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Internal fruit rot, caused by Fusarium lactis, is as an important disease of greenhouse sweet pepper. Fungal growth was studied microscopically during anthesis and fruit development. Hyphae were observed on the stigmatal surface one day after inoculation (DAI), and in the transmitting tissues of the style and inside the ovary at 5 and 6 DAI. Symptomless seeds from infected fruits yielded colonies of F. lactis when cultured axenically, and typical disease symptoms were observed when fruits were dissected at 45 DAI. Isolates of F. lactis and the related species F. proliferatum and F. verticillioides, which are also associated with internal fruit rot, produced the mycotoxins beauvericin, moniliformin and fumonisin B1 in various combinations, both in infected fruits and in vitro. These findings suggest that internal fruit rot is initiated through infection of the stigma and style during anthesis, and that mycotoxin contamination of infected fruit could pose a health concern. / Plant Science

No description available.

Thesis (M.Sc. (Horticulture)) -- University of Limpopo, 2022 / The South African Avocado Industry has recently announced plans to expand exports into new markets, such as the United States (US). As a requirement for these markets, fruit of high quality must be stored at ultra-low temperature to mitigate phytosanitary risks. However, ‘Hass’ avocado fruit are susceptible to chilling injury when stored at temperatures below 3°C. Moreover, CI development resulted in uneven ripening and disease infestation due to damaged cell membranes. Therefore, the objective of this study was to evaluate the potential of methyl jasmonate (MeJA) and salicylic acid (SA) on quality maintenance of 'Hass' avocado fruit during ultra-low cold storage. Matured ‘Hass’ avocado fruit were harvested at commercial dry matter (22%). The experiment was conducted using a completely randomized design (CRD) with eight replications per treatment. Treatment concentrations for methyl jasmonate (MeJA) were 0 (control), 10 and 100 μmol•L−1 , while those for salicylic acid (SA) were 0 (control), 1.0, 2.0 and 3.0 mM. After treatments, fruit were stored at 2°C for 31 days and thereafter, ripened at ambient temperature (±25°C) until fully ripe. During ripening, fruit were evaluated for weight loss, exocarp colour, firmness, chilling injury, as well as physiological (vascular browning) and pathological disorders (fruit rot). In this study, dipping fruit in MeJA solution significantly (P < 0.05) reduced ‘Hass’ avocado fruit firmness loss. Moreover, MeJA showed a significant effect (P < 0.05) on hue angle (h°) but did not significantly affect (P > 0.05) visual colour rating, chroma (C*), lightness (L*) and weight loss. The results showed that ‘Hass’ avocado fruit treated with 10 μmol•L−1 MeJA reduced weight loss when compared with 100 μmol•L−1 MeJA from day 2 to day 8 of ripening. Overall results showed a visual change in ‘Hass’ avocado fruit exocarp colour, with eye colour changing from rating 1 (emerald-green) to 3 (olive- green) for control and fruit treated with MeJA throughout the ripening days. Furthermore, MeJA reduced ‘Hass’ avocado fruit external chilling injury, physiological and pathological disorders. With respect to SA treatments, the result showed that dipping fruit at 1.0 and 2.0 mM SA had a significant effect (P < 0.05) on reducing firmness loss during ripening. Salicylic acid (1.0 mM) reduced and alleviated ‘Hass’ avocado fruit external chilling injury during ultra-low cold storage. Furthermore, result showed that 1.0 and 2.0 mM SA treatments had significant affect (P < 0.05) on firmness loss. Moreover, a significant effect was observed on visual colour and C* but did not affect (P > 0.05) L* and h°. Fruit treated with SA showed poor exocarp colour development with extended exposure to ultra-low cold storage, as a result, developed chilling symptoms. The treatment of ‘Hass’ avocado fruit with 1.0 mM SA inhibited the incidence of fruit rot and vascular browning when compared with control and fruit treated with 2.0 and 3.0 mM SA. In conclusion, 10 and 100 μmol•L−1 MeJA and 1.0, 2.0 and 3.0 mM SA effectively preserved ‘Hass’ avocado fruit quality during storage at ultra-low temperature. / Agricultural Sector Education Training Authority (AgriSeta) and National Research Foundation (NRF)