Modeling the skin pattern of fishes

Complicated patterns showing various spatial scales have been obtained in the past by coupling Turing systems in such a way that the scales of the independent systems resonate. This produces superimposed patterns with different length scales. Here we propose a model consisting of two identical reaction-diffusion systems coupled together in such a way that one of them produces a simple Turing pattern of spots or stripes, and the other traveling wave fronts that eventually become stationary. The basic idea is to assume that one of the systems becomes fixed after some time and serves as a source of morphogens for the other system. This mechanism produces patterns very similar to the pigmentation patterns observed in different species of stingrays and other fishes. The biological mechanisms that support the realization of this model are discussed

Relative importance of inoculum sources of Guignardia citricarpa on the citrus black spot epidemic in Brazil.

Guignardia citricarpa, the causal agent of citrus black spot (CBS), forms ascospores and conidia in citrus leaf litter and only conidia on fruit and twigs. The objective of this work was to determine the relative importance of inoculum sources of ascospores and conidia in the progress of CBS under natural conditions in Brazil. A first experiment was conducted in an orchard subdivided into two areas. In one area, fallen leaves were removed and in the other area fallen leaves were maintained. In each area, two treatments were established: 1) CBS symptomatic mature fruit remained on the trees after the new fruit set, and 2) CBS symptomatic mature fruit were harvested before the new fruit set. A second experiment was carried out in a CBS-free experimental orchard where detached symptomatic fruit and leaf litter on the orchard floor and detached symptomatic fruit and dead twigs on the tree canopy were distributed to investigate the spread of disease. In the first experiment disease incidence was similar for all treatments in all years. However, in 2003, in the area without leaf litter (absence of the ascospores source), disease intensity and the rate of progress of disease incidence were higher when there was overlap of mature and young fruit. In the second experiment, only detached symptomatic fruit and dead twigs on the tree canopy were able to spread CBS in two years of the experiment. The distance of disease spread was less than 80 cm from these inoculum sources. The removal of fallen leaves was not sufficient to completely suppress the disease because of the presence of conidia in fruit and dead twigs. Therefore the reduction of conidia sources should be considered in CBS management in Brazil

Dinâmica temporal da população do ácaro Brevipalpus phoenicis e da leprose dos citros sob condições naturais de epidemia.

A densidade populacional do ácaro veto r de Citrus leprosis virus (CiLV), Brevipalpus phoenicis, num talhão, é o principal indicador para a tomada de decisão de medidas de controle da leprose dos citros. Há pouca informação sobre o crescimento da incidência de plantas com leprose dos citros isoladamente ou em conjunto com a população do ácaro. Este trabalho teve por objetivo caracterizar o progresso temporal da população de B. phoenicis e da incidência de leprose dos citros e a relação entre essas populações, sob condições naturais de epidemia. Dois talhões de laranja doce, cvs. Valência e Natal, foram monitorados de 2002 a 2004, em intervalos de 22 dias, em média. O crescimento da incidência da doença foi lento e estimativas da taxa de progresso da doença foram bastante baixas, variando de 0,0126 a 0,0448 para 'Valência' e de 0,0044 a 0,0525 para 'Natal'. A quantidade de inóculo inicial nos ramos cresceu significativamente de um ciclo para outro. Ao final do período, a incidência foi de 32% das plantas de 'Valência' e de 6,8% na cv. Natal. Apesar de não ser sistêmica, a leprose dos citros comporta-se como poliética com acúmulo de inóculo de ano para ano, especialmente nos ramos. A incidência não esteve correlacionada com a presença de ácaros na planta em levantamentos anteriores, mas apresentou correlação positiva significativa (P<O,OOI) com a própria incidência da doença registrada anteriormente. Isto indica que a presença de sintomas, e não somente a de ácaros, deve ser considerada em amostragens visando controle da doença. Palavras-chave adicionais: Citrus leprosis virus, incidência, análise temporal. ABSTRACT Temporal dynamics of populations of Brevipalpus phoenicis mite and citrus leprosis under natural epidemic conditions The density of mite Brevipalpus phoenicis, vector of Citrus leprosis virus (CiLV), is determinant for decisions on control measures for citrus leprosis. Little information on the progress of incidence of trees with citrus leprosis has been compiled, either separately or together with the mite population. This study aimed to characterize the temporal growth of B. phoenicis populations and leprosis incidence on citrus trees and the relationship with these populations, under natural conditions. Two sweet orange groves, one with 'Valencia' and the other with 'Natal', were monitored from 2002 to 2004, every 22 days. The increase in disease incidence was slow and estimates of disease growth rate were quite low, varying from 0.0126 to 0.0448 for 'Valencia' and from 0.0044 to 0.0525 for 'Natal'. The initial inoculurn quantity on the branches increased significantly from one cycle to the next. After the three years of observation, the incidence reached 32% in Valencia and 6.8% in Natal trees. Although not systemic, citrus leprosis has a polyetic performance, building up inoculurn year after year, especially on the branches. The incidence was not correlated with the mite density on the trees in previous data collections, but presented a significant positive correlation (P<O.OO1) with the disease incidence reported earlier. This indicates that the presence of symptoms, rather than only the mites, must be taken into consideration in sampling aiming at disease control

Critério para classificação de risco de regiões do Alerta Fitossanitário do psilídeo-dos-citros no cinturão citrícola de São Paulo e Triângulo/Sudoeste Mineiro.

