Aims:  A Bacillus amyloliquefaciens strain, surviving epiphytically on the surface of fruit, was isolated while searching for naturally occurring biological control agents. This bacterial strain was characterized for its antifungal activity against seven selected fungal postharvest pathogens of citrus. Methods and Results:  To understand the antifungal activity, seven postharvest fungal pathogens were screened for growth inhibition by B. amyloliquefaciens strain. Assays using B. amyloliquefaciens lipopeptide extracts showed a strong inhibitive activity. The inhibitory effect was observed in abnormal conidial germination and germ tube development when conidia were treated with different lipopeptide extract concentrations. Further analysis using PCR and chromatography confirmed the presence of fengycin, iturin and surfactine, of which iturin A showed the strongest and most common inhibitory effect. The results are supported by site‐directed mutagenesis analysis, targeted to suppress the biosynthesis of iturin A production. Fruit trials confirmed disease development inhibition when the antagonist was applied 1 day prior to or 1 day after fungal application. Conclusions:  We conclude that the iturin family of lipopeptides are vital in the antagonism of B. amyloliquefaciens against the seven citrus postharvest pathogenic fungi tested. Significance and Impact of the Study:  We elucidated the principal mechanism used by B. amyloliquefaciens PPCB004 to suppress postharvest disease development on stored fruits.

If South African citrus exporters wish to retain their competitive edge in the European market and access new markets such as the United States of America, it is of quarantine importance to distinguish between the citrus black spot pathogen, Guignardia citricarpa, and the harmless endophyte, G. mangiferae. The endophyte is not a sanitary or phytosanitary concern. This paper describes the design of species-specific primers that are able to detect and distinguish between these two Guignardia species. Application of the primer set CITRIC1 and CAMEL2 in conjunction with the ITS4 primer yielded polymerase chain reaction (PCR) amplicons of approximately 580 bp and 430 bp for G. citricarpa and G. mangiferae, respectively. Results obtained with these primers are in accordance with sequence data, and repeated tests verified accuracy and sensitivity. A BLAST search revealed no matches other than G. citricarpa and G. mangiferae, and no positive PCR results were obtained with Colletotrichum gloeosporioides, which is the most common contaminant in black spot lesions. We are, therefore, able to distinguish G. citricarpa and G. mangiferae unequivocally using a PCR-based method. This method was further improved to directly isolate DNA from fruit lesions by means of the DNeasy Plant Mini Kit (Qiagen). This eliminates the prior need for culturing the slow-growing organism, thereby shortening the time required to one day to test for and verify the presence or absence of the pathogenic G. citricarpa in export consignments.

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Strict quarantine measures for the export of South African citrus fruit to European and US markets require the development of sensitive and accurate detection methods for the pathogen Phyllosticta citricarpa -a fungus causing citrus black spot disease. Because of the presence of other, non-pathogenic Phyllosticta species, rapid and accurate verification of the Phyllosticta species present on exported citrus fruit is important to producers, exporters and regulatory authorities to prevent unnecessary losses. We have analysed over 800 samples collected over 7 years and have compared sample preparation and detection protocols applied in different environments: nurseries, production systems including phytosanitary inspections in orchards, pack houses and export terminals in order to compile protocols for the detection of P. citricarpa. Standard procedures of sample preparation and DNA extraction were adapted to suit diverse inoculum sources. Low pathogen numbers in symptomless green leaves, for example, obliged the use of a wet-dry enrichment technique constituting the stimulation of fungal growth for easier detection. Physical maceration was adapted for sturdy material using liquid nitrogen or bead beating. The use of a two-step polymerase chain reaction (PCR) with nested primers significantly increased both the sensitivity and the specificity of the PCR performed on soil samples, overcoming problems with relatively impure DNA extracts and low pathogen numbers. The assays have proven to be highly consistent, thereby providing a reliable, reproducible and highly sensitive detection and diagnostic service to the southern African citrus industries in order to sustain market access.

This test was conducted at the North Alabama Horticulture Substation, Cullman. Tomato transplants were set on Jun 13. Plots consisted of 3 rows, 25 ft long (88-inch centers), with 5-ft alleys. A randomized complete block design with 4 replications per treatment was used. Sprays were initiated when fruit began to set. All applications were made with a Super Blue Boy 6000 high clearance sprayer. Treatments were applied on Aug 5, 12, 26, Sep 2, 9 and 27. For disease control, Manzate 200 (at 1.6 lb ai/acre) was applied early in the season and Difolafan (at 1.0 lb ai/acre) was used late in the season. Tomatoes were harvested 5 times (Aug 25, Sep 1, 8, 16 and 23). Damage and yield data were taken from the middle row of each plot. All fruits were examined visually, and dissected when necessary, to determine damage by the fruitworm.