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

E-typing for nematodes: an assessment of type specimen use by nematode taxonomists with a summary of types deposited in the Smithsonian nematode collection

We assessed 301 taxonomic papers published in nine journals between 1999-2011 to determine the use of type specimens and to evaluate the habitat focus and the number of new species described per year. A total of ca 100 new nematode species were described every year, primarily from terrestrial habitats. Two-thirds were terrestrial, 16% were aquatic and the remaining 9% were animal-parasitic nematodes. Only 2.5% of the taxonomic literature reported a comparative study of type material for making a decision on the identity of the target taxon. The overwhelming majority (i.e., 97.5%) relied only on literature comparisons. Our closer scrutiny of the 61 papers revealed a number of shared problems: a third stated that inadequacy of original descriptions, or unavailability/inaccessibility of type specimens had hindered them from unequivocally determining the identity of their species. Fourteen percent reported a discrepancy between the text descriptions and the illustrations, and a tenth revealed the absence of designated types for taxa relevant to their work. A similar number indicated deterioration of types to be a reason for either making wrong conclusions in previous descriptions, or for rendering their descriptions incomplete. We argue for E-typing of nematodes as a solution to enhance the future accessibility of type specimens. We stress the need for a concerted effort between museum curators, nematological journals and nematological societies to address the problem and thereby to forge a brighter future for the science

Tomato (Solanum lycopersicum) and root-knot nematodes (Meloidogyne spp.): a century-old battle

The encounter between Meloidogyne species and tomato is many centuries old. Meloidogyne species are known to cause high levels of economic loss worldwide in a multitude of agricultural crops, including tomato. This review was initiated to provide an overview of the damage potential of Meloidogyne spp. on cultivars of tomato (Solanum lycopersicum), and to compile the different studies done on the management of Meloidogyne spp. on tomato with particular emphasis on the Mi resistance gene. Numerous studies have been conducted to assess the damage potential of root-knot nematode on various tomato cultivars; its yield loss potential ranges from 25 to 100%. A range of management options from using synthetic nematicides to soilless cultures have been tried and are available for managing Meloidogyne spp. Resistant commercial cultivars and rootstocks carrying the Mi gene have been used successfully to manage Meloidogyne incognita, M. javanica and M. arenaria. However, virulent populations have been detected. Relying on a single root-knot nematode management strategy is an outdated concept and different management options should be used in an integrated management context by considering the whole system of disease management. In future management of Meloidogyne species, care must be taken in directly extrapolating the tolerance limit determined elsewhere, since it is affected by many factors such as the type of initial inoculum and physiological races of Meloidogyne spp., environmental conditions, types of cultivars and experimental approaches used

Heat stability of resistance in selected tomato breeding lines against Meloidogyne incognita and M. javanica populations under elevated soil temperatures

In tomato, the only commercially available source of resistance to root-knot nematodes (RKN) is the Mi-1 gene that confers resistance to Meloidogyne incognita, M javanica and M arenaria. However, its effectiveness was limited at higher soil temperatures. A study was initiated with the objective to check the durability of the potential resistance genes found in some tomato breeding lines after screening in controlled glasshouse conditions <= 27 degrees C by exposing them to higher soil temperatures at 28, 32 and 36 degrees C for 24 and 48 h periods. The aggressive Jittu and Babile M incognita and Jittu and Koka M javanica populations originally collected from Ethiopia were used. When seedlings reached the four-leaf stage, each tube was inoculated with 50 freshly (< 24 h) hatched infective second-stage juveniles (J2). Immediately after inoculation, the seedlings were exposed continuously for 24 and 48 h in a warm water bath at 28, 32 and 36 degrees C, respectively. A control was kept separately in ambient temperature (24 degrees C 2 degrees C). The external ambient temperature and the soil temperature inside the tube while in the water bath were simultaneously recorded using a TESTO data logger. Temperature, tomato breeding lines and time had a significant effect on the number of J2 of Jittu and Babile M incognita and Jittu and Koka M javanica populations that penetrated the roots. The utility of the potential resistance found in the breeding lines during the controlled growth chamber resistance screening experiment was limited at higher soil temperatures, especially at 32 and 36 degrees C. At 36 degrees C there was no significant difference found on the mean number of penetrated J2 of Jittu and Babile M incognita and Jittu and Koka M javanica populations inside the roots of all the tested breeding lines compared to 'Marmande' (a susceptible control) after 48 h of heat exposure after inoculation. More J2 were found in the roots of the tested breeding lines after 48 h compared to 24 h heat exposure after inoculation for each soil temperature level tested and for both populations of M incognita. It is clear from our observations that local tomato breeding lines with resistance potential can be used when soil temperatures remain below 32 degrees C. Differences were observed between breeding lines depending on the RKN population used at higher temperatures and this knowledge can help in further optimising the development of sustainable resistance under local Ethiopian circumstances

