Evaluation of biological seed treatments in combination with management practices for the control of seed-borne late blight in potato

Using an effective fungicide in combination with good management practices during seed tuber cutting and storage, prior to planting, is essential to reducing late blight. The efficacy of two biocontrol agents (Bacillus subtilis and Trichoderma harzianum), and a commercially formulated mixture of the chemical fungicides fludioxonil plus mancozeb, applied as seed treatments in combination with different management practices, were evaluated for the control of seed piece decay caused by Phytophthora infestans. Treatments were made 10 days prior to planting and at planting, and tubers were stored at either 18 degrees C and 95%RH with forced air ventilation at 5950 l min (1)(optimal conditions), at 25 degrees C in the dark without ventilation (sub-optimal conditions), or not stored prior to planting. Seed piece and sprout health were evaluated in vitro and agronomic impacts in field experiments. Results showed that the biocontrol agents provided good control of seed piece decay when seed was re-stored under optimal conditions, but not under sub-optimal conditions. Under optimal conditions, treatment with T. harzianum provided better control of seed piece decay than B. subtilis, reducing disease incidence and severity on average by 73% and 86% respectively. B. subtilis reduced disease incidence and severity on average by 27.5% and 54.5% respectively. Treatment with fludioxonil + mancozeb reduced seed piece decay incidence and severity under both storage regimes. Under optimal conditions, disease incidence and severity was reduced on average by 73% and 86.5% respectively. Under sub-optimal conditions, disease incidence and severity was reduced on average by 45% and 59% respectively. (C) 2012 Elsevier Inc. All rights reserved.