RESUMO
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.
RESUMO
Phytophthora citrophthora from citrus in eastern Corsica and Spain consists of distinct clonal lineages. In South Africa the extent of genetic variation among citrus-associated P. citrophthora isolates is unknown. This was investigated with isolates from South Africa (n =60), Spain (n =10) and six isolates representing three P. citrophthora groups CTR1, CTR2 and CTR3 previously identified with isozyme polymorphisms (Mchau and Coffey 1994). South African and Spanish isolates belonged to two lineages (G1, G2) based on an internal transcribed spacer (ITS) phylogeny, random amplified microsatellites (RAMS) and random amplified polymorphic DNA (RAPD) profiling. Although combined RAMS and RAPD data identified 14 genotypes, unweighted pair group method with arithmetic mean (UPGMA) analyses grouped the isolates into two clusters corresponding to lineages G1 and G2. Lineage G1 predominated among isolates from South Africa (92%) and Spain (100%). Phylogenetic analyses of the ß-tubulin, cytochrome c oxidase subunit I (COX1) and ITS regions did not support the hypothesis that the two lineages represent distinct phylogenetic species but suggested that isozyme group CTR2 and possibly CTR3 are species distinct from P. citrophthora sensu stricto. Mating-type analyses, using tester strains from groups CTR2 and CTR3 revealed that most G1 lineage isolates (n =57) were sterile but that some were of the A1 mating type (n =8) whereas all G2 lineage isolates were A2 (n =5). The mating-type designation was confirmed with P. capsici tester strains. However, when A1 (G1 lineage) and A2 (G2 lineage including CTR1 reference isolates) mating-type isolates were paired in all possible combinations, no oogonia or antheridia were produced. This suggests that only tester strains P. capsici, CTR2 and CTR3 were able to produce sexual structures and that lineages G1 and G2 are sterile and reproductively isolated, which is supported by molecular data.
