Document: CHR-3-35-42

Insecticide treatment increases fine root longevity in peach (Prunus persica).

WELLS, C.* ¹, D.EISSENSTAT ² and D.M.GLENN ³

University of Nevada Reno, Reno NV 89557 ¹
The Pennsylvania State University, University Park PA 16802 ²
USDA Appalachian Fruit Research Station, Kearneysville, WV 25430 ³

Abstract:
The effects of aboveground insect herbivory on plant performance in both natural and agricultural systems are well documented. However, our understanding of belowground herbivory is much more limited. A number of authors working with rhizotrons and minirhizotrons have noted insects feeding on and around roots, but the consequences of these interactions for root life history have rarely been examined in detail. In the present experiment, we used nondestructive belowground imaging technology to assess the effects of soil insect suppression on the production and longevity of peach (Prunus persica) fine roots (< 1 mm diameter) over the course of two growing seasons. The experiment was conducted at the USDAARS Appalachian Fruit Research Station in Kearneysville, WV using six 15-yr.-old peach trees. Two clear butyrate observation tubes (minirhizotrons) were installed beneath each tree at an angle of 30 from the vertical in April 1996. Soil drench treatments were applied around individual minirhizotron tubes at monthly intervals and consisted of 1L of water (control) or 250 microliters of the broad-spectrum insecticide chlorpyrifos in 1 L of water. Roots which grew against the surface of the minirhizotron tubes were videotaped at two- to four-week intervals during the 1996-97 and 1997-98 growing seasons. The effect of insecticide treatment on the risk of root mortality in each year was estimated using a Cox proportional hazards regression performed with SAS PROC PHREG. The application of broad-spectrum insecticide was associated with a significant increase in fine root longevity. Median lifespans were 46 to 125 days longer for roots on insecticide-treated tubes compared with roots from control tubes. In addition, the development of brown pigmentation was significantly delayed in roots which were treated with insecticide. The effects of insecticide application did not appear to be due to increased soil fertility, as accumulation of NO₃-, NH₄+, and PO₄₂- on mixed bed ion-exchange resin was similar in treated and untreated soil. The results presented here indicate that interactions with belowground insects can significantly influence root longevity and may alter the rate at which roots undergo developmental changes in anatomy and physiology.

Keywords: minirhizotron, root lifespan, root herbivory

This abstract is being presented at: 3:15 PM in session:
Oral Session #12: Roots.