|GOUWS-MEYER, REINETTE - Tshwane University|
|MCLEOD, ADELE - University Of Stellenbosch|
Submitted to: Acta Horticulturae
Publication Type: Abstract Only
Publication Acceptance Date: 2/14/2018
Publication Date: 1/17/2020
Citation: Gouws-Meyer, R., Mcleod, A., Mazzola, M. 2020. Potato scab management with Brassica biofumigation and effect of volatiles on Streptomyces growth. Acta Horticulturae. https://doi.org/10.17660/ActaHortic.2020.1269.4.
Technical Abstract: Common scab of potato is an economically important soilborne disease that is caused by various Streptomyces species. The disease is very difficult to control, but biofumigation has shown some potential. Biofumigation consists of the incorporation of Brassica spp. crop residues containing glucosinolates that upon cell disruption are hydrolysed by the enzyme myrosinase to yield a diversity of biologically-active hydrolysis products, of which volatile isothiocyanates are the most toxic to soil microbes. Common scab was significantly reduced through incorporation of fresh and air-dried residues of Brassica oleracea var. capitata (cabbage) when applied prior to two consecutive potato field plantings, but not in a subsequent third potato planting. In contrast, the incorporation of only cabbage root tissue was never effective in suppressing disease incidence. The in-vitro effect of volatile emissions from various Brassica species on pathogenic and non-pathogenic Streptomyces isolates was also evaluated using two bioassay methods. An in-vitro agar plate bioassay showed that, in general, volatile emissions from water activated freeze-dried tissue of B. juncea/S. alba mix and B. napus were superior to those from B. oleracea var italica and B. oleracea var capitata for suppression of growth and sporulation of the 14 Streptomyces isolates examined. Volatiles generated from root tissue were more effective than shoot tissue in limiting growth of Streptomyces. In a chamber bioassay that used freshly macerated Brassica tissue, B. oleracea var capitata and B. juncea/S. alba mix suppressed sporulation but not hyphal growth of the 78 evaluated Streptomyces isolates. Unlike the agar plate bioassay, B. oleracea var capitata and B. juncea/S. alba mix were equally effective at suppressing sporulation of the Streptomyces isolates. The chamber bioassay also showed that the Brassica tissue volatiles were bacteriostatic, since isolates re-grew when removed from the chamber and transferred to fresh media. Significant components of both the pathogenic (50%) and non-pathogenic (20%) Streptomyces population examined were unaffected by the Brassica tissue derived volatiles. This suggests that soil biofumigation could significantly influence composition of the Streptomyces community in agricultural soils.