VARIOUS SPECIES OF GLOEOSPORIUM IN STORED APPLES IN FINLAND PENTTI TALVIA Agricultural Research Centre, Department of Plant Pathology, Tikkurila Received May 19, 1960 In storage trials on apples carried out in the years 1952—1955 by the Depart- ment of Plant Pathology, the most important cause of losses in the stored fruit was apple rot caused by the fungus Gloeosporium (8). Jamalainen determined the causal agent to be Gloeosporium album Osterw. and mentioned that possibly other species of Gloeosporium were also involved in causing the disease. Since 1954 the Department of Plant Pathology has continued its trials on stored apples in order to determine the various species of Gloeosporium found in this fruit during storage. Apple growers throughout the country wr ere requested to send diseased apples to the Department for investigation. In the storage period 1954/55 determinations were made on 13 apple varieties from 9 different locations in southern Finland. In the period 1956/57 ten apple varieties from five localities were included in the trials. In the autumn 1957 the Department received for investigation 9 varie- ties of apples infected with rot from 11 growers throughout the country. In addition, determinations were made during the trial period 1957/58 on the Gloeosporium species occurring in apples in the Department’s own storage trials. The experimental material in the years 1954—58 included a total of 20 apple varieties from 17 different localities in Finland. The trial material was stored in a cellar where the temperature averaged 4° C. and the relative humidity approximately 92 %. Determinations of the fungus species in the diseased apples were made during the storage period on the basis of the form and shape of the acervuli as well as on the size and form of the conidia. Table 1 shows results of determinations made in the period 1954—58 on the occurrence of Gloeosporium species in apples from various localities in Finland. G. perennans Zeller & Childs was found in apples from all of the localities and ap- pears to be the principal species in many areas. The second most widespread species was G. album, which, together with G. perennans, is the cause of extensive damage to stored apples in Finland. The third species, G. fructigenum Berk., is much less important as a cause of apple rot in this country. 4 https://www.c-info.fi/en/info/?token=xWmyZQxqAa4pz3n-.lL40oij63Q-x21dD0T_sxA.CNBfOyGYbGProcGUIgQcs8hoXSEjEf0g1puad-K91x6IVpBCiQFLh5YejZmcAOUeuqcIj8zNaUWQG6uXMCBZKKqdt-58HszN6gZqABM5IdHxeJSz2P9lCaZKEYtttB7MmoBofnzX2RxGuICTJ15pw7scjHQ0LWTuUfOy 240 Table 1. Occurrence of Gloeosporium species in diseased apple material from different regions of Finland 1954—58. Species determinations made on the basis of acervuli and conidial shape and size. No. of No. of Gloeosporium species Plant geographical province apple examined ~G~äibütn G. fructi- G. peren- and locality varieties diseased genum nans app*es % % % Regio aboensis Lohja 8 376 19 3 78 Nummi 1 7 29 0 71 Piikkiö 6 177 38 4 58 Särkisalo 1 19 0 0 100 Tenhola 1 2054 43 2 55 Nylandia Espoo 2 64 56 0 44 Helsinki 1 18 39 0 61 Tikkurila 7 1900 78 1 21 Hyvinkää 1 97 17 4 79 Järvenpää 4 98 28 0 72 Satakunta Karkku 1 26 54 0 46 Köyliö 1 61 34 3 63 Tavastia australis Kangasala 1 40 0 0 100 Pälkäne 2 48 6 0 91 Tyrväntö 3 341 9 0 91 Vanaja 2 11 18 0 82 Savonia australis Lauritsala 1 45 13 0 87 Since the apple samples from several of the localities were limited these results do not give a completely accurate picture of the extent of Gloeosporium fungi in Finland. Investigations made at the Lindö Estate at Tenhola in southwestern Finland upon apples of the Wealthy variety show that the relative proportions of the Gloeo- sporium species can vary considerably in the same apple variety, even in closely located orchards. For example, in one orchard containing trees older than ten years, determinations on 1455 diseased apples showed that G. perennans was the causal agent in 72 % and G. album in 26 % of the infected fruit. In a second orchard located two kilometers distant and containing trees younger than ten years of age, the proportions of the two species was almost reversed; out of 599 infected apples G. album was responsible for 84 % of the diseased fruit and G. perennans for only 15 %. Moisture conditions during the growing season appear to have an effect on the relative occurrence of Gloeosporium species in stored apples (10). Determinations