesticides are often used; however, the breakdown of the effectiveness of these pesticides after continuous application, i.e., pesticide resistance, has become a critical issue. The other issues include, but are not limited to, adverse effects on human health, nature, and winemaking. On the other hand, biopesticides derived from microorganisms, their products, plant extracts, etc., are considered relatively safer and more sustainable options. This study evaluated the efficacy of biopesticides and novel chemicals against ripe rot and sour rot through field trials over two years at four locations in northern Virginia. Although no clear-cut winners were among the tested treatments, one of the tested chemicals (a potassium-based plant nutrient formulation) provided consistent disease suppression (up to 83%) against ripe rot. In the case of sour rot, several treatments, including a biologically derived insecticide, produced comparable disease suppression (up to 73%) compared to the current standard application. These safer options can be included in the spray schedule without compromising the level of disease control, meanwhile aiding the sustainability of the spray program in the long run.

Sour rot of tomatoes, caused by Geotrichum candidum, occurs in the field and postharvest settings regularly, although postharvest losses are severe only in some years on the Eastern Shore of Virginia (ESV) and other tomato production regions. Fungicide products and cultural control methods are tested for efficacy utilizing a traditional wounding technique that does not properly reflect natural sour rot infections. A new inoculation technique was optimized for G. candidum using negative pressure to infiltrate the tomato stem scar with pathogenic spores. This new method creates consistently high rates of infection and more successfully creates infections in mature green and breaker fruit. The population of G. candidum on the Eastern Shore of VA (ESV) was characterized using multilocus sequencing technique. The resulting phylogenetic tree defines four distinct groups, including two with uncommon loci that distinguish them from the majority of the population. Thirty-seven G. candidum isolates were inoculated to media amended with ten fungicides and antimicrobial compounds commonly used in tomato production and postharvest treatments. Propiconazole and tebuconazole completely inhibited growth of all colonies. Cultivar trials were conducted to determine if resistance or tolerance to G. candidum occurs. Ten commonly grown round and Roma cultivars on the ESV were similarly susceptible to G. candidum, even at low inoculum levels. Field and postharvest surveys of sour rot on tomato fruit attempted to correlate disease incidence with weather conditions in order to better understand the cause of sporadic infection. Few patterns were seen consistently throughout harvest periods and years. Rainfall was positively correlated with disease 2-3 days before surveys and temperature was negatively correlated with disease 5-7 days before surveys. No in-field weather conditions were correlated with postharvest disease incidence. Greenhouse trials were conducted to assess the influence of water congested tomato fruit on susceptibility to sour rot. Tomato plants were exposed to water inundation to mimic rainfall and varying levels of irrigation, both in order to congest tomato fruit. Though water congestion was achieved, tomato fruit were equally susceptible to sour rot infections. / Ph. D.

Submitted by MARIANA NADJARA KLEIN null (mariana_klein28@hotmail.com) on 2017-01-12T18:03:07Z No. of bitstreams: 1 TESE MARIANA definitiva 12.01.17.pdf: 1548852 bytes, checksum: ab76519552913b27064c77dfab05d64a (MD5) / Approved for entry into archive by LUIZA DE MENEZES ROMANETTO (luizamenezes@reitoria.unesp.br) on 2017-01-16T16:32:22Z (GMT) No. of bitstreams: 1 klein_mn_dr_jabo.pdf: 1548852 bytes, checksum: ab76519552913b27064c77dfab05d64a (MD5) / Made available in DSpace on 2017-01-16T16:32:22Z (GMT). No. of bitstreams: 1 klein_mn_dr_jabo.pdf: 1548852 bytes, checksum: ab76519552913b27064c77dfab05d64a (MD5) Previous issue date: 2016-12-20 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A eficiência de biocontrole de Aureobasidium pullulans ACBL-77 foi avaliada contra Geotrichum citri-aurantii, agente causal da podridão azeda em citros, e suas interações foram estudadas in vitro e in vivo. Para isso, foram avaliados: (i) a eficiência de biocontrole da podridão azeda por A. pullulans ACBL-77; (ii) o efeito de diferentes meios de cultivo na produção de células da