Diseases of Amaranthus spp. caused by Pythium aphanidermatum and Macrophomina phaseolina

Abstract

Experimental plantings of several species and crosses of Amaranthus were monitored during the 1990–1992 growing seasons to identify diseases that might limit commercial production of grain amaranth in Missouri. Two diseases, previously unreported on the Amaranthus spp. being evaluated in Missouri, are described. Pythium stem canker, caused by Pythium aphanidermatum, was observed when high temperatures coincided with prolonged periods of soil saturation. Tan cankers with black borders developed at the soil line on nearly mature (flowering) plants and lodging was associated with 2.7% of plants examined. Of the species and crosses examined, A. cruentus (cultivar K436) and A. hypochondriacus × A. hybridus (cultivars K432, K433, and K593) were affected most severely by the disease. Differences in susceptibility among the 11 cultivars suggest the potential for the development of disease-resistant cultivars. Charcoal rot, caused by Macrophomina phaseolina, affected A. hypochondriacus × A. hybridus (cultivars K432 and K433) growing in two mid-Missouri locations in 1990. Key words: Amaranthus cruentus, Amaranthus hypochondriacus, Amaranthus hypochondriacus × Amaranthus hybridis, charcoal rot, grain amaranth, stem canker.