Date of Award
Master of Science
Sooty blotch and flyspeck (SBFS) is a serious late-season disease complex that colonizes the cuticle of apples (Malus x domestica Borkh). SBFS causes considerable economic loss to growers by reducing the market value of fruit. In addition, management of SBFS causes indirect economic losses due to the cost of frequent applications of protectant fungicides. Little is known about responses of recently discovered members of the SBFS complex to environmental factors. The optimal temperature for mycelial growth of two isolates of each of five common Midwestern SBFS species (Dissoconium sp. DS1, Colletogloeum sp. FG2, Peltaster sp. P2, Peltaster sp. CS1, and Pseudocercosporella sp. RH1) and one previously described North Carolina species (Peltaster fructicola PI) was determined in vitro growth chambers. The isolates were evaluated at 10, 15, 20, 25, 30 and 35°C in growth chambers for 7 weeks in darkness. Mycelial growth was estimated by measuring the diameter of each colony every 7 to 11 days. Generally, optimum growth occurred at 20 to 25°C for all six species, with slower growth at 10 and 15°C and little to no growth at 30 or 35°C. Determining the temperature requirements for SBFS fungi can contribute to development of more effective disease management strategies. One feasible alternative to reduce SBFS to market-acceptable levels is post-harvest washing and brushing. The effectiveness of five post-harvest dip treatments (NaOCl at 200 and 500 [mU]g/ml, CIO₂ at 1 and 5 [Mu]g/ml, and fruit soap) were evaluated for removal of SBFS on apples. After a 7-minute dip treatment, apples were brushed for 15, 30, 60, or 90 s on a grading line. Percent disease was determined before and after treatment of 'Honey Gold' apples from Iowa and Wisconsin in 2002 and 'Golden Delicious' apples from Kentucky and North Carolina in 2003. Removal of SBFS in all treatments was variable, but generally exceeded the no-dip control. Increasing the brushing time significantly increased removal of SBFS signs. Post-harvest SBFS removal treatments therefore may provide growers with alternatives for improving appearance of SBFS - blemished apples to meet fresh-market standards.
Sandra Milena Hernandez
Hernandez, Sandra Milena, "Response of sooty blotch and flyspeck complex to optimum temperature and post-harvest removal on apples by brushing combined with dip treatments" (2005). Retrospective Theses and Dissertations. 18789.