RESUMO
Strawberry (Fragaria x ananassa) is an important crop in the U.S., and Florida is the second major producer in the country. In January 2020, an unknown fruit rot was observed in two strawberry fields in Dover (seedling selection) and Plant City (cultivar Florida127), Florida. Disease incidence varied from less than 1% in one field to up to 15% in the second field during some harvests where over-ripe fruit were present. Affected fruit had a water-soaked soft rot with a sour smell, and sometimes with white mycelium on the fruit surface. Direct isolation was performed from symptomatic fruit from each area by touching the surface of a lesion with a sterile needle and streaking the fungus over general isolation medium (Amiri et al. 2018). The fungus was incubated at 25°C and 12-h photoperiod for five days. Four single-spore isolates (20-46 and 20-47 from Plant City; 20-49 and 20-50 from Dover) obtained from different colonies were grown on potato dextrose agar (PDA). Colonies were white to cream, flat, with a powdery surface, and had a characteristic sour odor. Hyphae were hyaline, septate, growing in a dichotomous pattern and often disarticulating into arthroconidia, which were unicellular, spherical to cylindrical, measuring 4.8 to 9.5 × 3.5 to 5.6 µm (n = 50). Based on the morphological characteristics, the fungus was identified as Geotrichum candidum (De Hoog et al. 1986). To confirm the identity of the isolates, the ribosomal internal transcribed spacer (ITS-rDNA) and the translation elongation factor 1-alpha (TEF1-α) gene regions were amplified and sequenced using the primers ITS1/ITS4 (White et al. 1990), and EF1-728F/EF1-1567R (Carbone and Kohn 1999), respectively. Consensus sequences were deposited in the GenBank (accession numbers MT353975 to MT353978 for ITS-rDNA, and MT346367 to MT346370 for TEF1-α). The BLASTn analysis revealed 99% identity with reference sequences of G. candidum for ITS-rDNA (KU373122) and TEF1-α (MK397513). Phylogenetic analysis, including ITS sequences of G. candidum and other spp., obtained from GenBank, was performed using maximum likelihood and Bayesian inference methods, implemented in MEGA-X and MrBayes, respectively. The isolates were grouped within the G. candidum clade. The pathogenicity of the fungus (isolate 20-46) was evaluated in ripe and green strawberry fruit (cultivar Florida127). Non-wounded and superficially wounded (with a sterilized needle) fruit were inoculated with 20 µl of a spore suspension (1 × 107 spore/ml), prepared by washing the surface of a 5-day-old colony on PDA, with sterile deionized water (SDW) plus 0.01% (v/v) Tween 20. Wounded and non-wounded control fruit were treated with SDW. Fruit were maintained in moist containers at 25°C. Each treatment consisted of 12 fruit (three replicates, each containing four fruit) and was evaluated daily for 10 days. Symptoms of sour rot were visible as soon as 48 hr after inoculation, but only on ripe (100% incidence) and green (58% incidence) wounded fruit. Symptoms progressed to an intense water-soaking with the presence of a typical white mycelium on the surface. Control fruit remained symptomless. The fungus was successfully recovered from symptomatic fruit, fulfilling Koch's postulates. Although strawberry fruit rots caused by G. candidum have already been reported in Pakistan and China (Hussain et al. 2016; Ma et al. 2018), this is the first report of this species causing sour rot on strawberry in the U.S. The disease may be a minor problem on damaged or over-ripe fruit, but further studies might be needed to determine its importance, distribution, and potential strategies for control.
