Waldir Cintra de Jesus Junior

Escalas diagramáticas para avaliação da severidade do cancro cítrico

Diagrammatic scales are important tools for disease severity assessment. Four diagrammatic scales for isolated small (SL), medium (ML), and large (LL) lesions and for symptoms associated with the leaf miner injuries (LM), were developed to standardize the severity assessments of citrus canker caused by Xanthomonas axonopodis pv. citri on leaves of citrus (Citrus sinensis). Each scale has eight levels of disease severity (percentage of diseased leaf area): 0.2 to 16% for SL; 0.6 to 25% for ML; 1.8 to 30% for LL and 0.5 to 30% for LM. Initially, six persons evaluated the severity of 447 digitalized images of symptomatic leaves using the four scales. Training was carried out and later on, disease severity was assessed in 115 new images. Linear regressions between actual and estimated disease severity were calculated by each person. All the scales were validated together considering the accuracy, precision and reproducibility of the evaluations. The scales were adequate to quantify the severity of citrus canker on leaves.

Análise da dinâmica e estrutura de focos da morte súbita dos citros

Citrus Sudden Death (CSD) is a new and destructive disease that affects sweet oranges (Citrus sinensis) and some mandarins (C. reticulata) grafted on Rangpur lime (C. limonia). Its etiology and transmission mechanisms are still unknown, epidemiologic study of the disease was recently initiated. Dynamics and structure analysis of foci technique (DSAF) was used to characterize CSD dissemination on 166 spatial distribution maps of CSD symptomatic trees from 51 blocks of northern Sao Paulo State and the southern of Triângulo Mineiro. According to DSAF, the CSD epidemic begins with unitary foci randomly distributed in the block. At an incidence up to 2%, most of the foci were composed by an unique plant. Later, the disease progresses more by increasing the number of foci than by increasing the size of the focus. This was indicated by an increase in the number of foci up to 18% of disease incidence and by the reduced number of plants per focus (less than four plants per focus at 20% of incidence). In most cases (71.5%), foci expanded more within-row than across-row. Compactness reduction of foci with increase in CSD incidence suggests that larger foci are less compact and, thus, that disease dissemination does not occur in a homogenous and continuous way around the first affected tree. The observed patterns are similar to those of diseases caused by an infectious agent, which is transmitted by a vector.

Injuries caused by citrus leafminer (Phyllocnistis citrella) exacerbate citrus canker (Xanthomonas axonopodis pv. citri) infection

After the introduction of citrus leafminer in Sao Paulo State, an increase in the number of new plants infected with citrus canker has been observed. The interaction between these two organisms is known, but there is no information about how the leafminer damage intensifies citrus canker incidence and severity. The objectives of this paper were to evaluate the effects of leafminer damage in citrus canker infection and its influence on the monocyclic components of the disease on Citrus limonia. Higher incidence of diseased plants, AUDPC (area under the disease progress curve), disease severity and shorter incubation periods were observed in plants inoculated after insect infestation. These factors explain the association found between the higher citrus canker intensity and the damage caused by the insect and show, albeit partially, the consequences of these changes in the spread of the pathogen under natural conditions of infection.

Citrus Sudden Death Is Transmitted by Graft-Inoculation and Natural Transmission Is Prevented by Individual Insect-Proof Cages

Citrus sudden death (CSD) transmission was studied by graft-inoculation and under natural conditions. Young sweet orange trees on Rangpur rootstock were used as indicator plants. They were examined regularly for one or two characteristic markers of CSD: (i) presence of a yellow-stained layer of thickened bark on the Rangpur rootstock, and (ii) infection with the CSD-associated marafivirus. Based on these two markers, transmission of CSD was obtained, not only when budwood for graft-inoculation was taken from symptomatic, sweet orange trees on Rangpur, but also when the budwood sources were asymptomatic sweet orange trees on Cleopatra mandarin, indicating that the latter trees are symptomless carriers of the CSD agent. For natural transmission, 80 young indicator plants were planted within a citrus plot severely affected by CSD. Individual insect-proof cages were built around 40 indicator plants, and the other 40 indicator plants remained uncaged. Only two of the 40 caged indicator plants were affected by CSD, whereas 17 uncaged indicator plants showed CSD symptoms and were infected with the marafivirus. An additional 12 uncaged indicator plants became severely affected with citrus variegated chlorosis and were removed. These results strongly suggest that under natural conditions, CSD is transmitted by an aerial vector, such as an insect, and that the cages protected the trees against infection by the vector.

