Effects of soil amendments combined with solarization on the soil microbial community in strawberry cultivation using quantitative real-time PCR

Experiments were conducted in commercial fields of strawberry-growing areas of the Aydin Province of Turkey during two cropping seasons: 2010-2011 and 2011-2012. Each year, eight separate treatments were used: (1) untreated control (C), (2) solarization alone (S), (3) solarization + broccoli (SBr), (4) solarization + fava bean (SFB), (5) solarization + dry olive-mill wastewater (SDOMW), (6) solarization + rice hulls (SRH), (7) solarization + sulfur powder (SSu), and (8) solarization + vermicast (SVe). DNA was extracted from bulk soil samples before and after solarization. The populations of the major taxonomic groups of bacteria and soil-borne fungal pathogens of strawberry were quantitatively calculated by quantitative real-time PCR (qPCR) with specific primer pairs using standard curves. The marketable fruit yield was recorded in the experimental plots. After the 6-week solarization period, there were significant reductions for total bacteria and for alpha-Proteobacteria in all of the experimental plots, except for SDOMW. However, the abundance of beta-Proteobacteria significantly increased in all of the experimental plots (except for C and SFB in 2011). Significant increases in Firmicutes and Actinobacteria were also recorded in all of the treated plots. The highest significant increase was noticed with SDOMW treatments for total bacteria, alpha-Proteobacteria, beta-Proteobacteria, Firmicutes and Actinobacteria in both years. The target level of Verticillium spp. Rhizoctonia solani and Fusarium oxysporum decreased significantly in all of the treated plots after solarization in both years. The reductions of M. phaseolina were significant in S, SVe, and SSu and were the highest in SDOMW in 2011; these reductions were significant in S, SSu and SDOMW in 2012. The abundance of Trichoderma spp. decreased insignificantly in all of the experimental plots. The highest significant yields were obtained from the combination of SDOMW, SRH and SSu compared to solarization alone in both seasons.