Evaluation of tolerance to Fusarium oxysporum and Fusarium solani in Virginia-type tobacco (Nicotiana tabacum L.) varieties under controlled conditions in Northwestern Argentina

The production of tobacco (Nicotiana tabacum L.) in Argentina is centered in the northwestern region (NWA), where the incidence of root rots and stem diseases caused by Fusarium spp. has increased considerably in recent years. This study aimed to evaluate the pathogenicity levels of isolates of the F. oxysporum and F. solani complexes in different varieties of Virginia Type tobacco. The commercial varieties MB47, PVH229, NC71, K346, K326, and K394 were inoculated with six isolates of both complexes. The variables evaluated were the incidence and severity of the symptoms. The area under the disease progress curves (AUDPC) was calculated and subjected to analysis of variance (ANOVA). Also, disease epidemiological models were fitted to the experimental data. The MB47 variety was significantly less infected and the varieties K346, K326, and K394 had the highest AUDPC means, showing susceptibility to the isolates. The disease intensity curves were adequately described by the monomolecular and logistic models. The results provide, for the first time, information about the levels of tolerance to vascular wilt and root rot under controlled conditions for the main varieties of Virginia-type tobacco grown in NWA. Highlights: FOSC isolates produced mainly wilting, chlorosis, and growth reduction in tobacco plants; in contrast, FSSC isolates caused root rot, with characteristic necrotic lesions and root rot symptoms. The highest DSI scores were registered for Fo27 and Fo15, while the lowest DSI score was found for Fs98. The results obtained from the DSI scores were related to the mean AUDPC values of the isolates. MB47 and NC71 were significantly less infected than the other varieties, which registered low AUDPC values.

Identification and characterization of Phytophthora species associated with crown and root rot of pistachio trees in California.

Pistachio is one of the most widely cultivated nut crops in California with approximately 115,000 hectares of bearing pistachio trees. In recent years, several orchards were identified with declining trees leading to substantial tree losses. Symptoms included trees with poor vigor, yellowing and wilting of leaves, crown rot and profuse gumming on the lower portion of trunks. Thirty-seven Phytophthora-like isolates were obtained from crown rot tissues in the rootstock of grafted pistachio trees and characterized by means of multi-locus phylogeny comprising ITS rDNA, beta-tubulin and mt cox1 sequence data. The analysis provided strong support for the delineation and identification of three Phytophthora species associated with declining pistachio trees, including Phytophthora niederhauserii, P. mediterranea and P. taxon walnut. Pathogenicity studies in potted UCBI rootstocks (clonal and seeded) confirmed that all three Phytophthora species can cause crown and root rot of pistachio, thus fulfilling Koch’s postulates. The widespread occurrence of Phytophthora crown rot in recently planted pistachio orchards and the high susceptibility of UCBI rootstocks suggest this disease constitute an emerging new threat to the pistachio industry of California. To the best of our knowledge, this study is the first to report P. niederhauserii, P. mediterranea and P. taxon walnut as causal agents of crown and root rots of pistachio.

Identification of metalaxyl and ethaboxam insensitive Pythium sylvaticum pathogenic to pulse crops in Montana, USA.

Pythium root rot and damping-off caused by Pythium spp. are important diseases of pulse crops. In a 2016 pathogen survey from dry pea growing fields in Montana, along with commonly known causal agents P. ultimum and P. irregulare, an isolate identified as P. sylvaticum (LPPY17) was isolated from the rhizosphere of a diseased pea plant collected from Valley County, MT. Root rots and damping-off caused by P. sylvaticum have not previously been reported for chickpea, pea, and lentil crops. The isolate LPPY17 was tested for fungicide resistance in vitro, and results indicated a reduced sensitivity to metalaxyl and ethaboxam containing fungicides. LPPY17 was also tested for pathogenicity on chickpea, pea, and lentil seedlings in the greenhouse, and the results from the study revealed LPPY17 is capable of causing both root rots and damping off. Due to the potential pathogenicity and reduced fungicide sensitivity of this species, in the future it will be important to monitor for P. sylvaticum in pulse root rot surveys and diagnostics, as management options may be different from other common Pythium spp.

Review of Pythium species Causing Damping-off in Corn

Seedling blights and root rots caused by Pythium species account for almost twenty-five million dollars in annual losses to corn (Zea mays) production in the United States and Ontario. Variations in annual rainfall and increasing use of no-till agriculture can favor soilborne pathogens like Pythium. To date, forty-four species have been reported as pathogenic to corn in the United States. The average annual corn planting date in the United States has shifted approximately one week earlier in the past decade, exposing young corn plants to longer germination periods of generally cooler temperatures, favoring attack by Pythium. Optimal temperatures, aggressiveness, and response to chemical and biological treatment options vary by species. This review consolidates the species of Pythium reported as corn pathogens in literature to date. It also provides an insight into management strategies and discusses variations in fungicide sensitivity observed in corn-related Pythium species.

