Nematode–Microbe Complexes in Soils Replanted with Apple

Apple replant disease is a severe problem in orchards and tree nurseries. Evidence for the involvement of a nematode–microbe disease complex was reported. To search for this complex, plots with a history of apple replanting, and control plots cultivated for the first time with apple were sampled in two fields in two years. Shoot weight drastically decreased with each replanting. Amplicon sequencing of the nematode community and co-extracted fungal and bacterial communities revealed significant differences between replanted and control plots. Free-living nematodes of the genera Aphelenchus and Cephalenchus and an unidentified Dorylaimida were associated with replanted plots, as indicated by linear discriminant analysis effect size. Among the co-extracted fungi and bacteria, Mortierella and Methylotenera were most indicative of replanting. Some genera, mostly Rhabditis, Streptomyces and a fungus belonging to the Chaetomiaceae indicated healthy control plots. Isolating and investigating the putative disease complexes will help to understand and alleviate stress-induced root damage of apple in replanted soil.

Nematode-Microbe Complexes in Soils Replanted with Apple

Apple replant disease is a severe problem in orchards and tree nurseries. Evidence for the involvement of a nematode-microbe disease complex was reported. To search for this complex, plots with a history of apple replanting, and control plots cultivated for the first time with apple were sampled in two fields in two years. Shoot weight drastically decreased with each replanting. Nematodes were extracted from soil samples by floatation-centrifugation, washed on a 20 µm-sieve, and used for DNA extraction. Nematode communities and co-extracted fungi and bacteria were analyzed by high-throughput sequencing of amplified ribosomal fragments. The nematode community and co-extracted fungal and bacterial communities significantly differed between replanted and control plots. Free-living nematodes of the genera Aphelenchus, Cephalenchus, and an unidentified Dorylaimida were associated with replanted plots, as indicated by linear discriminant analysis effect size. Among the co-extracted fungi and bacteria, Mortierella was most indicative of replanting. Some genera, mostly Rhabditis, indicated healthy control plots. Isolating and investigating the putative disease complexes will help to understand and alleviate stress-induced root damage of apple in replanted soil.

Sugarcane mosaic virus (sugarcane mosaic).

