Erwin Aballay

Meloidogyne ethiopica, a major root-knot nematode parasitising Vitis vinifera and other crops in Chile

Enzyme phenotypes, specifically esterases (EST) and malate dehydrogenase (MDH), were used to characterise different species of Meloidogyne from Chile. Esterase activity was highly polymorphic and was the most useful in the identification of the different species. Using this enzyme it is possible to characterise and identify M. ethiopica in about 80% of samples on grapevine, kiwi and tomatoes. Another three species, M. javanica, M. hapla and M. arenaria, were identified on tomatoes, kiwi and pomegranate with only one or a few populations. It was possible to detect minor atypical (unidentified) phenotypes, generally in mixed populations with M. ethiopica. Only the profiles N1 and H1 of MDH were detected. N1 was not specific and H1 allowed identification of M. hapla. Contaminated nursery stock has probably resulted in serious infestation by M. ethiopica in vineyards in various localities in Chile.

Nematicide Effect of Various Organic Soil Amendments on Meloidogyne ethiopica Whitehead, 1968, on Potted Vine Plants

A B S T R A C T Five organic soil amendments were evaluated for their nematicide effect on root-knot Meloidogyne ethiopica Whitehead, 1968, on potted Vitis vinifera L. var. Chardonnay plants. The amendments included two immature composts: Compost A made with tea (Camellia sinensis (L.) Kuntze) residues, broiler litter and grape pomace; Compost B made with tea residues, rachis and grape pomace; and separately dried tea residues, grape pomace and broiler litter. These amendments were either incorporated or applied as cover to the substrate in 5 L pots at the beginning of spring. A chemical treatment with the nematicide fenamiphos and a control with substrate only were added for comparisons. The assay was composed of 11 treatments with six replicates, with a grape plant as experimental unit. Seven months later, the assessment of the treatments was carried out based on number of second stage juvenile, nodules, eggs per root gram and reproductive index. Fresh aerial and root plant weight were also measured. The chemical treatment presented the lowest final population of M. ethiopica. When evaluating the nematicide action of the organic amendments, compost A soil-incorporated and both grape pomace and solid dry tea residue as covers obtained low reproductive indexes, similar to the chemical treatment and control (P ≤ 0.05). No differences in aerial fresh weight were determined. However, the chemical treatment showed the smallest root mass as compared to compost B and solid dry tea residues, both as cover.

Molecular and morphological characterisation of species within the Xiphinema americanum -group (Dorylaimida: Longidoridae) from the central valley of Chile

Species of the Xiphinema americanum -group are among the most damaging nematodes for a diverse range of crops. This group includes 51 nominal species throughout the world. They are very difficult to identify by traditional taxonomic methods. Despite its importance in agriculture, the species composition of this group in many countries, including Chile, remains unknown. In order to identify the species in the central valley of Chile, we studied the morphological, morphometric and molecular diversity of 13 populations. Through classical taxonomic methods two species, X. inaequale and X. peruvianum , were identified with clear differences in the shape of the lip region. The DNA sequences of the ITS of ribosomal genes revealed divergences in the nucleotide sequences of the two species from 7.3% in ITS1 to 14.7% in ITS2. These results confirmed the presence of two distinct species, namely X. peruvianum and X. inaequale , in the northern and southern parts of the central valley of Chile, respectively. PCR-RFLP was developed for rapid species identification of these two species.

SOIL PROPERTIES INFLUENCING PHYTOPARASITIC NEMATODE POPULATION ON CHILEAN VINEYARDS

Lifecycle of phytoparasitic nematode takes place in the rhizosphere, therefore their breeding, parasitism and mobility dynamics are inevitably influenced by the soil-root interaction, A study was performed to evaluate the influence of Vitis rootstocks to some plant parasitic nematodes under different soil conditions. Nematode populations were assessed in Vitis vinifera L. var. Chardonnay plants grafted on two rootstocks (K5BB, SO4) and ungrafted ‘Chardonnay’ as a control in three diferent alluvial soils in the central zone of Chile. Soils were two Inceptisols of the Casablanca Valley (Valparaiso Region), the first one without soil structure and with a densification zone in depth (S1) and the second one with sandy textural class (S3). A third soil was a Mollisol (S2) more structured than the others, situated on a locality of Melipilla (Metropolitan Region). The soils were characterized physically and morphologically and nematode genera were identified and counted using a dissecting microscope. ‘Chardonnay’ presented the highest population of Meloidogyne spp. on the three soil conditions but only significant in S2 soil. The population of Xiphinema spp. and Mesocriconema xenoplax were not representative enough to relate them with either soil or the different rootstocks. The amount of Meloidogyne spp. was inversely related with the sand content but positively related with the more structured soil. The stepwise regressions resulted useful when relating nematode populations with multiple soil factors.

