Dispersal of Phytophthora capsici and P. parasitica in furrow‐irrigated rows of bell pepper, tomato and squash

Abstract

Dispersal of Phytophthora capsici and P. parasitica from point sources buried near the upper end of 74 m‐long irrigation furrows was studied with three annual host crops. Furrows next to tomato were inoculated with either P. capsici or P. parasitica, while furrows next to pepper and squash were inoculated with P. capsici only. Irrigation was carried out on a 14‐day cycle. Dispersal of each fungus in the water was monitored by transplants in the furrows and the incidence of infected tomato fruit along furrows. Disease gradients on roots and shoots of all hosts were also measured. Repeated irrigations dispersed P. capsici and P. parasitica up to 70 m from the source. Fruit infection increased with increasing distances downstream, suggesting an accumulation of secondary inoculum with the repeated flow of water. Conversely, gradients of disease severity on roots of tomato and pepper peaked at the source and rapidly decreased to low levels up to 32 m downstream. Fruit and root infection upstream from source was negligible. Root and crown rot in squash was highly variable, being confined to locations near the initial inoculum in some units while developing to severe levels several meters downstream in other units. Unlike the other hosts, squash petioles were in contact with the irrigation water and may have served as routes of invasion by P. capsici. Transport of inoculum from the furrow water to the roots was limited. P. capsici isolates were more virulent on tomato roots and caused a higher incidence of buckeye rot on tomato fruit than did isolates of P. parasitica.

Etiology of a Tuber Rot and Foliar Blight of Potato Caused by Phytophthora nicotianae

“…Zoospores can move considerable distances in contaminated water. In studies con ducted in irrigation furrows in bell pepper, tomato, and squash fields, P. parasitica was found to be dispersed up to 70 m from the point inoculum sources (6,49). During preliminary greenhouse studies involving soil infestation and foliar water splash inoculation with P. nicotianae zoospores, we observed and confirmed belowground stem and tuber infections in control plants.…”

Major Soilborne Pathogens of Field Processing Tomatoes and Management Strategies

“…Buckeye rot was found to cause significant tomato yield reduction in the furrow-irrigated zones of California in 1984, while the major pathogen was P. parasitica [ 39 ]. However, P. capsici was later found to be more virulent to tomatoes, which can also infect P. parasitica -resistant tomato varieties [ 42 , 43 ]. In recent years, buckeye rot is most common in the southeast and central states of the U.S. [ 44 ].…”

Spread of <i>Phytophthora capsici</i> in Black Pepper (<i>Piper nigrum</i>) in Vietnam

“…It can be explained that zoospores have two differently morphological flagella, thus they can swim in the soil and surface water from plants toward plants, even though towards other pepper gardens over long distance [23] [36]. This was investigated by [4], inoculum moved over 70 m from point sources of inoculum with furrow irrigation. Besides that, within a bush, the foliar infection outbreaks via rain splashes from lower portions to upper portions, while the adjacent plants, spreads through both rain splashes and windblown water droplets [19].…”