Differences in Leaf Morphological Parameters of Pear (Pyrus communis L.) Based on Their Susceptibility to European Pear Rust Caused by Gymnosporangium sabinae (Dicks.) Oerst.

European pear rust is an important disease; however, the relationship between its causal pathogen Gymnosporangium sabinae (Dicks.) Oerst. and host Pyrus communis L. is poorly understood. In this study, disease severity was measured, and leaf samples were collected over three years, and their leaf water content; leaf area; leaf mass per area; and epidermis, mesophyll, and vascular tissue width and stomatal density were measured and compared between susceptible and resistant genotypes for each year. Most genotypes either showed consistent disease symptoms or showed no symptoms during the study in terms of their susceptibility. A correlation between disease severity and mesophyll tissue thickness, and stomatal density and differences between several morphological parameters were found depending on the genotype’s susceptibility. The study showed that the following pear morphological traits were stable between the years: water content, leaf mass per area, spongy mesophyll thickness, phloem thickness, and stomatal density. When selecting for breeding, we found that candidates for traits that discern susceptible genotypes from resistant were mesophyll layer width, stomatal density, epidermis width, and xylem tissue width.

Pear rust in the conditions of north-eastern Forest-Steppe of Ukraine

Studies were conducted during 2017‒2019 based on the training laboratory of horticulture and viticulture of the Sumy National Agrarian University in the conditions of the North-Eastern Forest-Steppe of Ukraine. It was found that the pear was massively affected by rust. This is a fungal disease that was rarely found in fruit orchards of the North-Eastern Forest-Steppe of Ukraine. Rust infected pear trees very rarely in previous years. Only single spots were found on the leaves of the pear. Since 2015, the development of the disease has noticeably accelerated from year to year. There was a massive rust damage of the pear in the region in 2019. The prevalence of the disease reached 100 % in almost all varieties. Mostly the leaves were affected, not to a large extent the shoots of the pear. On the fruits of the external signs of the disease were not detected. During the years of research, weather conditions were optimal for the spread of fungal diseases. Only the aecial stage of the fungus was observed on the pear. The aecial stage of the pathogen is the most harmful. Affected pear leaves fall prematurely. Studies were conducted on pear varieties Lymonka, Petrovska, Medova, Osinnia Yakovlieva, Chyzhovska, Noiabrska, Bere Desiatova, Uliublenytsia Klappa, which showed different degrees of rust damage. The disease manifested itself most significantly (5 points) on the varieties, Uliublenytsia Klappa and Bere Desiatova. Not one of the varieties did not show high resistance to the pathogen. The pear of the Chyzhovska variety was less affected, with a defeat score of 3 (18.8 %) in 2017 and 4 (32.3 % and 44.1 %) in 2018‒2019. It is known that the life cycle of the rust pathogen Gymnosporangium sabinae (Dicks.) G. Winter occurs on two plants: pear and juniper. The pathogen from juniper goes on the pear and vice versa. Pear trees do not become infected from each other. On the territory adjacent to the fruit garden of Sumy National Agrarian University, a survey of plantings of different types of juniper was conducted. There were no visible signs of the disease on the juniper. At the same time, pear trees were highly infected with the pathogen. Perhaps the spores of the fungus can spread far through air currents. But at the same time, possible changes in the life cycle of the pathogen in the conditions of this region. Clarification of this circumstance requires deeper further research.

Occurrence and harmful effects of Gymnosporangium sabinae (Dicks.) Winter in Slovak Republc

The fungus Gymnosporangium sabinae (Dicks.) Winter was found only at three locations during the years 1965 to 1990 in Slovakia, they were the Arboretum at Mlyňany, Topoľčianky and Gbely (JUHÁSOVÁ 1973, 1975, 1998). We noticed a more frequent occurrence of this fungus during recent years. The life cycle, range of woody host plants and degree of damage on pear leaves at selected locations inSlovakia are described.

First Report of Gymnosporangium sabinae, European Pear Rust, on Bradford Pear in Michigan

Bradford pear, Pyrus calleryana Decne., is well known as an ornamental plant for its flowers, leaf color in fall, and disease resistance, making it desirable as a street tree. In August and October of 2008, the aecial stage of Gymnosporangium sabinae (Dicks.) G. Winter was collected from leaves of P. calleryana in Farmington, MI (Oakland County). The one tree had foliage that was severely affected by the rust fungus. Using published descriptions of G. sabinae as the synonym of G. fuscum, type of the genus Gymnosporangium (1–4), the Michigan specimen was identified and confirmed by comparison with previously reported European and U.S. specimens (BPI 118736 and BPI 856578). The diagnostic characteristics of G. sabinae include: spermagonia epiphyllous; aecia hypophyllous, roestelioid, 3 to 6 mm high; peridium balanoid (acorn shaped), becoming elongated at maturity, pale yellow, sides opening with lateral slits but remaining attached at light brown, pointed apex; peridial cells elongated, 51 to 68 μm long, outer walls smooth, inner walls and side walls sparsely echinulate; aeciospores globose to broadly ellipsoid, somewhat angular, surface slightly coronate, 22 to 32 × 22 to 36 μm, walls orange, 3.5 to 5.5 μm thick. This species is distinguished from other species of Gymnosporangium on Pyrus by the balanoid (acorn-shaped) peridium and the late season maturation of the aecial stage (4). Telia and teliospores of G. sabinae are produced on the alternate host, various species of Juniperus sect. Sabinae, but were not observed in Michigan. The specimen from Michigan is deposited in the U.S. National Fungus Collections (BPI 878928). G. sabinae is widely distributed in Europe, extending to Asia and North Africa, but is rarely reported in North America. It was accidentally introduced into California in the aecial stage on P. communis L. and the telial stage on Juniperus chinensis L. (2), as well as introduced into Canada (British Columbia) (3,4). The only previous report of G. sabinae on P. calleryana is in Germany (1). G. sabinae is known to attack commercial pear and ornamental juniper plants in Europe, thus it seems important to prevent the further spread of this fungus in North America. References: (1) U. Braun. Feddes Repert. Beih. 93:213, 1982. (2) G. Laundon. Mycotaxon 3:133, 1975. (3) A. H. McCain and D. Y. Rosenberg. Calif. Dep. Agric. Bull. 50:13, 1961. (4) J. A. Parmelee. Fungi Canadensis No. 43. Gymnosporangium fuscum, 1974.

Gymnosporangium sabinae. [Distribution map].

A new distribution map is provided for Gymnosporangium sabinae (Dickson) Winter. Hosts: Pyrus and Juniperus) spp. Information is given on the geographical distribution in Africa, Algeria, Morocco, Asia, China, Lebanon, Syria, Turkey, Europe, Austria, Belgium, Bulgaria, Cyprus, Czechoslovakia, Denmark, France, Germany, Greece, Italy, Netherlands, Norway, Poland, Portugal, Romania, Spain, Sweden, Switzerland, UK, England, Scotland, USSR, Astrakhan, Caucasus, Crimea, Ukraine, Yugoslavia, North America, Canada, British Columbia, USA, Alabama, California.