Rosangela A. Silva

Ocorrência de Pratylenchus brachyurus e Meloidogyne incognita na cultura do algodoeiro no Estado do Mato Grosso

In a survey carried out in the state of Mato Grosso, Brazil, the lesion nematode, Pratylenchus brachyurus, and the root-knot nematode, Meloidogyne incognita, were found, respectively, in 94% and 3.7% of a total of 623 root and soil samples representing 21,793 ha. No visible aboveground symptoms in cotton (Gossypium hirsutum) plants infected by P. brachyurus were observed, except for typical root lesions. In contrast, plants with M. incognita usually exhibited pronounced symptoms of damage. The high frequency (94%) of P. brachyurus was unexpected and is of concern considering the fact that soybean (Glycine max) and corn (Zea mays), are both susceptible to this nematode and are used in crop rotation programs.

Avaliação de danos causados por Pratylenchus brachyurus em algodoeiro

Three greenhouse experiments and one field experiment were carried out to evaluate the damage caused by the lesion nematode Pratylenchus brachyurus on cotton (Gossypium hirsutum) plants. In the first experiment, three isolates of P. brachyurus (Pb20, Pb21, and Pb22) from different regions of Brazil were inoculated (12,000 nematodes/plant) in plantlets of cotton cv. Delta Opal and Fibermax 966. The initial populations of 3,000 and 12,000 nematodes/plant, and 12,000 and 30,000 nematodes/plant were tested in the second and third experiments, respectively, to evaluate the effect of isolate Pb20 on growth of cotton cv. Delta Opal. The results of experiments 1, 2 and 3 suggest that P. brachyurus is a mild pathogen for cotton, since nematode densities lower than 12,000 did not reduce plant growth. The experiment 4 was conducted in three cotton fields in in the State of Mato Grosso confirmed these results, since no correlation was observed between the root population of P. brachyurus and cotton yield.

Fauna de fitonematóides em áreas preservadas e cultivadas da floresta amazônica no Estado de Mato Grosso

The aim of this work was to study the diversity of the fauna of plant-parasitic nematodes in preserved areas of the Amazon forest, Mato Grosso state (MT), and to assess the effect of agricultural land use on plant-parasitic nematode communities. Soil and root samples were collected in each location in the late spring during the rainy season of 2005, in two areas of primary vegetation in Nova Maringa (Northwest) and Guaranta do Norte (North) and two adjacent areas planted with teak trees (Tectona grandis) and pasture (Brachiaria brizantha). Fourteen taxa of plant-parasitic nematodes were identified at species level: Discocriconemella degrissei, D. limitanea, Dolichodorus minor, Helicotylenchus erythrinae, H. pseudorobustus, Meloidogyne exigua, M. javanica, Mesocriconema ornata, Paratrichodorus minor, Pratylenchus loosi, P. zeae, Rotylenchus caudaphasmidius, Xiphinema ensiculiferum and X. luci (for the first report of this in Brazil) and five at genus level (Atalodera sp., Hemicriconemoides sp., Meloidogyne sp., Paratylenchus sp., and Trophotylenchulus sp). These taxa, mainly those from primary vegetation, belong to families with different parasitic behavior, probably due to great plant diversity in the Amazon forest. Comparison between the two preserved areas revealed low index of similarity, as a consequence of the endemic flora in the Amazon forest, and no similarity was observed between preserved native vegetation and adjacent cultivated areas, demonstrating the high influence of agricultural activity on the plant-parasitic nematode communities. There is evidence of recent introduction of plant-parasitic nematodes in these cultivated areas; therefore measures should be taken to prevent the loss of economic sustainability in Amazonian soils.

Patogenicidade de Pratylenchus coffeae em plântulas de cafeeiro cv. Mundo Novo

The pathogenicity of two isolates of Pratylenchus coffeae from Brazil on coffee (Coffea arabica) seedlings cv. Mundo Novo was evaluated in two greenhouse experiments. In the first, the effect of initial population densities (Pi = 0; 333; 1,000; 3,000 and 9,000 nematodes per plant) was studied using an isolate of P. coffeae from Marilia, SP, Brazil (host: coffee). The data were adjusted for the Seinhorst non linear model Y = m + (1-m).Z Pi-T. At the end of the experiment (270 days after inoculation), all plants infested with 9000 nematodes and most of those infested with 3000 were dead. Growth and photosynthesis were reduced, starting at 333 and 1000 nematodes, respectively. In the second experiment, two isolates of P. coffeae from Marilia and Rio de Janeiro (host: Aglaonema sp.) were compared with respect to their pathogenicity, inoculating Pi = 8,000 nematodes per plant in coffee seedlings with two pairs of true leaves. Although photosynthesis was similarly reduced by both isolates, the Marilia isolate caused intense darkening of the roots, leaf chlorosis and stronger reduction of root and shoot growth. In both experiments, multiplication factors of the isolates were low, indicating that coffee is a poor host for both isolates of P. coffeae. The differential pathogenicity observed in the second experiment supports previous results in the literature showing differences between these isolates concerning morphological features and host ranges.

Patogenicidade de Pratylenchus brachyurus e P. coffeae em quiabeiro

The effect of Pratylenchus brachyurus and P. coffeae on the growth of okra (Abelmoschus esculentus) was evaluated in a greenhouse experiment. The anatomical changes caused by P. brachyurus were studied under laboratory conditions. Okra was a good host for P. brachyurus and one isolate of P. coffeae (K5), but only the former decreased its growth. The other isolate of P. coffeae used (M2) did not multiply on nor damage okra, so this plant can be used to differentiate both isolates. In contrast to typical Pratylenchus spp. host plant relationships, P. brachyurus did not cause well-delimited root lesions, but large extensions of decayed tissues. Necrosis in okra roots was observed ten days after inoculation, but P. brachyurus was not found in the stele of infected roots 15 days after inoculation.

Additional data on Aorolaimus banoae (Rashid, Geraert & Sharma, 1987) from the Brazilian Atlantic forest

A population of the little-known species Aorolaimus banoae was collected in the municipality of Cananeia, Sao Paulo state, Brazil, in a remnant of the once far more extensive Brazilian Atlantic Forest. As the original description of this species was based on only three females and nine males, additional morphometric and morphological data, including SEM studies, are presented. It is suggested that A. banoae is a member of the original fauna associated with the coastal Atlantic forest.