Resumo O monitoramento populacional de Diaphorina citri, o psilídeo--dos-citros, é essencial para o manejo regional deste inseto vetor da bactéria Candidatus Liberibacter asiaticus associada ao Huanglongbing (HLB), especialmente no cinturão citrícola de São Paulo e Triângulo/Sudoeste Mineiro, onde há a maior concentração populacional de D. citri e de plantas com sintomas da doença. Nesse sentido, o Fundo de Defesa da Citricultura (Fundecitrus) estabeleceu em 2013 o Alerta Fitossanitário para monitorar, por meio de armadilhas adesivas amarelas, a população do psilídeo em diferentes regiões do Estado de São Paulo e do Triângulo/Sudoeste Mineiro. Atualmente, o Alerta monitora 15 regiões e, a cada quinzena, gera dados de abundância (psilídeos/armadilha), ocupação (% de armadilhas com captura de psilídeos) e estádio de brotação predominante (V1 a V7) das plantas de citros. O presente trabalho avaliou séries temporais de abundância, de ocupação de psilídeos e de brotação dos citros para estabelecer critérios matemáticos para classificar as regiões quanto ao risco de ocorrência de psilídeos. Análises de correlação de séries de 2014 a 2016 indicaram que abundância e ocupação de psilídeos são variáveis altamente correlacionadas 1 Engenheiro-agrônomo, doutor em Ciências (Fitopatologia), analista da Embrapa Mandioca e Fruticultura, Campinas, SP.² Engenheiro-agrônomo, doutor em Agronomia (Fitopatologia), pesquisador da Embrapa Mandioca e Fruticultura, Cruz das Almas, BA. 3 Fundecitrus, Araraquara, São Paulo. 4 Engenheiro-agrônomo, doutor em Ciências (Fitotecnia), pesquisador da Embrapa Mandioca e Fruticultura, Araraquara, SP 6 BOLETIM DE PESQUISA E DESENVOLVIMENTO 144 (R2 = 0,88), permitindo o uso de dados da ocupação de psilídeos na otimização do sistema, por representar menor chance de erro, uma vez que se baseiam apenas em presença e ausência de D. citri nas armadilhas. Com os dados de ocupação, foram geradas medianas (M) e seus desvios absolutos médios para obtenção de limiares inferiores (LIM) e superiores (LSM) da mediana e definir o risco de cada região em relação ao próprio histórico de ocupação e em relação ao histórico de todas as regiões. Estabelecidos os critérios, quatro riscos foram definidos: baixo (verde) para as regiões que apresentam ocupação atual abaixo do LIM, médio (amarelo) para as regiões que presentam ocupação atual entre o LIM e a M, alto (alaranjado) para as regiões que apresentam ocupação atual entre a M e o LSM e extremo (vermelho) para as regiões que apresentam ocupação atual acima do LSM. Os mapas têm facilitado o monitoramento da população de psilídeo em cada região do cinturão citrícola e os riscos calculados servirão para a definição de critérios de emissão dos alertas de pulverização regional

Molecular epidemiology of Citrus Leprosis Virus C: a new viral lineage and phylodynamic of the main viral subpopulations in the Americas.

Despite the importance of viral strains/variants as agents of emerging diseases, genetic and evolutionary processes affecting their ecology are not fully understood. To get insight into this topic, we assessed the population and spatial dynamic parameters of citrus leprosis virus C (CiLV-C, genus Cilevirus, family Kitaviridae). CiLV-C is the etiological agent of citrus leprosis disease, a non-systemic infection considered the main viral disorder affecting citrus orchards in Brazil. Overall, we obtained 18 complete or near-complete viral genomes, 123 complete nucleotide sequences of the open reading frame (ORF) encoding the putative coat protein, and 204 partial nucleotide sequences of the ORF encoding the movement protein, from 430 infected Citrus spp. samples collected between 1932 and 2020. A thorough examination of the collected dataset suggested that the CiLV-C population consists of the major lineages CRD and SJP, unevenly distributed, plus a third one called ASU identified in this work, which is represented by a single isolate found in an herbarium sample collected in Asuncion, Paraguay, in 1937. Viruses from the three lineages share about 85% nucleotide sequence identity and show signs of inter-clade recombination events. Members of the lineage CRD were identified both in commercial and non-commercial citrus orchards. However, those of the lineages SJP were exclusively detected in samples collected in the citrus belt of São Paulo and Minas Gerais, the leading Brazilian citrus production region, after 2015. The most recent common ancestor of viruses of the three lineages dates back to, at least, ?1500 years ago. Since citrus plants were introduced in the Americas by the Portuguese around the 1520s, the Bayesian phylodynamic analysis suggested that the ancestors of the main CiLV-C lineages likely originated in contact with native vegetation of South America. The intensive expansion of CRD and SJP lineages in Brazil started probably linked to the beginning of the local citrus industry. The high prevalence of CiLV-C in the citrus belt of Brazil likely ensues from the intensive connectivity between orchards, which represents a potential risk toward pathogen saturation across the region