Submitted to: Mycorrhiza
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 21, 2007
Publication Date: April 3, 2007
Citation: Schreiner, R.P., Tarara, J.M. 2007. Deficit irrigation promotes arbuscular colonization of fine roots by mycorrhizal fungi in grapevines (Vitis vinifera L.) in an arid climate. Mycorrhiza. 17:551-562. Interpretive Summary: Understanding how irrigation alters grapevine growth and physiology in arid climates is critical to developing irrigation practices that maximize product quality and use water resources more efficiently. We examined the below-ground response of 'Cabernet Sauvignon' grapevines over three years to three irrigation regimens based on estimated vine water use. All vines received less irrigation water than needed for maximum growth, known as regulated deficit irrigation (RDI). Vines in the control RDI treatment (the current industry standard) received 60% of estimated vine water needs from two weeks after fruit set until fruit harvest. Other vines received less water (30% of estimated vine water needs) at discrete times, either early in the summer (between two weeks after fruit set until veraison) or late in the summer (between veraison and harvest). The growth of fine (feeder) roots was reduced in early deficit vines in two of three years, and in late deficit vines in one of three years. However, the level of beneficial fungal arbuscules (structures that indicate metobolite transfer between plants and mycorrhizal fungi) in fine roots was greater in both early and late deficit treatments. Irrigation did not consistently affect above ground vine growth or fruit quality parameters, although whole-vine photosynthesis was reduced by the added deficit. These findings suggest that high quality grapes can be produced in this region with even less water than the current RDI practice, due in part to a more efficient root system resulting from greater colonization by beneficial fungi
Technical Abstract: Regulated deficit irrigation (RDI) is a common practice applied in irrigated vineyards to control canopy growth and improve fruit quality, but little is known of how imposed water deficits may alter root growth and colonization by beneficial, arbuscular mycorrhizal fungi (AMF). Thus, root growth and mycorrhizal colonization were determined throughout the growing season for three years in 'Cabernet Sauvignon' grapevines exposed to three RDI treatments. Vines under standard RDI were irrigated at 60% of full-vine evapotranspiration (FVET) from two weeks after fruit set until harvest, a standard commercial practice. Early deficit vines were exposed to a more extreme deficit (30% FVET) during the period from two weeks after fruit set until the commencement of ripening (veraison), and thereafter reverted to standard RDI. Late deficit vines were under standard RDI until veraison, then exposed to a more extreme deficit (30% FVET) between veraison and harvest. The production of fine roots was reduced in both the early and late deficit treatments, but the reduction was more consistent in the early deficit vines because the additional deficit was imposed when roots were more rapidly growing. The frequency of arbuscules in fine roots was greater in both of the additional deficit treatments than in the standard RDI. It appears that grapevines compensated for lower production of fine roots by stimulating arbuscular colonization. Irrigation did not affect yield or quality of grapes, but reduced whole-vine photosynthesis during the additional deficit periods. It appears that high quality grapes can be produced in this region with less water than the current RDI practice, due in part to a more efficient root system resulting from greater arbuscular colonization by AMF.