Effects of different soil treatments on the development of Spongospora subterranea f. sp. subterranea in potato roots and tubers in the greenhouse

Powdery scab caused by Spongospora subterranea f. sp. subterranea (Sss) causes extensive losses in potato production systems globally. Two pot experiments were established in the greenhouse in summer 2013 and winter 2014 to evaluate the effectiveness of different soil chemicals, fumigant, amendments and biological control agents (BCAs) against Sss in the rhizospheric soil, potato roots and tubers. The study used visual assessment methods to assess the effect of treatments on root galling and zoosporangia production, and qPCR to measure Sss concentration in the soil and in the potato roots and tubers. All six soil treatments, namely metam sodium, fluazinam, ZincMax, calcium cyanamide, Biocult and a combination of Bacillus subtilis and Trichoderma asperellum recorded significantly (P < 0.05) lower numbers of zoosporangia in the roots compared to the untreated control. The same effect was observed on the concentration of Sss DNA in the roots at tuber initiation. A more diverse picture was obtained when root gall scores at tuber initiation and Sss DNA in the rhizospheric soil at tuber initiation and harvesting were compared. Significant differences (P < 0.05) were also noted in disease severity, disease incidence, and tuber yield between metam sodium, fluazinam, ZincMax, calcium cyanamide and the untreated control. Calcium cyanamide gave the highest tuber yield. The study demonstrated the potential of soil treatments such as metam sodium, fluazinam, ZincMax and calcium cyanamide in managing Sss in potatoes by reducing the pathogen both in the rhizospheric soil and the roots of the potato plant.The National Research Foundation (NRF), South Africa, and Potatoes South Africa.http://link.springer.com/journal/115402018-03-30hj2017Plant Production and Soil Scienc

Alternative hosts of Spongospora subterranea f. sp. subterranea in southern Africa

Spongospora subterranea f. sp. subterranea (Sss) is an obligate parasite that can only multiply within the living tissues of a host plant. To determine the host status of Sss in some of the crops and weeds commonly found in southern African fields, two greenhouse experiments were carried out. These experiments used both qPCR and light microscope examination to study the development of Sss in the roots of weeds and crops grown in inoculated soil. Zoosporangia and sporosori were observed microscopically in weed species Acanthospermum hispidum, Ageratum conyzoides, Bidens pilosa, Cleome monophylla, Datura stramonium, Euphorbia heterophylla, Oxalis latifolia, Physalis angulata, Setaria pumila and Tagetes minuta, whilst Ipomea plebia, Setaria verticillata and Galinsoga parviflora were non-hosts of Sss. Root galls were only observed on D. stramonium roots. The crops Allium cepa, Solanum lycopersicum, Zea mays, Avena sativa and Triticum aestivum were both zoosporangial and sporosorial hosts, whilst Phaseolus vulgaris and Brassica juncea were sporosorial hosts only. This study has added three new families to namely Oxalidaceae, Euphorbiaceae and Coppardaceae to the hosts of Sss. Two zoosporangial hosts were identified, namely Avena strigosa and Glycine max. These crops would be ideal to be included as trap crops in rotations with potatoes. The highest quantity of Sss DNA in weed species was recorded in the roots of P. angulata, N. physalodes and A. conyzoides, whilst in cultivated crops the highest quantity of Sss DNA was recorded in Brassica juncea followed by Avena strigosa. The study has shown the importance of weeds and some crops used in rotation with potatoes as alternative hosts of Sss and their potential to increase Sss inoculum level in the soil.Potatoes South Africahttps://link.springer.com/journal/106582021-05-12hj2020Plant Production and Soil Scienc

Effects of Different Soil Treatments on the Development of Spongospora subterranea f. sp. subterranea in Potato Roots and Tubers in the Greenhouse

Powdery scab caused by Spongospora subterranea f. sp. subterranea (Sss) causes extensive losses in potato production systems globally. Two pot experiments were established in the greenhouse in summer 2013 and winter 2014 to evaluate the effectiveness of different soil chemicals, fumigant, amendments and biological control agents (BCAs) against Sss in the rhizospheric soil, potato roots and tubers. The study used visual assessment methods to assess the effect of treatments on root galling and zoosporangia production, and qPCR to measure Sss concentration in the soil and in the potato roots and tubers. All six soil treatments, namely metam sodium, fluazinam, ZincMax, calcium cyanamide, Biocult and a combination of Bacillus subtilis and Trichoderma asperellum recorded significantly (P < 0.05) lower numbers of zoosporangia in the roots compared to the untreated control. The same effect was observed on the concentration of Sss DNA in the roots at tuber initiation. A more diverse picture was obtained when root gall scores at tuber initiation and Sss DNA in the rhizospheric soil at tuber initiation and harvesting were compared. Significant differences (P < 0.05) were also noted in disease severity, disease incidence, and tuber yield between metam sodium, fluazinam, ZincMax, calcium cyanamide and the untreated control. Calcium cyanamide gave the highest tuber yield. The study demonstrated the potential of soil treatments such as metam sodium, fluazinam, ZincMax and calcium cyanamide in managing Sss in potatoes by reducing the pathogen both in the rhizospheric soil and the roots of the potato plant.The National Research Foundation (NRF), South Africa, and Potatoes South Africa.http://link.springer.com/journal/115402018-03-30hj2017Plant Production and Soil Scienc