Rhizopus Head Rot of Confectionery Sunflower: Effects on Yield Quantity and Quality and Implications for Disease Management

Abstract

The effects of Rhizopus head rot, caused by Rhizopus oryzae, on the yield of confectionery sunflower and its quality were studied in field experiments conducted from 1994 to 1996. The extent of yield loss was related to the crop growth stage at inoculation. When heads were inoculated at the budding stage, loss was not apparent, because inoculated heads were not infected. When inoculated at the anthesis stage, loss was relatively high (42.5 to 99.1%), and both the number of achenes per head and the individual achene weight were reduced. When heads were inoculated at the seed development stage, yield was not reduced significantly (although the entire receptacle was rotted). Effects of Rhizopus head rot on measures of yield quality were examined as well. Inoculation with R. oryzae did not affect the size of the achenes at any crop growth stage. In contrast, the incidence of discolored achenes (an external sign of nutmeats with a bitter off-flavor) was affected by the disease at all crop growth stages. A survey in eight commercial fields from 1992 to 1996 found that, by the end of the season, incidence of disease ranged from 2.3 to 17.4%. However, since disease intensified late, resultant yield losses were minor and did not exceed 3.1%. Loss figures were estimated by means of a model that was developed and validated in the field experiments. The disease did affect the incidence of discolored achenes. Thus, the conclusion drawn is that the effects of Rhizopus head rot in confectionery sunflower on crop yield is of minimal concern, at least when disease intensifies late, as was the case in the studied fields, but management of the disease should be considered in some situations. The objectives would be to prevent a reduction in yield quality, not yield quantity.

Carbohydrate-active enzymes from the zygomycete fungus Rhizopus oryzae: a highly specialized approach to carbohydrate degradation depicted at genome level

“…As a causal agent of Rhizopus rot, R. oryzae produces endopolygalacturonases for maceration of plant seedlings, fruits and vegetables and plant structures such as flowers, bulbs and tubers [42-44]. The pectin structure in berries, black currants and apples has been shown to contain a high amount of D-galacturonic acid and a small amount of rhamnose residues, indicating the presence of unbranched pectin [45,46].…”

The family structure of the <I>Mucorales</I>: a synoptic revision based on comprehensive multigene-genealogies

“…2c, d) (Dennis 1983). Thus, these fungi play an important role as plant pathogens as well (Shtienberg 1997). Furthermore, some species of the Mucorales are facultative parasites of other fungi.…”

Rhizopus Stem Rot of Orobanche aegyptiaca caused by Rhizopus oryzae in China

“…Woolly masses of whitish mycelia interspersed with numerous black; spore‐producing sporangia may be evident externally and are especially conspicuous near infected tissues. (Shtienberg ; Kwon et al. ).…”

“…Rhizopus oryzae is a complex of closely related, heterothallic species (Ellis ) that are common, cosmopolitan saprotrophs in soil, dung and rotting vegetation (Shtienberg ; Kortekamp et al. ; Fang et al.…”