Apple Pathogen Research Articles

ThePhytophthoradiseases of apple

SummaryThe most important Phytophthora pathogens of apple are P. cactorum and P. syringae, although other species may be locally significant. P. cactorum is widespread in the apple growing regions of the world and causes girdling bark rots on the scion (collar rot) and on the rootstock (crown rot), necrosis of the fine root system (root rot) and fruit rot. P. syringae is a significant pathogen of apple only in north-western Europe, where it causes collar rot but is most damaging as a cause of rot in stored fruit. Several other species of Phytophthora have been implicated in crown rot and root rot.Bark rots due to Phytophthora spp. have distinctive features, such as mottled green/ orange/brown coloration of necrotic tissue, but may be confused with other causes of bark death. Isolation of the pathogen is therefore essential for diagnosis, and is now made easier than formerly by the use of selective media. Phytophthora fruit rot is usually distinctive, and isolation from diseased tissue is readily achieved ...

Immunofluorescence and protein A‐gold techniques in localization of plant pathogen antigens in Lowicryl K4M embedded tissue

SUMMARYThis paper investigates the use of Lowicryl K4M in the embedding of apple tissue for immunocytochemistry. The localization of the extracellular protease of the apple pathogen, Nectria galligena Bres., in infected apple tissue by immunofluorescence and protein A‐gold immunoelectron microscopy is also described. Infected apple tissue was fixed in 0.5% glutaraldehyde and 4% paraformaldehyde and embedded in Lowicryl K4M at 313 K. The protease was isolated and purified from rotted apple tissue by gel filtration and ion‐exchange chromatography. Monospecific antibodies against the protease were raised in rabbits and purified by protein A‐affinity chromatography. Incubation of apple tissue sections, infected with N. galligena, with the mono‐specific antibody and tetramethylrhodamine isothiocyanate (TRITC)‐conjugate, resulted in specific fluorescence of fungal hyphae and cytoplasm of apple cells. Similar localization of colloidal gold particles over hyphae and host cell cytoplasm was demonstrated employing protein A‐gold immunochemistry. The low temperature embedding resin Lowicryl K4M appears to provide adequate morphological preservation of apple tissue and excellent retention of antigenicity. TRITC conjugates and protein A‐gold may prove useful in immunocytochemical investigations of plant‐pathogen interactions.

A Review of Apothecial Production by Monilinia Fungi in Japan

The literature on apothecial production by Monilinia spp. is reviewed with particular attention given to Japanese work. Four stages of apothecial development are distinguished? stromatal development, stromatal maturation, apothecial initiation, and apothecial differentiation. Information is given on growth conditions which have been found suitable in laboratory studies for apothecial production by M. fructicola, M. fructigena, M. mali, and M. oxycocci. The temperature, light and moisture regimes, substrates, and incubation times used were similar to those that are encountered in the field in regions of Japan where apothecia are frequently found. The effect of weather conditions and of fruit size and time of ripening of hosts on apothecial production is discussed. The Monilinia fungi are characterized by the production of monilioid spores and stromatic tissue on which apothecia are borne (Honey, 1928). Members of the genus are pathogens of the Rosaceae and Ericaceae and some cause considerable economic losses to crops. Honey (1936) divided the genus into two sections based on the presence or absence in conidial chains of disjunctors (small structures which develop between mature conidia and facilitate spore dispersal). Those that do not possess disjunctors were included in the Junctoriae and those with dis? junctors, in the Disjunctoriae. There are about 30 known species of Monilinia of which nine have been recorded in Japan. Details of the Japanese Monilinia spp. are summarized in Table I. Most studies have been made on the species comprising the Junctoriae because of their economic importance as serious pathogens of apples, pears, and stone fruits. The diseases on fruits are usually referred to collectively as since brown lesions develop on infected tissues, particularly those of fruits. The biology and control of the Monilinia spp. causing brown rot have been reviewed by Wormald (1954) and more recently by Byrde and Willetts (1977), while Harada (1977) has published a report of his detailed studies on the Japanese species of Monilinia. In a more recent article, Batra (1983) reported an investigation of Monilinia spp. on Ericaceae. The sexual spore of Monilinia spp. is the ascospore produced in an apothecium. There are numerous reports in the literature of the discovery in the field of apothecia of most ofthe species. However, there are only a few reports of successful apothecial formation by these fungi in the laboratory, and consequently the factors involved in the initiation and differentiation of ascocarps of Monilinia are not well understood. Also most of the successful studies have been carried out in Japan and details ofthe work are not readily available to many western workers. The purpose of this article is to review the data available on apothecial pro? duction by Monilinia fungi, with particular reference to the Japanese species. Attempts are made to interpret the findings using published information on

The effects of a pesticide program on non-target epiphytic microbial populations of apple leaves.

