Replant diseases often occur when pome and stone fruits are grown in soil that had previously been planted with the same or similar plant species. They typically lead to reductions in plant growth, crop yield and production duration. In this project, greenhouse assays were used to identify a peach orchard soil that caused replant disease symptoms. Biocidal treatments of this soil led to growth increases of Nemaguard peach seedlings. In addition, plants grown in as little as 1% of the replant soil exhibited reduced plant growth. These results suggest that the disease etiology has a biological component. Analysis of roots from plants exhibiting various levels of replant disease symptoms showed little difference in the amounts of PCR-amplified bacterial or fungal rRNA genes. However, analysis using a stramenopile-selective PCR assay showed that rRNA genes from this taxon were generally more abundant in plants with the smallest top weights. Nucleotide sequence analysis of these genes identified several phylotypes belonging to Bacillariophyta, Chrysophyceae, Eustigmatophyceae, Labyrinthulida, Oomycetes, Phaeophyceae and Synurophyceae. Sequence-selective quantitative PCR assays targeting four of the most abundant phylotypes showed that both diatoms (Sellaphora spp.) and an oomycete (Pythium ultimum) were negatively associated with plant top weights.

New non-fumigant nematicides (fluensulfone, fluopyram and fluazaindolizine) were tested in greenhouse tomato trials aiming to evaluate its efficacy on the control of Meloidogyne incognita soil and root populations and plant produtivity. Plants of the cultivar Red Gnome were transplanted into 2,500 cm 3 fibre pots inoculated with 200 eggs of M. incognita/100 cm 3 of soil and treated with fluensulfone, fluopyram and fluazaindolizine, in two rates each. After eight weeks of incubation the plants were evaluated for fresh root and shoot weight, weight and number of fruits, egg mass number, population density and nematode reproduction factor. All nematicide treatments reduced the root gall index, the number of M. incognita egg masses, eggs/g root and the nematode reproduction factor when compared to the non-treated control. K E Y W O R D S chemical control, non-fumigant nematicides, root-knot nematode, Solanum lycopersicum

Fluorescent molecular probes were applied for detection of the plant parasitic nematode Meloidogyne incognita and the nematode-egg parasitic fungus Pochonia chlamydosporia var. chlamydosporia . A region in the M. incognita rDNA including ITS2 was selected for amplification and recognition with a real-time PCR assay, based on a combination of three specific motifs, each recognized by a specific fluorescent probe. Similarly, a Scorpion probe was designed for the RT-PCR quantification of P. c . chlamydosporia . For this purpose, the ITS-2 rDNA gene of the fungus was sequenced from a number of Italian isolates. A conserved region unique for P. c . chlamydosporia found in the ITS-2 rDNA gene was used. The probes allowed recognition of single juveniles of M. incognita and of the mycelium-or soil-extracted fungal DNA. The potentialities of the detection procedures are discussed.

Until the early 1990s, cyst nematodes were abundant pathogens in fields where hosts of Heterodera spp. were frequent members of crop rotations along California’s Central Coast. To mitigate damage caused by Heterodera schachtii and H. cruciferae, the soil fumigant 1,3-dichloropropene (1,3-D) was used by more than 43% of surveyed broccoli growers. Over the last few decades, use of 1,3-D and other nematicides has dramatically diminished, suggesting a decline in nematode disease pressure. The goal of this study was to examine the hypothesis that increased population densities of nematophagous fungi contribute to the low populations of Heterodera spp. in fields frequently cropped to their hosts. In 2016, soil samples were collected from 152 Brassica fields with a broad geographical distribution, from Santa Barbara County to Santa Cruz County. The average number of Heterodera cysts per 250 cm3 of soil ranged from 0.5 to 27.5, with 62% of the soils harboring no detectable cyst nematodes and only a few samples reaching a potentially damaging threshold level. A baiting experiment with H. schachtii and cabbage was performed in a greenhouse to detect nematophagous fungi associated with nematode females as their posterior end emerged and became exposed to the soil’s rhizosphere. An Illumina-based sequence analysis of these H. schachtii females identified several known nematophagous fungi, including members of the Hyalorbilia oviparasitica clade, Pochonia chlamydosporia, certain Fusarium spp., and others. These soils clearly harbor a diverse population of hyperparasitic fungi that could be biologically suppressing cyst nematodes below a damaging threshold. [Formula: see text] Copyright © 2020 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .