Dispersal of Venturia inaequalis Ascospores and Disease Gradients from a Defined Inoculum Source

Abstract

Aerial concentration of ascospores of Venturia inaequalis and incidence of apple scab were monitored in an orchard during the ascospore release seasons in 1999, 2000 and 2001 on susceptible (Jonagold) and moderately resistant (Schone van Boskoop) apple cultivars. A 1-ha orchard was divided into an inoculum source block (approximately 0.34 ha) and an inoculum-free block (approximately 0.66 ha) where inoculum was excluded by covering the soil surface with polythene sheets. Ascospore numbers and disease incidence were measured within the inoculum-free block at different distances from the inoculum block. Ascospores were sampled with three Burkard volumetric spore traps located at 0, 21 and 45 m from the border of the inoculum block. To determine the incidence of infection, clusters of leaves were assessed at six distances from the border of the infected source from the time the first symptoms appeared. Each year, the aerial ascospore concentration significantly decreased with distance from the source, as did the incidence of infected clusters. Cultivar susceptibility to apple scab markedly influenced incidence of infected clusters and disease gradients. The effect of horizontal distance from the source was identifiable up to 18 m and 33 m for cv. Schone van Boskoop and cv. Jonagold, respectively, beyond which disease was negligible. The disease gradients for cultivar Jonagold in 1999, 2000 and 2001 were well described by an exponential model with gradient coefficients of )0.036, )0.042 and )0.047, respectively. The number of infected clusters at the source border for this cultivar differed significantly over the 3 years. A single exponential model with a gradient coefficient of )0.035 adequately described the disease gradients for cultivar Schone van Boskoop in each of the 3 years. Further analysis showed highly significant correlations (r > 0.85, P < 0.01) between the annual cumulative spore catches and the annual mean number of infected leaf clusters in each year and for both cultivars. The aerobiological and epidemiological implications of these findings are discussed.U. S.

The genetic structure of a Venturia inaequalis population in a heterogeneous host population composed of different Malusspecies

“…Additionally, an IBD pattern was detected within each of these two subpopulations. Our work represents a rare example in pathogens where the dispersal evaluated by a fine scale IBD pattern appropriately fits with previously reported empirical field data [16,53]. Because many pathogen dispersal capabilities remain unclear, our validation of the IBD approach is particularly significant for epidemiologists and also has practical implications for plant breeders and landscape managers for the design of disease control strategies.…”

“…Second, IBD detection across this orchard highlighted restricted V. inaequalis dispersal over space. Holb et al [16] showed that the mean daily ascospore count in traps at 21 metres and 45 metres was approximately one-third and one-tenth of the sexual spores trapped at the source, respectively, highlighting that a substantial number of ascospores could travel at least 45 metres from the inoculum source. Lower dispersal abilities were previously reported by Kaplan [53] who observed that 99% of the spores are not able to spread more than 5 or 6 metres.…”

“…Lower dispersal abilities were previously reported by Kaplan [53] who observed that 99% of the spores are not able to spread more than 5 or 6 metres. Many factors can explain these dispersal distance differences, including orchard conditions and differences in wind direction and velocity (see [16]). In this study, we confirmed that dispersal of the greater part of V. inaequalis spores in orchards was intrinsically very restricted, which is in agreement with several other authors (e.g., [54-56]), who demonstrated that no scab lesion development was detected at 15 to 60 metres beyond an inoculum source.…”

“…The pathosystem Malus spp.- V. inaequalis is suitable to study both gene flow and host adaptation. Epidemiological studies suggest that both types of propagules are dispersed over short distances (< 50 metres) [16,17], which makes an IBD pattern possible at the orchard scale. Additionally, V. inaequalis is described as a good model for host adaptation in plant pathogens [7] because mating only occurs between strains that are able to infect identical hosts, thus facilitating the maintenance of adaptations to a host when host ranges do not overlap [18,19].…”

Temporal and Spatial Dispersal of Cladobotryum Conidia in the Controlled Environment of a Mushroom Growing Room

“…Conidial dispersal is a key factor in the spread of diseases within crops and is affected by water splash from rain or irrigation water and also by wind and air currents (16,17,21,22). The environment in a mushroom-growing room is very uniform and considerably different from that in greenhouses or outdoors, since the crop is grown indoors, in closed rooms, under very specific conditions of temperature, humidity, and air speed, delivered through an air-conditioning system (2,15).…”