Phytonematodes as a limiting biotic factor of agricultural production in the world (review)

Purpose. To analyze domestic and foreign scientific literature on the species composition and harmfulness of the world's most dangerous parasitic species of phytonematodes in crops. Results. Today, according to the available literature, the most dangerous species of phytonematodes include: gall nematode (Meloidogyne spp.), cyst-forming nematode (Heterodera spp. and Globodera spp.), root lesion nematode (Pratylenchus spp.), banana drill nematode (Radoholus similis), stem nematode (Ditylenchus dipsaci), pine stem nematode (Bursaphelenchus xylophilus), reniform nematode (Rotylenchulus reniformis), xiphinema index (Xiphinema index), false head nematode (Nacobbus aberrans), and rice leaf nematode (Aphelenchoides besseyi). Conclusions. The results of research on the prevalence and harmfulness of parasitic nematode species in crops convince us of the need for a more detailed study of this group of microorganisms. Due to the rapid development of molecular genetic methods in the last decade, scientists have been able to expand and improve their knowledge of identifying species, races and pathotypes of phytonematodes, their biological and environmental characteristics, and most importantly, to discover and understand extremely complex mechanisms of parasite and host plants. Nematologists are confident that further research in these and other areas in the future will create a basis for developing a new strategy for long-term and environmentally safe control of these dangerous plant parasites.

Incidencia de nemátodos asociados a las principales zonas productoras de café (Coffea arabica L.) en la región de Puno, Perú

El ámbito amazónico de la región Puno es una de las principales zonas productoras de café en el Perú, altamente susceptibles a nematodos fitoparásitos que pueden afectar la producción y propiciar el ingreso de otras plagas y enfermedades. Por ello se plantea como objetivos reseñar géneros de nematodos parásitos y de vida libre que se asocian al cultivo de café, identificar la especie del género Meloidogyne y evaluar incidencias poblacionales de nematodos asociados al cultivo según la altitud del lugar en las principales zonas productoras de la región, en los distritos de San Juan del Oro, San Pedro de Putina Punco y San Gabán. Se evaluaron 129 muestras de 11 campos de cultivo, entre altitudes de 800 y 1416 msnm, que fueron procesadas por el método de fluctuación centrifuga en solución de sacarosa. Se identificaron los siguientes ocho géneros de nematodos fitoparásitos: Meloidogyne spp., Helicotylenchus spp., Pratylenchus spp., Xiphinema spp., Mesocriconema spp., Dorylaimus spp., Tylenchus spp., Hemicycliophora spp., así como nematodos de vida libre, entre ellos el género Mononchus spp. Por medio de la prueba de electroforesis de isoenzima se identificó a Meloidogyne exigua. No se encontró diferencia de incidencia entre el género Meloidogyne spp. y nematodos de vida libre. Los géneros Helicotylenchus y Mesocriconema disminuyeron sus poblaciones a mayor altitud.

Studies on plant-parasitic nematodes associated with sweet potato (Ipomoea batatas L., Lam.) in Gombe State, Nigeria

Sweet potato (Ipomoea batatas L., Lam.) is one of the most frequently eaten food crops. Its production is affected by plant-parasitic nematodes as well as biotic factors. This study was conducted to document the different plant-parasitic nematodes (PPN) that limit the gainful production of sweet potato in Gombe State. Thirty soil core samples per hectare were collected at random from sweet potato farms in the three local government areas (Nafada, Kaltungo, and Yamaltu Deba) of Gombe state. The Whitehead and Hemming method and identification keys were used for the soil extraction and genera identification of the plant-parasitic nematodes respectively. A total of 15 plant-parasitic nematodes were recovered throughout the surveyed areas among which 7 are considered major nematode pests of global importance. Irrespective of the surveyed locations, Meloidogyne spp., was found to record the highest population density and prevalence value. The frequency of occurrence in Y/Deba and Nafada LGAs shows that Meloidogyne spp., wasthe most occurring (32 %) genera. In Kaltungo LGA however, Scutellonema spp., and Rotylenchusspp., were the most occurring (17 %) genera. There was a high similarity percentage (≥ 68 %) of PPN genera where 8 genera (Scutellonema spp., Nacobbus spp., Pratylenchus spp., Meloidogyne spp., Heterodera spp., Xiphinema spp., Trichodorus spp., and Rotylenchus spp.) were found to be common amongst the surveyed locations. This is the first report of plant-parasitic nematodes associated with sweet potato in Gombe state, Nigeria. Hence, it is critical to educate farmers in the regions about their effects on the crop and how to successfully manage them.

