Phytophthora Root and Collar Rot of Paulownia, a New Disease for Europe

Paulownia species are fast growing trees native to China, which are being grown in managed plantings in several European countries for the production of wood and biomasses. In 2018, wilting, stunting, leaf yellowing, and collapse, as a consequence of root and crown rot, were observed in around 40% of trees of a 2-year-old planting of Paulownia elongata × P. fortunei in Calabria (Southern Italy). Two species of Phytophthora were consistently recovered from roots, basal stem bark, and rhizosphere soil of symptomatic trees and were identified as Ph. nicotianae and Ph. palmivora on the basis of both morphological characteristics and phylogenetic analysis of rDNA ITS sequences. Koch’s postulates were fulfilled by reproducing the symptoms on potted paulownia saplings transplanted into infested soil or stem-inoculated by wounding. Both Phytophthora species were pathogenic and caused root rot and stem cankers. Even though P. palmivora was the only species recovered from roots of naturally infected plants, in pathogenicity tests through infested soil P. nicotianae was more virulent. This is the first report of Phytophthora root and crown rot of a Paulownia species in Europe. Strategies to prevent this emerging disease include the use of healthy nursery plants, choice of well-drained soils for new plantations, and proper irrigation management.

First Report of Neopestalotiopsis mesopotamica causing root and crown rot on strawberry in Ecuador

In Ecuador, strawberry production is located in the Andean region with an area of 1000 ha. Albion is the most popular cultivar due to its conical fruit shape, fruit size, bright red color, and sweetness. Since June 2014, farmers reported a reduction in the production cycle from 24 months to 6-8 months and a decreased yield of around 50% due to an unknown soil pathogen. Plant symptoms presented a reddish discoloration on new leaves, coming through the leaf apex to the petiole until turning wholly brown in old leaves leading to plant death. Additionaly, a brown-reddish spot inside the strawberry crown and root rot were reported (Fig. S1). In 2020, in Ecuador's most extensive production area, called Yaruqui (Pichincha province), 25 diseased plants were collected for pathogen isolation. The pathogen was isolated on water agar medium from the crowns internal tissue using 0.5 cm diseased plant fragments, previously disinfected with 2% sodium hypochlorite, and rinsed with sterile water. After two days, single hyphal tip was reisolated on potato dextro agar (PDA). A total of 18 pure isolates were grown at 25°C for 12 days, then 3-7 days of blacklight treatment was applied to induce sporulation. All the isolates presented a cottony beige mycelium with undulate edges. The conidia were ellipsoidal (range between 20.73 to 29 µm in length and 6.2 to 8.77 µm in width; n=60), multiseptated (4 segments) showing hyaline apical (3.8 to 5 µm) and basal (4.87 to 8 µm) cells, and three brown median cells, the second and third were darker than the fourth one, with one basal and 2 to 4 apical appendages (26.09 to 38.7 µm; Fig. S1). According to colony and conidia morphology, the isolates were identified as Neopestalotiopsis sp. (Dung et al. 2016; Essa et al. 2018; Maharachchikumbura et al. 2011). Five isolates were select randomly for DNA extraction and sequencing of the internal transcribed spacer (ITS) region (ITS4/ITS5), β-tubulin (Bt2b/ T1), and translation elongation factor 1-alpha (TEF-1a) region (EF1-728/ EF1-986) (Maharachchikumbura et al. 2014). DNA sequences obtained from each marker were identical for all isolates. Consensus sequences and alignment were built using ClustalX in MEGA X (Kumar et al. 2018). The consensus sequences were deposited in GenBank with the following accession numbers: ITS, MZ047602; β-tubulin, MZ054301; and TEF-1a, MZ054302. A multilocus Bayesian inference phylogenetic tree was constructed using the concatenated sequences in the Beast software (version 1.8.4)(Drummond et al. 2012; Maharachchikumbura et al. 2014). The isolate in our study clustered with isolates of Neopestalotiopsis mesopotamica with a posterior probability of 1, confirming its identity (Fig. S2). For Koch's postulates, healthy plants were grown in sterile soil for four months. Conidia of the pathogen were suspended in potato dextro broth (PDB) (1 x 104 conidia/ml), and it was sprayed on 15 healthy plants that previously had their crowns wounded with a sterile needle (0.6 cm deep) at the four cardinal points. The control treatment (15 plants) was wounded and sprayed with PDB alone. The plants were maintained at 25°C and more than 85% relative humidity (Sigillo et al. 2020). Twelve days after inoculation, plants showed reddish discoloration on new leaves, and old leaves presented low-level wilt, rusty color, and necrotic petioles. Forty-one days later, 75% of the treated plants had severe wilt or were dead, showing root and crown rot. Control plants presented no symptoms of the disease. Reisolation of the pathogen from the disease crown tissues was done on water agar and PDA as previously described. The isolates presented the exact morphology of pure cultures obtained from field diseased strawberry crowns. The pathogenicity test was performed twice. To our knowledge, this is the first report of Neopestalotiopsis mesopotamica being the causal agent of root and crown rot on strawberries in Ecuador. N. iranensis and N. mesopotamica have been reported as causal agents of strawberries fruit rot and leaf lesions in Iran (Ayoubi and Soleimani, 2016), and N. clavispora was reported to be causing root and crown rot on strawberry plants in Argentina (Obregon et al. 2018). Disease diagnosis contributes to providing strategies against this new disease. Further investigations are needed to find biological/chemical techniques or cultivar resistance to control this pathogen in strawberries in Ecuador.

