Black shank disease caused by Phytophthora nicotianae is the most devastating pathology in tobacco (Nicotiana tabacum). In Colombia, an increase in the severity of P. nicotianae has been reported when parasitic nematodes are active in tobacco plants. The main objective of this study was to determine the pathogenicity, leaf quality and interaction between P. nicotianae (Races 0 and 1) with Meloidogyne spp. on tobacco plants in samples collected in 15 farms of Colombia. To quantify the interaction between both pathogens, variables such as plant survival, index of pathogenicity, and chemical and physical quality of the leaves were measured. Within a confidence level of 95% there is evidence of a positive synergistic effect between Meloidogyne incognita, M. javanica and P. nicotianae (Races 0 and 1) in a variety-dependent manner. For ‘ICA Servita’ the variables of index of pathogenicity, of root-knots and fresh weight of root, reduced the leaf price because of the interaction. For ‘K346’, Race 0 of P. nicotianae apparently reduced the pathogenicity of M. javanica in contrast to P. nicotianae Race 1. In addition, ‘ICA Servita’ and ‘K346’ showed susceptibility to nematodes. At the end of the harvest of ‘ICA Servita’, the interaction caused a considerable decrease in the physical and chemical quality of tobacco leaves, resulting in lower weight and number of leaves, affecting the price of tobacco in the market with reductions of more than 50%. Plant mortality of ‘ICA Servita’ and ‘K346’ was 50 and 60%, respectively, in interactions with both pathogens.
Two new and one known species of Atetylenchus recovered from Dezful, Khuzestan Province, south-western Iran, are illustrated and described using morphological, morphometric and molecular data. Atetylenchus dezfuliensis n. sp. is characterised by medium-sized body 700-998 μm long, stylet 10.0-11.5 μm long, characteristic tail shape, first tapering regularly but then cylindrical to slightly clavate and 90-136 μm long, phasmids located at one-third anterior part of tail and short spicules 18.7 μm long. Atetylenchus longilabiatus n. sp. is characterised by small-sized body 593-720 μm long, prominent lip region, stylet 9.5-12.5 μm long, conical tail with hook-shaped terminus and 42-63 μm long, phasmids located near mid-tail and short spicules 17.5 μm long. Atetylenchus cf. graminus is characterised by small-sized body 643-787 μm long, stylet 10.7-11.7 μm long, vulva located at 51.7-55.1% of the body length, and conical tail with finely rounded end and 63-69 μm long. Molecular data are provided for the characterisation of this genus from these two new and one known species using ribosomal genes (18S and 28S rRNA). This genus is molecularly separated from Psilenchus, but closely related in both genes. These molecular markers showed different phylogenies for both genera; partial 18S showed their relationship with Tylenchidae, while 28S rRNA showed their relationship with Merliniidae. A key to the genus is provided for species identification.
The white-tip nematode, Aphelenchoides besseyi, is a seed-borne ectoparasite of the rice plant Oryza sativa. Nematodes in dried rice seeds are in dehydrated quiescence or anhydrobiosis and are reactivated by rehydration. To understand the persistent parasitism better, the effects of temperature on nematode survival were examined during prolonged periods of seed storage. There was a marked difference in the survival rate among different temperatures; survival was lower at 20 and 25°C than at −5 to 10°C after storage for 190 days. No nematodes survived a storage period of 1313 days at 20 and 25°C. When rice seeds were held at 5°C, the survival rate of nematodes decreased during a period of 7315 days. The estimated instantaneous rate of mortality per month was higher in the early and late parts of the period than in the middle part. Another nematode population also showed a reduction in the survival rate during 6553 days storage at 5°C. In storage at −30°C, survival was not affected during a period of 6485 days. After storage at −30°C for 6546 days, 96% of rice seeds germinated, whereas 60-96% of seeds of two groups germinated after storage at 5°C for 6610-7373 days. Therefore, prolonged storage of rice seeds at 5 or −30°C was unlikely to disrupt the connection between rice plants and A. besseyi.
Nematodes of the genus Meloidogyne are one of the major limiting factors in tomato production and a challenging problem in organic systems. This study aimed to investigate the effect of agro-industrial wastes, their forms of application and doses on tomato plants inoculated with Meloidogyne javanica. First, nematodes were multiplied on tomato under glasshouse conditions to simulate a naturally infested environment. At 60 days after inoculation, plant shoots were removed, new seedlings were transplanted into the pots, and the soil was amended with agro-industrial wastes. Treatments were as follows: rice husk, common bean hull, soybean hull, orange bagasse, poultry litter and waste mixture (wastes mixed in equal proportions) applied in three different forms (raw, powdered and biodigester effluent). A non-treated control and a composted waste mixture were also assessed. At 60 days after transplanting, plants were evaluated for nematode parameters. Powdered bean hulls, soybean hulls, orange bagasse and waste mixture provided the best results and were selected for dose-response investigations. A second experiment was conducted in two periods using, in addition to the selected wastes, a mixture of powdered bean hulls, soybean hulls and orange bagasse. Wastes were applied at doses of 0 (control), 2, 4, 6 and 8 t ha−1. Powdered bean hulls, soybean hulls, orange bagasse and waste mixtures at 5 t ha−1 gave the best nematode control, with reductions of 55-100%. The optimal doses for vegetative growth were 4 t ha−1 in the first period and 5 t ha−1 in the second period.