First report of the electron micrograph of "Candidatus Liberibacter" particles on citrus in Brazil

“Candidatus Liberibacter” is the causal agent of the Huanglongbing (HLB) (= greening), which is considered one of the most important and destructive disease of Citrus spp. in the world. Symptoms similar to HLB were observed in Brazil since March 2004. It is normally confined to some parts of the plant; however it can occurs throughout the tree. Affected sectors show a variety of chlorotic leaf symptoms, poor growth and bear abnormal, distorted and small fruits. A blotchy mottle is the most important leaf symptom for diagnosis. Leaf samples were collected from symptomatic and asymptomatic trees and processed by conventional techniques to be analyzed by electron microscopy. Liberibacter-like particles were found in very low frequency within the sieve tubes of veinlet of symptomatic leaves but not in symptomless leaves (Figure 1A). At higher magnification the envelope characteristic of the “Candidatus Liberibacter” was clearly visible (Figure 1B). The corpuscles were surrounded by two triple-layered membranes, an inner (cytoplasmic) membrane and an outer membrane. Depending upon the plane of the section bacterial all appeared with round to elongated elliptic bacilliform shape. Morphologically, these corpuscles were similar to the presumed “Candidatus Liberibacter” found in sieve tubes of plants affected by HLB and greening (Garnier et al., IOCV Conference 9:115-124. 1984). Two research groups (ColettaFilho et al., Plant dis. 88:1382. 2004; Teixeira et al. Plant dis. 89:107. 2005) detected the “Candidatus Liberibacter” by molecular approach. There is a prevalence of a novel form, designated “Candidatus Liberibacter americanus” (Teixeira et al. Plant dis. 89:107. 2005). The present observation offers visual evidence to the molecular detection and identification of “Candidatus Liberibacter” as the causal agent of HLB-like disease affecting citrus in Brazil. FIG. 1 A Liberibacter-like particles in sieve tube on Citrus spp. in Sao Paulo State, Brazil (Bar = 0,6μm) and B High magnification of the particles showing the cell membrane (inner) and the outer cell wall (arrows) (Bar = 0,09μm).

Aplicação de silicato de potássio e crescimento foliar da cana-de-açúcar - DOI:10.5039/agraria.v6i1a902

Avaliou-se o efeito da aplicacao de doses crescentes de silicato de potassio sobre o crescimento foliar da cana-de-acucar em condicoes controladas. O experimento foi conduzido em delineamento inteiramente casualizado, com seis repeticoes e seis tratamentos constituidos por doses de silicato de potassio (0, 40, 80, 160, 200 e 240 g L -1 ). A aplicacao foliar de silicato de potassio influenciou de forma quadratica o crescimento foliar da cana-de-acucar. O maximo crescimento de area foliar e producao de materia seca das folhas foram obtidos com as doses de 66,6 e 40,0 g L -1 de silicato de potassio, respectivamente. Na dose de 51,0 g L -1 de silicato de potassio, obteve-se o maximo valor estimado da razao de area foliar. O teor de potassio (K) presente na materia seca da folha +1 respondeu de forma linear as doses de silicato de potassio. Entretanto, o elevado teor de K em funcao da aplicacao de altas doses de silicato de potassio reduziu o crescimento foliar da cana-de-acucar. Portanto, para a obtencao do maximo crescimento foliar da cana-de-acucar, a dose de silicato de potassio a ser aplicada deve estar compreendida entre 40,0 e 66,6 g L -1 .

Determinação das condições climáticas que favorecem o desenvolvimento da ferrugem e da mancha angular do feijoeiro

This study was carried out to determine the effect of temperature and foliage wetness on the development of rust and angular leaf spot on common bean (Phaseolus vulgaris). Three field experiments were performed during three different growing seasons: from October to December 1998 (spring); May to August 1999 (winter) and from February to May (autumn). All trials were set in completely randomized block designs with three replicates and two treatments. The treatments were: 1) Inoculation with Uromyces appendiculatus and 2) Inoculation with Phaeoisariopsis griseola. the weather conditions prevalent in each of the seasons determined the maximum disease levels of each disease. Temperatures around 16 °C that prevailed during the winter favored foliage wetness and was beneficial for rust occurrence leading to higher values of maximum rust severity (Ymax=1.3) and growth rates (0.09, 0.04 and 0.07 on 34, 55 and 62 days, respectively). During spring and autumn conditions angular leaf spot was more intense and the values of maximum rust severity were equal to 2.6 and 3.5, respectively. Spring growth rates were 0.06, 0.02 and 0.15 on 46, 60 and 67 days, respectively, while autumn conditions led to growth rates of 0.13 and 0.38 on 51 and 58 days, respectively. Based on these results it can be concluded that winter conditions were more favorable for rust epidemics, while spring and autumn conditions were more favorable for angular leaf spot epidemics.