First Report of Meloidogyne javanica on Globe Artichoke in Florida, USA

Globe artichoke (Cynara cardunculus var. scolymus L.) is native to the Mediterranean region and cultivated worldwide for its edible flower buds and the medicinal value of its leaves (Pignone and Sonnante 2004). In 2019, artichokes were planted on 29 km2 predominantly in California, with a yield of over 100 million kg (USDA 2020). It has been grown as a specialty crop in Florida since 2017 (Agehara 2017a). Meloidogyne spp. (root-knot nematodes/RKNs) can lead to yield losses to artichoke (Greco et al. 2005). In June 2020, artichokes (cv. Imperial Star) with stunting, wilting, and galled-root symptoms were observed in a research field with sandy soil located at the University of Florida Gulf Coast Research and Education Center (UF/GCREC), Wimauma, Florida. The goal of this report was to identify the RKN species collected from two symptomatic artichoke roots. Morphological measurements (mean, standard deviation and range) of 15 second-stage juveniles (J2s) included body length = 409.1 ± 31.6 (360.3 - 471.3) µm, body width = 15.4 ± 1.6 (12.4 - 18.8) µm, and stylet length = 14.7 ± 0.7 (13.9 -16.1) µm. Perineal patterns of five matured females had a high dorsal arch and double lateral lines. Morphological characteristics of the RKN cultures were consistent with the description of M. javanica (Eisenback and Triantaphyllou 1991). DNA was extracted respectively from two RKN females isolated from the diseased artichoke roots. The nematode species was confirmed with primers Fjav/Rjav and resulted in ≈ 670 bp fragment (Zijlstra et al. 2000). The COXII region of mtDNA was amplified by C2F3/1108 (Powers and Harris 1993), and the sequencing results were submitted to the NCBI with GeneBank Accession No. MZ397905. The molecular sequences had 100% identity with M. javanica in COXII (MK033440 and MK033439). The pathogenicity test was conducted in the greenhouse at UF/GCREC from May to August 2021 (temperature = 26.7 ± 4.1°C, relative humidity = 83.9 ± 14.6 %). Each of the ten 6.5-in-diameter plastic pots containing 3.8-L pasteurized soil was seeded with one artichoke seed. Five pots were inoculated with 5000 eggs of the field RKN cultures 4-week after planting, and five pots served as the untreated control. Two months after inoculation, galled symptoms were only observed in inoculated plants with an average gall index (Bridge and Page 1980) of 6.2 ± 2.2; 99,240 ± 72,250 eggs were extracted from each root system, and the nematode reproduction factor was 19.9 ± 14.4. Meloidogyne spp. has been reported on artichoke in Europe, Asia, and South America (Greco et al. 2005). This is the first report of RKN on artichoke in the United States. Meloidogyne javanica caused severe root gall symptoms and visible aboveground damage in the form of chlorosis, stunting, and wilting of artichoke planted at the UF/GCREC research farm. Meloidogyne javanica is the predominant RKN species at the UF/GCREC research farm and one of the most common RKNs in Florida (Gu and Desaeger 2021). Artichoke is a new crop in Florida, and RKNs is likely to be one of the main soilborne problems for its production in the state. Its long growing season (October - May) (Agehara 2017b) allows for high nematode reproduction rates. Several new growers have already reported RKN as a problem in their fields. For artichoke to become a commodity in Florida, managing RKNs will be critical. This report provides new information on the risk that RKNs pose to artichoke, a newly established specialty crop in Florida.

Retraction: Montiel-Rozas et al. Effect of Plant Extracts and Metam Sodium on the Soilborne Fungal Pathogens, Meloidogyne spp., and Soil Microbial Community. Agronomy 2020, 10, 513

Following publication [...]

Bacterial volatile-mediated suppression of root-knot nematode (Meloidogyne incognita)

Root-knot nematodes (Meloidogyne spp.) are obligate plant parasites that cause severe economic losses to agricultural crops worldwide. Due to serious health and environmental concerns related to the use of chemical nematicides, the development of efficient alternatives is of great importance. Biological control through exploiting the potential of rhizosphere microorganisms is currently accepted as an important approach for pest management in sustainable agriculture. In our research, during screening of rhizosphere bacteria against the root-knot nematodes Meloidogyne incognita, Ochrobactrum pseudogrignonense strain NC1 from the rhizosphere of healthy tomatoes showed strong nematode inhibition. A volatile nematicidal assay showed that the cell-free fermentation filtrate in the first-row wells of 12-well tissue culture plates caused M. incognita juvenile mortality in the second-row wells. Gas chromatography-mass spectrometry (GC-MS) analysis revealed that dimethyl disulfide (DMDS) and benzaldehyde were the main volatile compounds produced by strain NC1. The nematicidal activity of these compounds indicated that the LC50 against the M. incognita juveniles in the second-row wells and the fourth-row wells were 23.4 μmol/mL and 30.7 μmol/mL for DMDS and 4.7 μmol/mL and 15.2 μmol/mL for benzaldehyde, respectively. A greenhouse trial using O. pseudogrignonense strain NC1 provided management efficiencies of root-knot nematodes of 88 to 100% compared with the untreated control. This study demonstrated that nematode-induced root-gall suppression mediated by the bacterial volatiles DMDS and benzaldehyde presents a new opportunity for root-knot nematode management.

Quantification of Root-Knot Nematode Infestation in Tomato Using Digital Image Analysis

Tomato is the most popular vegetable globally. However, in certain conditions, the vegetable is susceptible to plant parasites such as the root-knot nematode (RKN; Meloidogyne spp.). A proper detection method is required to identify RKN and eliminate related diseases. The traditional manual quantification of RKN using a microscope is a time-consuming and laborious task. This study aims to develop a semi-automated method to discern and quantify RKN based on size using an image analysis method. The length of RKN was assessed using three novel approaches: contour arc (CA), thin structure (TS), and skeleton graph (SG) methods. These lengths were compared with the manual measurement of RKN length. The study showed that the RKN length obtained by manual measurement was highly correlated to the length based on this method, with R2 of 0.898, 0.875, and 0.898 for the CA, TS, and SG methods, respectively. These approaches were further tested to detect RKN on 517 images. The manual and automated counting comparison revealed a coefficient of determination R2 = 0.857, 0.835 and 0.828 for CA, TS, and SG methods, respectively. The one-way ANOVA test on counting revealed F-statistic = 4.440 and p-value = 0.004. The ratio of length to width was investigated further at different ranges. The optimal result was found to occur at ratio range between 10–35. The CA, TS, and SG methods attained the highest R2 of 0.965, 0.958, and 0.973, respectively. This study found that the SG method is most suitable for detecting and counting RKN. This method can be applied to detect RKN or other nematodes on severely infected crops and root vegetables, including sweet potato and ginger. The study significantly helps in quantifying pests for rapid farm management and thus minimise crop and vegetable losses.