Introduction: In the past, SCMV and other SCMD-causal viruses have caused serious losses in various maize and sugarcane-growing regions, including Hawaii, Egypt, Natal (South Africa), Argentina, Puerto Rico, Cuba, Australia, USA (Koike and Gillaspie, 1989; Fuchs and Grüntzig, 1995; Chen et al., 2002) and several other countries in South America (Perera et al., 2012 and references therein). Epidemics have been followed by replacement of susceptible noble-type canes by hybrid canes with tolerance or, better still, resistance and the propagation of resistant maize genotypes (Silva-Rosales et al., 2015 and references therein). The evolution of new strains of SCMV has required a continuing breeding programme to prevent heavy losses. Losses caused by SCMV are mainly (1) a reduced yield of the crop, (2) the need to include mosaic resistance when breeding new cultivars, and (3) the slowing of the interchange of cultivars between countries because of quarantine concerns over the introduction of new strains of SCMV. Crop Losses: Crop losses caused by SCMV depend on many factors, including the susceptibility of the cultivars to the prevailing strains of SCMV, the incidence of infection, the prevailing environmental conditions, the stage of growth when infection occurs, and interaction with other agents affecting the crop. Crop losses can vary from negligible to severe. Some documented instances of heavy losses in sugarcane crops due to mosaic outbreaks are as follows. In the 1980s, losses on some farms in the Isis district of Queensland, Australia, were estimated to be about 50% (Jones, 1987). In some commercial plantings of cv. Q95 from an infected source, the infected plants had fewer tillers and were less vigorous than apparently healthy plants nearby (Ryan and Jones, 1986). In Guatemala in 1974-1976, many stunted stools of mosaic-affected cv. Q83 were responsible for lack of uniformity in fields near Santa Lucia. The cane tonnage in these fields was seriously reduced (Fors, 1978). Estimations of Potential Losses in Experiments: Sugarcane In Natal, South Africa, plots of sugarcane cv. NCo376 (highly susceptible) and N12 (moderately resistant) were established with either infected or healthy cane. The plots were harvested regularly and tested serologically for SCMV to the 6th ratoon. There was a decline in the number of shoots showing mosaic symptoms in both cultivars during the experiment. However, mean yield reductions were 22% for infected NCo376 and 16% for N12 compared with yields of initially healthy cane (Cronje et al., 1994). In Brazil, plots in two locations were planted with 0, 25, 50 and 100% initial SCMV infection. Virus spread was noticeable for cv. CB46/47, but negligible for cv. IAC50/134. For CB46/47 yield losses between initially healthy and 25% infected plots were 27% and 19% in the two locations; with 100% infection, yield reduction was 71% in both areas. For IAC50/134 the only significant difference in yield was between 0 and 100% infection, an 18% reduction in diseased plots in both areas (Matsuoka and Costa, 1974). In Java, Indonesia, field trials with 0 and 100% SCMV-infected seed cane gave sugar yield reductions of 9.3% for POJ3016 and 11.1% for POJ3067 associated with the disease (Kuntohartono and Legowo, 1970). In Spain, when healthy sugarcane was planted between rows infected by SCMV, the cultivars CO62/175 and NA56/79 were sufficiently resistant for commercial production, but losses of 0.4-0.5 t/ha were found for every 1% infection between the 2nd and 4th cutting (Olalla Mercade et al., 1984a). In Pakistan, mosaic-free seed cane gave a significantly higher yield of cane (48.5 t/ha) than mosaic-infected seed cane (44.5 t/ha) (Ahmad et al., 1991). Maize In East Africa, 10 susceptible maize hybrids had yield losses of 18-46% when inoculated with SCMV in the seedling stage (Louie and Darrah, 1980). In Germany, SCMV was more prevalent than MDMV, but had a similar effect on growth and yield of maize. Early infection reduced plant height by 25%, total weight by 38% and ear weight by 27% (Fuchs et al., 1990). Disease Complexes: SCMV and related potyviruses may occur in disease complexes with other plant pathogens; either additive or synergistic effects may occur. In Louisiana, USA, losses in sugarcane caused by Sorghum mosaic virus (formerly called SCMV-H) and ratoon stunting disease (RSD, caused by the bacterium Leifsonia xyli subsp. xyli) were additive in cv. CP67-412, but synergistic (greater than the sum of each disease separately) in CP65-357 (Koike, 1982). In Spain, RSD symptoms were associated with the presence of SCMV, and damage by RSD was greatest in fields with clear mosaic symptoms (Olalla Mercade et al., 1984b). In Thailand, inoculation of the downy mildew-susceptible maize cv. Guatemala with an SCMV-like virus increased susceptibility to Peronosclerospora sorghi only slightly, whereas with the resistant Suwan 1 maize cv., the virus increased susceptibility from 27 to 61% (Sutabutra et al., 1976). In many African (especial East African) countries, SCMV and some of the SCMD-causal viruses may also interact synergistically with Maize chlorotic mottle virus (genus Machlomovirus; family Tombusviridae) to cause maize lethal necrosis disease, an emerging debilitating disease of maize (Niblett and Claflin, 1978; Wangai et al., 2012) that can cause total crop loss.

Holistic diagnosis and Cannabis microbiome.

The concept of holistic diagnosis used in this chapter has three layers of meaning. First, a plant is a system and all parts of the system should be viewed as a whole. Diagnosis should be based on an entire plant instead of on a single piece of plant material. Secondly, the approach of 'all things considered' should be practised when finding pests, pathogens, or factors that contribute to an observed plant problem. This approach considers the diagnosis process to be an investigation instead of a specific test for a single pathogen. Thirdly, all factors found in a disease are related and each of them may have a unique role in disease initiation and progression. Cannabis pest and disease complex holistic diagnosis, including disease complexes involving nematodes and soilborne pathogens are described, as well as microbiota and microbiome (including epiphytes and endophytes) and their benefits and drawbacks.

Parasitic control at housing in cattle: a modern rationale

Anthelmintic treatment at housing remains the cornerstone of common nematode and trematode management in the UK, taking advantage of the low re-infection risk once away from pasture. Treatment removes any endoparasite burdens acquired during the grazing season and reduces effects on productivity through the winter, as well as levels of larvae and eggs shed onto the pasture at spring turnout. This article covers the four most common parasitic disease complexes encountered in the UK that benefit from treatment at housing.

