Maria de Fátima Silva Muniz

Reaction of coffee genotypes to different populations of Meloidogyne spp.: detection of a naturally virulent M. exigua population

The reaction of seven genotypes of Coffea arabica to 10 Meloidogyne spp. populations collected mainly from coffee plantations in Brazil and Costa Rica was evaluated under greenhouse conditions. The inoculum consisted of 10,000 eggs per plant. Evaluations were done 8 months after inoculations considering the root fresh weight, gall and egg mass indices, number of eggs per gram of root and reproduction factor (RF). The cultivars Obata IAC 1669-20, Sarchimor IAC 4361 and Tupi Amarelo IAC 5111 exhibited susceptibility to the four Brazilian M. exigua populations tested. However, cv. Tupi Vermelho IAC 1669-33 revealed resistance (RF value of 0.7) to the M. exigua population from Lavras, Minas Gerais State, Brazil. A population of M. exigua from Bom Jesus de Itabapoana, Rio de Janeiro State, Brazil, was highly virulent on cv. IAPAR 59 (RF= 165.7), bearing resistance gene Mex-1, and was also virulent on genotype Paraiso (H 419-5-4-5-2) (RF=396.2). A Meloidogyne sp. population on coffee from Garca, Sao Paulo State, Brazil, reproduced at low rates (RF ranging from 0.1 to 3.9) on all genotypes. All tested cultivars were susceptible to M. incognita and M. paranaensis. M. mayaguensis of guava from Parana State, Brazil, reproduced at low rates in all coffee genotypes; however, another population of coffee, from Costa Rica, was more aggressive and showed RF value that ranged from 0.8 to 12.4. Results of this study point for the first time to the ability of a naturally occurring M. exigua population to overcome the resistance conferred by the Mex-1 gene.

Intensidade da ferrugem asiàtica (Phakopsora pachyrhizi H. Sydow & P. Sydow) da soja [Glycine max (L.) Merr.] nas cultivares Conquista, Savana e Suprema sob diferentes temperaturas e periodos de molhamento foliar

The asian rust (Phakopsora pachyrhizi Sydow) which has been reported in areas of tropical and subtropical climates around the world, causes significant soybean [Glycine max (L.) Merr.] yield reduction. The disease progress is influenced by biotic factors as interaction pathogen-host and abiotic factors of the environment. The objective of this work was to study the effects of temperature and leaf wetness period in the asian rust progress in the cultivars Conquista, Savana and Suprema. The experiment was conducted at the Department of Plant Pathology at Federal University of Lavras, in growth chamber at temperatures of 15, 20, 25 and 30 °C and leaf wetness periods of 0,6, 12, 18 and 24 hours. The plants were inoculated by spraying a suspension of inoculum of P. pachyrhizi at concentration of 104 urediniospores.mL-1. Severity and incidence data were integrated by the area under disease progress curve for severity (AUDPCS) and incidence (AUDPCI). Non-linear regression models were adjusted for the disease severity (AUDPCS) and incidence (AUDPCI). Volume under the response surface of temperature and leaf wetness was calculated for incidence (VURSI) and severity (VURSS) to detect differences between cultivars. Higher soybean rust intensity occurred with leaf wetness above 15 hours and temperatures close to 20 oC, for the three tested cultivars. Temperatures above 30 oC and below 15 oC reduced the disease progress. Disease intensity was reduced in leaf wetness below 6 hours. All cultivars were susceptible, but higher VURSI and VURSS occurred in Conquista cultivar, followed by Savana and Suprema cultivars. Disease intensity was not statistically different between Savana and Suprema cultivars. Temperature and leaf wetness were different among cultivars for AUDPCI.

Caracterização de isolados de Phytophthora drechsleri, agente causal da podridão mole de raízes de mandioca

Nine Phytophthora isolates from cassava (Manihot esculenta) were characterized based on morphology and morphometry of propagative structures, growth at 10, 15, 20, 25, 30 and 35 oC, and by evaluating its pathogenicity. Sporangia produced on nonsterile soil extract were ovoid, nonpapillate and persistent, formed in a sympodium or unbranched sporangiophores, 24.6 to 57.4 µm long x 14.8 to 37.7 µm wide, and length-breadth ratio was 1.0 - 2.6. Chlamydospores were rarely observed. Oospores produced in single spore culture on V8 agar medium were aplerotic, and 13.1 to 34.4 µm in diameter. Antheridia were amphigynous, measuring 8.2 - 24.6 µ x 8.2 - 19.7 µ ; oogonia ranged from 19.7 to 41.0 µm in diameter. Culture growth was greatest at 25 oC in V8 agar medium. The isolates that were pathogenic to plants and detached roots of cassava were identified as Phytophthora drechsleri Tucker.