of the fungus species infecting Melba-variety apples grown at the Department of Plant Pathology orchard were made in the years 1956 and 1957. These two years differed considerably from one another in terms of precipitation during the growing season. In the year 1956 May, July and especially September (only 7 days of rainfall) were 241 dryer than normal whereas August was a rainy month. In 1957, on the other hand, precipitation during the early part of the summer was normal whereas August and September were characterized by abundant rainfall (in September there were 22 days ofrainfall). In the former year 1956, investigations on 650 Melba apples showed 36.4 % to be diseased, of which 97.5 % were infected by G. album and 2.5 % by G. perennans. In 1957 a total of 1680 apples were investigated; of these 51.7 % were infected, and the relative amounts of the Gloeosporium species were 81.2 % G. album and the remainder G. perennans. Gloeosporium perennans Zeller & Childs G. perennans is known as an important causal agent of apple rot, especially in fruit preserved in cold storage (5, 6, 12). In addition to infecting the fruit, this fungus also forms small cankers or areas of bark blight in the branches of the tree. In such infected areas watery, greyish-coloured, stroma-like acervuli are formed which, during warm temperature conditions, produce abundant conidia. The conidia then infect the fruit via the stomata. Later during the period of storage, round decaying spots appear on the apple. These spots contain acervuli which develop first under the epidermis and after break through to the surface. Numerous conidia are formed in these acervuli at low temperatures (2°—4° C.). In Sweden (11) and in Denmark (15) G. perennans, together with G. album, is the most important cause of apple rot. In Norway (16) the species has been known since 1950 but is of small significance in that country. In England (6), Holland (12), New Zealand (5), and in North America (1) G. perennans is an important causal agent of rot in stored apples. Gloeosporium perennans cannot be distinguished morphologically from G. mali- corticisCordl. (3). The ascospore stage of G. perennans is known by the names Pezicula rnalicorticis (Jacks.) Nannf. and Neofabrea malicorticis (Cord.) Jacks. It has been found in North America, in Holland and in England (4, 7,9), but only in winter cankers of Pyrus species. The infection caused by G. perennans appears generally on the surface of the apple but sometimes it occurs also on the stipe. The infection spots are brown in colour, and are usually surrounded by a darker border. The acervuli are forced through the epidermis to the surface where they expand and become filled with a grey mass of conidia. In apples stored in moist conditions the infection spots with their acervuli are often watery in appearance. The infection spreads rapidly to the interior of the apple and the entire fruit becomes shrivelled. The conidia are one-celled, elongate, and are straight or slightly curved (Fig. la). A light-coloured vacuole-like area is often visible in the center of the conidium. The length of the conidium varies on the average, from 11.6 to 17.6/< (5.8—25.3 /x). The average value of conidium length as determined by 480 measurements on conidia from 12 apple varieties was 14.96 /x. The width of the conidia varied from 2.8 to 4.9 /x (1.0—5.9 u) with an average value of 3.95 t*. According to Oort (12) the size of the conidia of G. perennans 242 varies with the ranges 7.2—20.0 /1 X 3.0—6.4 u (average 13.6 X 4.0 /i). Microconidia are also generally produced by this fungus. Conidia isolated from infected apples have been cultured on 5 % oat-agar and on 3 % glucose-agar. The mycelium is lightcoloured and abundant conidia are for- med. Gloeosporium album Osterw. G. album, which has many synonyms, is, together with G. perennans, an impor- tant cause of apple rot. It is responsible for great losses of fruit in cold storage in many countries, such as Sweden, Norway, Holland, England, Switzerland and New Zealand (5, 11, 12, 13, 16, 18). Conidia are formed on the dead branches of the fruit tree and subsequently infect the apples principally via the stomata. At the site of infection brown-coloured spots surrounded by a dark border appear. These spots are often lighter in colour than those of G. perennans and are found usually on the surface of the apple but sometimes also at the base of the stipe. Round, light-coloured