Biodiversity of Meloidogyne spp. from major tomato growing areas of Ethiopia

Root-knot nematodes (Meloidogyne spp.) are among the biotic factors that limit tomato production worldwide. The objectives of this study were to assess the distribution and identify Meloidogyne spp. and associated problems from major tomato growing areas of Ethiopia. A total of 212-rhizosphere soil and 123 root samples were sampled from 40 localities during 2012/13 growing season. A total of 646 respondents participated in the questionnaire to assess knowledge and practice of farmers and factors associated with RKN damage on tomato. Out of the 212 soil samples collected, 47.2% were found infested by various Meloidogyne species 8 weeks after the start of the bioassay test. Out of the 123 root samples collected, 65% had root galls. The highest prevalence (100%) of RKN was found on samples collected from Adami Tullu, Babile, Erer Gota, Hurso, Jittu, Tikur Wuha, Tepo Choronke, Zeway and Koka. The highest incidence (100%) of RKN was found from Adami Tullu, Jara Weyo, Babile, Erer Gota, Hurso, Jittu, Tikur Wuha, Tony farm, Tepo Choronke, Zeway and Koka localities based on direct observation of galls on collected root samples. Out of the 646 respondents, 43.3% reported to have RKN damage symptoms when shown the symptoms while 56.7% of them did not report damage. The highest significant effect on the dependent variable RKN damage on tomato roots comes from the previous crop, soil texture, awareness about RKN and source of irrigation water used. The presence of Meloidogyne incognita, M. javanica, M. arenaria and M. hapla on tomato was confirmed using a combination of molecular and biochemical identification tools. Five isolates of Meloidogyne spp. were not properly identified and could be new species. The two tropical species, M. incognita (48.4%) and M. javanica (41.2%) were the most prevalent species. Both species were also co-infesting tomato plants. Meloidogyne hapla was detected for the first time in an open tomato production farmer's field at Zeway' locality with 1620m.a.s.l. elevation. The occurrence of these Meloidogyne species alone, or in mixed populations from samples collected, clearly shows that RKN are widespread in major tomato growing areas of Ethiopia. In the near future, the economic importance of M. arenaria and M. hapla on tomato production in Ethiopian agriculture should be investigated

The importance and management strategies of cereal cyst nematodes, Heterodera spp., in Turkey

WOS: 000349853800001Cereal cyst nematodes (CCNs) can cause significant economic yield losses alone or in combination with other biotic and abiotic factors. The damage caused by these nematodes can be enormous when they occur in a disease complex, particularly in areas subject to water stress. Of the 12 valid CCN species, Heterodera avenae, H. filipjevi, and H. latipons are considered the most economically important in different parts of the world. This paper reviews current approaches to managing CCNs via genetic resistance, biological agents, cultural practices, and chemical strategies. Recent research within the soil borne pathogen program of the International Maize and Wheat Improvement Center has focused on germplasm screening, the potential of this germplasm as sources of resistance, and how to incorporate new sources of resistance into breeding programs. Breeding for resistance is particularly complicated and difficult when different species and pathotypes coexist in nature. A lack of expertise and recognition of CCNs as a factor limiting wheat production potential, combined with inappropriate breeding strategies and slow screening processes limit genetic gains for resistance to CCNs.Turkey Ministry of Agriculture and Livestock; International Wheat and Maize Improvement Centre (CIMMYT, Mexico); ILCI private agriculture research companyThe authors would like to thank the Turkey Ministry of Agriculture and Livestock, the International Wheat and Maize Improvement Centre (CIMMYT, Mexico), and ILCI private agriculture research company for supporting this work. Editing assistance from Emma Quilligan (CIMMYT) is appreciated