Effects of low temperature on development of the vesicular-arbuscular mycorrhizal association between Glomus caledonium and Allium cepa

Effects of low temperature on development of the vesicular-arbuscular mycorrhizal association between Glomus caledonium and Allium cepa

Note s and brief articles H. radi cata roots with nematode-infected n odules and swellings which were also quite heavil y infected with a mycorrhizal ...

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Note s and brief articles H. radi cata roots with nematode-infected n odules and swellings which were also quite heavil y infected with a mycorrhizal fungus. Although Riazi-Hamadani et al. (1977) failed to find nematodes associated with the n odules on the tomato plant, there does seem to be som e parallel between th ei r findings and those of Roncadori & Hussey ( 1977). We thank Dr R. J. Sward for help in sp o re id e n tifica tion , Professor L. L. Stubbs for help w ith interpretat ion of symptoms, and the Tasman Vaccine Laboratories (Au st .) Pry Ltd, Dandenong, for y-irradiating the soil. The senior author wa s su p p or ted during this study b y a Univer sit y of Melbourne Postgraduate Research S cholarship.

REFERENCES

BOWDEN, H. J. M . & CAWSE, P. A. (1964 a). Effects of ionizing radiation on soils and subsequent cro p growth . S oil S cience 97, 252-259. BOWDEN, H. J. M. & CAWSE, P. A. (t964 b). Some effects of gamma radiation on compo sition of the soil solution and soil organic mailer. S oil S cience 98, 355-361. EVANS, P. S. (1970). Root growth of Lolium p erenne L. 1. Effect of plant age, seed weight , and nutrient concentration on root weight , length and number of apices . New Zealand Journal of Botany 8, 344-356. GERDEMANN, J. W. & NICOLSON, T. H. (1963). Spores of mycorrhizal Endogone species extracted from soil by

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wet sieving and decanting. Tr ansactions of the British My cological Society 46, 234-244. H OAGLAND, D . R . & ARNON, D . 1. (1938). The water curve method for growing plant s without soil. Californian Agricultural Experimental Sta tion Circular 374 (revised , 1950). M OSSE, B. (1959). The regular germ ination of resting spores and some observations on the growth requirements of an Endogene sp . causing vesicular-arhuscular mycorrhiza, Transactions of the British Mycological S ociety 42, 273-286. PHILLIPS, J. M . & HAYMAN, D. S. (1970). Improved procedur es for d earing roots and sta ining para sitic and vesicular-arbuscular mycorrhi zal fungi for rapid assessment of infection . Tran sactions of the British Mycological Society 55, 158-160. RIAZI -HAMADANI, A., PARBERY, D . G . & BEILHARZ, VYRNA C. (1977). Vesicular- arbu scular mycorrhizal nodule s on tomato . Transactions of the British My cological S ociety 68, 138-14°. RONCADORI, R. W . & HUSSEY, R. S. (1977). Interaction of th e endomycorrhizal fung us Gigaspora margarita and root-knot nemat ode on co tto n . Phytopathology 67, 1507- 1511. SALONJUS, P.O., ROBI NSON, J. B. & CHASE, F. E. (1967). A comparison of autoclaved and irradiated soils as media for microbial colonization experiments. Plant and S oil ':7, 239-248. SWARD, R. J. (1978). Infection of Australian heathland plants by Gigaspora margarita (a vesicular-arbuscular mycorrhizal fungu s). Australian Joumal of Botany 26, 253-264. SWARD, R. J., HALLAM, N . D . & HOLLAND , A. A. (1978). E ndogene spores in a heathland area of south-eastern Australia. A ustralian J ournal of Botany 26, 29-43.

EFFECTS OF LOW TEMPERATURE ON DEVELOPMENT OF THE VESICULAR-ARBUSCULAR MYCORRHIZAL ASSOCIATION BETWEEN GLOMUS C A L E D O N IU M AND ALLIUM CEPA BY M . T. CHILVERS AND M.

