José F. da Silva

A novel, highly divergent ssDNA virus identified in Brazil infecting apple, pear and grapevine

Fruit trees of temperate and tropical climates are of great economical importance worldwide and several viruses have been reported affecting their productivity and longevity. Fruit trees of different Brazilian regions displaying virus-like symptoms were evaluated for infection by circular DNA viruses. Seventy-four fruit trees were sampled and a novel, highly divergent, monopartite circular ssDNA virus was cloned from apple, pear and grapevine trees. Forty-five complete viral genomes were sequenced, with a size of approx. 3.4 kb and organized into five ORFs. Deduced amino acid sequences showed identities in the range of 38% with unclassified circular ssDNA viruses, nanoviruses and alphasatellites (putative Replication-associated protein, Rep), and begomo-, curto- and mastreviruses (putative coat protein, CP, and movement protein, MP). A large intergenic region contains a short palindromic sequence capable of forming a hairpin-like structure with the loop sequence TAGTATTAC, identical to the conserved nonanucleotide of circoviruses, nanoviruses and alphasatellites. Recombination events were not detected and phylogenetic analysis showed a relationship with circo-, nano- and geminiviruses. PCR confirmed the presence of this novel ssDNA virus in field plants. Infectivity tests using the cloned viral genome confirmed its ability to infect apple and pear tree seedlings, but not Nicotiana benthamiana. The name Temperate fruit decay-associated virus (TFDaV) is proposed for this novel virus.

The Hemileia vastatrix effector HvEC‐016 suppresses bacterial blight symptoms in coffee genotypes with the SH1 rust resistance gene

Summary A number of genes that confer resistance to coffee leaf rust (SH1–SH9) have been identified within the genus Coffea, but despite many years of research on this pathosystem, the complementary avirulence genes of Hemileia vastatrix have not been reported. After identification of H. vastatrix effector candidate genes (HvECs) expressed at different stages of its lifecycle, we established an assay to characterize HvEC proteins by delivering them into coffee cells via the type‐three secretion system (T3SS) of Pseudomonas syringae pv. garcae (Psgc). Employing a calmodulin‐dependent adenylate cyclase assay, we demonstrate that Psgc recognizes a heterologous P. syringae T3SS secretion signal which enables us to translocate HvECs into the cytoplasm of coffee cells. Using this Psgc‐adapted effector detector vector (EDV) system, we found that HvEC‐016 suppresses the growth of Psgc on coffee genotypes with the SH1 resistance gene. Suppression of bacterial blight symptoms in SH1 plants was associated with reduced bacterial multiplication. By contrast, HvEC‐016 enhanced bacterial multiplication in SH1‐lacking plants. Our findings suggest that HvEC‐016 may be recognized by the plant immune system in a SH1‐dependent manner. Thus, our experimental approach is an effective tool for the characterization of effector/avirulence proteins of this important pathogen.

Sugar metabolism and developmental stages of rubber tree (Hevea brasiliensis L.) seeds

Changes in the concentration of sugars and sucrose metabolism enzymes can characterize the developmental stages of a seed. In recalcitrant species such as Hevea brasiliensis L., little is known about these changes. We aimed to evaluate the three main stages of development of rubber tree seedsxa0-xa0histodifferentiation, cell elongation and accumulation of reserves. The activities of acid and neutral invertases (E.C. 3.2.1.26) and sucrose synthase (EC 2.4.1.13), and the concentrations of reducing sugars (RS), total soluble sugars (TSS) and sucrose (Suc) were determined concomitantly with the histochemical and anatomical evaluation of seed structure. Histodifferentiation in rubber tree seeds occurs up to 75u2009days after anthesis (DAA). The concentration of RS is high and of Suc is low during seed histodifferentiation, which occurs along with a visible increase in the number of cell divisions. After that period, there is an increase in the concentration of Suc (mg g-1 ) and in the number and size of starch granules, and a decrease in the concentration of RS (mg g-1 ). At that point, cell elongation occurs. At 135 DAA, there is an inversion in the concentration of these two sugars and an increase in reserve accumulation. Thus, in seeds of the evaluated clone, the period up to 75 DAA is characterized as the histodifferentiation stage, while from that time up to 120 DAA the cell elongation stage takes place. The final stage of seed maturation and reserve accumulation begins at 135 DAA, and the seed, including the embryo, is completely formed at 175 DAA.

Controle químico de plantas daninhas em cultivos sucessivos de milho e feijão

This trial was carried out at the Sooretama Experimental Farm, in Linhares, State of Espirito Santo, Brazil, in order to evaluate the efficiency of herbicides on weed control in sucessive crops of corn and beans. The comercial mixture of atrazine plus metolachlor was more efficient to control weeds in corn (Zea mays) crop than atrazine and metolachlor applied alone. The comercial rate of 8,04 l ha-1 led to the highest yield of corn (7004,92 kg ha-1). The tank mixture of fomesafen plus sethoxydim was more efficient to control weeds in the field bean (Phaseolus vulgaris) crop than linuron and metolachlor applied alone. The tank mixture of 0,74 l ha-1 of fomesafen plus 0,74 l ha-1 of sethoxydim showed the highest yield of bean (1454,05 kg ha-1).

