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• Study of Erwinia amylovora colonization and migration on blossoms of susceptible and tolerant apple cultivars

  15-19.

  E. Mihalik

  A. Radvánszky

  L. Dorgai

  T. Bubán

  Views:

  132

  The stigmata of detached flowers of susceptible and tolerant apple cultivars were inoculated with about 10⁴ gfp labeled Erwinia amylovora . There were no apparent differences in the colonization, multiplication and survival of the bacteria on the stigmatic surface of the culivars. Bacteria were washed down to the hypanthium surface 24 hours after inoculation. The visual symptoms of the infection were the discoloration and shrinkage of the floral parts. The gradual browning associated with the infection appeared first on the surface of the hypanthium followed by the discoloration of the style. The color of the filaments turned into brown only 120 hours after the inoculation. Bacterial cells were not detected in the tissues of the styles and filaments. The traits of the hypanthium surface are of prominent importance in the progression of the infection. The wrinkled surface, the convex shape of the outer epidermal cell walls with thin cuticle and the sunken stomata helped to preserve a water film for a longer period providing medium for the motility of the bacteria in the susceptible cultivar. Bacteria were restricted to small water droplets on the flat and waxy surface of the hypanthium of the tolerant cultivar and only a few were able to enter the tissues.

  Large bacterium aggregations were detected in the intercellular spaces of the parenchyma of the susceptible cultivar 48 hours after the inoculation. In the next period the Erwinia amylovora cells gradually invaded the intercellulars of the hypanthium wall, the wall of the ovary and the pedicel. Low level of bacterium aggregation was found in the intercellulars of the tolerant cultivars. It is suggested that the progression of the infection was inhibited also by physiological factors.

• Real-case application of mycorrhizal inoculums on Capsicum annuum L. var. longum cv. Szegedi and Kalocsai

  75-79.

  I. Hernádi

  K. Posta

  Views:

  175

  The aim of this study was to test the use of commercially available arbuscular mycorrhiza (AM) inoculant Symbivit, a mixture of six species of Glomus spp., in spice pepper field cultivation. The inoculants containing arbuscular mycorrhizal fungi (AMF) was able to establish a symbiosis in the rhizosphere of pepper plants and mycorrhizal inoculation increased fresh and dry weights of shoots of spice pepper cv. Szegedi and only fresh weight of Kalocsai type. There were no significant differences in the root weights due to treatment only in fresh weight of Kalocsai pepper type. Treated plants of both variants exhibited an increase in cumulative crop production compared with control non-treated plants and the growth response of pepper was higher for var. Szegedi than var. Kalocsai. Mycorrhizal inoculation had a great positive effect on external hyphal length of AMF also showing differences in that between Kalocsai and Szegedi variants. The root colonization showed seasonality by treated and non-treated plants. The lowest degree of colonization was observed in June in general and colonization percent increased during vegetative development and there was a slight decrease at harvesting. In conclusion, it can be stated that inoculation with Symbivit containing mycorrhizal fungi could be an integral part of spice pepper production.

• Prediction infection risk on the basis of weather-related factors and Erwinia amylovora colonization in apple and pear flowers

  39-54.

  T. Bubán

  E. Rutkai

  L. Dorgai

  S. V. Thomson

  Views:

  156

  Current infection risk prediction models utilize environmental parameters and field records, but do not take into account the estimated inoculum potential within the orchard. The object of this study was to survey the accuracy of three simple prediction methods under Hungarian climatic conditions, which could easily be used by the farmers. We also tested whether the accuracy of infection risk predictions can be improved by taking into consideration the incidence and/or rate of flower colonization by Erwinia amylovora.

  After preliminary investigations in 1999-2001, data concerning the weather-related infection risk were recorded in 5 apple and 1 pear orchards in 2002, and in 12 apple and I pear orchards in 2003. The weather data were processed by the easy-to-use risk assessment models of the mean temperature prediction line (MTL), Smith's Cougarblight 98C and Billing's integrated system (BIS), and by the Maryblyt^TM 4.3 computer-assisted model for reference. The population size of E. amylovora in the flower samples was estimated within an order of magnitude by PCR.

  For all years and orchards tested, Maryblyt indicated 35 days on which there was an acute infection risk. The same days were indicated by all 3 methods in 23 cases (66%), 8 days were indicated by 2 methods (23%) and 4 days were indicated by 1 method only. A similarly good correlation was found for prediction of the date of the first massive infection risk: in 2003, for instance, there was a perfectly consistent prediction by all 4 models in 9 of the 13 participating orchards. A coincidental forecast was provided by 3 of the 4 models in the other 4 orchards.

  The results indicate that any of the risk assessment models could provide an increased accuracy of the actual infection risk prediction if combined with an estimation of the incidence of Erwinia amylovora colonization in the open flowers. We found no convincing differences in the size of the epiphytic population in flowers of cultivars possessing high or low susceptibility to Erwinia amylovora.

  We conclude that the easy-to-use methods tested could be used by the fanners to recognize weather-related risks, especially when coupled with an estimation of the proportion of the pathogen-infested flowers. This local prediction would provide rapid information (faster than the regional forecast systems) specifically for a given orchard.