J. F.

DAFT

Department of B iological Sciences, Th e Un iv ersity, Dundee DDt 4HN, Sc otland Little is known of the effects of low temperatures on the development of vesicular-arbuscular mycorrhizas (VA M ) in plant roots . Hayman (19 74) showed that at 14 DC growth stimulation by Glomus mosseae (N icol. & Gerd. ) Gerd. &Trappe decreased, and he attributed this to a deficiency of functional arbuscules. Later, the same author (H aym an , 1977) reported that phosphorus (P) translocation in Glomus fa sciculatum (T ha xte r sensu Gerd. ) Gerd. & Trappe was reduced at 10 DC, and sugges ted that at 7 0 benefits of VAM infection may be negligible . Low-temperature regimes may in d u ce the endoTra ns. Br . mycol, S oc. 79 (1), (1982).

phyte G igaspora calospora (N icol. & Gerd.) Gerd. & Trappe to grow parasit ically (F u rl an & Fortin, 1973)· We have found that, in bulbous ho sts such as Hyacinthoides nonscripta (L. ) Chouard ex Rothm., and cultivars of Narcissus L. and Crocu s L., endophytes in the field contin ue to develop and appear active in the winter when temperatures fluctuate around 50 (D aft, Chilvers & Nicolson, 1980 ; Chilvers & Daft, 1981 ). The aim of the present experiments was to determine the effects of a series of decreasing temperature treatments,

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Notes and brief articles Temperature Treatments ~20

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B

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115

Harvests

Fig. 1. Effects of temperature on the developmentof mycorrhizaland control onion plants. (A) Growth of mycorrhizal(e) and control (0) shoots. (B)Absolute growth rate (AGR) of shoots of mycorrhizal (e) and control (0) plants. (e) Relativegrowth rates (RGR) of shoots of mycorrhizal Ce) and control (0) plants. (D) Development ofVAM infection in roots: root length infected (RLI) (.); root weight infected CRWI) CA).

similar to those to which bulbous geophytes in the United Kingdom are exposed during winter periods, on the development of an established and active endophyte infection in onion plants. Seeds of Allium cepa L. cv. Rijnsberger Conquest were soaked for one day in distilled water and sown in thirty 105 mm plastic pots containing washed, Trans. Br. mycol, Soc. 79 (1), (1982).

sterilized, seashore sand to which P was supplied at a rate of 80 mg Ca a(P 0 a)2. kg sand". Five seeds were planted and thinned to three per pot after germination. Half the pots, designated mycorrhizal, were inoculated with Glomus caledonium spores previously isolated from a local field and maintained for one generation time on Zea mays L. An aliquot

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Notes and brief articles containing approximately 30 spores was pipetted below each onion seed ling to ensure heavy infection. Control seedlings received a spore- free filtrate . The plants were grown in a Sherer eEL 8 growth cabinet (average light intensity, 5'4 klx ; 15'5hday/8'5hnight cycle; 75 % r.h .). These conditions give optimal growth of onions (Butt, 1968). The sequence oftemperature treatments and the length of time in days after sowing were zoo (35 d), 15° (27 d), 10° (z5 d), 5° (25 d) and zoo (25 d). The pots were randomized weekly and supplied with Hoagland's nutrient soluti on (Downs & Hellmers, 1975) minus the phosphate salt. After each treatment peri od, plants from three mycorrhizal and three control pots were harvested (harvests H,-H s)' Fre sh weights of root s and shoots and dr y weights of shoots were determined . The root systems were stained with trypan blu e (Phillips & Hayman, 1970), cut into 20 mm segments, mounted on 76 mm x 39 mm slides and examined microscopically. The mean dry weight of shoots from the mycorrhizal plants was greater than that of the controls throughout the experiment (Fig. 1, A) and significantly greater (P < 0'05 ) at harvests H, and H s - The absolute growth rates (AGR) and relative growth rates (RG R) of plants (H unt, 1978) were estimated from the dry weight s of equally ranked shoots at consecutive harvests. The AGR of the mycorrhizal plants was greater than that of the controls throughout the experiment (Fi g. 1, B) except at the first harvest. It continued to increase as the temperature decreased to 15° and 10°, but then declined rapidly as the temperature was reduced to 5°, although it still remained above that of the control plants . The rates of change of the AGR, i.e. the acceleration of growth, between harvests H 2 and H, (the 10° treatment) and harvests H. and H. (the zoo treatment immediately after the 5° treatment) were almost identical at 0'035 and 0'°36 mg. day ? respe ctively . This suggested that the potential ability of the VAM endophyte to grow in the roots was not seriously affected by the 5° treatment. However, the RGR of mycorrhizal plants decreased with lowering temperature, and during the 5° treatment was lower than that of the controls (F ig. 1, C) . The development of the endophyte in the onion roots is presented as the percentage root length infected (R LI) and as the root weight infected (RW I) (Fig. 1, D ). The RLI continued to increase , but at a slower rate during the 100 treatment, after which the level of infection was relat ively constant through the 5° treatment. Howe ver, du ring the low-temperature peri od the roots continued to Trans. Br . my col. S oc. 79 ( 1), ( 1982).

