Charcoal rot of sugar beet

Abstract does not appear. First page follows.

Introduction

Charcoal rot of sugar beet (Beta vulgaris L.), caused by Macrophomina phaseoli (Maubl.) Ashby, was found in August, 1932, in Sutter County in the Sacramento Valley and subsequently near Davis, Marysville, Walnut Grove, and on Victoria Island in the delta region west of Stockton. The incidence of infection in numerous fields ranged from 8 to 30 per cent ⁽⁵⁾.4 Field observations indicated that the fungus attacks half-grown and mature sugar beets during the season of prevailing high temperatures and is probably confined to the hot, interior valleys. It is not known to cause damping-off of sugar-beet seedlings. Inspection of sugar-beet plantings in the cool, coastal valleys has shown them to be free from infection.

In studies of a seedling blight of beans (Phaseolus vulgaris L.) caused by this fungus, Kendrick ⁽³⁾ showed that the disease was favored by high temperatures. Later, under controlled conditions, Tompkins and Gardner ⁽⁶⁾ corroborated Kendrick’s results and found that the fungus from charcoal rot of sugar beet grew throughout a temperature range of 12° to 37° C, with an optimum at 31° and was pathogenic to bean seedlings at high temperatures.

A brief discussion on symptoms of the disease, the causal organism, and pathogenicity of the fungus is presented in this paper.

Symptoms of the Disease

The leaves of diseased plants show pronounced wilting and eventually turn brown and die. Dead leaves remain firmly attached to the crowns. When an infected plant is pulled from the soil, the symptoms of charcoal rot are distinctive enough to readily differentiate it from all other known root rots of sugar beet. Externally, infection is usually confined to the crown region as indicated by brownish-black5 lesions of irregular size and shape (fig. 1) and with a silvery sheen.