Mechanisms of Subsurface Drip Irrigation-Mediated Suppression of Lettuce Drop Caused by Sclerotinia minor

Abstract

Subsurface drip irrigation and associated mandatory minimum tillage practices significantly reduced the incidence of lettuce drop (Sclerotinia minor) and the severity of corky root on lettuce compared with furrow irrigation and conventional tillage. Three possible mechanisms for the drip irrigation-mediated disease suppression were examined in this study: qualitative and quantitative differences in the soil microflora under furrow and subsurface drip irrigation; their antagonism and potential bio-control effects on S. minor; and the physical distribution of soil moisture and temperature relative to the two irrigation methods. To determine if the suppressive effects under subsurface drip irrigation were related to changes in soil microflora, soils were assayed for actinomycetes, bacteria, and fungi during the spring and fall seasons. The effects of the irrigation methods on microbial populations were nearly identical during both seasons. In the spring season, the total number of fungal colonies recovered on potato dextrose agar amended with rose Bengal generally was greater in soils under drip irrigation than under furrow irrigation, but no such differences were observed during the fall. Numbers of actinomycetes and bacteria were not significantly different between irrigation methods during either season. No interaction between sampling time and irrigation methods was observed for any of the microbial populations during both seasons. Thus, the significant effect of sampling time observed for actinomycete and bacterial populations during the spring was most likely not caused by the irrigation treatments. There were also no qualitative differences in the three groups of soil microflora between the irrigation treatments. Even though some fungal, actinomycete, and bacterial isolates suppressed mycelial growth of S. minor in in vitro assays, the isolates came from both subsurface drip- and furrow-irrigated soils. In in planta assays, selected isolates failed to reduce the incidence of drop in lettuce plants. The soil moisture under subsurface drip irrigation was significantly lower at all depths and distances from the bed center after an irrigation event than under furrow irrigation. The soil temperature, in contrast, was significantly higher at both 5 and 15 cm depths under drip irrigation than under furrow irrigation. The suppression of lettuce drop under subsurface drip irrigation compared with furrow irrigation is attributed to differential moisture and temperature effects rather than to changes in the soil microflora or their inhibitory effects on S. minor.

Weed Control, Yield, and Quality of Processing Tomato Production under Different Irrigation, Tillage, and Herbicide Systems

“…Enhanced weed control has also been reported with subsurface drip irrigation (Bell et al 1998;Grattan et al 1988;Phene et al 1987) compared to furrow irrigation. Thus, the use of subsurface drip irrigation may resolve problems concerning the adoption of conservation tillage by reducing the need for maintenance of furrows and augmented pesticide use.…”

Drought Adaptation in the Ningxia Hui Autonomous Region, China: Actions, Planning, Pathways and Barriers

“…Drip irrigation is an effective water-saving method, which was established in Germany more than a century ago [69]. Now, the method is widely used for agricultural production in arid, semi-arid and sub-tropical countries [70][71][72][73][74][75][76][77][78][79][80][81][82][83][84]. It was introduced to China in 1994 [85], and while the NX region's government has been trying to promote these irrigation methods through financial subsidies, such promotion is very difficult in rural areas for a variety of reasons (see Section 5).…”

Cultural Practices Influencing Biological Management of Crop Diseases

“…A combination of subsurface drip irrigation and minimum tillage practices more effectively reduced the incidence of lettuce drop disease caused by Sclerotinia minor and the severity of corky root disease caused by Rhizomonas suberifaciens , compared with furrow irrigation and conventional tillage. Differential moisture and temperature effects were considered to be responsible for disease suppression (Bell et al 1998 ) . The effect of three irrigation methods, daily drip, 3-day drip and alternate row furrow irrigation on the incidence of Phytophthora root rot disease caused by Phytophthora capsici in pepper ( Capsicum annuum ) was compared.…”