A critique of current methods in nematode taxonomy

Morphology based nematode taxonomy and biodiversity studies have historically challenged most biologists. In the past few decades, there have been efforts to integrate molecular methods and digital 3D image-capturing technology in nematode taxonomy, the former to enhance the accuracy of identification of such a taxonomically challenging group and the latter to communicate morphological data. While the employment of these two methods is growing in recent taxonomic, biodiversity andbiogeographic studies, a movement to abandon traditional phenotypic identification methods altogether has emerged. Proponents try to justify this trend by citing the challenging gap between the high estimated number of undescribed species and the limited ability of traditional taxonomy to accomplish the task of documenting such diversity. Here we present a review of the various techniques used in the taxonomy of free-living and plant parasitic nematodes and critique those methods in the context of recent developments and trends including their implications in nematode taxonomy, biodiversity and biogeography.Key words: Species delimitation, taxonomic methods, genetic and molecular methods, traditional taxonomy, nematode biodiversity

Vertical Distribution of Pasteuria penetrans Parasitizing Meloidogyne incognita on Pittosporum tobira in Florida

Pasteuria penetrans is considered as the primary agent responsible for soil suppressiveness to root-knot nematodes widely distributed in many agricultural fields. A preliminary survey on a Pittosporum tobira field where the grower had experienced a continuous decline in productivity caused by Meloidogyne incognita showed that the nematode was infected with Pasteuria penetrans. For effective control of the nematode, the bacterium and the host must coexist in the same root zone. The vertical distribution of Pasteuria penetrans and its relationship with the nematode host in the soil was investigated to identify (i) the vertical distribution of P. penetrans endospores in an irrigated P. tobira field and (ii) the relationship among P. penetrans endospore density, M. incognita J2 population density, and host plant root distribution over time. Soil bioassays revealed that endospore density was greater in the upper 18 cm of the top soil compared with the underlying depths. A correlation analysis showed that the endospore density was positively related to the J2 population density and host plant root distribution. Thus, the vertical distribution of P. penetrans was largely dependent on its nematode host which in turn was determined by the distribution of the host plant roots. The Pasteuria was predominant mostly in the upper layers of the soil where their nematode host and the plant host roots are abundant, a factor which may be a critical consideration when using P. penetrans as a nematode biological control agent

Reference soil groups map of Ethiopia based on legacy data and machine learning-technique: EthioSoilGrids 1.0

Up-to-date digital soil resource information and its comprehensive understanding are crucial to supporting crop production and sustainable agricultural development. Generating such information through conventional approaches consumes time and resources, and is difficult for developing countries. In Ethiopia, the soil resource map that was in use is qualitative, dated (since 1984), and small scaled (1 : 2 M), which limit its practical applicability. Yet, a large legacy soil profile dataset accumulated over time and the emerging machine-learning modeling approaches can help in generating a high-quality quantitative digital soil map that can provide better soil information. Thus, a group of researchers formed a Coalition of the Willing for soil and agronomy data-sharing and collated about 20 000 soil profile data and stored them in a central database. The data were cleaned and harmonized using the latest soil profile data template and 14 681 profile data were prepared for modeling. Random forest was used to develop a continuous quantitative digital map of 18 World Reference Base (WRB) soil groups at 250 m resolution by integrating environmental covariates representing major soil-forming factors. The map was validated by experts through a rigorous process involving senior soil specialists or pedologists checking the map based on purposely selected district-level geographic windows across Ethiopia. The map is expected to be of tremendous value for soil management and other land-based development planning, given its improved spatial resolution and quantitative digital representation.</p

Description of Helicotylenchus gerti sp. n. and new records of some species of Helicotylenchus (Steiner, 1945) from Ethiopia (Nemata: Hoplolaimidae)

One new and seven known species, belonging to the genus Helicotylenchus are reported from Ethiopia. Helicotylenchus gerti sp. n. is characterized by a hemispherical lip region, first two lip annuli broader than rest of lip annuli (1.0-1.3 vs 0.5-0.6 mm), stylet length (22-24 mm), exceptional size of median bulb valve (5-8 mm long and 4 mm wide), and presence of a long (6-9 mm) non-annulated digitate ventral tail projection. Morphometrics of Ethiopian populations of H. californicus, H. digonicus, H. dihystera, H. egyptiensis, H. martini, H. multicinctus and H. willmottae are provided. Six of these seven species (H. californicus, H. digonicus, H. dihystera, H. egyptiensis, H. martini and H. willmottae) are new records for Ethiopia.En esta contribución se presentan una especie nueva y siete ya conocidas del género Helicotylenchus procedentes de Etiopia. La nueva especie, Helicotylenchus gerti sp. n., se distingue por su región labial hemisférica, los dos primeros anillos labiales más anchos que el resto (1.0-1.3 vs 0.5-0.6 mm), estilete de 22-24 mm de longitud, valvas del bulbo medio de excepcional tamaño (5-8 mm de longitud y 4 mm de anchura), y presencia de una larga (6-9 mm) proyección digitiforme ventral y sin anillos en el extremo de la cola. Se aportan medidas de poblaciones etíopes de H. californicus, H. digonicus, H. dihystera, H. egyptiensis, H. martini, H. multicinctus y H. willmottae. Seis de estas siete especies (H. californicus, H. digonicus, H. dihystera, H. egyptiensis, H. martini and H. willmottae) se citan por vez primera en Etiopía

