Integration of Elicitors and Less-Susceptible Hybrids for the Control of Powdery Mildew in Organic Tomato Crops.

Powdery mildew is a serious economic problem in Mediterranean tomato production. The disease is currently controlled by fungicides (especially sulfur) in both conventional and organic production. Four factorial greenhouse experiments were conducted in successive cropping seasons (autumn 2005, autumn 2006, spring 2006, and spring 2007) to assess the main and combined effects of (i) a less-susceptible hybrid ('Elpida'), (ii) chitin soil amendment, or (iii) Milsana or chitosan elicitor foliar treatments on the severity of powdery mildew and crop performance. Analysis of variance revealed significant effects of cropping season on disease severity and crop yield. All control practices reduced disease severity; reductions of approximately 40, 30, 15, and 15% were achieved by Milsana foliar treatment, the use of a less-susceptible hybrid, chitosan foliar treatment, and chitin soil amendment, respectively. In the season with the highest disease pressure, higher yields were obtained with the less-susceptible hybrid Elpida whereas, in the three seasons with no or low disease pressure, the use of the more susceptible hybrid 'Bison' produced higher yields. Milsana and sulfur treatments did not significantly affect yield (yields were slightly lower compared with untreated control plants) and, therefore, their use cannot be recommended based on the results obtained.

Effect of alternative treatments on seed-borne Didymella lycopersici in tomato.

AIMS: To quantify the phytotoxicity and effect of alternative seed treatments based on acidified nitrite and elicitors of plant resistance (Tillekur and Chitosan) against seed-borne inocula of Didymella lycopersici. METHODS AND RESULTS: Treatments tested were: nitrite [sodium nitrite in citric acid buffer (pH 2)] at 30, 100 and 300 mmol l(-1) and three exposure times (10, 20 and 30 min); Tillekur (in water) at 12.5, 25, 50, 100 and 200 mg ml(-1); Chitosan (in 0.05% acetic acid) at 2.5, 5, 10 and 50 mg ml(-1). Efficacy of treatments was determined in growth chamber experiments. Nitrite at 300 mmol l(-1) was completely effective, as was the fungicide, at controlling disease when applied for less than 20 min. Tillekur was as effective as the fungicide postemergence, but proved to be phytotoxic pre-emergence. Chitosan was significantly less effective than the other treatments. CONCLUSIONS: The high efficacy and low cost of acidified nitrite indicates that it is a suitable alternative to fungicides. SIGNIFICANCE AND IMPACT OF THE STUDY: There is currently a lack of effective seed treatments that can be used in organic and low-input crops. Treatments identified in this study can be considered as an effective alternative to chemical control against seed-borne fungal pathogens.