Potential for the Pathogenicity of Plant-Parasitic Nematodes Associated with Blueberries in Georgia and North Carolina

Ring (Mesocriconema ornatum) nematode in Georgia (GA) has been associated with blueberry replant disease. A survey of plant-parasitic nematodes (PPNs) from production blueberry fields in GA and North Carolina (NC) was previously presented and evaluated from an abundance perspective. However, PPNs are often patchily distributed, occurring in close physical association with infected plant roots. Soil cores may or may not sample the areas of high nematode abundance, and nematode counts tend to be highly variable because of this patchiness. To evaluate the survey data for potentially unrecognized blueberry PPNs, we reanalyzed nematode survey data from NC and GA using multivariate analyses that integrate both patterns of occurrence and patterns in relative abundance. Indicator species analysis identified ring nematode in GA as a potentially pathogenic nematode, consistent with previous confirmation of pathogenicity through a container study. Indicator species analysis also identified two potentially pathogenic nematodes in NC blueberries: awl (Dolichodorus spp.) and sheath (Hemicycliophora spp.) nematodes. Of the two nematodes, awl shared a similar position in the NC blueberry nematode community when compared with ring nematode in GA. However, awl nematode relative abundance was low enough, when compared with ring nematode in GA, to suggest that although it is likely parasitic on NC blueberries, it may not be pathogenic. Our analysis from a previous survey suggests that PPNs are unlikely to be a threat to NC blueberry production. However, if blueberry replant disease emerges in NC, then ring, awl, and sheath nematodes should be considered as potential causal agents.

First report of two Mesocriconema (Nematoda: Criconematidae) species in mulberry trees in Costa Rica

Soil samples were collected from the rhizosphere of mulberry (Morus alba L.) trees, in a 1,000 m² plot, at the Experimental Farm Santa Lucia, in Barva, Heredia, Costa Rica, in August 2013. The plants showed symptoms of yellowing, declining and poor development. Specimens of two ring nematode were collected from the soil and identified as Mesocriconema sphaerocephalum (Taylor 1936) Loof 1989 and M. anastomoides (Maqbool & Shahina 1985) Loof & De Grisse 1989, based on the morphological and morphometrical analysis of females. Both nematodes have been previously found in Costa Rica. However, this is the first report of nematodes from the Criconematidae family associated to mulberry trees and it provides additional information on the distribution of this phytoparasite.

First report of Mesocriconema xenoplax (Nematoda: Criconematidae) in Greece and first record of Viburnum sp. as a possible host for this ring nematode

In 2005, root and soil samples were collected from the rhizosphere of Viburnum sp. plants in the yard of a house in Kifissia, Attica, Greece. The plants showed symptoms of yellowing and declining and all were dead within, approximately, one year. The roots were infected with the fungus Rosellinia necatrix. Several specimens of a ring nematode were recovered from soil and identified as Mesocriconema xenoplax based on morphological and morphometrical analysis of females. The nematode had been previously found on grapevines in Samos and Crete islands. This is the first report of M. xenoplax in Greece and the first record of Viburnum sp. as a host for this ring nematode. Additional information regarding distribution of this nematode in Greece is needed.

Influence of Ring Nematode Infestation and Calcium, Nitrogen, and Indoleacetic Acid Applications on Peach Susceptibility to Pseudomonas syringae pv. syringae

