Cheryl L. Lennox

DMI sensitivity and cross-resistance patterns of Rhynchosporium secalis isolates from South Africa

Abstract Isolates of R. secalis were collected yearly from the Ruens area of the Western Cape during the 1993–1995 growing seasons. These isolates were evaluated in vitro to determine sensitivity to triazole fungicides (triadimenol, tebuconazole, flusilazole and propiconazole). The sensitivity fluctuated but in 1995 isolates were significantly less sensitive towards triadimenol than in the previous two years. In a second experiment, isolates collected from two fields with a 5–6 year history of triadimenol seed treatments and tebuconazole applications were evaluated for their fungicide sensitivity. A significant positive correlation was observed between tebuconazole and triadimenol sensitivity among R. secalis isolates from these fields. However, such a correlation was not found within the R. secalis population collected during 1993–1995 where shorter crop rotation patterns and a range of fungicides were applied. In a third experiment, the fungicide sensitivity of local R. secalis isolates was evaluated towards two new triazole fungicides, namely bromuconazole and triticonazole. Correlation coefficients observed between these new triazoles and those previously applied in South Africa were not significantly positive. The lack of significant cross-resistance has important practical implications for management of fungicide resistance.

First Report of Coniella granati Fruit Rot and Dieback on Pomegranate (Punica granatum) in the Western Cape of South Africa

Shoot dieback and necrotic black lesions were observed on pomegranate trees (Punica granatum Linn.) in commercial orchards in South Africa near Ladismith and Malmesbury in 2011. Postharvest fruit rot was identified from an orchard near Malmesbury in 2011. Affected fruit decayed after two months storage (5 – 7 C) and were covered with globose brown pycnidia (mean length x width: 113 x 102 μm; diameter range 72 – 149 μm; 40 spores). Fungal cultures isolated from fruit and shoot symptoms were morphologically identified as Coniella granati Sacc. Petrak and Sydow (synonym Pilidiella granati Saccardo; Alvarez et al., 2016). Hyphae were septate with hyaline, one-celled, ellipsoid to fusiform conidia (10.15 to 14.39 x 2.67 to 4.42; average of 20 spores: 11.35 × 3.28 μm). Sequence data of the translation elongation factor alpha gene (TEF1, MG255164), and internal transcribed spacer region (ITS1-5.8S-ITS2; Genbank Accession No. KU666470, KU666471) confirmed identifications with 99-100% similarity to reference sequ...

The Effect of Leaf Shredding on Apple Scab in South African Orchards

The South African apple industry currently relies entirely on chemical fungicides to control apple scab (Venturia inaequalis). In this study, the effectiveness of sanitation strategies in reducing scab incidence and severity in South African orchards was evaluated. Over three seasons, leaf shredding with no fungicide sprays was tested against a nonsprayed, nonshredded negative control, a positive control that followed a commercial fungicide program, and a combined treatment of a commercial fungicide program with leaf shredding. Two treatment replicates were applied in a randomized block design in each of two orchards. Scab incidence and severity on fruit and leaves were assessed weekly from green-tip until fruit-set in the following spring. Pooled data from the 3 years revealed that fruit scab incidence and severity and leaf scab severity (51, 55, and 39%, respectively, P < 0.05) and leaf scab incidence (33%, P < 0.1) were significantly lower in the leaf-shredding treatment than in the negative control. This is the first study to evaluate the effect of leaf shredding in reducing scab in South African orchards. Results indicate that this treatment is highly effective and should be integrated into scab management strategies in future, but should be customized to suit South African orchard conditions.

Morphological and molecular identification of fungi associated with South African apple core rot

Core rot is a major contributor to postharvest losses in apples worldwide. Pathogens most commonly associated with the disease are Alternaria spp. and Penicillium spp. Although both genera show specific morphological characteristics, they can be difficult to identify to species level. In this study, Alternaria spp. (49) and Penicillium spp. isolates (97), associated with pre- and post-harvest apple core rot-symptoms and isolates from potential inoculum sources were identified using molecular methods. Initially, dry core rot causing Alternaria spp. were identified morphologically in an average of 70% of infected fruit pre-harvest and 32% postharvest. Furthermore, 78% of mouldy core rot causing pathogens were identified as Alternaria spp. preharvest and 40% postharvest. Wet core rot was associated with Penicillium spp. in 64% of cases preharvest and 36% postharvest. Species identity of a selection of samples was confirmed using the endopolygalacturonase (endo-PG) gene, the ITS region, and the anonymous genomic regions (OPA1–3, 2–1), which resulted in the identification of A. alternata, A. arborescens, A. dumosa, A. eureka and A. tenuissima. Penicillium species were identified through ITS sequencing and partial beta-tubulin polymerase chain reaction – random fragment length polymorphisms (PCR-RFLP) for the samples collected from wet core rot symptoms. Phylogenetic analyses separated the Alternaria spp. into five clades, including three separate clades for A. alternata, A. tenuissima and A. arborescens, respectively. This is the first report of A. eureka and P. polonicum as potential core rot pathogens. Phylogenetic analysis identified Penicillium ramulosum and P. expansum as the most commonly occurring species associated with WCR symptoms.