Effect of Brassicaceae seed meals with different glucosinolate profiles on Rhizoctonia root rot in wheat

The soil-borne pathogen Rhizoctonia solani AG 8 causes major yield losses in wheat (Triticum aestivum. L) production worldwide. Plant tissues of Brassicaceae species contain glucosinolates that are hydrolyzed in the presence of the enzyme myrosinase into products with pesticidal properties. Growth chamber studies were conducted to determine the effect of the Brassicaceae seed meals (SMs) from Brassica juncea, Brassica napus and Sinapis alba on the suppression of the R. solani AG 8 infection of winter wheat. Pasteurized sandy soils were amended with intact and denatured SMs of rape seed and mustard at a rate of 0.5% by soil weight. Regardless of the glucosinolate type and content, all intact and denatured Brassicaceae significantly reduced the infection of winter wheat seedlings by R. solani AG 8 compared to the un-amended control. However, soils amended with S. alba SMs had the lowest severity of Rhizoctonia root rot relative to other amended soils. Phytotoxicity arising from the use of Brassicaceae SMs was observed particularly in soils amended with high glucosinolate-containing SMs. These studies demonstrate that Brassicaceae SMs can be used to manage disease caused by R. solani AG-8. However, future studies will need to focus on strategies for diminishing the crop growth-reducing effects associated with Brassicaceae SM amendment to fully maximize these fungicidal benefits. (C) 2013 Elsevier Ltd. All rights reserved.Keywords: Rhizoctonia solani AG-8, Biopesticide, Brassica juncea, Brassica napus, Sinapis alba, Glucosinolate, Seed mealKeywords: Rhizoctonia solani AG-8, Biopesticide, Brassica juncea, Brassica napus, Sinapis alba, Glucosinolate, Seed mea

Studies on Seedbed Sterilisation, Disease and Weed Control Methods for Paprika (Capsicum Annuum L.) in the Smallholder Farming Sector of Zimbabwe.

The objective of this study carried out in 2000/01, 2001/02 and 2002/03 rainy seasons in Chinyika Resettlement Area (CRA) was to develop cost effective crop protection practices in the nursery and field for paprika production. A survey carried out in CRA in 2001/02 rainy season revealed that most farmers lacked knowledge of paprika diseases identification. Ten percent of the farmers did not sterilise their seedbeds and those who did, used the method of burning of brushwood. Forty percent of the paprika farmers did not apply any fungicides for disease control during the course of production, where as among those who did, the majority sprayed only once a season. Laboratory analysis of samples taken from the farmers fields revealed that, powdery mildew (Leveillula spp) (35.6%), bacterial leaf spot (24.4%) and grey leaf spot (Stemphylium spp)(18.1%) were the major paprika diseases in CRA. Soil sterilization methods of seedbeds namely; burning of cowdung, brushwood or maize cobs, solarisation and methyl bromide were investigated. Solarisation raised soil temperatures to as high as 39.4 0C at 5cm soil depth. Burning of brushwood and cowdung treatments resulted in significantly (p0.05) from Z$59 410/ha achieved by alternating sulphur and a mixture of copper oxychloride - mancozeb mixture fortnightly in 2000/01 rainy season. There were no statistical differences (p>0.05) between spraying after scouting and acibenzolar-s-methyl application treatments. The most cost – effective disease management practice was alternating spray of sulphur and copper oxychloride-mancozeb mixture fortnightly. The effect of weed management methods on disease and yield of paprika were also investigated at two sites. The weeding treatments were; hand hoe weeding at 2 and 6 weeks after transplanting (WAT), re-ridging at 3,6 and 9 WAT, 160l a.i/ha alachlor (Lasso) a day after transplanting and a tank mixture of alachlor 80l a.i/ha and oxidiazon (Ronstar) at 96la.i/ha a day before transplanting and a no weeding treatment (control). Major weeds observed in the two seasons at both sites were; mexican clover [Ricardia scabra (L)], black jack [Bidens pilosa (L.)], stinkblaar [Datura stramonium (L)] and Apple of Peru [Nicandra physalodes (L.)]. In 2000/01 season hand weeding treatments had the lowest AUDPC disease incidence, weed density and highest marketable yield. In the 2001/02 season, both herbicide treatments had the same effect as hand weeding and re-ridging on AUDPC and marketable yield. Weed density and biomass were statistically the same across all treatments except the control in 2001/02 season. Hand weeding operations resulted in highest added profits. The use of herbicides and a supplementary hand weeding between 5-6 WAT is the best economic option for weed control