Limestone-Mediated Suppression of Fusarium Wilt in Spinach Seed Crops

Abstract

Fusarium wilt of spinach is caused by the soilborne fungus Fusarium oxysporum f. sp. spinaciae and occurs in most regions of spinach production. The disease is favored by acid soils and warm temperatures, and the fungus can survive extended periods as chlamydospores or by asymptomatic colonization of the roots of nonhost plant species. The 10- to 15-year rotation required to minimize losses to Fusarium wilt is the primary constraint on spinach seed production in the maritime Pacific Northwest, the only region of the United States suitable for this cool-season, daylength-sensitive crop. Raising soil pH with agricultural limestone (97% CaCO3) results in a transitory, partially suppressive effect on spinach Fusarium wilt. A field trial was completed from 2009 to 2012 to assess the potential for annual applications of agricultural limestone at 0, 2.24, and 4.48 tons/ha for 3 years prior to a spinach seed crop to improve Fusarium wilt suppression compared with the level of suppression attained from a single limestone amendment at 4.48 tons/ha. Three proprietary female spinach lines were planted that ranged from highly susceptible to partially resistant to Fusarium wilt. Three successive annual applications of limestone at 4.48 tons/ha reduced midseason wilt incidence by an average of 20%, increased spinach biomass by 33%, and increased marketable spinach seed yield by 45% compared with plots amended once with the same rate of limestone in the spring of planting. The suppressive effect increased with increasing rate of limestone amendment, with the greatest difference observed when limestone was applied at between 0 and 2.24 tons/ha annually for 3 years. The effects on seed yield were greatest for the partially resistant female line, followed by the moderately susceptible and highly susceptible female lines. Overall, the results demonstrate that annual applications of agricultural limestone on acid soils of the maritime Pacific Northwest of the United States can enhance suppression of spinach Fusarium wilt, potentially reducing the required rotation interval by as much as 50%, thereby doubling the capacity for spinach seed production in the United States.

Lessons from 10 years of stakeholder adoption of a soil bioassay for assessing the risk of spinach Fusarium wilt

“…The application of agricultural limestone increased the average pH of the 248 soils tested from 2014 to 2019 by nearly 1.0 compared to the 147 soils tested from 2010 to 2013. These results support demonstrations that the increase in soil pH resulting from increasing rates of agricultural limestone amendment increases the incidence of Verticillium wilt of spinach (du Toit et al, 2011;Gatch & du Toit, 2017). However, the soil bioassay is completed in midwinter each year, when the daylength is too short to trigger bolting of the spinach inbred lines, so that Verticillium wilt symptoms do not develop as symptoms of this disease only develop on spinach after bolting is initiated (du Toit et al, 2005).…”

Linking the Belowground Microbial Composition, Diversity and Activity to Soilborne Disease Suppression and Growth Promotion of Tomato Amended with Biochar

“…The biochar-elicited increase in potting mixture pH (6.5 vs.7.3 in the non-amended control and biochar-amended treatment, respectively) may also have played a role in promoting bacterial growth 63 . Some studies have shown that different soil amendments which increase soil pH also cause decreases in soilborne diseases caused by Fusarium species 64 65 .…”

Liming Positively Modulates Microbial Community Composition and Function of Sugarcane Fields

“…Concerning acidic soils, long-term liming helps to alleviate soil acidity, enhancing neutrophilic bacterial growth [20], microbial biomass, and soil respiration [21]. In addition, various crop systems, such as cucumber, watermelon [22], spinach [23], and tomato [24], have shown that liming effectively inhibits pathogen populations and incidence in these crops. Several studies have shown that the application of lime in sugarcane cropping systems can not only effectively alleviate soil acidification, but also improve soil nutrient status and crop productivity.…”