The biology and pathology of the fungus Rhizopusstolonifer, cause of black mould disease of table grapes in Israel

Abstract

Rhizopus stolonifer causes severe losses to Israeli grape exports. The fungus develops on mature berries in the field, during storage at temperatures above 08C and during shelf‐life. It was isolated from naturally contaminated soils throughout the year, and from fruits after mid‐June. The airborne spore population increased in vineyards at the time of fruit maturation and was related to the proximity of stone‐fruit orchards. The size of this population was highly correlated with disease incidence and thus may be a satisfactory tool for disease prediction. Intact young berries were more resistant than mature ones to Rhizopus inoculation, in both the vineyard and in the laboratory. Mechanical wounding, or chloroform dips, dramatically increased the susceptibility of young berries. The decline in acidity and the increase in the soluble solids content during growth and maturation of the berry were accompanied by an increase in susceptibility to inoculation. Scanning electron microscopy showed the fruit surface to be covered with white amorphous structures. At higher magnifications small cracks (approximately 1 μm in length) were observed on the surface but in no case was fungal penetration noticed through these cracks. In artificially inoculated fruits the fungus germinated near the wound and developed vigorously inside and around the fissure, producing sporangia. The young sporangium is covered by a smooth external layer which is compressed against the sporangiospores. After lysis of the cover, the young hexagonal sporangiospores can be observed. With maturation, the columella collapses and the mature sporangiospores are dispersed. In naturally infected berries, an important path for fungal penetration is the incomplete connection between the berry and the pedicle. Heavily infested berries become disconnected from their pedicles. Two chemicals applied to the surrounding atmosphere, orthophenyl phenate (as a fog) and calcium hypochlorite (as chlorine vapour), significantly decreased postharvest decay in artificially inoculated berries.

Biological Control of Post-harvest Disease of Blue Mould (Penicillium expansum) of Pear Fruit by using Antagonist Microorganisms under Laboratory and Cold Storage Conditions

“…This may be explained by the fact that T. harzianum is a strictly wound -parasite, so it can penetrate host tissues only through bruises and fresh wounds, especially in the fields through harvesting, handling, insects, and rodents (Barnes, 1979;Lisker et al, 1996). A similar significant effect was obtained in a previous study in controlling P. expansum on unwounded apple fruits (Batta, 2004) when these fruits were dipped for 30 in formulated T. harzianum conidia before being inoculated by P. expansum compared to the wounded fruits.…”

Direct penetration of Rhizopus stolonifer into stone fruits causing rhizopus rot

“…Rhizopus stolonifer infection has already been reported for several hosts. The infection on grapes can occur due to the release of cellular substances caused by injuries to berry pedicels or incomplete connections between berry and pedicel (Lisker et al, 1996;Tavares & Silva, 2006). Furthermore, it was found that the removal of the raspberry receptacle during harvest resulted in a cavity, which released substances that promoted a favourable humidity and nutrient supply for Rhizopus development (Davis, 1991).…”

Rhizopus stolonifer (Soft Rot)

“…Eventually, dark sporulation forms a mass of black sporangia at their tips, covering the entire surface of the commodity. Lisker et al (1996) reported that germinating Rhizopus spores in inoculated grapes were observed after 12-15 h; one h later, germ tubes started to develop and, after 24 h, fruit was covered by hyphae. For tomatoes, no germination took place by 5 h (Fig.…”

“…For the control of this fungus, calcium and sodium hypochlorite have also been tested on table grapes cv. 'Shami' and tomatoes 'V 2 type', respectively (Abdell-Mallek et al 1995;Lisker et al, 1996), resulting in an average efficiency of 100% on table grapes and 47% on tomatoes. Scientific research has proved that ozone (O 3 ) is another method for controlling decay caused by R. stolonifer.…”