Eficiência dos herbicidas oxadiazil, oxadiazon, oxyfluorfen e Imazapyr sobre a cultura de pinus

The selectivity of some herbicides were evaluated on Pinus caribaea var. Hondurensis seedlings as well as these herbicide efficiencies in the weed control. When the tubule-produced seedlings were 20 cm height they were transplanted at 2,0 m x 2,0 m spacings in fourrows plots with 10,0 m length. The treatments with oxadiazil (600; 800 and 1000 g ha-1), oxadiazon (1140; 1520 and 1900 g ha-1), oxyfluorfen (720 g ha-1), imazpyr (250 g ha-1) and controls (weeded and without weeding) were disposed in a randomized block design with four replications. Seven days after transplantation, the herbicides were applied using a CO2 pressured costal sprayer which was calibrated to provide a 200 L ha-1 solution. The main weeds causing a larger infestation were Brachiaria plantaginea and Ipomoea grandifolia while Galinsoga parviflora and Bidens pilosa were responsible for a minor one. The oxadiazil showed an excellent control on B. plantaginea, I. grandifolia and G. parviflora; although not being efficient to control Bidens pilosa, it provided a superior control to the one observed in oxadiazon. Oxadiazon showed efficiency until 45 days after the treatment for B. plantaginea, G. parviflora and until 90 days for I. grandifolia as well. Either oxyfluorfen or imazapyr showed an excellent weed control. Among the herbicides evaluated, only imazapyr must not be recommended for on the top application for Pinus caribeae var. Hondurensis, due to the toxicity provoked.

Efeito do 2,4-D e do glifosate no controle da parte aérea e dos rizomas da losna

It is difficult to obtain an efficient mechanical and chemical control of wormwood (Artemisia verlotorum) because this weed has a great capacity to sprout and is tolerant to most herbicides. The rate of 1,662 kg/ha of 2,4-D reduced the number of living plants from 34 to 6 after 30 days application. However, glyphosate (0,856 kg/ha) reduced the number of living plants from 27 to 10 in field conditions. After 60 days application, the number of living plants was reduced from 34 to 18 by 0,811 kg/ha of glyphosate. However, no differences were found for application rates of 2,4-D at the same conditions. None of treatments showed satisfactory performance in relation to wormwood after 90 days application in field conditions. In greenhouse, glyphosate treatments reduced rhizome sprout, though, no differences were found for application rates of 2,4-D. The rates of 1,0 and 0,865 kg/ha of glyphosate resulted in lower dry matter weigth of aerial part of the wormwood and its rhizomes, respectively. Leaf area was reduced with glyphosate (0,983 kg/ha) at the same conditions.

Controle químico da losna em plantio direto de trigo

It is difficult to obtain an efficient mechanical and chemical control of wormwood (Artemisia verlotorum) because this weed has a great capacity to sprout and is tolerant to most herbicides. Natural areas infested with wormwood were treated with glyphosate and 2,4-D. Glyphosate was more efficient than 2,4-D on wormwood control. The application of 2,4-D did not cause significant differences on wormwood control 90 days after treatment. However, the glyphosate had prolonged effect, decreasing the number of living plants until 90 days after its application. Intermediary rates were more effecient than higher rates on wormwood control. Higher values of all studied characteristics of wheat crop were obtained with intermediary rates of both herbicides. Higher yield of wheat (3787 kg/ha) were obtained when 0,721 kg/ha of glyphosate associated with 1,152 kg/ha of 2,4-D was applied.

Efeitos do controle de plantas daninhas, com herbicidas, na produção e qualidade fisiológica de sementes de amendoim (Arachis hypogaea L.)

Com o objetivo de avaliar o efeito de herbicidas no controle de plantas daninhas, na producao e na qualidade fisiologica das sementes de amendoim (Arachis hypogaea L. Tatu), foi instalado um experimento no campo, em solo Podzolico Vermelho-Amarelo Câmbico, fase terraco, com 2,8% de materia orgânica e textura argilosa. Usaram-se os tratamentos: testemunha com capina, testemunha sem capina, trifuralin a 0,58 kg do i.a./ha; vernolate a 3,6 kg do i.a./ha; nitralin a 0,75 kg do i.a./ha; fluorodifen a 0,9 kg do i.a./ha e pendimethalin a 1,5 kg do i.a./ha. Avaliaram-se a populacao inicial, a producao de sementes, producao de casca, o amendoim com casca, e o numero de plantas daninhas. Realizaram-se tambem, testes de avaliacao da qualidade fisiologica das sementes de amendoim, os quais foram constituidos pelo teste-padrao de germinacao apos 20, 40 e 80 horas de permanencia das sementes na câmara de envelhecimento precoce, que estava regulada para funcionar a 42°± 3°C e 95% de umidade relativa. No campo observou-se predominância de trevo (Oxalis sp), picao-branco (Galinsoga parviflora Cav.) e tiririca (Cyperus rotundus L.). Trifuralin, fluorodifen e pendimenthalin fo-ram os herbicidas da maior eficiencia no controle do trevo, enquanto para tiririca o tratamento com nitralin nao diferiu da testemunha capinada, e para o picao-branco, o tratamento com pendimethalin controlou totalmente esta planta daninha. Para a producao de sementes de amendoim, nao houve diferencas entre os tratamentos. A producao de casca e a producao de amendoim com casca, o tratamento com fluorodifen diferiu apenas da testemunha sem capina, suplantando-a. A ocorrencia de patogenos nas sementes da testemunha sem capina, e o herbicida nitralin prejudicaram a germinacao das sementes. O tratamento das sementes de amendoim na câmara de envelhecimento precoce, pelo periodo de 20 horas, promoveu nas sement es do tratamento testemunha sem capina e do tratamento com trifl uralin, deteriorizacao precoce. Para o periodo de permanencia de 40 horas, na câmara de envelhecimento precoce os tratamentos testemunha com capina e fluorodifen nao foram envelhecidos precocemente.