Antifungal Nanoformulation for Biocontrol of Tomato Root and Crown Rot Caused by Fusarium oxysporum f. sp. radicis-lycopersici

Tomatoes (Solanum lycopersicum L.) are the most cultivated and important vegetable crop in the world. These plants can wilt during crop growth due to fusarium wilt (fusariosis), a disease that damages tomato vascular systems. The Fusarium isolated and analyzed in this work correspond to Fusarium oxysporum f. sp. radicis-lycopersici. The isolates were molecularly identified, and analysis was done on the in vitro effects of the nanoemulsions (previously obtained from extracts of Chilean medicinal plants of the genera Psoralea and Escallonia) to inhibit mycelial and conidial germination of the isolates. Subsequently, the nanoemulsions were evaluated under greenhouse conditions for preventive control of fusariosis in the root and crown, with high levels of disease control observed using the highest concentrations of these nanoemulsions, at 250 and 500 ppm.

Genetics of Resistance to Common Root Rot (Spot Blotch), Fusarium Crown Rot, and Sharp Eyespot in Wheat

Due to soil changes, high density planting, and the use of straw-returning methods, wheat common root rot (spot blotch), Fusarium crown rot (FCR), and sharp eyespot (sheath blight) have become severe threats to global wheat production. Only a few wheat genotypes show moderate resistance to these root and crown rot fungal diseases, and the genetic determinants of wheat resistance to these devastating diseases are poorly understood. This review summarizes recent results of genetic studies of wheat resistance to common root rot, Fusarium crown rot, and sharp eyespot. Wheat germplasm with relatively higher resistance are highlighted and genetic loci controlling the resistance to each disease are summarized.

