Sampling procedures and damage thresholds for root-knot nematode (Meloidogyne javanica) on pineapple

The relationship between the population density of root-knot nematode (Meloidogyne javanica) and pineapple yield was studied by establishing different nematode densities in field plots at 3 sites. Differences in nematode populations between treatments were apparent 9–22 months after planting, but yields in the plant crop were similar, regardless of nematode density. In the ratoon crop, yields in treatments with less than 10 nematodes/200 mL soil at 9–22 months were reduced by about 10%. Yield reductions of more than 25% occurred when population densities were greater than 50 nematodes/200 mL soil. These results demonstrate that economically significant crop losses from root-knot nematodes can occur in pineapple when the population density at 12 months is greater than 1–5 nematodes/200 mL soil. The sampling procedures required to obtain reliable estimates of M. javanica in pineapple fields were determined by studying nematode distribution in 2 fields in south-east Queensland. Nematodes were extracted from more than 100 individual soil cores on a 5 by 5 m grid and populations were found to have a clumped rather than random distribution. A composite sample of 41 cores in 1 field and 72 cores in the other gave a relatively precise estimate of the population of root-knot nematodes (i.e. standard error : mean ratio of 0.3). These data suggest that a 50-core sampling unit is appropriate when nematode population density is being estimated for decision-making purposes

Effect of copper fungicide on Colletotrichum gloeosporioides and other microorganisms on avocado leaves and fruit

An investigation into the effect of copper fungicide on non-target microorganisms on avocado (cvv. Hass and Nabal) showed that populations of filamentous fungi, yeasts, and bacteria on leaves were at least 10-fold less after a single application of copper than on unsprayed leaves. This detrimental effect of copper on microorganisms on the phylloplane was confirmed in random samples collected from 5 commercial avocado orchards with regular pesticide spray programs but where isolated unsprayed trees were also available. An intensive 16-month study was carried out on 2 adjacent orchards, 1 that was sprayed with copper fungicide at monthly intervals from October to April each year, and the other that had not been sprayed for at least 6 years. Populations of filamentous fungi, yeasts, and bacteria on leaves and fruit were 10–100-fold lower in the sprayed orchard than in the unsprayed orchard. However, populations in the sprayed orchard recovered during the winter non-spray periods to levels comparable to the unsprayed orchard. In 1993 and 1994, fruit were harvested from both orchards, ripened, and assessed for anthracnose caused by Colletotrichum gloeosporioides. In both years, there was significantly less disease in unsprayed fruit (mean disease rating 1.13 and 0.32, respectively) than in sprayed fruit (mean disease rating 1.83 and 2.18, respectively). These results show that copper fungicide is detrimental to phylloplane microorganisms and suggest that those organisms are providing some natural suppression of C. gloeosporioides on avocado

Observation of hard scattering in photoproduction events with a large rapidity gap at HERA

Events with a large rapidity gap and total transverse energy greater than 5 GeV have been observed in quasi-real photoproduction at HERA with the ZEUS detector. The distribution of these events as a function of the $\gamma p$ centre of mass energy is consistent with diffractive scattering. For total transverse energies above 12 GeV, the hadronic final states show predominantly a two-jet structure with each jet having a transverse energy greater than 4 GeV. For the two-jet events, little energy flow is found outside the jets. This observation is consistent with the hard scattering of a quasi-real photon with a colourless object in the proton.Comment: 19 pages, latex, 4 figures appended as uuencoded fil