Nematicidal effect of rhizobacteria on plant-parasitic nematodes associated with vineyards

The action of metabolites and exoenzymes from rhizobacteria on different plant-parasitic nematodes has an influence on the nematicidal efficacy of the microbe. Seven rhizobacteria, divided into two bacterial groups, were evaluated in vitro for nematicidal activity on Meloidogyne ethiopica and Xiphinema index. The direct effect of their filtrates on egg hatching and juveniles of M. ethiopica as well as mobile stages of X. index was evaluated during a 72-h period. The production of four exoenzymes and two metabolites associated with nematode mortality was investigated. Molecular characterization of three isolates was performed, and the physiological profiles and lipase activity of all isolates were obtained using the BIOLOG EcoPlate system. While chitinase and collagenase were measured using the BIOLOG MT2 plate system, protease, hydrogen cyanide and hydrogen sulphide were directly determined in Petri dishes. Nematode mobile stages exposure to the bacterial filtrate revealed a nematicidal effect up to 93.7% on X. Index and up to 83.3% on M. ethiopica. The control of egg hatching varied between 35 and 85%. A positive correlation was found between the mortality of both nematode mobile stages and the concerted activities of the bacterial enzymes as well as the level of the volatile metabolites. The nematicidal effect of rhizobacteria strains varies by nematode genera and among the developmental stages evaluated.

Tolerancia de Algunos Portainjertos a Tylenchulus Semipenetrans Cobb 1914 en Chile

La resistencia de algunos portainjertos de vid (Vitis vinifera L.) a Tylenchulus semipenetrans Cobb 1914 fue evaluada en un ensayo desarrollado en un predio donde existio una vina establecida en ese sector. Los portainjertos utilizados fueron VR O39-16, 420 A, Kober 5BB, 110 Richter, Harmony, Courdec 1613, Ramsey y SO4. La variedad Cabernet Sauvignon se uso como control. Se realizo un muestreo y analisis de suelos al momento de la plantacion en 1995 y un segundo muestreo de suelos y raices el ano 2000 para determinar la presencia de juveniles y hembras adultas. Los portainjertos mas resistentes fueron Ramsey y 110 Richter; los otros se comportaron en forma similar al testigo.

Control of plant-parasitic nematodes using cover crops in table grape cultivation in Chile

A study to evaluate the effect of a three-year rotation with cover crops for the management of plant-parasitic nematodes (PPNs) was performed in two vineyards producing table grapes ( Vitis vinifera L.) in a semiarid region in the north of Chile. In the first vineyard, located in Copiapo valley (trial I), the crops used in the rotations or monoculture were fava bean ( Vicia faba ) cv. Aguadulce, rape ( Brassica napus var. napus ) cv L-456, forage turnip ( B. rapa var. rapa ) cv. Barkant, barley ( Hordeum vulgare ) cv. Aurora, oat ( Avena sativa ) cv. Urano-INIA, and mustard greens ( Brassica juncea ). At the second vineyard employed in the study, located in Huasco valley (trial II), the same crops and varieties were used in a rotation system with the incorporation of crop/goat manure mixtures or manure only at a rate of 10 Mg ha -1 . In both studies, two control treatments were included: a nontreated control and a chemical control in which ethoprop was applied at a rate of 7 kg ha -1 . The results from trial I indicated no significant differences between the cover crop rotation treatments and controls for Xiphinema index and for the other PPNs populations. In trial II, treatments 4 (manure) and 5 (manure and crop rotation) showed significantly lower values compared to treatment 2 (chemical control), with the highest X. index levels, but no differences from the control. No differences were detected for the other PPNs. Se realizo un estudio destinado a evaluar el efecto de cultivos de cobertura en rotacion durante tres anos, sobre el control de nematodos fitoparasitos en dos plantaciones de uva de mesa en una region semiarida del norte de Chile. La primera plantacion correspondio a un parronal en Copiapo (ensayo I), donde los cultivos utilizados en rotacion o en monocultivo fueron haba ( Vicia faba ) cv. Aguadulce; raps ( Brassica napus var. napus ) cv L-456; rabano forrajero ( B. rapa var. rapa ) cv. Barkant; cebada ( Hordeum vulgare ) cv. Aurora; avena ( Avena sativa ) cv. Urano-INIA y mostacilla ( Brassica juncea ). El segundo parronal utilizado para el estudio esta ubicado en la localidad de Huasco (ensayo II), donde se utilizaron los mismos cultivos y variedades, en un sistema de rotacion, incorporandose ademas una mezcla de cultivos sembrados sobre guano de cabra y guano de cabra solo, en dosis de 10 Mg ha -1 . En ambos estudios se incluyo un control absoluto y un control quimico, ethoprop, en una dosis de 7 kg ha -1 . Bajo las condiciones de este estudio, los resultados indican que en el ensayo I, no hubo diferencias significativas en los tratamientos basados en los cultivos de cobertura en rotacion y el control de poblaciones de Xiphinema index asi como en el resto de los fitoparasitos. En el ensayo II, solo se observan diferencias entre los tratamientos en base solo a guano y guano y rotaciones con el tratamiento quimico, siendo este ultimo el menos efectivo de todos los tratamientos. En el resto de los fitoparasitos, no hay diferencias despues de tres anos de evaluaciones.