First Report of Anthracnose Caused by Colletotrichum nymphaeae on Strawberry Fruits in Central Argentina.

Strawberry (Fragaria x ananassa) production in Argentina extends to around 1700 hectares. Coronda city, located in Santa Fe province, is an important strawberry producer due to ideal agroecological conditions for culture and a high specialization for production. In November 2021, anthracnose symptoms were observed on strawberries cvs. 'San Andreas' and 'Splendor' in Coronda (31°58'S, 60°55'W), central Argentina. During these years, the incidence of the disease reached 40% of the production. Symptoms included 2-3 mm circular to irregular dark brown spots which enlarged rapidly and became sunken. Under high humidity conditions, concentric rings of pinhead-size salmon-colored acervuli developed on the lesions. The causal agent was isolated by touching acervuli with a sterile needle and monosporic cultures were obtained on PDA after 10 days at 25°C, with a 12-h light period. Colonies were white to gray on the top and orange on the underside, where concentric rings of salmon acervuli were clearly distinguished. The width and length of one hundred conidia were examined in three isolates (CF1, CF2, and CF3), ranging from 3.27 to 5.53 µm (avg.= 4.3 µm), and from 10.37 to 19.52 µm (avg.= 14.27 µm), respectively. The conidia were hyaline, smooth-walled, aseptate, and cylindric-clavate with one end round and one end acute. These morphological characteristics correspond to species belonging to the C. acutatum complex (Damm et al. 2012; Liu et al. 2022). To accurately identify the species, DNA was extracted from isolates, and ß-tubulin (TUB2), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and histone (HIS3) genes were partially amplified and sequenced (Vieira et al. 2020). TUB2, GAPDH, and HIS3 sequences presented a 100% of identity with species of Colletotrichum nymphaeae. The nucleotide sequences were deposited in GenBank (OR271556-OR271558, TUB2; OR271559-OR271561, GAPDH; and OR271562-OR271564, HIS3). Multilocus phylogenetic analyses performed with reference sequences (Damm et al. 2012) showed that the three isolates clustered with C. nymphaeae, in accordance with BLAST results. To confirm pathogenicity, each isolate was inoculated in eight detached fruits of the cultivar from which it was originally obtained. Two drops of 10 µl of conidial suspension (1x105 conidia per ml) were deposited in non-wounded areas on fruits previously disinfested with 1% sodium hypochlorite solution for 1 min and rinsed twice with sterile distilled water. Drops of sterile water were deposited in eight fruits as control. Pathogenicity tests were repeated twice. Fruits were kept in moist chamber (80+5% relative humidity) at 25°C for ten days. First symptoms appeared 4 days after inoculation. After that, all of the isolates produced symptoms identical to those previously described, whereas the controls remain symptomless. The pathogen was re-isolated from lesions, and identified as C. nymphaeae by morphological characteristics and based on the TUB2 sequences, as previously described. Strawberry anthracnose in Argentina was previously associated with Colletotrichum acutatum, C. gloeosporioides and C. fragariae species based on morphological characteristics (Ramallo et al. 2000; Monaco et al. 2000) but molecular identification was not performed until today. To our knowledge, this is the first report of C. nymphaeae causing anthracnose on strawberry in Argentina. This accurate identification will help to develop more efficient management strategies.

An Update on Phytochemicals and Pharmacological Activities of the Genus Persicaria and Polygonum.

The discovery of new pharmaceutical identities, particularly anti-infective agents, represents an urgent need due to the increase in immunocompromised patients and the ineffectiveness/toxicity of the drugs currently used. The scientific community has recognized in the last decades the importance of the plant kingdom as a huge source of novel molecules which could act against different type of infections or illness. However, the great diversity of plant species makes it difficult to select them with probabilities of success, adding to the fact that existing information is difficult to find, it is atomized or disordered. Persicaria and Polygonum constitute two of the main representatives of the Polygonaceae family, which have been extensively used in traditional medicine worldwide. Important and structurally diverse bioactive compounds have been isolated from these genera of wild plants; among them, sesquiterpenes and flavonoids should be remarked. In this article, we firstly mention all the species reported with pharmacological use and their geographical distribution. Moreover, a number of tables which summarize an update detailing the type of natural product (extract or isolated compound), applied doses, displayed bioassays and the results obtained for the main bioactivities of these genera cited in the literature during the past 40 years. Antimicrobial, antioxidant, analgesic and anti-inflammatory, antinociceptive, anticancer, antiviral, antiparasitic, anti-diabetic, antipyretic, hepatoprotective, diuretic, gastroprotective and neuropharmacological activities were explored and reviewed in this work, concluding that both genera could be the source for upcoming molecules to treat different human diseases.

PthA4AT , a 7.5-repeats transcription activator-like (TAL) effector from Xanthomonas citri ssp. citri, triggers citrus canker resistance.

Transcription activator-like effectors (TALEs) are important effectors of Xanthomonas spp. that manipulate the transcriptome of the host plant, conferring susceptibility or resistance to bacterial infection. Xanthomonas citri ssp. citri variant AT (X. citri AT ) triggers a host-specific hypersensitive response (HR) that suppresses citrus canker development. However, the bacterial effector that elicits this process is unknown. In this study, we show that a 7.5-repeat TALE is responsible for triggering the HR. PthA4AT was identified within the pthA repertoire of X. citri AT followed by assay of the effects on different hosts. The mode of action of PthA4AT was characterized using protein-binding microarrays and testing the effects of deletion of the nuclear localization signals and activation domain on plant responses. PthA4AT is able to bind DNA and activate transcription in an effector binding element-dependent manner. Moreover, HR requires PthA4AT nuclear localization, suggesting the activation of executor resistance (R) genes in host and non-host plants. This is the first case where a TALE of unusually short length performs a biological function by means of its repeat domain, indicating that the action of these effectors to reprogramme the host transcriptome following nuclear localization is not limited to 'classical' TALEs.

Novel demonstration of RNAi in citrus reveals importance of citrus callose synthase in defence against Xanthomonas citri subsp. citri.

Citrus is an economically important fruit crop that is severely afflicted by citrus canker, a disease caused by the bacterial phytopathogen, Xanthomonas citri subsp. citri (Xcc). GenBank houses a large collection of Expressed Sequence Tags (ESTs) enriched with transcripts generated during the defence response against this pathogen; however, there are currently no strategies in citrus to assess the function of candidate genes. This has greatly limited research as defence signalling genes are often involved in multiple pathways. In this study, we demonstrate the efficacy of RNA interference (RNAi) as a functional genomics tool to assess the function of candidate genes involved in the defence response of Citrus limon against the citrus canker pathogen. Double-stranded RNA expression vectors, encoding hairpin RNAs for citrus host genes, were delivered to lemon leaves by transient infiltration with transformed Agrobacterium. As proof of principle, we have established silencing of citrus phytoene desaturase (PDS) and callose synthase (CalS1) genes. Phenotypic and molecular analyses showed that silencing vectors were functional not only in lemon plants but also in other species of the Rutaceae family. Using silencing of CalS1, we have demonstrated that plant cell wall-associated defence is the principal initial barrier against Xanthomonas infection in citrus plants. Additionally, we present here results that suggest that H2O2 accumulation, which is suppressed by xanthan from Xcc during pathogenesis, contributes to inhibition of xanthan-deficient Xcc mutant growth either in wild-type or CalS1-silenced plants. With this work, we have demonstrated that high-throughput reverse genetic analysis is feasible in citrus.