4.8.2
SEED TREATMENT OF COWPEA SEED TO CONTROL FUNGAL STEM PATHOGENS

TAS AVELING1, JE SMITH2 and L KORSTEN2

1Department of Botany and 2Department of Microbiology and Plant Pathology, University of Pretoria, Pretoria 0002, South Africa

Background and objectives
During surveys of cowpea fields in various areas of South Africa, Colletotrichum dematium, C. truncatum and Phoma exigua were found to cause destructive stem diseases. The latter two pathogens have been reported as being seedborne in cowpea [1], and C. dematium in various legumes [2] but not cowpea. The aim of this study was to determine whether C. dematium is seedborne in cowpea and to evaluate seed treatments for the control of this pathogen, C. truncatum and P. exigua.

Materials and methods
The standard agar seed health test was conducted to determine whether C. dematium is seedborne in cowpea. Ten fungicides were evaluated for their efficacy in reducing the pathogens in vitro and C. dematium in vivo, including benomyl, captan, fludioxonil, imazalil/iprodione, iprodione, mancozeb, thiram and triadimenol. An untreated control, hot water soak, sodium hypochlorite treatment and biological control agent were also included. Seeds were artificially inoculated with C. dematium, treated, and percentage germination and percentage infection determined. Percentage emergence and disease incidence were determined in greenhouse experiments.

Results and conclusions
C. dematium was found to be seedborne in cowpea. Mancozeb and imazalil/iprodione were effective in inhibiting mycelial growth of all the fungal species tested. Thiram and fludioxonil inhibited the Colletotrichum spp., and benomyl and triadimenol inhibited P. exigua. Only imazalil/iprodione (half the recommended rate) and thiram significantly reduced percentage germination. With the exception of mancozeb and imazalil/iprodione, both at half the recommended dosage, all treatments significantly decreased the percentage infection of artificially inoculated cowpea seeds. All treatments, except benomyl and the hot water treatment, significantly increased percentage emergence in greenhouse experiments when compared to the control, and percentage disease incidence was significantly reduced by all treatments except mancozeb at the recommended rate.

References
1. Emechebe AM, McDonald D, 1979. PANS 25, 401-404.
2. Neergaard P, 1977. Seed Pathology. Macmillan, London.