The epiphytic microbial community was quantitatively and qualitatively altered when a standard pesticide schedule that comprised applications of an insecticide, a bactericide, and a fungicide was applied to McIntosh apple trees. Effects on non-target organisms were observed for two seasons by three indirect methods and three direct methods: plating of leaf washings, imprinting of leaves onto five different media, spore fall patterns, light microscopy, scanning electron microscopy, and isolation of propagules from leaves incubated in humidity chambers. Magnitude of reduction of bacteria, filamentous fungi, yeasts, and actinomycetes varied annually and between categories of microflora. Populations from treated leaves were reduced 10- to 1000-fold in 1976 and up to 50-fold in 1977. Qualitatively, fluorescent pseudomonads and lactic acid-type bacteria were among those depressed by pesticide. Fungal populations on treated leaves were less diverse than on control leaves. Aureobasidium was only slightly affected and incidence of Sporobolomyces was substantially higher on treated leaves than on controls. The results suggest that numbers of antagonists to foliar pathogens of apple which may occur as part of the natural epiphytic microbial community may be reduced by current pesticide programs and hence have possible implications for the development of biological approaches to integrated control strategies.

A taxonomic study ofPseudomonas papulansRose 1917

Abstract A taxonomic study was made of Pseudomonas papulans Rose 1917, the blister spot pathogen of apple. Although this organism differed from P. syringae van Hall 1902 in a number of characters, it is considered that the apple blister spot pathogen should be classified as Pseudomonas syringae pathovar papulans (Rose 1917) comb. nov.

Effect of a host-specific toxin (AM-toxin I) produced by Alternaria mali, an apple pathogen, on the ultrastructure of plasma membrane of cells in apple and Japanese pear leaves

AM-toxin I (4 μg/ml), a host-specific toxin of Alternaria mali, caused permeability changes in susceptible apple and Nijisseiki pear leaves within 5 min of treatment. The first effect of the toxin appeared on plasma membranes of susceptible apple cells. One hour after toxin treatment, slight invaginations were evident in plasma membranes near plasmodesmata. Six hours after treatment, the spaces between cell wall and invaginated plasma membrane contained lomasome-like vesicles, membranous fragments, and desmotubules extending from plasmodesmata. The membranous materials appeared to originate from the plasma membrane. Thirty-one hours after treatment, necrotic cells of susceptible leaves showed the general disruptions of cellular membranes which might be caused by secondary effects of the toxin. The similar changes of plasma membrane and plasmodesmata also were found in Nijisseiki pear cells treated with AM-toxin I (4 μg/ml) for 1 h and 6 h. The invaginations of the plasma membrane at plasmodesmata were the first ultrastructural modifications in the toxin-treated Nijisseiki cells. AM-toxin I did not affect the ultrastructure of resistant apple and Chojuro pear cells. These results indicate that the initial sites for the toxin may be on the plasma membrane of the susceptible apple cells. Furthermore, the results suggest that the plasma membrane modifications are associated with permeability changes in the toxin-treated, susceptible plant cells except for original host cells treated with the toxin.

The biosynthesis of benzoic acid in Bramley's Seedling apples infected by Nectria galligena Bres

Radioactive benzoic acid was synthesized from glucose- 14C and l-phenylalanine- 14C in apples infected with Nectria galligena and in apples infused with protease extracted from tissue rotted by N. galligena. Phenylalanine ammonia-lyase (PAL) activity was rapidly induced in apples infused with the fungal protease but a lag phase occurred following inoculation with the pathogen. Production of benzoic acid was maximal approximately 3 days after maximum PAL production. Enzymes extracted from necrotic apple tissue converted phenylalanine to cinnamic and benzoic acids. P. expansum, a non-protease producing apple pathogen, did not induce either PAL activity or elicit benzoic acid accumulation in apples.