Field Susceptibility of Four Peach Rootstocks to «Phytophtora citrophthora» and «P. syringae»

Four two-year-old peach rootstocks were assessed for susceptibility to Phytophthora citrophthora and P. syringae. Peach rootstocks reacted differently to each Phytophthora species. GF677 rootstock was the less susceptible to P. syringae. The other rootstocks inoculated with this fungus did not differ significantly in the average necrosis length produced. Also peach rootstocks inoculated with P. citrophthora showed different level of susceptibility. Inoculation of GF677 plants with P. citrophthora produced the largest necrosis of all rootstocks tested. There were no significant differences in the lesion lengths of PR204, GF305, and KID I plants. The results from laboratory experiments with both fungi were similar to those from the field experiments: any observed differences can be attributed to differences in the physiology of the plant tissues and in the aggressiveness of the fungi

Seasional Variation in Crown Rot of GF677 and KID I Peach Rootstocks by «Phytophthora cactorum», «P. citrophthora» and «P. syringae»

Seasonal variation in extent of colonization of GF677 and KID I peach rootstocks by P. cactorum, P. citrophthora, and P. syringae was examined on excised twigs in vitro, and by stem inoculations in the experimental field of the Pomology Institute, Naoussa, Greece. Shoot segments of the previous growing season were cut and inoculated in the laboratory in the last ten days of August, 1998, and at monthly intervals thereafter until July 2000. At the same time, rootstock stems were also inoculated directly with mycelium of the pathogens every month. Disease severity was assessed 14 days after inoculation. Both P. cactorum and P. citrophthora showed two peaks in the extent of colonization, one in April-June, and one in September and October. In contrast, no colonization of plants occurred in July-August or in January-February. P. syringae also had two peaks in its extent of colonization, one in November- December and one in March. This fungus was inactive during May-October and January. The maximum and minimum extent of pathogen colonization on plants coincided with maximum and minimum growing temperatures of the fungi. The identification of seasonal variations in the susceptibility of peach trees to Phytophthora may facilitate the timing of disease control measures which should coincide with periods when fungal growth is most rapid

Effectiveness of metalaxyl, fosetyl-Al, dimethomorph, and cymoxanil against Phytophthora cactorum and P. citrophthora of peach tree

Metalaxyl, fosetyl-Al, dimethomorph and cymoxanil were applied as a soil drench to evaluate their ability to control in vitro and in vivo Phytophthora cactorum and P. citrophthora, agents of crown rot of peach tree. In the in vivo assays, metalaxyl, applied as soil drench at 2 g/tree, was the most effective, reducing growth of P. cactorum and P. citrophthora. Fosetyl-Al was less effective against both pathogens, while cymoxanil and dimethomorph did not inhibit growth. When scraped stem cankers were painted with metalaxyl, fosetyl-Al or dimethomorpth at 150 g/l Phytophthora colonization was inhibited, but cymoxanil applied in the same way was ineffective. In the in vitro tests, metalaxyl and dimethomorph at concentrations as low as 100 mg l-1 completely inhibited growth of P. cactorum and P. citrophthora. Fosetyl-Al only did so at concentration of 1500 mg l-1 and over. Cymoxanil was less effective since even at 2000 mg l-1 it did not prevent mycelial growth of P. cactorum and P. citrophthora. This study demonstrated that Phytophthora diseases of peach tree can be controlled by metalaxyl applied as a soil drench and by metalaxyl, fosetyl-Al and dimethomorph painted on scraped stem cankers

A Temperature Conditioned Markov Chain Model for Predicting the Dynamics of Mosquito Vectors of Disease

Understanding and predicting mosquito population dynamics is crucial for gaining insight into the abundance of arthropod disease vectors and for the design of effective vector control strategies. In this work, a climate-conditioned Markov chain (CMC) model was developed and applied for the first time to predict the dynamics of vectors of important medical diseases. Temporal changes in mosquito population profiles were generated to simulate the probabilities of a high population impact. The simulated transition probabilities of the mosquito populations achieved from the trained model are very near to the observed data transitions that have been used to parameterize and validate the model. Thus, the CMC model satisfactorily describes the temporal evolution of the mosquito population process. In general, our numerical results, when temperature is considered as the driver of change, indicate that it is more likely for the population system to move into a state of high population level when the former is a state of a lower population level than the opposite. Field data on frequencies of successive mosquito population levels, which were not used for the data inferred MC modeling, were assembled to obtain an empirical intensity transition matrix and the frequencies observed. Our findings match to a certain degree the empirical results in which the probabilities follow analogous patterns while no significant differences were observed between the transition matrices of the CMC model and the validation data (ChiSq = 14.58013, df = 24, p = 0.9324451). The proposed modeling approach is a valuable eco-epidemiological study. Moreover, compared to traditional Markov chains, the benefit of the current CMC model is that it takes into account the stochastic conditional properties of ecological-related climate variables. The current modeling approach could save costs and time in establishing vector eradication programs and mosquito surveillance programs

Susceptibility of Twenty-Three Kiwifruit Cultivars to Pseudomonas syringae pv. actinidiae

One of the best methods to control plant disease is the use of resistant cultivars. The purpose of this study is to evaluate 23 kiwifruit genotypes and cultivars for susceptibility to four strains of Psa (biovar 3) in alaboratory setting. The results showed that all the bacterial strains were pathogenic. There was no statistical difference among the bacterial strains tested. None of the kiwifruit cultivars tested were immune to Psa. There was a statistical difference in the level of susceptibility among cultivars. The cultivars Sorelli and D495/312 were the most susceptible, while the cultivar A501/44 was the most resistant. However, the above results must be verified in field conditions

The detection, identification and potential for the control of Phytophthora in Prunus spp

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