The impact of leaf rust on spring wheat in the winter rainfall region of South Africa

Abstract

In a field trial established near Malmesbury in the Western Cape during 1999 the effect of Puccinia triticina on yield and quality of the bread wheat (Triticum aestivum L.) cultivar SST 75 was determined. Information on the efficacy of different foliar fungicide treatments in controlling leaf rust was also obtained. The fungicides bromuconazole (140 g a.i. ha-1 ), epoxiconazole/carbendazim (112.5/112.5 g a.i. ha-I ), flusilazole/carbendazim (1001 50 g a.i. ha-I ), flutriafol (125 g a.i. ha-I ), propiconazole (100 g a.i. ha-I ), cyproconazole (40 g a.i. ha-I ), tebuconazole (187.5 g a.i. ha-I ), and tebuconazole/carbendazim (125/100 g a.i. ha-I ) were sprayed in single applications at either growth stage 16 and 37, and in double applications at both these growth stages. The application of the eight fungicides at both seven and flag leaf stages resulted in a mean decrease of 65% in the AUDPC, calculated for leaf rust severity. In the control plots 23% siftings (seed <1.5 mm) were obtained followed by 20%, 13% and 12% for the seven leaf, flag leaf and combined seven and flag leaf treatments, respectively. Combined seven and flag leaf treatments resulted in a mean yield increase of 56%, followed by 50% and 15% for the flag leaf and seven leaf treatments, respectively. Over treatments applied, yield increases varied from 24% for bromuconazole to 53% for epoxiconazole/carbendazim. Yield was negatively correlated with the AUDPC (R = -0.88 [77% of variance accounted for]). The application of the flag leaf and combined seven and flag leaf treatments resulted in a significant increase in the hectolitre mass (kg hi-I). Protein content, over fungicides applied, varied from 12.5% for the combined seven and flag leaf treatments to 12.8% for the seven leaf treatment. The results of the study emphaSised the economic importance of leaf rust as well as the value of controlling foliar rust diseases genetically.

Microsatellite analysis of selected Puccinia triticina races in South Africa

“…This was ascribed to regular fungicide applications in commercial wheat as well as deployment of the Lr34/Yr18 resistance gene (Pretorius et al 2007). Despite this decline in disease occurrence, leaf rust has previously caused significant losses in the Free State and Western Cape in particular (Boshoff et al 2002;Pretorius et al 2007). Several factors contribute to changes in virulence profiles of pathogen populations.…”