Contents lists available at ScienceDirect Applied Soil Ecology journal homepage: www.elsevier.com/locate/apsoil Rhizosphere microorganisms affected by soil solarization and cover cropping in Capsicum annuum and Phaseolus lunatus agroecosystems Nancy Kokalis-Burelle a, ⁎ , Robert McSorley b,1 , Koon-Hui Wang c , Shubin K. Saha d , Robert J. McGovern e,1 a USDA, ARS, U.S. Horticultural Research Laboratory, Ft. Pierce, FL 34945, USA b Entomology and Nematology Department, University of Florida, Gainesville, FL 32611, USA c Department of Plant and Environmental Protection Sciences, University of Hawaii, Honolulu, HI 96822, USA d Department of Horticulture, University of Kentucky, Lexington, KY 40506, USA e Plant Pathology Department, University of Florida, Gainesville, FL 32611, USA ARTICLE INFO Keywords: Bell pepper Cowpea Crotalaria juncea Fungal pathogens Lima bean Rhizobacteria Sunn hemp Vigna unguiculata ABSTRACT Field experiments were conducted to evaluate the effects of soil solarization or cover crop on bell pepper (Capsicum annuum) and lima bean (Phaseolus lunatus) rhizosphere microorganisms. In Experiment I, flat surface solarization (FSS), raised bed solarization (RBS), cowpea (Vigna unguiculata) cover crop alone (CP), and the combination of cowpea cover crop followed by raised bed soil solarization (CP + RBS) were compared with methyl bromide fumigation (MB) and an untreated control (UTC) for effects on rhizosphere bacteria and fungi on bell pepper. In Experiment II, effects of cover crop on rhizosphere microorganisms were examined on lima bean in a 3 × 3 split-plot experiment with three summer cover crop treatments: sunn hemp (SH) (Crotalaria juncea), cowpea (CP), and fallow (F) as main plots, and three organic amendments: sunn hemp hay (SHH), cowpea hay (CPH), and no hay (NH) as subplots. Rhizosphere bacteria including siderophore producers, gram-positive spore- formers, and fluorescent pseudomonads were assessed, as well as two fungi, Fusarium oxysporum and Rhizoctonia solani. In year 1 of Experiment I, CP + RBS reduced F. oxysporum and R. solani in the rhizosphere, resulting in levels similar to those in MB fumigation. This was not observed in year 2. Heavy rainfall in year 2 resulted in a severe outbreak of Pythium on bell pepper, which was most destructive in MB fumigated plots. Effects of so- larization and cover crop on rhizosphere bacteria also differed between years. Fluorescent pseudomonads were abundant across treatments in year 1, but were greatly reduced in year 2, when the Pythium outbreak occurred. In Experiment II, populations of rhizobacteria on lima bean were not affected by cover crop in either year. At the end of year 1, isolation of R. solani from lima bean roots increased in SHH plots. SH cover crop reduced gram- positive spore forming bacteria and fluorescent pseudomonads. In year 2, CP followed by CPH had higher levels of fungi and bacteria than CP followed by either NH or SHH. Overall, cover crop amendments did not result in consistent enhancement of rhizobacteria, and some treatments resulted in increased abundance of pathogenic fungi. The most consistent treatment for reducing rhizosphere fungal populations was MB. 1. Introduction Use of cover crops and green manure can reduce pathogen activity and improve crop health by increasing soil organic matter, releasing allelopathic compounds, and by supporting beneficial rhizosphere mi- crobial populations. These beneficial rhizosphere microorganisms in- crease the availability and uptake of mineral nutrients (Cleyet-Marcel et al., 2001), serve as antagonists to pathogens (Loper, 1988), and induce systemic resistance (Kloepper et al., 2004; Van Loon et al., 1998). About 7 to 10% of the rhizobacteria isolated from roots of potato (Solanum tuberosum, L.), sugar beet (Beta vulgaris, L.), and tomato (Ly- copersicum esculentum, L.) exhibited antagonistic activity against cyst and root-knot nematodes (Sikora, 1992). A review of literature on ne- matode-antagonistic rhizobacteria revealed that 31% of publications are on Pseudomonas spp., 23% are on Bacillus spp., and 14% are on chitinolytic bacteria (Cadet, 1998; Jonathan et al., 2000; Hasky et al., http://dx.doi.org/10.1016/j.apsoil.2017.06.001 Received 14 February 2017; Received in revised form 2 May 2017; Accepted 5 June 2017 ⁎ Corresponding author. 1 Retired. E-mail address: nancy.burelle@ars.usda.gov (N. Kokalis-Burelle). Abbreviations: CAS, Chrome Azurol S medium; CP, cowpea cover crop; CPH, cowpea hay; F, fallow; FSS, flat surface solarization; MB, methyl bromide; NH, no hay; OSM, Ohio State medium; RBS, raised-bed solarization; SS, soil solarizatio; SH, sunn hemp; SHH, sunn hemp hay; TSA, tryptic soy agar; UTC, untreated control Applied Soil Ecology 119 (2017) 64–71 0929-1393/ Published by Elsevier B.V. MARK