Thomas Thomidis

Testing variability in pathogenicity ofPhytophthora cactorum, P. citrophthora andP. syringae to apple, pear, peach, cherry and plum rootstocks

The relative virulence ofPhytophthora cactorum andP. syringae originating from almond trees, and ofP. citrophthora originating from citrus, to apple, pear, peach, cherry and plum rootstocks, was studiedin vivo andin vitro. Results of the different experiments were in good agreement. All testedPhytophthora isolates showed little virulence to pear rootstocks-causing only minor crown rot symptoms - and no virulence at all to apple rootstocks. In contrast, they were highly virulent to stone fruit rootstocks, causing crown rot disease. The non-pathogenicity of these isolates to pome rootstocks could be interpreted as strict host specificity.

Studies on Diaporthe eres as a new pathogen of peach trees in Greece.

Phomopsis sp., the imperfect stage of the genus Diaporthe, is an increasingly common fungal pathogen of peach (Prunus persica). This study is the first report of the occurrence of a shoot blight and canker disease of peach in Greece caused by the fungus Diaporthe eres. The pathogen caused distinct cankers with abundant gumming on shoots of peach and nectarine trees. The rate of development of D. eres in vitro was reduced as temperatures increased from 25 to 30°C or decreased from 25 to 15°C, and was totally inhibited at 35 and 10°C. Storage at 10°C of peach fruit inoculated with D. eres controlled the development of fruit rot. Pathogenicity tests showed that 27 peach and nectarine cultivars grown in Imathia Prefecture, Greece, were equally susceptible to D. eres. The fungicides thiophanate methyl, carbendazim, tebuconazole, iprodione, and the mixture of cyprodinil:fludioxonil were evaluated against the development of D. eres and the disease symptoms. Thiophanate methyl, carbendazim, and tebuconazole significantly inhibited the growth of D. eres whereas iprodione and the mixture of cyprodinil:fludioxonil were less effective in inhibiting mycelial growth and disease symptoms. The sensitivity of 24 isolates of D. eres to carbendazim, thiophanate methyl, and tebuconazole was also tested. The results showed that most of the isolates used were sensitive to these fungicides, with some isolates showing a level of insensitivity. In general, the disease caused by D. eres could be a threat for peach cultivation in Greece and its management should be investigated in the field.

Neofusicoccum parvum associated with fruit rot and shoot blight of peaches in Greece

Shoot blights and fruit rots comprise the most serious diseases of peaches in Greece. In this study, the importance of the fungus Neofusicoccum parvum as a casual agent of a fruit rot and shoot blight of peach trees in Greece was investigated. This pathogen was isolated from both immature and mature peach fruit of the cultivar “Catherine” and later on from mature fruit of the peach cultivars “Andross”, “RedHaven”, “Sun Crest” and “Sun Cloud”. In the first year of investigation, N. parvum was found causing preharvest fruit rot and shoot blights of peach trees only at the location “Ammos-Mesi-Meliki Verias” in the prefecture of Imathia (the main peach production area of Greece) at incidences of 30 and 8%, respectively. However, in 2006 N. parvum was isolated from more locations such as Diavatos, Veria, Kopanos and Agia Marina in the prefecture of Imathia, but only at less than 3% of the total surveyed rotted peach fruit and blighted shoots. The pathogen overwintered as sub-epidermal pycnidia in blighted shoots or mummified fruit that remained on peach trees. This study also showed that the optimum temperature for mycelial growth and conidial germination of N. parvum was 25 ºC. Pathogenicity tests using peach fruit showed that isolates of N. parvum and Diplodia seriata (isolated from pistachio grown in the same region) showed no significant differences in their virulence. In laboratory inoculation tests using detached shoots from 25 peach and nectarine cultivars, N. parvum isolates obtained from rotted peaches caused different size cankers on these cultivars. The cultivar Big Top was the most susceptible while the cultivar Maria Bianca the least susceptible.

