Temporal Dynamics of Phytophthora Blight on Bell Pepper in Relation to the Mechanisms of Dispersal of Primary Inoculum of Phytophthora capsici in Soil

Abstract

The effect of components of primary inoculum dispersal in soil on the temporal dynamics of Phytophthora blight epidemics in bell pepper was evaluated in field and growth-chamber experiments. Phytophthora capsici may potentially be dispersed by one of several mechanisms in the soil, including inoculum movement to roots, root growth to inoculum, and root-to-root spread. Individual components of primary inoculum dispersal were manipulated in field plots by introducing (i) sporangia and mycelia directly in soil so that all three mechanisms of dispersal were possible, (ii) a plant with sporulating lesions on the soil surface in a plastic polyvinyl chloride (PVC) tube so inoculum movement to roots was possible, (iii) a wax-encased peat pot containing sporangia and mycelia in soil so root growth to inoculum was possible, (iv) a wax-encased peat pot containing infected roots in soil so root-to-root spread was possible, (v) noninfested V8 vermiculite media into soil directly as a control, or (vi) wax-encased noninfested soil as a control. In 1995 and 1996, final incidence of disease was highest in plots where sporangia and mycelia were buried directly in soil and all mechanisms of dispersal were operative (60 and 32%) and where infected plants were placed in PVC tubes on the soil surface and inoculum movement to roots occurred with rainfall (89 and 23%). Disease onset was delayed in 1995 and 1996, and final incidence was lower in plants in plots where wax-encased sporangia (6 and 22%) or wax-encased infected roots (22%) were buried in soil and root growth to inoculum or root-to-root spread occurred. Incidence of root infections was higher over time in plots where inoculum moved to roots or all mechanisms of dispersal were possible. In growth-chamber studies, ultimately all plants became diseased regardless of the dispersal mechanism of primary inoculum, but disease onset was delayed when plant roots had to grow through a wax layer to inoculum or infected roots in tension funnels that contained small volumes of soil. Our data from both field and growth-chamber studies demonstrate that the mechanism of dispersal of the primary inoculum in soil can have large effects on the temporal dynamics of disease.

Agronomical management influence on the spatiotemporal progress of strawberry dry wilt in Michoacan, Mexico

“…Remarkably, A+G had the smallest aggregates, but the restrictive space could explain the highest displacement of the inoculum within the row. This level of dispersal is consistent with root pathogens, because it depends on the spatial pattern of host population, especially when disease transmission requires contact between healthy and susceptible tissues, that is, root to root (Sujkowski et al, 2000;Willocquet et al, 2000) and the airborne pathogens have a less restrictive dispersion. Since 2006, Fusarium wilt of strawberry has increased in incidence and severity in California, USA.…”

“…However, only statistical differences (p=0.05) were found in Tamándaro and between this with the T values of Villafuerte and Ario de Rayón (2003-04 cycle) and between Villafuerte (A+G) and Tamándaro (T) (2004-05 cycle) ( Table 1). The mechanism of dispersal of the primary inoculum in soil can have large impacts on disease onset, progress, and final incidence (Sujkowski et al, 2000), in this study the shape of the epidemic curve (c) in all cases was sigmoidal asymptotic, typical of low-level epidemics with limited inoculum dispersal. In this case, statistical differences were also detected between the curve shapes being clearer between Tamándaro (A+G) and the other localities in both cycles.…”

Effect of prior tillage and soil fertility amendments on dispersal of Phytophthora capsici and infection of pepper

“…Zoospores released from sporangia can move rapidly in these soils to infect roots and crowns of plants. Zoospore movement in soils can be affected by soil texture and porosity (Ristaino 1991;Ristaino et al 1993;Sujkowski et al 2000). Disease will progress more rapidly if inoculum movement occurs through the soil to roots than via root growth to inoculum (Ristaino et al 1994).…”

“…Mason jars containing the V-8 vermiculite medium were autoclaved for 1 h at 120°C on two consecutive days before the inoculation of P. capsici. Isolate R-16 was grown at 25°C for 4 weeks on V-8 vermiculite media [500 cm 3 vermiculite, 250 ml of V-8 broth (800 ml of water, 200 ml of V-8 juice, and 2 g of CaCO 3 in 1-l jars)] (Sujkowski et al 2000).…”

“…Plant spacing within rows was 6 cm (<0.3 m field spacing). V-8 vermiculite medium (50 cm 3 ) containing sporangia and mycelia of the pathogen was placed in the transplant hole of one plant in the centre row at one end of each flat Sujkowski et al 2000) to simulate a point source of inoculum.…”