Produção de clamidósporos de Pochonia chlamydosporia em diferentes substratos

Clamidósporos são estruturas de sobrevivência do fungo nematófago Pochonia chlamydosporia. Objetivou-se, com este trabalho, avaliar diferentes substratos, teores de água e formas de inóculo para a produção in vitro de clamidósporos de P. chlamydosporia. Inicialmente, testaram-se os substratos grãos de milho triturado, grãos de arroz e casca de café e os tipos de inóculo meio líquido concentrado ou diluído (1:40) e discos de cultura, colonizados por P. chlamydosporia. Posteriormente, testou-se o substrato grãos de milho triturado suplementado ou não com caldo de batata com os inóculos do fungo nas formas de discos de micélio ou suspensão aquosa. As maiores produções de clamidósporos g-1 de substrato foram obtidas nos substratos grãos de milho triturado e casca de café, e as melhores formas de inóculo foram meio líquido diluído (1:40) e discos de micélio. A suplementação do substrato grãos de milho triturado com caldo de batata não aumentou a produção de clamidósporos do fungo e a melhor forma de inóculo do fungo foi a de discos de micélio. Além disso, testaram-se os substratos canjica, grãos de arroz, casca de café e fibra de coco, umedecidos com diferentes quantidades de água; o substrato casca de café umedecido por diferentes períodos; a casca de café enriquecida ou não com sacarose e farinha de arroz e o substrato grãos de arroz esterilizado no forno micro-ondas com diferentes quantidades de água. Apenas o substrato grãos de arroz, em todas as quantidades de água testadas, apresentou maior produção de clamidósporos. Não houve diferença na produção de clamidósporos no substrato casca de café umedecido por diferentes períodos e apenas quando a casca de café foi enriquecida com farinha de arroz, apresentou maior média de clamidósporos g-1 de substrato. Todos os tratamentos apresentaram grande produção de clamidósporos g-1 quando o substrato utilizado foi o de grãos de arroz tratados no forno de micro-ondas. O melhor meio de cultivo de P. chlamydosporia para a produção de clamidósporos foi o substrato contendo grãos de arroz.Chlamydospores are survival structures of the nematophagous fungus Pochonia chlamydosporia. The objective of this study was to evaluate different substrates, different contents of water and kinds of inoculum for the production of Pochonia chlamydosporia chlamydospores. The substrates evaluated were: milled maize, rice grains and coffee husk; all of them were inoculated with disks of culture, concentrated liquid media or diluted liquid media (1:40) colonized by P. chlamydosporia. Besides, the substrates milled maize, supplemented or not with potato broth, and inoculated with fungus disks or aqueous suspension were evaluated. Milled maize and coffee husk were the best substrates for chlamydospores production. The best inoculum kinds were disks of culture and diluted liquid media (1:40) colonized by P. chlamydosporia. The supplementation of milled maize with potato broth did not improve the production of chlamydospores, and the best inoculum form was disks of fungus. Moreover, it was also studied the substrates rice grains, coffee husk and coconut fibers with different rates of water; the substrate coffee husk moistened by different periods; the supplementation of coffee husk with rice flour or dextrose; and the substrate grains of rice sterilized in microwave oven with different rates of water. The substrate grains of rice, in all of the amounts of water tested showed increase in production of chlamydospores. There was no difference in the chlamydospores production of the coffee husk substrate, when moistened by different periods of time and only when it was supplemented with rice flour it showed higher mean of clamydospores per gram of substrate. All treatments evaluated showed higher production of chlamydospores in the substrate grains of rice treated in the microwave oven. The best substrate for the production of chlamydospores of P. chlamydosporia was the rice grains

Root‐lesion nematodes of potato: current status of diagnostics, pathogenicity and management

Root‐lesion nematodes of the genus Pratylenchus are migratory endoparasites with worldwide economic impact on several important crops including potato, where certain species like P. penetrans, P. neglectus and P. scribneri reduce the yield and quality of potato tubers. Morphological identification of Pratylenchus spp. is challenging, and recent advancements in molecular techniques provide robust and rapid diagnostics to differentiate species without need of specialist skills. However, the fact that molecular diagnostics are not available for all Pratylenchus species means that there are limitations in worldwide application. In general, root‐lesion nematodes are difficult to manage once introduced into agricultural land and damage can be related to pathogenicity and population densities. In addition, root‐lesion nematodes interact with fungi such as V. dahliae, resulting in disease complexes that enhance the damage inflicted on the potato crop. Management interventions are often focused on limiting nematode reproduction before planting crops and include the application of nematicides, and cultural practices such as crop rotation, cover crops, biofumigation, and biological control. Understanding the limitations of the available crop protection strategies is important and there are many gaps for further study. This review discusses the status of the diagnosis, distribution, pathogenicity and management of the main species of root‐lesion nematodes, reported to infect potatoes worldwide, and highlights areas for potential future research