Efficacy of Seed Priming With Cucurbitacin Phytonematicides Against Meloidogyne incognita on Pea

The cost and environment concerns of existing drench-application technologies of cucurbitacin phytonematicides resulted in conceptualization of the priming-and-drying (PAD) technology of seeds with hypogeal germination. The preliminary observations suggested that the PAD technology improved seed germination, plant growth, and vigor in pea (Pisum sativa), with limited information on suppression of root-knot (Meloidogyne species) nematodes. Post-soaking pea seeds in geometric concentrations of Nemarioc-AL and Nemafric-BL phytonematicides, seedlings were raised in greenhouse and on microplot experiments during 2019 and validated in 2020. At 60 days after inoculation with 300 eggs + second-stage juveniles (J2) of M. incognita seasonal data were pooled. Gall rating, eggs in root, and J2 in root vs. Nemarioc-AL phyto nematicide in greenhouse and on microplot exhibited negative quadratic relations, with models explained by 80–85% and 89–94% associations, respectively. Similarly, for the respective sites negative quadratic models for nematode variables vs. Nemafric-BL phytonematicide were explained by 82–93% and 90–94% associations, respectively. In conclusion, pea seed remnants belowground gradually released cucurbitacins into the rhizosphere throughout the growing period, thereby suppressing nematode population densities, and therefore, the PAD technology has the potential for assessment in a large-scale application of cucurbitacin phytonematicides for pea production.

Interactive Effects of Filamentous Fungi and Cucurbitacin Phytonematicide on Growth of Cowpea and Suppression of Meloidogyne enterolobii

Cowpea [(Vigna unguiculata (L.) Walp)] is highly susceptible to the emerging guava root-knot nematode, Meloidogyne enterolobii, with available management options being limited due to the withdrawal of effective fumigant nematicides from the agrochemical markets. Filamentous fungi, available as Biocult (a.i. Glomus species + Trichoderma asperellum Lieckf and Nirenberg) and Nemafric-BL phytonematicide (a.i. cucurbitacin B) each improves plant growth and suppresses nematode population densities. However, when filamentous fungi like Biocult are combined with other biocontrol agents, the combined effects either have synergestic or antagonistic effects on the test variables. The combined effects of Biocult and cucurbitacin phytonematicides on plant growth and nematode suppression remain undocumented. The objective of this study was therefore to determine the combined effects of Biocult and Nemafric-BL phytonematicide on growth of cowpea var. Eureka and suppression of M. enterolobii population densities. Eureka was subjected to the effects of the two products in a 2 × 2 factorial experiment on a field infested with M. enterolobii. At harvest, the interaction of Biocult and Nemafric-BL phytonematicide was highly significant (P ≤ 0.01) on plant and nematode variables, with a two-way table used to assess the findings. Relative to untreated control, Biocult alone increased plant growth variables from 15 to 74%. Similarly, NemafricBL phytonematicide increased plant variables from 14 to 61%, whereas the combined effects significantly increased dry shoot mass (19%) and dry harvestable leaf mass (21%), but did not have significant effects on plant height and stem diameter. Relative to untreated control, Biocult alone reduced nematode eggs in root (80%), J2 in root (84%) and J2 in soil (53%), whereas the combined relative effects of the two products did not have significant effects on nematode population densities. In conclusion, Biocult and Nemafric-BL phytonematicide had antagonistic effects on growth of cowpea and suppression of M. enterolobii population densities and therefore, should be used separately in cowpea production.

Entomophilic nematodes, Diploscapter coronatus and Oscheius tipulae from Afghanistan

Several soil samples from different habitats in Badakhshan province of Afghanistan were collected to isolate and characterize bacteria feeding nematodes. The Galleria mellonella-baiting method was used for the isolation of the Afghan insect-associated nematodes. The nematodes were studied using morphological and morphometric data. The Oscheius specimen was characterized by a longer body (630-820 µm) and shorter pharynx (125-145 µm), whereas other morphological characters were not unusual. The Diploscapter specimen had an annulated cuticle, with lip region width 1.5 times shorter than the stoma, and had separated pharyngeal corpus from the isthmus and vulva located in the middle of the body. The molecular data were derived using three loci; 18S, 28S (D2/D3 segment), and ITS rRNA region, which were utilized to measure the genetic distance. The phylogenetic analysis was conducted to reconstruct the relationship tree. Both morphological and molecular approaches confirmed the identity of nematode isolates as Oscheius tipulae and Diploscapter coronatus. This is the first report of insect-associated nematodes from the soil of Afghanistan. Both species were capable of infecting and killing G. mellonella larvae in less than 96 h.

Redescription of Paratrophurus anomalus (Rhabditida: Dolichodoridae) from South Africa

Paratrophurus anomalus is redescribed from the North-West Province, South Africa, associated with the rhizosphere of a willow tree, a dominant ornamental tree in the province. This population is characterised by its adult body length (696 (625-834) μm for female and 706 μm for male), lateral field with four longitudinal incisures, cephalic framework well cuticularised, lip region smooth and lacking annuli, female stylet 19.6 (18-21) μm long, female tail cylindrical, 35 (31-38) μm long, c′ = 2.3 (2.1-2.8), with thick hyaline region forming 31-43% of the tail length, spicules 22 μm long and gubernaculum 12 μm long. Morphologically, P. anomalus is very similar to P. kenanae and P. dissitus, although they differ on the basis of lip region morphology, stylet length, hyaline tail region, and spicule length. In addition, SEM observations are provided for the first time for this species along with a new host and new geographical record of the species from South Africa, providing new information for the revision of Paratrophurus. Molecular analysis of P. anomalus using ITS rDNA showed a close relationship with P. bursifer, P. bhutanensis and Bitylenchus species. In addition, principal component analysis was done for 14 character states of species in the genus.

