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The morphology, life cycle, behaviour, dispersal, ecology, host range, distribution, molecular diagnosis, interaction with other parasites, and control (i.e. through cultural and chemical methods, and use of resistant crops) of lesion nematodes (Pratylenchus spp.), burrowing nematodes (Radopholus spp.), rice root nematodes (Hirschmanniella spp.), stem and bulb nematode (Ditylenchus dipsaci), bud and leaf nematodes (Aphelenchoides fragariae and A. ritzemabosi), A. besseyi, and pinewood nematode (Bursaphelenchus xylophilus) are described in this chapter.

Quantitative real-time PCR (qPCR) techniques are being increasingly used to provide accurate and reliable methods to identify and quantify cryptic organisms in soil ecology. Entomopathogenic nematode (EPN) diversity in Florida is known to be extensive and our phylogenetic studies of the D2D3 and ITS regions showed the occurrence of an additional species-complex in the Steinernema glaseri-group in widely separated locations of the peninsula. To address ecological studies, we developed and used qPCR assays to detect and quantify six species of EPN that are naturally distributed in Florida citrus orchards (Steinernema diaprepesi, Steinernema riobrave, Heterorhabditis indica, Heterorhabditis zealandica, Heterorhabditis floridensis and an undescribed species in the S. glaseri group) and an exotic species, S. glaseri. Species-specific primers and TaqMan ® probes were designed from the ITS rDNA region. No nonspecific amplification was observed in conventional or qPCR when the primers and probes were tested using several populations of each of the Florida species and other exotic EPN species. Standard curves were established using DNA from pure cultures. We optimised a protocol for extracting nematodes and DNA from soil samples that can detect one EPN added to nematode communities recovered by conventional extraction protocols. A survey of an 8-ha orchard in April 2009 compared the EPN spatial patterns derived from qPCR to that obtained by baiting soil samples with Galleria mellonella larvae. The patterns were also compared to those derived from the same site in 2000-01 by repeatedly (12 sampling events) baiting soil in situ with caged larvae of the root weevil Diaprepes abbreviatus. The qPCR assay was more efficient than the Galleria baiting method for detecting the EPN species composition in population mixtures. Moreover, the spatial patterns of EPN in this orchard were remarkably stable over the course of nearly a decade. The pattern of H. zealandica detected at the site 8 years earlier was related to those derived by qPCR (P = 0.002) and from sample baiting (P = 0.02). The spatial pattern of H. indica derived from qPCR, but not that from sample baiting, was also related to the earlier pattern (P = 0.01). The qPCR assay developed here is a fast, affordable and accurate method to detect and quantify these EPN species in soil and offers great potential for studying the ecology of EPN. Ann Appl Biol 158 (2011) 55-68 No claim to original US government works 55 Annals of Applied Biology

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While the role of herbivore-induced volatiles in plant-herbivore-natural enemy interactions is well documented aboveground, new evidence suggests that belowground volatile emissions can protect plants by attracting entomopathogenic nematodes (EPNs). However, due to methodological limitations, no study has previously detected belowground herbivore-induced volatiles in the field or quantified their impact on attraction of diverse EPN species. Here we show how a belowground herbivore-induced volatile can enhance mortality of agriculturally significant root pests. First, in real time, we identified pregeijerene (1,5-dimethylcyclodeca-1,5,7-triene) from citrus roots 9–12 hours after initiation of larval Diaprepes abbreviatus feeding. This compound was also detected in the root zone of mature citrus trees in the field. Application of collected volatiles from weevil-damaged citrus roots attracted native EPNs and increased mortality of beetle larvae (D. abbreviatus) compared to controls in a citrus orchard. In addition, field applications of isolated pregeijerene caused similar results. Quantitative real-time PCR revealed that pregeijerene increased pest mortality by attracting four species of naturally occurring EPNs in the field. Finally, we tested the generality of this root-zone signal by application of pregeijerene in blueberry fields; mortality of larvae (Galleria mellonella and Anomala orientalis) again increased by attracting naturally occurring populations of an EPN. Thus, this specific belowground signal attracts natural enemies of widespread root pests in distinct agricultural systems and may have broad potential in biological control of root pests.

In August, eight 4-m tall citrus trees were pruned by removing the top third of their canopy. Eight unpruned trees served as controls. Root growth, which was examined nondestructively with minirhizotrons over a four-month period, tended to be less in the pruned than unpruned trees seven days after pruning and this difference was significant (P < 0.05) from 14 to 49 days after pruning. Total reducing and ketone sugars (includes free fructose, sucrose and fructans) in the fine roots were less in pruned than unpruned trees 20 days after pruning, but not thereafter. By 30 days after pruning, at least 20% of the roots of the pruned trees at a soil depth of 9 to 35 cm apparently died. By 63 days after pruning, root length density had recovered to that of the unpruned trees, although starch reserves were 18% less in the fine roots of pruned than unpruned trees at this time. Nine to eleven months after pruning (May to July), total biomass of leaves and fine roots to a depth of 1 m were similar in pruned and unpruned trees. However, fruit biomass harvested in April from pruned trees was only 24% of that in the unpruned trees. In May, nonstructural carbohydrates in the fine and coarse roots of pruned trees were generally greater than in unpruned trees, possibly reflecting previous differences in fruit production.

SUMMARYAmong closely related citrus genotypes growing in high phosphorus (P) orchard soils, there is a tendency for less mycorrhizal-dependent (M-dependent) species to have lower rates of root colonization than more M-dependent species. We hypothesized that the less M-dependent the citrus species the more limited is their carbohydrate (CHO) allocation to the M fungus. In a glasshouse study at low and high P supply, lower total incidence of Glomus intraradices FL 208, intensity of vesicles formation, and accumulation of 16: l^j cis fungal fatty acid as measures of root colonization were related to lower mycorrhizal dependency (MD; M plant d. wt/non-mycorrhizal (NM) plant d. wt expressed at low P supply) in five citrus genotypes. At high P supply, when host carbon (C) production was not affected by P nutrition, less M-dependent genotypes had consistently lower starch concentrations in their root and shoot tissues than did more M-dependent genotypes, irrespective of M inoculation. At low P supply, M plants were more heavily colonized by G. intraradices and had lower starch levels than the M plants supplied with additional P. At high P, M plants of the more dependent genotypes allocated more C to starch pools relative to the NM plant than the least dependent genotype. Concentration of sucrose in tissues did not vary consistently with the dependency of citrus genotypes or with M inoculation except in high P NM plants, when less M-dependent genotypes had lower levels of sucrose in their roots than the more dependent species. At high P supply, sucrose concentrations were lower in colonized roots than in NM roots. Across citrus genotypes, sucrose in M fibrous roots decreased relative to that in NM roots with increase in root colonization suggesting that more sucrose was allocated for growth and maintenance of G. intraradices in roots of M-dependent species. The concentration of reducing sugars in root tissues varied in relation to MD of citrus genotypes in the same way as that of starch and sucrose, but was less responsive to M colonization. Responses of total non-structural CHO in tissues indicated that more heavily colonized plants at low P expended more C to acquire P than did M plants of similar biomass and P status grown at high P supply. Total CHO pools increased with MD of citrus genotypes, providing evidence than C allocation patterns in the host affect M colonization.

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