Effect of Soil Plowing and Fertilization on the Susceptibility of Four Olive Cultivars to the InsectBactrocera oleae and the FungiSphaeropsis dalmatica andSpilocaea oleagina

Susceptibility to the insectBactrocera oleae and the fungiSpilocaea oleagina andSphaeropsis dalmatica was investigated in four olive cultivars, two for table fruit production (Kalamon and Chondrolia Chalkidikis) and two for oil production (Lianolia and Koroneiki). Cv. Chondrolia Chalkidikis was the most susceptible to all three pathogens, followed by cv. Kalamon. Soil plowing and the organic fertilizer Bio-Trust® (10-3-6+8% MgCO3+10% CaCO8) increased the susceptibility of all four tested olive cultivars to the insect and the two fungi. Correlations were found between the attacks byB. oleae and infections byS. oleagina andS. dalmatica on the four olive cultivars.

Influence of Rootstocks, pH, Iron Supply (in Nutrient Solutions) and Agrobacterium radiobacter on Chlorophyll and Iron Concentration in Leaves of a Peach Variety

ABSTRACT In this study, the influence of rootstocks, pH, iron (Fe) supply (in nutrient solutions), and Agrobacterium radiobacter on the leaf chlorophyll and Fe concentration of the peach cultivar ‘Sun Crest’ was investigated. The results showed that chlorophyll index (SPAD-502) and active Fe differed significantly at different pH levels. Chlorophyll index was highest at pH 6.0 and 9.0 and lowest at pH 7.0 and 8.0 Leaf active Fe concentration was highest at pH 6.0 and 7.0 Significant differences between rootstocks and interactions were also found. Chlorophyll index was highest in the leaves of GF677, Antafuel and MRS 2/5, while the leaves of seedling had the lowest chlorophyll index and chlorophyll a and b concentration. The chlorophyll index in the leaves of St. Julien 655/2 did not differ from those of MRS 2/5. However, seedling had the highest leaf active Fe concentration. Supply of trees with different Fe levels (in solutions) did not affect positively the leaf chlorophyll index, chlorophyll a and b concentration, or active Fe concentration. The leaf chlorophyll index and active Fe in the rootstocks GF677, Antafuel, and Siberian C were significantly reduced in trees inoculated with Agrobacterium radiobacter.

Preliminary evaluation of nine fungicides for control ofPhytophthora cactorum andP. citrophthora associated with crown rot in peach trees

Excised twig assay and excised stem inoculation were used to evaluate nine fungicides (metalaxyl, fosetyl-Al, copper hydroxide, copper sulfate, copper oxychloride, captan, quintozene, propamocarb and chlorothalonil) againstPhytophthora cactorum andP. citrophthora associated with crown rot in peach trees. Segments were soaked in fungicide solutions at different concentrations and then inserted vertically intoP. cactorum orP. citrophthora cultures growing on cornmeal agar plus antibiotics, or inoculated by inserting a mycelium-bearing agar plug directly into the cambium. Following incubation, the bark was scraped off and length of necrosis was measured. Metalaxyl was the only fungicide that inhibited canker development on segments at the manufacturer-recommended concentration. Fosetyl-Al, captan, copper hydroxide and copper sulfate inhibited canker development at 3, 4, 4 and 8 gl-1, respectively. The other fungicides did not affect canker length significantly compared with non-treated twigs, with the exception of propamocarb, which reduced the development ofP. cactorum on excised stems. The tested methods enabled rapid and effective evaluation of a large number of chemicals to prevent crown rot diseases caused byPhytophthora in the laboratory.