First report of Fusarium commune causing root and crown rot on maize in Italy

Maize (Zea mays L.) is a cereal crop of great economic importance in Italy; production is currently of 62,587,469 t, with an area that covers 628,801 ha, concentrated in northern Italy (ISTAT 2020). Fusarium species are associated with root and crown rot causing failures in crop establishment under high soil moisture. In 2019 maize seedlings collected in a farm located in San Zenone degli Ezzelini (VI, Italy) showed root and crown rot symptoms with browning of the stem tissues, wilting of the seedling, and collapsing due to the rotting tissues at the base of the stem. The incidence of diseased plants was approximately 15%. Seedlings were cleaned thoroughly from soil residues under tap water. Portions (about 3-5 mm) of tissue from roots and crowns of the diseased plants were cut and surface disinfected with a water solution of NaClO at 0.5% for 2 minutes and rinsed in sterile H20. The tissue fragments were plated on Potato Dextrose Agar (PDA) amended with 50 mg/l of streptomycin sulfate and incubated for 48-72 hours at 25oC. Over the 80 tissue fragments plated, 5% were identified as Fusarium verticillioides, 60% as Fusarium spp., 35% developed saprophytes. Fusarium spp. isolates that showed morphological characteristics not belonging to known pathogenic species on maize were selected and used for further investigation while species belonging to F. oxysporum were discarded. Single conidia of the Fusarium spp. colonies were cultured on PDA and Carnation Leaf Agar (CLA) for pathogenicity tests, morphological and molecular identification. The colonies showed white to pink, abundant, densely floccose to fluffy aerial mycelium. Colony reverse showed light violet pigmentation, in rings on PDA. On CLA the isolates produced slightly curved macronidia with 3 septa 28.1 - 65.5 µm long and 2.8-6.3 µm wide (n=50). Microconidia were cylindrical, aseptate, 4.5 -14.0 µm long and 1.5-3.9 µm wide (n=50). Spherical clamydospores were 8.8 ± 2.5 µm size (n=30), produced singly or in pairs on the mycelium, according to the description by Skovgaard et al. (2003) for F. commune. The identity of two single-conidia strains was confirmed by sequence comparison of the translation elongation factor-1α (tef-1α), and RNA polymerase II subunit (rpb2) gene fragments (O’Donnell et al. 2010). BLASTn searches of GenBank, and Fusarium-ID database, using the partial tef-1α (MW419921, MW419922) and rpb2 (MW419923, MW419924) sequences of representative isolate DB19lug07 and DB19lug20, revealed 99% identity for tef-1α and 100% identity to F. commune NRRL 28387(AF246832, AF250560). Pathogenicity tests were carried out by suspending conidia from a 10-days old culture on PDA in sterile H2O to 5×104 CFU/ml. Fifty seeds were immersed in 50 ml of the conidial suspension of each isolate for 24 hours and in sterile water (Koch et al. 2020). The seeds were drained, dried at room temperature, and sown in trays filled with a steamed mix of white peat and perlite, 80:20 v/v, and maintained at 25°C and RH of 80-85% for 14 days with 12 hours photoperiod. Seedlings were extracted from the substrate, washed under tap water, and observed for the presence of root and crown rots like the symptoms observed on the seedlings collected in the field. Control seedlings were healthy and F. commune was reisolated from the symptomatic ones and identified by resequencing of tef-1α gene. F. commune has been already reported on maize (Xi et al. 2019) and other plant species, like soybean (Ellis et al. 2013), sugarcane (Wang et al. 2018), potato (Osawa et al. 2020), indicating that some attention must be paid in crop rotation and residue management strategies. To our knowledge this is the first report of F. commune as a pathogen of maize in Italy. References Ellis M L et al. 2013. Plant Disease, 97, doi: 10.1094/PDIS-07-12-0644-PDN. ISTAT. 2020. http://dati.istat.it/Index.aspx?QueryId=33702. Accessed December 28, 2020. Koch, E. et al. 2020. Journal of Plant Diseases and Protection. 127, 883–893 doi: 10.1007/s41348-020-00350-w O’Donnell K et al. 2010. J. Clin. Microbiol. 48:3708. https://doi.org/10.1128/JCM.00989-10 Osawa H et al. 2020. Journal of General Plant Pathology, doi.org/10.1007/s10327-020-00969-5. Skovgaard K 2003. Mycologia, 95:4, 630-636, DOI: 10.1080/15572536.2004.11833067. Wang J et al. 2018. Plant Disease, 102, doi/10.1094/PDIS-07-17-1011-PDN Xi K et al. 2019. Plant Disease, 103, doi/10.1094/PDIS-09-18-1674-PDN