An undescribed species from the rhizosphere of tamarisk, Tamarix passerinoides, Telotylenchus tamariscus n. sp., is illustrated and described based on morphological, morphometric and molecular approaches. The new species is characterised by female characters including body size of ca 1 mm, areolated lateral fields, cephalic region rounded, distinctly set off from the body contour, stylet 19.5 (18.5-20.5) μm long with posteriorly directed basal knobs, pharyngeal glands overlapping intestine dorso-laterally, subcylindrical tail bearing 32 (25-37) cuticular annuli and ending in an annulated terminus, and male spicules and gubernaculum 27 (25-29) and 13 (12.5-14.5) μm long, respectively. Morphologically, our population comes close to several known species of the genus, including T. avaricus, T. aerolatus, T. indicus, T. ventralis, T. paaloofi and T. namibiensis. In the 18S rRNA phylogenetic tree, it occupied a phylogenetic position in close affinity with two sequences of T. ventralis. In the 28S rRNA tree, the genus Telotylenchus did not form a monophyletic group, our isolate clustering with an unknown population of Histotylenchus and four isolates of Tylenchorhynchus mediterraneus in a clade well separated from another clade that included three other isolates tentatively named as Telotylenchus sp.
During quarantine inspections, a new species of Hoplotylus was detected from the rhizosphere of the Japanese maple, Acer palmatum, imported into China from Japan. Hoplotylus japonicus n. sp. is characterised by a stout 431-602 μm long body, well-developed 20.0-24.5 μm long stylet with tulip-shaped knobs having rounded sides in lateral view and a rounded anterior margin, excretory pore located slightly posterior to the hemizonid, usually empty, spermatheca, conical tail with a spike-like projection, which is distally smooth on the dorsal side, and males not found. It was morphologically compared with four currently known species of the genus, viz., H. femina, H. montanus, H. silvaticus, and H. sjacobi. In molecular phylogenetic analyses using 18S, 28S and internal transcribed spacer (ITS) ribosomal DNA sequences, the new species formed a clade with the only currently sequenced species of the genus, H. femina, in all phylogenies. This is the second species of the genus characterised by molecular data and the second species recovered from Japan.
Anomala corpulenta is one of the major white grubs that cause serious damages in peanut production. To develop an environmentally friendly method to control A. corpulenta larvae, the efficacy of species of entomopathogenic nematodes (EPN), application rate and larval stage against A. corpulenta were determined. Results showed that Steinernema longicaudum X-7 and S. glaseri B-4-1 were the most virulent species, which caused 77.8 and 84.4% corrected mortalities of the 2nd instar larvae at 25°C 14 days after treatments. Corrected mortalities of A. corpulenta caused by EPN were significantly affected by EPN application rate. A decrease but no significant difference in susceptibility from the 2nd to the 3rd instar was observed for the test EPN species S. longicaudum, S. glaseri and Heterorhabditis bacteriophora. The field experiments indicated that S. longicaudum and S. glaseri applied at a relatively high rate (⩾5.0 × 103 infective juveniles (IJ) plant−1, i.e., 7.5 × 108 IJ ha−1) were able to provide not only control efficacy against A. corpulenta with ⩾92.7% reduction of larvae and ⩽5.06% of damaged pods, and the peanut yield increase was as good as phoxim, but also gave better control persistency compared to phoxim. Our findings indicated that EPN could be an effective strategy for the management of A. corpulenta in peanut fields.
The nematicidal activity of the essential oil of Cymbopogon citratus and its main components were studied. During in vitro assays with Meloidogyne incognita second-stage juveniles (J2), the oil showed an LC50 of 166 μg ml−1. In vivo assays that exposed J2 to the LC50 oil concentration significantly reduced galls and eggs on tomato roots. According to gas chromatography-mass spectrometry analyses, the main components of the essential oil were geranial (42.7%) and neral (33.0%). The combination of these two isomers, known as citral, had an enhanced nematicidal activity at low concentrations as shown by in vitro tests through a synergistic interaction with undecan-2-one. In assays with tomato plants inoculated with M. incognita J2, the combination of citral (600 μg ml−1) and undecan-2-one (300 μg ml−1) showed a high reduction in the number of galls (63.4%) and eggs (56.3%) in relation to Tween 80® control. The citral/undecan-2-one combination showed a synergistic nematicidal activity against M. incognita during in vitro and in vivo assays.
The ectoparasitic nematode, Scutylenchus rugosus, is common in Europe and Asia, feeding on several plant species and limiting productivity. Its seasonal population fluctuation was monitored on maize and wheat crops, in glasshouse and open field conditions, respectively. Its survival in the absence of a host plant was also investigated in a microplot field trial. The population of S. rugosus increased gradually during 4 months of maize growth in glasshouse conditions, and more than 50% increase occurred during the second month after sowing. Under wheat growth, in open field conditions, the lowest population was observed during July, 1 month after wheat harvesting, and the highest in August, after the first post-harvest irrigation. About 50% of the nematode population survived after a 5-month period of drought in the absence of a host and the percentage of surviving nematodes was greater under a dry soil regime than under a dry-wet regime. Most of the inactive S. rugosus were adults. After 24 h of soil wetting, most inactive nematodes resumed their activity and the optimum temperature for activation was 25°C.