levedura; (iii) a incorporação de fontes nutricionais na otimização da atividade antagônica; (iv) a competição de nutrientes entre os microrganismos; (v) o efeito dos nutrientes na produção de células da levedura e na quantificação de biofilme e sua relação no biocontrole da doença; (vi) a sobrevivência da levedura em frutos cítricos; (vii) a interação entre os microrganismos em microscopia eletrônica de varredura; (viii) o efeito da aplicação da levedura na qualidade de frutos cítricos, e, finalmente, (ix) o efeito de A. pullulans na atividade das enzimas possivelmente envolvidas com a indução de resistência de frutos. Pelos resultados obtidos nesse trabalho, verificou-se que, nos frutos tratados preventivamente com A. pullulans ACBL-77 a porcentagem de controle foi maior do que quando os tratamentos foram realizados de maneira curativa. O meio de cultivo batata-dextrose-ágar foi o que promoveu maior quantidade de células da levedura. A incorporação de micronutrientes, como ácido bórico, cloreto de cobalto e molibdato de amônio (1 mM) em meio de cultivo da levedura favoreceu a ação antagônica in vitro. Sulfato de amônio 1 % e sacarose 0,5 % promoveram aumento na porcentagem de inibição da germinação de conídios. Porém, a adição de sulfato de amônio 1% no cultivo da levedura estimulou a produção de biofilme e, consequentemente, aumentou sua ação antagônica contra a doença in vivo. Aplicação de A. pullulans, previamente cultivada em meio acrescido de sulfato de amônio (1%), favoreceu a sobrevivência da levedura em ferimentos de frutos cítricos e provocou deformações nas hifas do fitopatógeno. A aplicação da levedura não alterou a qualidade de frutos cítricos, mas aumentou as atividades das enzimas envolvidas com a defesa dos frutos a patógenos. Esses resultados mostram a importância da adição e do tipo de nutriente, quando da formulação de um bioproduto a base deste isolado, visando a sua utilização em escala comercial. Além disso, esse é o primeiro relato de uma correlação positiva do aumento na quantificação de biofilme produzido por A. pullulans, em função da fonte de nutriente, com o aumento da sua atividade antagônica. / The biocontrol efficiency of Aureobasidium pullulans strain ACBL-77 was evaluated against Geotrichum citri-aurantii, the causal agent of sour rot in citrus, and their interactions were studied in vitro and in vivo. For this purpuse, were evaluated (i) the biocontrol efficiency of A. pullulans ACBL-77 against the pathogen; (ii) the effect of different culture media on the production of yeast cells; (iii) the incorporation of nutritional sources in optimizing the antagonistic activity; (iv) the competition for nutrients between the microorganisms; (v) the effect of nutrients on yeast cell and biofilm production and their relation in the biocontrol of disease; (vi) the survival of yeast in citrus fruits; (vii) the interaction between the microorganisms by scanning electron microscopy; (viii) the effect of A. pullulans applications in the citrus fruits quality; (ix) the effect of ACBL-77 in the activity of the enzymes possibly involved with resistance induction. In the results this study, were verified that in the fruits treated with A. pullulans ACBL-77, preventively, the control percentage was higher than the curative treatment. The potato-dextrose-agar medium promoted the highest amount of yeast cells. The incorporation of micronutrients, such as boric acid, cobalt chloride and ammonium molybdate (1 mM), favoured the antagonistic action of A. pullulans in vitro. Ammonium sulphate 1mM and sucrose 0.5% favoured the yeast during the competition between the microorganisms. However, the addition of ammonium sulphate at 1% in the yeast culture stimulated biofilm production and consequently increased the antagonistic activity against the pathogen in vivo. The application of A. pullulans to fruits allowed the better survival of yeast in wounded sites of citrus fruit. The yeast was found to be able to form biofilm on citrus, deforming the pathogen hyphae. The application of yeast did not change the quality of citrus fruits, but increased the activities of the enzymes possibly involved in the defense of the fruits to pathogens. These results show the importance of the addition of nutrients and the types of nutrients in A. pullulans based-formulations when aiming for their use on a commercial scale. Additionally, this is the first report of a positive correlation between the increase in the quantity of biofilm produced by A. pullulans, depending on the nutrient source, with increased antagonistic activity.