Caracterização de isolados de Phytophthora patogênicos a Citrus sinensis no Estado de Alagoas

Nine Phytophthora spp. isolates from the rhizosphere of infected orange (Citrus sinensis) plants in Alagoas were characterized based on colony morphology, morphology and morphometry as well as reproductive structures, and cardinal growth temperatures. All cultures were heterothallic, with papillate, ovoid or subspherical sporangia measuring 24.6 - 78.7 µm long x 16.4 - 49.2 µm wide, average 49.1 x 33.3 µm. The length-breadth ratio was 1.1 - 2.3, average 1.5. Chlamydospores were mostly terminal, 13.1 - 45.9 µm in diameter, average 27.3 µm. Oogonia were globose, 14.8 - 34.4 µm in diameter, average 26.4 µm containing aplerotic oospores 11.5 - 29.5 µm in diameter, average 22.7 µm and amphigynous antheridia 6.6 - 16.7 µm x 8.2 - 16.7 µm (average 10.6 µm x 12.0 µm). The greatest mycelial growth was observed at 25-30 oC in modified carrot agar medium. All isolates grew at 35 oC and were pathogenic to lemon (Citrus limonia) cv. Cravo seedlings and ripened fruits of orange (C. sinensis) cv. Pera. The isolates were identified as Phytophthora nicotianae (= P. parasitica) of the A1 mating type.

Correlations among methods to estimate lipid reserves of second-stage juveniles and its relationships with infectivity and reproduction of Meloidogyne incognita

We studied the correlations between the processes used to estimate the body lipid of second-stage juveniles (J2) of Meloidogyne exigua and M. incognita, and the infectivity and reproduction of the M. incognita J2. The lipids were quantified by image analysis of the area stained red with Oil Red O dye and by the dark area of the non-stained J2. The content of neutral lipids of stained J2 of M. exigua and M. incognita correlated positively to the lipid index, body mass lipid and the dark area of J2. The period of incubation of J2 decreased the neutral lipids content and correlated significantly with the reductions of infectivity and reproduction. The period of 6 days incubation of M. incognita resulted in losses of more than 50% of the neutral lipid content, representing the threshold period for infectivity on tomato, whereas, for reproduction, the threshold was 3 days incubation.

Caracterização de Fusarium solani f. sp. piperis, produção de fitotoxina e incidência da fusariose no norte de Minas Gerais

Root rot caused by Fusarium solani f. sp. piperis is one of the major diseases affecting black pepper in the north of Minas Gerais State, Brazil. The aims of this study were to quantify the disease incidence in the main black pepper growing areas of Northern Minas Gerais State, to identify the causal agent of root rot, to test the pathogenicity of isolates and to evaluate the effect of Fusariumsolani f. sp. piperis filtrates on both detached leaves from black pepper and Trichoderma asperellum. The incidence of root rot was randomly evaluated in 1,000 or 500 plants at zigzag. The reaction of black pepper cv. Cingapura was evaluated against two fungal filtrates (FPC1 and FPB2), and the isolate FPB2 was used to evaluate the reaction of cultivars Cingapura and Guajarina. Another experiment was performed to study the influence of FPB2 filtrate dilutions on the leaves of cultivar Cingapura. To evaluate the effect of toxins of the filtrates on the Mycelial Growth Index (MGI) of T. asperellum, a trial was carried out with different concentrations and two filtrates. The disease incidence in the sampled areas was 31.5 to 100% for the municipalities of Bocaiuva and Montes Claros, respectively. Based on the sexual compatibility test, the isolates were identified as F. solani f. sp. piperis. Nine isolates were pathogenic when inoculated in seedlings of black pepper at four-month development. FPB2 filtrate produced the greatest severity (average of 93.6% necrotic leaf area), compared to FPC1 isolate (5.8%). The cultivar Cingapura was more sensitive to the action of the filtrate. The FPB2 filtrate dilution reduced the percentage of diseased leaf area. Furthermore, the increase in the concentrations of FPC1 filtrate contributed to increase the MGI of T. asperellum, whereas FPB2 filtrate showed opposite effect, reducing the MGI of this antagonistic fungus.

Podridão de frutos de melancia causada por Sclerotium rolfsii no estado de Alagoas

A new fruit rot disease caused by Sclerotium rolfsii on watermelon (Citrullus lanatus) was observed in the State of Alagoas. The pathogenicity of the fungus was confirmed by artificial inoculations.This is the first report of S. rolfsii causing fruit rot in watermelon in Northeast of Brazil.

FIRST REPORT OF Phytophthora nicotianae CAUSING ROOT ROT OF SOURSOP IN NORTHEASTERN BRAZIL

In 2013, soursop trees showing symptoms of root rot were observed in a field in Maceio, state of Alagoas, Brazil. It was isolated Phytophthora sp. which pathogenicity was confirmed in the host seedlings. Morphological and physiological characteristics in carrot-agar modified medium were consistent with Phytophthora nicotianae description. The PCR sequences products obtained with ITS1/ITS4 primers were compared to sequences of ribosomal DNA of Phytophthora species from the GenBank database observing high identity with other P. nicotianae isolates. A phylogenetic tree was performed to compare the isolate with other sequences of P. nicotianae, which clustering has been verified with 99% of bootstrap, confirming the morphophysiological studies. This is the first report of this pathogen on annonaceous plants in the Northeastern Brazil.