Challenges with Managing Disease Complexes during Application of Different Measures Against Foliar Diseases of Field Pea

Studies were undertaken across five field locations in Western Australia to determine the relative changes in disease severity and subsequent field pea yield from up to four foliar pathogens associated with a field pea foliar disease complex (viz. Didymella, Phoma, Peronospora, Septoria), across four different pea varieties sown at three different times and at three different densities. Delaying sowing of field pea significantly (P<0.05) reduced severity of Ascochyta blight (all five locations) and Septoria blight (1 location), increased severity of downy mildew (4 locations), but had no effect on seed yield. In relation to Ascochyta blight severity at 80 days after sowing, at all locations the early time of sowing had significantly (P<0.05) more severe Ascochyta blight than the mid and late times of sowing. Increasing actual plant density from 20-25 plants m-2 to 58-78 plants m-2 significantly (P<0.05) increased the severity of the Ascochyta blight (4 locations) and downy mildew (1 location), and increased seed yield at four locations irrespective of sowing date and three locations irrespective of variety. Compared with varieties Dundale, Wirrega and Pennant, variety Alma showed significantly (P<0.05) less severe Ascochyta blight (1 location), downy mildew (1 location) and Septoria blight (1 location). Grain yield was highest for the early time of sowing at three locations. Varieties Alma, Dundale and Wirrega significantly (P<0.05) out yielded Pennant at four locations. The percentage of isolations of individual Ascochyta blight pathogens at 80 days after the first time of sowing varied greatly, with Didymella ranging 25-93% and Phoma from 6- 23% across the five field locations. This fluctuating nature of individual pathogen types and proportions within the Ascochyta blight complex, along with variation in occurrence of Peronospora and Septoria, highlights the challenges to understand and manage the complexities of co-occurring different foliar pathogens of field pea. While the search for more effective host resistance continues, there is a need for and opportunities from further exploring and exploiting cultural management approaches focussing on crop sequence diversification, intercropping, manipulating time of sowing and stand density, and application of improved seed sanitation and residue/inoculum management practices. We discuss the constraints and opportunities towards overcoming the challenges associated with managing foliar disease complexes in field pea.

Current Insights into Migratory Endoparasitism: Deciphering the Biology, Parasitism Mechanisms, and Management Strategies of Key Migratory Endoparasitic Phytonematodes

Despite their physiological differences, sedentary and migratory plant-parasitic nematodes (PPNs) share several commonalities. Functional characterization studies of key effectors and their targets identified in sedentary phytonematodes are broadly applied to migratory PPNs, generalizing parasitism mechanisms existing in distinct lifestyles. Despite their economic significance, host–pathogen interaction studies of migratory endoparasitic nematodes are limited; they have received little attention when compared to their sedentary counterparts. Because several migratory PPNs form disease complexes with other plant-pathogens, it is important to understand multiple factors regulating their feeding behavior and lifecycle. Here, we provide current insights into the biology, parasitism mechanism, and management strategies of the four-key migratory endoparasitic PPN genera, namely Pratylenchus, Radopholus, Ditylenchus, and Bursaphelenchus. Although this review focuses on these four genera, many facets of feeding mechanisms and management are common across all migratory PPNs and hence can be applied across a broad genera of migratory phytonematodes.

Temporal progression of foliar plant diseases in corn hybrids

The environment’s impact on foliar disease growth in annual crops and the various types of differentiation must be investigated to adapt effective disease control strategies. We studied the temporal progression of foliar disease complexes in 14 commercial corn (Zea mays L.) hybrids during the 2015/2016 crop season (Ipameri, Goiás, Brazil). The experiment consisted of 10 blocks and evaluated foliar disease severity using a diagrammatic scale. The evaluations occurred at 47, 53, 59, 74, 81 and 95 days after planting. At each time point, a plant was chosen randomly from each block (10 plants total), and the diseases causing foliar damage were identified. The areas under the disease progression curves (AUDPCs) and yields were calculated. Dependent variables were evaluated using a principal component analysis to study relationships between the hybrids and the disease severity on each leaf (biplot). Heatmaps were used to determine which leaves demonstrated the greatest disease severity and temporal disease progression, and an adjusted linear correlation model was used to predict yield relative to AUDPC. The foliar disease complex consisted of helmintosporiosis, common rust, macrospora leaf spot, cercosporiosis and maize white spot. The Ns90PRO© hybrid showed limited disease progression and; therefore, was considered more resistant and consequently had a lower AUDPC value. The Dow2B610PW© hybrid showed greater disease progression. Agroceres7098PRO2© had a greater yield and consequently a lower AUDPC value, while Lg6050PRO2© had a lower yield and a higher AUDPC value. In general, the more advanced the phenological stage, the more severe the leaf disease; however, disease progression (from plant base to plant tip) was genotype- dependent.