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.

First Report of Pseudomonas viridiflava Causing a Bacterial Blight of Artichoke Bract Leaves.

In 2006, a disease was observed on two artichoke (Cynara scolymus L. cv. Lardati) fields in Crete, Greece, covering ~2 ha. Symptoms developed after several days of rainy and windy weather and >70% of capitula were affected, resulting in unmarketable produce. Initial symptoms were water-soaked, dark green spots on bracts with many sunken, necrotic, often elongated lesions, each with a brown-black center and surrounded by a water-soaked halo with a dark red-brown margin. Symptoms were more severe on inner bracts. Isolations from symptomatic, surface-disinfected bracts onto King's B agar medium (KB) consistently yielded yellow bacterial colonies that produced a green-blue fluorescent pigment. Ten selected artichoke isolates, all gram-negative, presented the LOPAT profile (- - + - +) and were levan negative, oxidase negative, potato rot positive, arginine dihydrolase negative, and showed tobacco hypersensitive reaction. All isolates used L-arabinose, D(-)-tartrate, and L-lactate, but not sucrose, L(+)-tartrate, or trigonelline. Results were identical to those obtained with the reference strain of Pseudomonas viridiflava NCPPB 1249 (3), and strains PV3005 and PV3006 from eggplant (1). Based on these biochemical tests, 10 isolates were identified as P. viridiflava group II members of the LOPAT determinative scheme of Lelliott (1,2). Two artichoke isolates (PV608 and PV609) were selected for molecular characterization. The identity and phylogenetic analysis were determined by multilocus sequence typing with the gyrB, rpoD, and rpoB genes (PV608 Accession Nos. JN383375, JN383363, and JQ267546; PV609 Accession Nos. JN383376, JN383364, and JQ267547). BLAST searches showed highest nucleotide sequence identity (96%) with GenBank sequences of P. viridiflava reference strains NCPPB 963 and CFBP 2107. Pathogenicity of 10 artichoke isolates and reference strains was tested twice on detached capitulum bracts of artichoke cv. Lardati, as well as 4-week-old tomato plants of cv. ACE, and Chrysanthemum indicum cv. Reagan plants. Each isolate was inoculated onto 10 bracts by placing 15 µl of bacterial suspension (5 × 106 CFU/ml) of a 48-h culture in KB broth on the surface of the bract, and pricking the bract through the drop of bacterial suspension with a sterile needle. Each isolate was also inoculated onto five tomato and five chrysanthemum plants by dipping a sterile toothpick in the appropriate bacterial culture and pricking the surface of the stem. Ten control plants were inoculated similarly with sterile, distilled water. Inoculated bracts and plants were kept in boxes lined with moist filter paper at 25 to 30°C and 80 to 100% relative humidity. Lesions developed on detached bracts within 72 h and were similar to those observed on the naturally infected plants. On tomato and chrysanthemum plants, pith necrosis and wilting symptoms were induced within 1 week of inoculation. Symptoms were not observed on control bracts and plants. Bacterial colonies were reisolated from bract lesions and stems with pith necrosis, but not from control plants, and the reisolates had the same LOPAT profile as the original isolates of P. viridiflava, thus fulfilling Koch's postulates. To our knowledge, this is the first report in the world of P. viridiflava causing a disease of artichoke bracts. References: (1) D. E. Goumas et al. Eur. J. Plant Pathol. 104:181, 1998. (2) Lelliott et al. J. Appl. Bacteriol. 29:470, 1966. (3) M. L. Saunier et al. Appl. Environ. Microbiol. 62:2360, 1996.

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.