Two field experiments were conducted to study the effects of added nitrogen, calcium, and indoleacetic acid, in the presence or absence of ring nematodes (Mesocriconema xenoplax), on susceptibility of peach to bacterial canker. When noninfested soil was inoculated with ring nematodes, peach tree susceptibility to bacterial canker infection caused by Pseudomonas syringae pv. syringae was dramatically increased after a period of 2 years. However, no evidence was found that ring nematode infestation increased tree water stress or, in turn, altered plant calcium uptake. Soil fumigation with methyl bromide prior to planting in a commercial orchard significantly reduced both nematode populations and peach tree susceptibility to bacterial canker infection when compared with nonfumigated treatments. In both experiments, tree susceptibility, as measured by canker length following inoculation of stems with P. syringae pv. syringae, was negatively correlated with plant tissue nitrogen content and positively correlated with tissue calcium content. A principal components analysis showed that tissue nitrogen and calcium levels were negatively correlated, and that high-nitrogen, low-calcium tissues were less susceptible to bacterial canker than low-nitrogen, high-calcium tissues. These results indicate that the increased susceptibility of peach to P. syringae pv. syringae under nematode infestation conditions is mediated by both nutritional effects (primarily nitrogen) and nutritional-independent effects, but do not support previous reports of beneficial effects of calcium for reducing bacterial canker.

Performance of Containerized and Bare-root Transplants with Soil Fumigants for Florida Strawberry Production

Field studies were conducted in three Florida locations (Bradenton, Gainesville, and Quincy) during 1998-99 and 1999-2000 to: 1) compare the performance of two transplant systems under diverse MBr alternative programs in `Chandler' strawberry (Fragaria ×ananassa), and 2) determine the efficacy of these treatments on soilborne pest control in strawberry. Fumigant treatments were: 1) nonfumigated control, 2) methyl bromide plus chloropicrin (MBr + Pic) at a rate of 350 lb/acre, 3) Pic at 300 lb/acre and napropamide at 4 lb/acre, 4) 1,3-dichloropropene (1,3-D) plus Pic at 35 gal/acre and napropamide at 4 lb/acre, 5) metam sodium (MNa) at 60 gal/acre and napropamide at 4 lb/acre, and 6) MNa followed by 1,3-D at 60 and 12 gal/acre and napropamide at 4 lb/acre, respectively. Strawberry transplants were either bare-root or containerized plugs. There were no significant fumigant by transplant type interactions for strawberry plant vigor and root weight per plant, whereas ring nematode (Criconema spp.) and nutsedge (Cyperus rotundus and C. esculentus) populations, and total marketable fruit weight were only infl uenced by fumigant application. The nonfumigated plots had the lowest strawberry plant vigor and root weight per plant in all three locations. In most cases, plant vigor and root biomass per plant increased as a response to any fumigant application. With regard to the transplant type, bare-root transplants had similar plant vigor as plugs in two of the three locations. Fumigation improved nutsedge and ring nematode control. All fumigants had higher early and total marketable yield than the nonfumigated control, whereas transplant type had no effect on total fruit weight.

Creating a Short Life Site for Prunus Rootstock Evaluation on Land with No Innate Mesocriconema xenoplax Population

Peach tree short life (PTSL) is associated with the presence of ring nematode, Mesocriconema xenoplax, and poor orchard management practices. Finding a noncommercial field site to evaluate rootstocks for PTSL resistance is increasingly difficult. The time needed to create a PTSL test site was investigated. In 1994, a site not planted in peaches for >80 years was identified in Byron, Ga. Analysis of preplant soil samples revealed that there were no M. xenoplax on the site. One-third of the land was planted to peach and infested with 1600 ring nematodes per tree in Spring 1994 (P2) and another one-third in Spring 1995 (P1). The remaining one-third of the land received no trees or ring nematode and served as the control (F2). In Fall 1995, trees were removed from P1 and P2 plots and all treatments were replanted to peach in 1996. In 1997, tree death resulting from PTSL occurred only in P2 (7%). By 2000, PTSL tree death reached 41% in P2, 16% in P1, and 4% in F2 plots. Nematode populations were higher (P < 0.05) in P1 (649 ring nematode/100 cm3 soil) than in F2 (221 ring nematode/100 cm3 soil) plots, whereas populations in P2 (300 ring nematode/100 cm3 soil) plots did not differ from those in P1 or F2 plots. Establishing a PTSL screening site was possible 3 years after M. xenoplax introduction; PTSL development among treatments in the subsequent planting was dependent upon cumulative population exposure of trees to M. xenoplax.