Redescription of Basiria gracilis (Thorne, 1949) Siddiqi, 1963 (Rhabditida, Tylenchidae) from South Africa

Basiria gracilis is redescribed from North West Province, South Africa, associated with willow (Salix sp.), which is a dominant ornamental tree species in the province. B. gracilis is characterised by its female body length (692-994 µm), lateral field with two longitudinal incisures, weakly cuticularised labial framework, high lip region lacking annuli, stylet 8-13 µm long, axial spermatheca filled with small rounded sperm, conical-elongated female tail with round to pointed terminus (103-146 µm, c=6.1-7.4, c'=8.8-12.1). Morphologically, B. gracilis is closely related to B. paragracilis but the taxa are differentiated on the basis of lip region and stylet morphology. In addition, B. gracilis is reported for the first time from South Africa. Line drawings, LM and SEM illustrations are given for the species.

New data on known species of Hirschmanniella and Pratylenchus (Rhabditida, Pratylenchidae) from Iran and South Africa

Hirschmanniella anchoryzae from Iran and Pratylenchus hippeastri from South Africa were recovered during a survey of plant-parasitic nematodes belonging to the family Pratylenchidae. Both species were studied using morphological and molecular techniques. Hirschmanniella anchoryzae is identified based on the flattened head, short stylet (19–22 µm), excretory pore position (anterior to pharyngo-intestinal junction), spicule length (27–30 µm), and existence of an axial mucro at the tail end. Phylogenetic analysis using 28S rDNA showed monophyly of Hirschmanniella which Iranian H. anchoryzae placed close to H. halophila (EU620464; EU620465). This result was supported by the principal component analysis of Hirschmanniella species. SEM observation of the South African population of P. hippeastri showed the presence of two annuli in the lip region. Morphometric characters resembled those of specimens earlier reported from South Africa. Hierarchal cluster using morphometrical criteria showed that the Floridian (USA) and South African populations form a group. However, the principal component analysis showed variation within this species. The molecular study of P. hippeastri populations using 18S, ITS, 28S rDNA, and COI of mtDNA showed that all P. hippeastri cluster in one group and confirmed the identification of the species using both morphological and molecular techniques. In addition, the results indicated that South African populations group close to the USA populations. Illustrations of both species including light and scanning electron microscopy observations for P. hippeastri are provided.

Determination of Tylenchulus semipenetrans Biotype in Zebediela and Champagne, Republic of South Africa

The biotype of the citrus nematode (Tylenchulus semipenetrans) from Zebediela and Champagne Citrus Estates, Republic of South Africa, was determined using 2-year-old differential hosts, namely, grape (Vitis vinifera cv. Richter 110), carrizo citrange (Citrus sinensis × Poncirus trifoliata), rough lemon (C. jambhiri), olive (Olea europaea cv. Misson), and trifoliate orange (P. trifoliata). The study was conducted under greenhouse conditions with 10 replicates. Nematodes from Zebediela and Champagne were extracted from roots through mechanical shaking, sieving, and incubation in Baermann trays and inoculated at 10,000 and 40,000 eggs and juveniles per plant, respectively. Results demonstrated that the citrus nematode from Zebediela had reproductive factors greater than one on grape, rough lemon, trifoliate orange, and carrizo citrange, but lower than one on olive. Reproductive factors were less than one for all differential hosts with the Champagne population, with olive having the lowest value. Differential-host tests using Zebediela and Champagne nematode populations suggested that the T. semipenetrans biotype is poncirus.

Osmolyte Allocation in Response to Tylenchulus semipenetrans Infection, Stem Girdling, and Root Pruning in Citrus

Previous studies indicated that Tylenchulus semipenetrans infection reduced concentrations of inorganic osmolytes, (Na, Cl, K), in roots, along with leaf K in citrus. However, infection increased leaf Na and Cl, along with carbohydrates in roots. Pruning of roots also increased carbohydrates in intact roots, whereas shoot pruning increased carbohydrates in shoots. Carbohydrates are translocated as reducing sugars, which collectively form organic osmolytes. Because changes in concentrations of osmolytes regulate osmotic potential in plant cells, we hypothesize that increasing concentrations of organic osmolytes in an organ displaces inorganic osmolytes. We measured the osmotic potentials of young citrus trees under nematode infection, stem girdling, and root pruning at two salinity levels. All treatments reduced leaf osmotic potentials at four sampling times. At harvest, 16 days after pruning and girdling treatments, organs with higher carbohydrates had lower inorganic osmolytes and vice versa, regardless of the treatment. Pruning simulated effects of nematode infection, whereas girdling reduced the effects of nematodes. Results suggested that high organic osmolytes in roots displace inorganic osmolytes, thereby avoiding very low osmotic potentials.