EFFECT OF CHITOSAN PRETREATMENT ON THE QUALITY OF STRAWBERRIES DURING COLD STORAGE

The paper is focused on improving the technology of storing strawberries. It has been investigated how pretreatment of berries with aqueous solutions of low-molecular-weight chitosan of three concentrations (0.1%, 0.3%, 0.5%) affects the quality parameters of strawberries during refrigeration. The treated berries and the reference (untreated sample) were stored in 500 g perforated plastic containers at 0±2°C for 14 days. It has been found that strawberries treated with chitosan solutions had significantly smaller weight loss than the reference. At the end of storage, this parameter was 9.7% in the reference and 7.0–8.6% in the treated berries. It has been established that the respiration rate of the strawberries decreased sharply on the first day, which was caused by refrigerated storage, and continued to decline until the end of storage. Finally, this parameter attained the value 3.3 mg CO2/kg-1h-1in the reference and 2.2–3.0 mg CO2/kg-1h-1 in the treated berries. The hardness of the strawberries at the end of storage was 0.10–0.14 kg/cm2. The change in the lustre level of the berries has been observed. It has been established that on the 14th day of storage, the surface of the untreated berries was dull. The best characteristics have been observed for treatment at the chitosan concentration 0.5%. The effect of chitosan films on the sensory characteristics of berries has been investigated. It has been found that the pretreatment did not impair the taste of the berries. The results of the tasting evaluation indicate that the taste, aroma, and colour were better in the variants with the treatment concentrations 0.3 and 0.5%. However, as for the appearance and consistency, the experts preferred the berries treated at the concentration 0.5%. After two weeks’ storage, the strawberries have been found to be damaged by four fungal diseases. The infections found in the samples were Botrytis cinerea (grey mould), Rhizopus stolonifer (black mould), Whetzelinia sclerotiorum (white mould), and Penicillium spp. It has been established that pretreatment of strawberries with chitosan solutions reduces the development of phytopathogenic diseases. It has been shown that chitosan-based edible coatings have a positive effect on strawberries, increasing their shelf life and improving their quality. A conclusion has been drawn about the technology of application of chitosan solutions and about their concentrations.

Storage fungi of cabbage and their control

Botrytis cinerea Pers. ex Fr. was found in 40—100 %, in most cases 60—80 %, of the stored cabbages examined during 1975—80. The correlation between the B. cinerea—% and the trimming losses was highly significant when storage lasted for more than 5 months. The trimming losses in infected cabbage lots were 30—50%, while in healthy lots they were only 10—20 %. The numbers of B. cinerea remained constant on the same lots, irrespective of the duration of storage. The fungus caused a considerable amount of spoilage at rather low storage temperatures of—0.5—0°C. Alternaria brassicicola (Schw.) Wiltshire, Plenodomus lingam (Tode ex Fr.) Höhnel, Typhula brassicae (Berg, ex Fr.) Vang, Whetzelinia sclerotiorum (Lib.) Korf & Dumont, and an otherwise unidentified fungus, which presumably belonged to the Basidiomycetes and was only found growing on living cabbages, were present in small numbers or else were significant pathogens in individual stores in certain years only. Spraying with benomyl or thiophanatemethyl one or two weeks before harvesting decreased to a highly significant degree the numbers of B. cinerea on the cabbages, the commercial quality increasing by 8—25 %. Spraying during the growing season did not affect the numbers of any of the other storage pathogens.

Sclerotinia Blight of Peanuts in Oklahoma and Occurrence of the Sexual Stage of the Pathogen1

Sclerotinia blight of peanuts was discovered in Oklahoma in 1972. The disease is caused by Sclerotinia sclerotiorum (Lib.) de Bary varieties “Minor” and “Major” Purdy (Whetzelinia sclerotiorum (Lib.) Korf & Dumont). S. sclerotiorum “Minor” is more prevalent. Sclerotinia blight has been found in seven of the 23 major peanut-producing counties in Oklahoma since its discovery and it is regarded as a major peanut disease. Both fungal varieties overwintered in the field as sclerotia and produced apothecia and ascopores from late April to early June. Peanut plants exposed to natural ascospore discharges in the field became infected with both varieties of the fungus.

Seed-borne fungi on cruciferous cultivated plants in Finland and their importance in seedling raising

The seed-borne fungi of cabbage, swede, turnip, rape, turnip rape, radish and black radish and their importance in seedling raising have been examined in this study. The seed lots used in the study were on sale at seed merchants in Finland during the period 1968 —1976. Alternaria brassicicola (Schw.) Wiltshire was the most common pathogen, being more common on cabbage than on any of the other plant species. 91 % of the white cabbage and red cabbage seed lots were infected. The mean A. brassicicola contents of the infected seed lots were 29.5 % and 30.6 %. Plenodomus lingam (Tode ex Fr.) Höhnel occurred in 10 % of the white cabbage and 27 % of the red cabbage seed lots, the fungus content varying from 0.5 % to 14 %. The fungus was also found on cauliflower, swede and radish. Alternaria brassicae (Berk.) Sacc. was found in 4 % of the cabbage and in 31 % of the rape seed lots at fungus contents of 0.5—6.5 %. Alternaria raphani Groves & Skolko was found in 30 % of the radish and black radish seed lots at fungus contents of 0.5—8 %. The following fungi were also found on the seeds of Cruciferous plants: Pleospora herbarum (Pers.) Rabenh., Whetzelinia sclerotiorum (Lib) Korf & Dumont, Botrytis cinerea Pers., Ulocladium concortiale (Thum.) Simmons, Fusarium spp. and Rhizoctonia solani Kühn as well as 18 fungus genera and species either saprophytic or pathogenic to other plants. When the Alternaria brassicicola content of the seeds was 20 % it caused 10 % damping-off damage on the sand substrate. A similar level of damage occurred on the peat substrate when the fungus content reached 70 %. In addition to causing damping off and damaging the seedlings, the fungus also slowed-down seedling growth without apparently damaging them. When the seedlings were grown at a lower temperature the amount of damage caused by A. brassicicola was much less than that which occurred when a higher temperature was used. Plenodomus lingam caused as much damping-off as there were seeds infected with the fungi. Other seed-borne fungi had no importance in seedling raising. Sphagnum fuscum peat, which is used in Finland as a growth substrate, reduced the amount of damping-off caused by seed-borne fungi in comparison to disinfected substrates and prevented the spread of A. brassicicola and P. lingam from diseased to healthy seeds. Dressing the seeds with thiram proved to be very effective against A. brassicicola.

Effects of phenylthiourea on growth and sclerotial formation of Sclerotium rolfsii and Whetzelinia sclerotiorum

The growth rate of Sclerotium rolfsii and Whetzelinia sclerotiorum was reduced when 5 × 10−4 to 2 × 10−3 M l-phenyl-2-thiourea (PTU) was incorporated into synthetic media and potato dextrose agar (PDA). Whetzelinia sclerotiorum produced heavy aerial mycelia and few, if any, sclerotia in synthetic glucose-nitrate liquid medium containing 10−3 and 2 × 10−3 M PTU. At the same PTU concentrations in PDA, W. sclerotiorum formed abnormal sclerotia covered with a yellowish green exudate. Sclerotium rolfsii produced unusual patterns of aerial mycelia and no sclerotia on media containing 2 × 10−3 M PTU. With 5 × 10−4 and 10−3 M PTU, S. rolfsii produced sclerotial initials and some of these developed into atypical clumps of sclerotia. A yellow pigment developed when S. rolfsii grew on media containing PTU.