Bot Gummosis of Lemon (Citrus × limon) Caused by Neofusicoccum parvum

Identification of Lasiodiplodia species inciting stem rot of dragon fruit in India through polyphasic approach

Lasiodiplodia species commonly thrive as endophytes, saprobes, and plant pathogens in tropical and subtropical regions. Association of Lasiodiplodia species causing stem rot in dragon fruit in the coastal belt of Odisha, eastern India, has been illustrated here. The stem rot disease was characterized by yellowing of the stem, followed by softening of the stem tissues with fungal fructifications of the pathogen in the affected tissues. On the basis of macro- and micromorphological characteristics, the four fungal isolates recovered from diseased stems were identified initially as Lasiodiplodia species. By comparing DNA sequences within the NCBI GenBank database as well as performing a multigene phylogenetic analysis involving the internal transcribed spacer region (ITS-rDNA), β-tubulin (β-tub), and elongation factor-alpha (EF1-α) genes, the identity of Lasiodiplodia isolates was determined. The isolate CHES-21-DFCA was identified as Lasiodiplodia iraniensis (syn: L. iranensis) and the remaining three isolates, namely CHES-22-DFCA-1, CHES-22-DFCA-2, and CHES-22-DFCA-3, as L. theobromae. Although pathogenicity studies confirmed both L. iraniensis and L. theobromae were responsible for stem rot in dragon fruit, L. iraniensis was more virulent than L. theobromae. This study established the association of Lasiodiplodia species with stem rot in dragon fruit using a polyphasic approach. Further investigations are required, particularly related to on host-pathogen-weather interaction and spatiotemporal distribution across the major dragon fruit-growing areas of the country to formulate prospective disease management strategies. This is the first report on these two species of Lasiodiplodia inflicting stem rot in Hylocereus species in India.

A super absorbent polymer containing copper to control Plenodomus tracheiphilus the causative agent of mal secco disease of lemon

The aim of this study was to determine the effectiveness of a Super absorbent polymer (SAP) containing copper (SAP-Cu) in controlling mal secco disease (MSD) of lemon caused by the fungus Plenodomus tracheiphilus. Super absorbent polymer containing copper was characterized by atomic absorption spectrometry (AAS) and UV-VIS spectroscopy. In vitro tests were performed to determine the inhibitory effects of SAP-Cu against the pathogen on both potato-dextrose-agar medium and naturally infected lemon cuttings. Super absorbent polymer was able to absorb up to about 200 and 30 times its weight of ionized water and copper (II) sulfate solution (Cu²⁺ ions at the concentration 236 mM), respectively. The distribution of copper released on twigs after 24 h of contact with SAP-Cu was determined by secondary ion mass spectrometry with time-of-flight analyzer (ToF-SIMS). Super absorbent polymer containing copper significantly inhibited the viability of P. tracheiphilus in lemon twigs. Overall, the results of this study showed that the SAP could be a suitable carrier of antifungal compounds.

Stilbocrea banihashemiana sp. nov. a New Fungal Pathogen Causing Stem Cankers and Twig Dieback of Fruit Trees

Stem cankers and twig dieback were the most serious disease of fig (Ficus carica) and loquat (Eriobotrya japonica) noticed in a survey of fruit tree orchards in the Fars Province, Iran. Isolates of Bionectriaceae were consistently recovered from symptomatic fig and loquat trees. Phylogenetic analyses of multiple nuclear loci, internal transcribed spacer regions (ITS) of rDNA, RNA polymerase II subunit 2 (rpb2), and translation elongation factor 1-α (tef1), combined with morphological observations, revealed that isolates could be referred to a still unknown taxon, which was formally described as Stilbocrea banihashemiana sp. nov. Phylogenetically, isolates from fig and loquat trees clustered in a well-supported monophyletic group within the Stilbocrea clade of Bionectriaceae, closely related to S. walteri. Stilbocrea banihashemiana sp. nov. was characterized by the lack of stilbella-like asexual structure in both natural substrates and pure cultures and produced two morphologically distinct types of conidia, globose and cylindrical, formed on short and long simple phialides. In pathogenicity tests, S. banihashemiana sp. nov. induced stem cankers in both fig and loquat, wood discoloration in fig and twig dieback in loquat. Pathogenicity tests also showed that the potential host range of this novel pathogen includes other economically relevant horticultural trees.

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.

Inhibitory Activity of Shrimp Waste Extracts on Fungal and Oomycete Plant Pathogens

(1) Background: This study was aimed at determining the in vitro inhibitory effect of new natural substances obtained by minimal processing from shrimp wastes on fungi and oomycetes in the genera Alternaria, Colletotrichum, Fusarium, Penicillium, Plenodomus and Phytophthora; the effectiveness of the substance with the highest in vitro activity in preventing citrus and apple fruit rot incited by P. digitatum and P. expansum, respectively, was also evaluated. (2) Methods: The four tested substances, water-extract, EtOAc-extract, MetOH-extract and nitric-extract, were analyzed by HPLC-ESI-MS-TOF; in vitro preliminary tests were carried out to determine the minimal inhibitory/fungicidal concentrations (MIC and MFC, respectively) of the raw dry powder, EtOAc-extract, MetOH-extract and nitric-extract for each pathogen. (3) Results: in the agar-diffusion-assay, nitric-extract showed an inhibitory effect on all pathogens, at all concentrations tested (100, 75, 50 and 25%); the maximum activity was on Plenodomus tracheiphilus, C. gloeosporioides and Ph. nicotianae; the diameters of inhibition halos were directly proportional to the extract concentration; values of MIC and MFC of this extract for all pathogens ranged from 2 to 3.5%; the highest concentrations (50 to 100%) tested in vivo were effective in preventing citrus and apple fruit molds. (4) Conclusions: This study contributes to the search for natural and ecofriendly substances for the control of pre- and post-harvest plant pathogens.