clusters of conidiophores develop in the infection spots and often assume the form of a ring in the surface of the spot. Under moist conditions white, ray-like aerial hyphae grow out from the infected area. According to Guthrie (7) the perfect stage of G. album is Pezicula alba Guthrie. The conidia of G. album are one-celled, cylindrical and usually curved (Fig. I b). Sometimes they are discharged in white, ribbon-like masses. The length of the coni- dia was found to vary from 17.9 to 24.9 /i (13.8 —28.0 u) with an average figure of 20.75 u obtained from measurements of 440 conidia on 14 apple varieties. Their width ranged from 2.3 to 3.8 u (2.1—4.5 u) with an average of 2.86 u- According to Osterwalder (13) the size of Gloeosporium album conidia are on the average 24 X 3 /i and according to Oort (12) 22.5 (16.5 —29.0) x 3.7 u (3.2—4.0). When cultured on oat-agar and on glucose-agar, G. album grows very slowly. It forms a white-coloured mycelium but produces very few conidia. Fig. 1. a) G. perennans, b) G. album, c) G. fructigenum. X 760. 243 Gloeosporium fructigenum Berk. G. fructigenum Berk, is the imperfect stage of Glomerella cingulata (Ston.) Spauld. & Sehr, and has many synonyms (cf. 2). The imperfect stage of this fungus has been isolated from a wide number of various plants. In 1935 Rainio (14) deter- mined the fungus as the causal agent of anthracnose in an agave plant growing in a greenhouse in Finland. G. fructigenum is widely distributed in both the tropics and in temperate regions. It occurs in Scandinavia and other European countries as well as in North America, but it is not important as a cause of apple rot (1, 11, 12, 13, 15, 16, 18). It is, however, believed to be responsible for fruit rot in cherries. olives and in certain tropical fruit (3). G. fructigenum infects apples usually at sites of injury, but it is also capable of penetrating through the epidermis. Brown-coloured depressed spots are formed at the site of infection and small, dark acervuli gradually develop in these spots. Under pressure from the expanding conidial mass the epidermis breaks and the conidia are released to the exterior. In moist conditions masses of conidia accumulate asreddish- coloured globules on the surface of the acervuli. The disease spreads slowly within the apple, and many weeks may pass before the apple is completely decayed. The conidia are one-celled, colorless, cylindrical, and straight or slightly curved (Fig. 1 c). The length of the conidia ranges from 15.2 to 18.0 p and averages 16.1 p Table 2. Occurrence of Gloeosporium species in apple varieties cultivated in Finland. Species determi- nations made on apple rot material received in 1954—58 on the basis of acervuli and conidial shape and size. Areas of No. of Gloeosporium species Apple variety cultivation examined ~G7älbüm G.fructi- G. peren- diseased genum nans apples % % % Antonovka 6 567 17 4 79 Atlas 1 18 29 5 66 Cellini 2 15 67 0 33 Harlamovski 1 53 51 0 49 Harmaa Gylling (= grey Gylling) 1 18 39 0 61 Joyce 1 99 39 0 61 Kaikuvuori 2 14 79 0 21 Kelt, kaneli (= yellow canel) ..1 19 0 0 100 Kirkniemi 1 54 26 6 68 Lepaan liereä (= lepaa round) 1 156 1 0 99 Linda 2 42 64 0 36 Lobo 5 183 5 0 95 Melba 1 1118 84 0 16 Oranie 1 10 10 0 90 Safran-Pohjola 1 29 76 0 24 Sariola 3 166 20 1 79 Signe Tillish 1 76 20 0 80 Slavjanka 1 35 40 0 60 Wealthy 5 2568 52 2 46 Äkerö 5 142 48 0 52 244 on the basis of 100 measurements from five apple varieties; their width is 4.3 to 5.4 n with an average of 4.9 u- According to Arx (2) the size of the conidia of G. fructi- genum averages 12—22 x 4—6 /i. On oat-agar and glucose-agar the fungus forms a grey mycelium and produces conidia. Gloeosporium species in the material studied It has been determined in previous investigations in Finland that there are considerable differences in resistance to Gloeosporium rot among different apple varieties (8). Table 2 shows the occurrence of the various species of Gloeosporium in different apple varieties. None of the apple varieties were found to be completely Table 3. Occurrence of Gloeosporium species at various dates in stored apples at Tikkurila and at Ten- hola, 1956/57 and 1957/58. Department of Plant Pathology Lindö, Tenhola Tikkurila Date of 1956—57 1957—58 1956—57 1957—58 examination Melba Anto- Wealthy Melba Wealthy novka «/) o<3 «/) Wj 00 COis £ $ iE r r Q « « Q Q « ~ R ~ R ~ R s*S - R ~ R R R R R X 5 R R R R RR St St St St St St 7S « <3 o u