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grow slowly and the RWI increased as the endophyte maintained its level of infection in the roots. In the initial 200 treatment the endophyte rapidly established itself in the roots . Arbuscules were visible at all stages of development at HI (nascent, mature and senescent) although the majority were newl y formed. A number of roots at this time also cont ained spherical-to-ovoid vesicles . By harvest H 2 the infection was very extensive, with abundant arbuscules and vesicles in all stages of development ; chlamydospores were also noted in some of the root systems, Numbers of intra-radical chlamydospores markedly increased by H , and in some instances their exten sive development caused the root tissue to rupture. Decreasing the temperature slowed the longitudinal spread of the fungus in the roots and the mycelium became less branched, with fewer arbuscules. After the 5° treatment at H., the smaller infect ion units looked moribund, perhaps due to lack of reserves . Towards the extremities of the internal mycelial network the hyphae were thin, unbranched, and showed little lateral colonization of the roots . In older areas of the infect ion septate hyphae were visible ; these were presumably formed as the endophyte removed reserves from its moribund mycelium in a similar manner to that noted by Nicolson (1959) in external hyphae. During the low-temperature conditions young and mature arbuscules were present (F ig. 2, A), although they were poorly branched and had a Spartan structure. Numerous vesicles were still visible but many had collapsed, or had become deformed ; others had, or were in the process of changing into, chlamydospores (Fig. 2, B). The external production of chlamydospores commenced during the 10° treatment. Most spores were, however, seen attached to the roots after the 50 treatment at H., but their induction may have taken place earlier. With the removal of the temperature limitation to growth, the endophyte rapidly resumed its colonization of the roots. By harvest H s' the hyphae had returned to their highly branched habit and many nascent arbuscules and vesicles were visible . The formation of large numbers of internal chlam ydospores, possibly triggered initially by the low-temperature treatments, cont inued despite the ameliorated conditions. The presence of arbuscules in various stages of development, throughout the course of the experiment, was considered to be an indication of their potential activity. The average life span of active arbuscules in onion , during which time transfer of P takes place (Rh odes & Gerdemann, 1980), is

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Notes and brief articles

A

Fig.

2.

Appearance of the endophyte. (Al Appearance of arbuscules at H., immediately after the 5° treatment ( x 800). (B) Extensive intra-radical chlamydospore formation ( x 60).

Trans. Br. mycol. Soc. 79 (r), (1982) .

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Notes and brief articles reported to be between one and six days (Bevege & Bowen, 1975; Cox & Tinker, 1976). During the cold period G. caledonium maintained its level of infection in the onion roots. VAM fungal st rain s may be able to grow at lower temperatures if they have not been selected over long periods under warm glasshouse cond itio n s . Previous unpublished work with Narcissus cv . Cheerfulness has shown that the same strain of G. caledomum was unable to infect roots at 6°, but could do so at 9°. This factor , together with the possibility of low-temperature stimulation of chlamydospore formation, sugges ts that temperature may play an important role in the control of the life cycles of VA endophytes in nature . During the 5° period the RGR of the m yco rrhizal onions dropped to below that of the controls, which may possibly indicate that the endophyte wa s parasitic on its host. There has been no demonstration of a significant and continuing parasitism of a host plant by its m ycorrhiza s, but low temperatures acting in combinatio n with other factors, such as host competition for limited P resources, low light or water deficiency may result in a significant parasitic effect. M. T. C. is in d ebted to the Natural Environment Research Council for financial support during the course of this study.