New records of Criconematidae (Nemata) from Ethiopia

Sporadic surveys over the past twenty years in different areas of Ethiopia have shown several associations between plant-parasitic nematode genera and various crops; however, taxonomic studies of the nematodes of Ethiopia are almost non-existent. During a survey in the 2002 cropping season in the south, west and southwestern parts of this country, seven Criconematidae species were found of which all are new records for the country except P. leptos Raski, 1975. The species found are C. crassianulatum (de Guiran, 1963) Raski & Luc, 1985, Criconema mutabile (Taylor, 1936) Raski & Luc, 1985, Criconemoides goodeyi de Guiran, 1963, Discocriconemella limitanea (Luc, 1959) De Grisse & Loof, 1965, Ogma decalineatum (Chitwood, 1957) Andr.ssy, 1979, Paratylenchus leptos Raski, 1975 and P. pandatus (Raski, 1976) Siddiqi, 1986. Short notes, discussions and illustrations are given for five well-known species viz. C. crassianulatum, C. mutabile, D. limitanea, O. decalineatum and P. leptos. Two males of P. leptos were found for the first time and are described. The lesser known C. goodeyi and P. pandatus, which has only been found for the second time now, are described and illustrated in more detail.Una serie de muestreos esporádicos realizados a lo largo de los .últimos veinte años en diferentes .reas de Etiopía han puesto de manifiesto la existencia de distintas asociaciones entre géneros de nematodos fitoparásitos y varios cultivos; no obstante, son muy escasos los estudios taxonómicos sobre nematodos en Etiopía. Durante un muestreo realizado en la .poca de recolección en distintas .reas del sur, oeste y suroeste de Etiopía, se encontraron siete especies de la familia Criconematidae, todas las cuales, excepto P. leptos Raski, 1975, son nuevas citas para el país. Las especies encontradas son C. crassianulatum (de Guiran, 1963) Raski et Luc, 1985, Criconema mutabile (Taylor, 1936) Raski et Luc, 1985, Criconemoides goodeyi de Guiran, 1963, Discocriconemella limitanea (Luc, 1959) De Grisse et Loof, 1965, Ogma decalineatum (Chitwood, 1957) Andrássy, 1979, Paratylenchus leptos Raski, 1975 y P. pandatus (Raski, 1976) Siddiqi, 1986. Se aportan observaciones, discusiones e ilustraciones para las cinco especies que son bien conocidas: C. crassianulatum, C. mutabile, D. limitanea, O. decalineatum y P. leptos. De P. leptos se describe por primera vez el macho a partir de dos ejemplares encontrados. Por .último, se describen e ilustran con más detalle las especies C. goodey y P. pandatus, las cuales han sido halladas por segunda vez

Damage potential of meloidogyne incognita populations on selected tomato genotypes in ethiopia

Reliable data are required to relate the effect of initial population density (Pi) on plant growth, biomass, and yield for specific crop-nematode associations under local conditions. In Ethiopia, no information is available on the effect and relationship between Pi of Meloidogyne incognita and damage to tomato cultivars. Hence, the effect of a series of Pi of two populations ofM incognita on tomato cultivars Assila, Chochoro, Moneymaker, and Tisey and the breeding line CLN-2366B on growth, yield, and the relationship with final nematode population density (Pf) were studied. Each tomato cultivar was inoculated with a geometric series of Pi (0, 0.125, 0.5, 1, 2, 4, 8, 16, 32, 64, 128, and 256 J2/100 g dry soil) and grown until senescence. The relationship between Pi and Pf was fitted to the Seinhorst population dynamics model (Pf = (M * Pi) I (Pi + M/a) while the effect of Pi on different plant parameters was fitted to the Seinhorst yield model (Y = Ymax*(m + (1 - m)* Z boolean AND ((Pi-T)/T)). Based on the damage model all the tested plant parameters were negatively affected by both populations ofM incognita. The Jittu M. incognita population had greater effect on the majority of tomato parameters compared to the Babile population. Based on reproduction factors (RF), all the tomato cultivars were good hosts for both populations ofM incognita. The highest RF was obtained at lower Pis (0.125 J2/100 g dry soil) and was reduced with increasing Pi on all cultivars. Severity of root galling and number of egg masses per root system increased with increasing inoculum levels of both nematode populations. The seedlings of all tomato genotypes died at the higher Pi value (256 J2/100 g dry soil) except for Assila. The cultivar Tisey was highly susceptible to both the Babile and Jittu populations and all the seedlings died at Pi >= 16 J2/100 g dry soil. Moneymaker seedlings died at Pi >= 64 J2/100 g dry soil. For all the plant parameters studied, Tisey had the lowest damage threshold T whereas Assila (except for root weight) had greater T. A difference was observed among the tomato genotypes on minimum yield (m) for the different plant parameters against the Babile and Jittu populations. Determination of T and m of a given crop variety for the prevailing Meloidogyne species in fields to be planted (local setting) is vital

Survey of plant parasitic nematodes and banana weevil on Ensete ventricosum in Ethiopia

Twenty five sites, representative of seven agro-ecological zones of enset (Ensete ventricosum) crops, were sampled between September 1998 and January 1999. At each site, five 1-2 year old enset plants were sampled to check for the presence of nematodes present in their roots. The predominant nematode species found was Pratylenchus goodeyi (prominence value = 5640 per 100 g fresh root weight (FRW)), followed by Aphelenchoides ensete (prominence value = 137 per 100 g FRW), and Meloidogyne spp. (prominence value = 26 per 100 g FRW). Leaves of young enset plants often showed severe streak-like symptoms. Aphelencoides ensete was the only nematode isolated from these leaves and may be associated with the streak-like symptoms. A total of 71 different enset cultivar names were recorded during the survey, with different levels of P. goodeyi. Split pseudostem traps failed to detect the banana weevil, Cosmopolites sordidlus