Spatial pattern of black spot incidence within citrus trees related to disease severity and pathogen dispersal

Abstract

Guignardia citricarpa , the causal agent of citrus black spot, forms airborne ascospores on decomposing citrus leaves and water-spread conidia on fruits, leaves and twigs. The spatial pattern of diseased fruit in citrus tree canopies was used to assess the importance of ascospores and conidia in citrus black spot epidemics in São Paulo State, Brazil. The aggregation of diseased fruit in the citrus tree canopy was quantified by the binomial dispersion index ( D ) and the binary form of Taylor's Power Law for 303 trees in six groves. D was significantly greater than 1 in 251 trees. The intercept of the regression line of Taylor's Power Law was significantly greater than 0 and the slope was not different from 1, implying that diseased fruit was aggregated in the canopy independent of disease incidence. Disease incidence ( p ) and severity ( S ) were assessed in 2875 citrus trees. The incidence-severity relationship was described ( R 2 = 88·7%) by the model ln( S ) = ln( a ) + b CLL( p ) where CLL = complementary log-log transformation. The high severity at low incidence observed in many cases is also indicative of low distance spread of G. citricarpa spores. For the same level of disease incidence, some trees had most of the diseased fruit with many lesions and high disease severity, whereas other trees had most of the fruit with few lesions and low disease severity. Aggregation of diseased fruit in the trees suggests that splash-dispersed conidia have an important role in increasing the disease in citrus trees in Brazil.

Efeito do manejo cultural e químico na incidência e severidade da mancha-preta dos citros

“…Em áreas onde o patógeno se encontra estabelecido há mais tempo, como em Rio Claro e Mogi Guaçu, a contribuição dos conídios ao incremento da doença tem maior importância do que os ascósporos, que são importantes no início da epidemia por aumentar o número de plantas com a doença (SPÓSITO et al, 2008). Portanto, nesses municípios, ao se aplicar de 6 a 7 vezes o fungicida, reduziu-se a intensidade da doença, fazendo com que fosse observada a contribuição adicional do conjugado rastelo mecânico e trincha na redução do número de ascósporos e, portanto, a redução da incidência da doença em frutos cítricos.…”

Spatial Patterns of Brown Rot Epidemics and Development of Microsatellite Markers for Analyzing Fine-Scale Genetic Structure ofMonilinia fructicolaPopulations Within Peach Tree Canopies

“…Most studies have focused on quantifying two-dimensional patterns of disease among trees (i.e., on an x-y plane), whereas the number of studies explicitly considering three-dimensional disease patterns within canopies (i.e., in an x-y-z cube) has been limited (2,16,28). This is largely due to difficulties associated with accurately mapping and analyzing the hundreds or thousands of points that make up the structurally complex tree canopy.…”

The profitability of precision spraying on specialty crops: a technical–economic analysis of protection equipment at increasing technological levels

“…The fundamental rationale of this selective approach relies on the uneven spatial distribution exhibited by the symptoms of several diseases, with typical patch structures evolving around discrete foci, especially during the early stages of an infection's development (Everhart et al 2013;Sposito et al 2008;Waggoner and Aylor 2000). The targeted spraying of disease foci (and of surrounding buffer areas) can control the infection's establishment and prevent its epidemic spread to the whole field (West et al 2003) while significantly reducing the total amount of pesticide applied.…”