REFERENCES

BEVEGE, D . I. & BOWE}';, G. D . (1975). Endogone strain and host-plant differences in development of vesiculararbuscular mycorrhizas. In Endomy corrhi z as (ed. F. E. Sanders, B. Mosse & P. B. Tinker), pp . 77- 86. London : Academic Press. B UTT, A. M . (1968). Vegetative gr owth, morphogenesis and car bohydra te co ntent uf the onion plant as a function of light and temperature under field and

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controlled conditi ons. M ededeling en Landboutuhogesch001

Wa geningen, N ederlarul86 ( 10).

CHILVERS, M . T. & DAFT, M . J. (1981). Mycorrhizas of the Liliiftorae. II. Mycorrhiza formation and incidence of root hairs in field grown Narcissus L. , Tulipa L . and C rocus L. cultivars . N ew Phytologist 89 , 247-261Co x, G. & TI NKER, P. B. (1976). Translocation and tran sfer of nutrient s in vesicular-arbuscular mycorrhizas. 1. The arbuscule and pho sphorus tran sfer: a quantitative ultra structural stud y. New Phytologist 77, 37 1-378. DAFT,M. j.,CHILVERS,M. T. & NICOLSON,T . H . (1980). Mycorrhizas of th e Lil iiflorae . I. M orphogenesis of Endymion non- scriptus (L.) Garck e and its mycorrhizas in nature. New Phytologist 85, 181-189. DOWNS, R. J. & HELLMERS, H. (1975). En vironment and Experimental Control of Plant G rowth. Lond on : Academi c Press. . FURLAN, V. & FORTIN, J. A. (1973). Forma tion of end omy corrhizae by Endogone calospora on Allium cepa under three temp erature regimes. Naturaliste C anadien 100,467-477. HAYMAN, D . S. (1974). Plant growth responses to vesicular-arbuscular rnycorrh iza, VI. Effect of light and tem perature. New Phytologi st 73, 71-80. HAYMAN, D . S. (1977). Mycorrhizal effects on white clover in relation 10 hill land improvement. Agricultural R esearch Council R esearch Re vie w 3, 8z-85 . H UNT, R. (1978). Plant Gr owth Analy sis. London : In stitute of BiologyJ Edward Arn old. NICOLSON, T . H. (1959). Mycorrhiza in the Gramineae. I. Vesicular-arbuscular endophytes, with special reference to the external phase. Tra nsactions of the British M ycological S ociety 4z, 421-43 8. PHILLIPS, J. M . & HAYMAN, D . S. (1970). Improved procedur es for clearing roots and staining parasitic and vesicular-arbu scular mycorrhizal fung i for rapid assessment of infection . Tran sactions of th e British My cological Soci ety 55, 158-160. RHODES, L. H. & GERDEMANN, J. W. ( 1980). Nutrient translocation in vesicular--arbuscular mycorr hizas. In Cell ular Interact ions in Symbiosis and Parasiti sm (ed , C. B. Cook, P. W. Pappa s & E. D . Rudolph ). Columbus , Ohio: Oh io State University Press .

HEBELOMA SPP . AS MYCORRHIZAL ASSO CIATES OF BIRCH BY N . J. GIL TRAP* Department of Botany, Th e University , Sh effield S IO zTN, U.K .

Species of the genus Hebeloma have been sho wn experimentally to form ectomycorrhizas with Quercus robur (Sh em akhan ova, 1956), Pseudotsuga menziesii (T r ap p e, 196 7), Pinus oirginiana (H acs-

* Present addre ss : Department of Plant Biology, University of Hull, Hull HU6 7RX, U .K. Tra ns. Br , myc ol, S oc. 79 ( I), ( 1982).

kaylo & Bruchet, 1972 ) and P . radiata (C h u -C hou, 1979). In addition, since several species p roduce fru iting bodies under B etula spp. (T rap p e, 1962 ; Bruchet, 1970 ; Giltrap, 1979), they have been as sumed to be m ycorrh izal w ith this genus also. However, un ly H. mesophaeum has been ve r ified experimentally (M osca, 1963 ). This study examined

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