Genetic sources of resistance to root rots chicory

Relevance. One of the significant problems in the technology of obtaining root chicory is the protection of root vegetables from the defeat of root rots. The most common lesions of root vegetables chicory various pathogenic species of fungi causing phomosis (Phoma rostrupii Sacc.), gray rot (Botrytis cinerea (R.) Fr.J), wet bacterial rot (Erwinia carotovora (Jones) Holt.). An important place in solving this problem is the breeding of new varieties that are resistant to major diseases and adapted to the conditions of cultivation in the soil-climatic conditions of the chicory-seeding zone. This requires, first of all, to determine the range of donor varieties of the sign of resistance to root rots, both during the growing of culture, and during long-term storage.Material and methods. In 2018-2020, studies were carried out to assess gene sources of different ecological and geographical origin (including against a provocative background) in the Non-Black Earth Zone of the Russian Federation and to isolate donors of resistance to root rot from them. Research on the Rostov Vegetable experimental station on chicory.Results. Studies have shown that the defeat of root vegetables chicory root rots genetic sources were very different from each other, so Harpachi, Luxor did not affect the. root rots neither on the usual nor on provocative backgrounds.

Biocontrol agents and resistance inducers reduce Phytophthora crown rot (Phytophthora capsici) of sweet pepper in closed soilless culture

Twelve trials, in closed soilless culture under controlled conditions, were carried out to evaluate the efficacy of resistance inducers (based on K-phosphite and K-silicate used alone or in combination), and of experimental biocontrol agents (Trichoderma sp. TW2, a mixture of Pseudomonas FC 7B, FC 8B, and FC 9B, Fusarium solani FUS25, Pseudomonas sp. PB26), and a commercial formulation of Trichoderma gamsii + T. asperellum, against diseases caused by Phytophthora capsici of sweet pepper. The products were applied using three different protocols, and effects on incidence of Phytophthora crown, stem and root rots (% dead plants), disease development (area under the disease progress curve; AUDPC), and plant fresh weights were evaluated. Potassium phosphite, applied directly at standard P2O5:K2O, 1.30 + 1.05 g L-1) and at half standard rates, onto growing media, or via nutrient solution, and before infestation of peat plant growing medium with P. capsici, provided the best disease management in a dose-dependent manner, with an 80% reduction of Phytophthora crown, stem and root rots for the standard dosage and for both types of application. These treatments also reduced proportions of dead plants by 47% from the standard rate and by 62% at the half standard rate, when applied via the nutrient solution or directly to the substrate. K-silicate alone partially reduced the percentage of dead plants, with efficacy of 20–23%. No improvement in disease control was observed when K-silicate was applied in combination with phosphite, while K-silicate alone or combined with K-phosphite reduced disease development, compared to untreated controls. Biocontrol agents (BCAs), applied preventively, reduced Phytophthora crown, stem and root rots, with similar or better results than those from the commercial mixture of Trichoderma asperellum + T. gamsii. Among the tested BCAs, Fusarium solani FUS25 provided the most consistent disease reduction (60–65%) and gave increased plant fresh weights. All the tested BCAs reduced disease development, with a similar trend for different disease pressures. The least AUDPC values, compared to the non-treated controls, were from Fusarium solani FUS25, followed by the tested Pseudomonas strains and Trichoderma sp. TW2. These results indicate the potential for potassium phosphite and biocontrol agents in management of Phytophthora crown, stem and root rots of pepper grown in soilless systems.

Understanding Root Rot Disease in Agricultural Crops

Root rot diseases remain a major global threat to the productivity of agricultural crops. They are usually caused by more than one type of pathogen and are thus often referred to as a root rot complex. Fungal and oomycete species are the predominant participants in the complex, while bacteria and viruses are also known to cause root rot. Incorporating genetic resistance in cultivated crops is considered the most efficient and sustainable solution to counter root rot, however, resistance is often quantitative in nature. Several genetics studies in various crops have identified the quantitative trait loci associated with resistance. With access to whole genome sequences, the identity of the genes within the reported loci is becoming available. Several of the identified genes have been implicated in pathogen responses. However, it is becoming apparent that at the molecular level, each pathogen engages a unique set of proteins to either infest the host successfully or be defeated or contained in attempting so. In this review, a comprehensive summary of the genes and the potential mechanisms underlying resistance or susceptibility against the most investigated root rots of important agricultural crops is presented.