Effect of swathing on alternaria black spot in Brassica rapa canola in Saskatchewan

Abstract

Effect of swathing on alternaria black spot in Brassica rapa canola in Saskatchewan. Can. J. Plant Sci. 79: 299-302. From 1990299-302. From to 1997, experiments were conducted comparing the effect of swathing versus straight combining on seed infection by Alternaria species and on quality of harvested seed. This was done at several locations in Saskatchewan using a number of cultivars of Brassica rapa and B. napus. The level of A. brassicae in harvested seed was significantly higher in straight-combined than in swathed treatments. Green seed count and seed weight were not affected by treatment. Seed germination was reduced, but not always significantly, with straight combining compared to swathing. This data support the recommendation for swathing at the optimal time to reduce alternaria black spot when the potential for disease development is high. Swathing reduces the time for disease development because it reduces the time of ripening compared with straight combining. Le pouvoir germinatif des graines était moins bon, quoique pas toujours significativement au plan statistique, après moissonnage-battage qu'après andainage. Ces observations viennent conforter la recommandation d'andainer au stade de maturité optimale de façon à réduire l'infection de la tache noire à un moment où ses possibilités de développement sont particulièrement fortes. L'andainage, en effet, laisse moins de temps à la maladie de se développer du fait qu'il raccourcit la durée de maturation par rapport au moissonnage-battage. Mots clés:Tache noire, Alternaria brassicae, canola, andainage Alternaria black spot, caused by Alternaria brassicae (Berk.) Sacc. and A. raphani Groves & Skolko, is found worldwide and is endemic in the northern canola growing areas of the Canadian prairie provinces, where it can cause substantial yield reductions of up to 36% (Rude et al. 1994;Verma and Saharan 1994;Seidle et al. 1997;Duczek et al. 1998). This disease also reduces seed quality by increasing the green seed count, reducing seed weight, and decreasing the percent germination in harvested seed. Alternaria alternata (Fr.) Keissl. is also frequently isolated from seed but it is considered nonpathogenic. Because plants are most affected by this disease late in the season Vanterpool (1963) recommended swathing, which hastens the ripening process, as a means of control. The purpose of this study was to determine the effect of swathing on alternaria black spot. MATERIALS AND METHODS Time of SwathingThe test was conducted in commercial fields of Brassica rapa canola at Medstead, Saskatchewan, and relied upon naturally occurring inoculum for infection. Seeding occurred on 26-28 May, on different dates each year, using a press drill with 15-cm row spacings. The cultivars were AC Parkland in 1995, Tobin in 1996, and AC Boreal in 1997. A randomised complete block design with four or five replicates was used. Each plot was 3 m long by 1.2 m wide with 1 m of crop on either side to serve as a guard. On each swathing date, eight rows of plants from the centre 2 m o...

Medium-term trends in dark leaf and pod spot epidemics in Brassica napus and Brassica rapa in Lithuania

“…Alternaria blight-affected pods mature earlier, causing a premature shattering of pods, subsequently the seeds from infected pods are small and rugose (Verma & Saharan 1994). The disease causes significant seed losses of rapeseed and mustard in the countries of the Indian continent (Meah et al 2002, Shrestha et al 2005 and is an economically important disease of canola in Canada (Kharbanda & Tewari 1996, Duczek et al 1998). On the contrary, dark spot was reported to become more of a local problem since 1982 in the UK (Hardwick et al 1989) while in Germany A. brassicae was identified as accompanying pathogen of Botrytis cinerea and was assumed to have no economic importance (Söchting & Vereet 2004).…”

Morphological and physiological variation among different isolates of Alternaria spp. from Rapeseed-Mustard

“…Around the initial site of host leaf Alternaria morphologically produces a series of concentric rings [2]. A. brassicae is a necrotrophic pathogen produce lesion on leaves, stem and siliquae which affect seed quantity, quality by reducing oil content, seed size and seed colour [8]. This disease may cause significant losses in both temperate and tropical Brassica crops [20].…”

Yield and quality of canola seed as affected by stage of maturity at swathing

“…Swathing has also been reported to reduce the effects of alternaria black spot, caused by Alternaria brassicae (Berk. ), in canola (Duczek et al 1999).…”