Development and implementation of cost-effective strategies to manage brown rot of peach trees in Imathia, Greece

Development of cost-effective strategies to manage brown rot caused by Monilinia laxa of peach implies a better understanding of the susceptibility of different cultivars and pre-harvest contamination. This study investigated the susceptibility of 24 peach and nectarine cultivars to shoot blight caused by Monilinia spp. and found various levels of susceptibility, with the nectarine cultivar Tasty Free scored as the most susceptible. Studies on the the existence and detection of latent infections by Monilinia spp. in three peach (‘A37’, ‘Andross’, and ‘E-45’) and three nectarine (‘Venus’, ‘Fantasia’, and ‘Tasty Free’) cultivars were also conducted. The results showed that latent infections were detected only in nectarine cultivars when fruit were collected on 23 May and 22 June. In contrast, nectarine fruit collected on 7 June and all peach cultivars tested had no detectable latent infection. This study also indicated that the fungicide thiophanate methyl applied at the pit hardening stage reduced significantly the percentage of latent infection and subsequently preharvest fruit rots. Finally, a disease forecast model to predict blossom blight, caused by M. laxa, was evaluated in the Prefecture of Imathia, Greece. Trees, sprayed according to the model predictions, showed a statistically lower percentage of blighted shoots than those of unsprayed trees.

Effect of zinc on the leaf mineral content, yield, fruit weight and susceptibility of peaches to Monilinia laxa

The effect of zinc sulfate and zinc chelate on the leaf mineral content, yield and fruit weight of the peach variety Andross was investigated in a Greek orchard. Foliar application of a 25% zinc sulfate solution on 25 February and 2% zinc chelate solution on 20 May increased the zinc content of leaves and no toxicity was observed. In contrast, foliar application of 6% zinc sulfate and soil application of zinc sulfate at a rate of 200 g/tree on 25 February did not affect the zinc content of leaves. However, zinc sulfate applied to the soil at a rate of 200 g/tree significantly increased fruit yield. Statistically, the mean fruit weight and the susceptibility of fruit to Monilinia laxa did not differ between treatments. However, postharvest fruit susceptibility to M. laxa increased when fruit were dipped in a zinc chelate solution.

Documentation of field and postharvest performance for a mature collection of quince (Cydonia oblonga) varieties in Imathia, Greece

Abstract In this study, the adaptation of 49 quince (Cydonia oblonga) varieties in Naoussa, northern Greece was investigated. All varieties bloomed after 6 April. Apart from the varieties 11107 and 11150, the ripening period of fruits for all varieties was between 27 September and 6 October. The most productive varieties were 11111, 11113, 11108, 11102, 11103, 11114, and 11115. Productivity ranged from 97 to 125 kg per tree. Apart from 11111, relatively low fruit drop percentage was observed for these varieties. Varieties 11111, 11113, 11108, 11102, 11103, 11114, and 11115 were relatively tolerant to natural infections from fire blight. After 4 months of cool storage (2–4°C), varieties 11111, 11113, 11108, 11102, 11103, 11114, and 11115 were moderately susceptible to bitter pit and breakdown. Varieties 11102, 11103, and 11113 were resistant to decay, whereas 11108, 11111, 11114, and 11115 were moderately resistant. Varieties 11102 and 11103 were resistant to scald, whereas varieties 11111, 11113, 11108, 11114, and 11115 showed moderate susceptibility to scald.

Variation in virulence of Greek isolates ofPhytophthora citrophthora as measured by their ability to cause crown rot on three peach rootstocks

The virulence ofPhytophthora citrophthora isolated from various host-plants on three peach rootstocks (GF677, PR204, KID I) was examined. There was no significant difference among the rootstocks with respect to their susceptibility to testedP. citrophthora isolates. The most virulent isolate originated from sycamore (Acer pseudoplatanus); isolates from pistachio trees (Pistacia vera) also showed high virulence but were significantly less virulent than the sycamore isolate. Isolates originating from plum (Prunus domestica), almond (Prunus amygdalus) and lemon (Citrus limon) trees were moderately virulent on peach rootstocks; those from cyclamen (Cyclamen persicum) showed the lowest virulence of those tested. There was thus great variation in virulence among the testedP. citrophthora isolates. It is possible that the isolates ofP. citrophthora from sycamore, pistachio, plum, almond and lemon trees are a threat to peach trees, whereas the low virulence of the isolates from cyclamen hosts suggests that these pathogens are not a serious threat to peach trees.