RESUMO
A produção da soja pode ser afetada pela ocorrência de várias doenças. Dentre estas, a ferrugem, causada pelo fungo Phakopsora pachyrhizi, tem se destacado. Atualmente, novas estratégias de controle para essa doença devem ser pesquisadas. Assim, este trabalho teve como objetivo avaliar a eficiência do silicato de potássio (KSi), acibenzolar-S-metil e fungicidas no controle da ferrugem da soja. Um experimento foi conduzido em condições de campo, em delineamento em blocos ao acaso, utilizando-se 10 tratamentos, com três repetições. Foi utilizada a cultivar 'Monarca' por ser suscetível à ferrugem. Os tratamentos utilizados foram: T1 - testemunha (pulverização com água); T2 - KSi (1,2kg ha-1); T3 - KSi (2,4kg ha-1); T4 - KSi (3,6kg ha-1); T5 - KSi (4,8kg ha-1); T6 - tebuconazole (125g de i.a. ha-1); T7 - cloreto de potássio (61,72g L-1); T8 - mancozebe (2400g de i.a. ha-1); T9 - mancozebe (2400g de i.a. ha-1) + KSi (1,2kg ha-1) e T10 - acibenzolar-S-metil (125g de i.a. ha-1). As plantas da bordadura foram inoculadas com uma suspensão de 5x10(5) uredosporos mL-1 no estádio V4 para constituírem fonte de inóculo, para as parcelas centrais. As plantas foram pulverizadas com os produtos que constituíram os tratamentos T2, T3, T4, T5, T7, T8 e T9 nos estádios V5, R1, R4 e R5.4 e os tratamentos T6 e T10 nos estádios R1, R4 e R5.4. As plantas foram pulverizadas com atomizador costal manual de bico cônico empregando-se um volume de calda de 200L ha-1. Foram realizadas cinco avaliações da severidade da ferrugem nos terços inferior, médio e superior das plantas utilizando-se uma escala diagramática variando de 0,6 a 78,5 por cento, e os dados obtidos foram utilizados para calcular a área abaixo da curva do progresso da ferrugem (AACPF). Não houve efeito significativo das doses de KSi na AACPF e severidade máxima (Ymax) nos terços inferior, médio e superior das plantas, além da produtividade. Os tratamentos 8, 9 e 10 apresentaram eficiência intermediária ...
Soybean production can be affected by the occurrence of several diseases. Among them, the rust, caused by the fungus Phakopsora pachyrhizi, has been outstanding. Nowadays, new strategies to control soybean rust need to be searched. Therefore, this study aimed to evaluate the efficiency of potassium silicate (KSi), acibenzolar-S-methyl and some fungicides on the control of soybean rust. An experiment was carried out under field conditions in a randomized complete block design with 10 treatments and three replications. The cultivar 'Monarca' was used because it is susceptible to rust. The treatments used were: T1 - control (plants sprayed with water); T2 - KSi (1.2kg ha-1); T3 - KSi (2.4kg ha-1); T4 - KSi (3.6kg ha-1); T5 - KSi (4.8kg ha-1); T6 - tebuconazol (125g de a.i. ha-1); T7 - potassium cloride (61.72g L-1); T8 - mancozeb (2400g de a.i. ha-1); T9 - mancozeb (2400g de a.i. ha-1) + KSi (1.2kg ha-1) and T10 - acibenzolar-S-methyl (125g de a.i. ha-1). Plants from the two lateral lines were inoculated with a suspension of 5x10(5) uredospores/mL at the V4 growth stage to produce inoculum to infect plants at the two central lines. Plants were sprayed with the products that constituted the treatments T2, T3, T4, T5, T7, T8, and T9 at V5, R1, R4, and R5.4 growth stages; and the treatments T6 and T10 at R1, R4, and R5.4 growth stages. Plants were sprayed using a costal sprayer in a volume of 200L ha-1. A total of five disease severity evaluations at the low, medium and high part of the plant canopy were done using a diagrammatic scale ranging from 0.6 to 78.5 percent. Data were used to calculate the area under rust progress curve (AURPC). There was no effect of the KSi rates on AURPC and final disease severity (Ymax) at the low, medium and high part of the plant canopy. Yield was also unaffected. The treatments 8, 9, and 10 had an intermediary efficiency on rust control. The treatment 6 was the most efficient on rust control giving the lowest ...
