Báo cáo khoa học: "Physiological and pathological aspects of long-term storage of acorns"

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article Original Physiological and pathological aspects of long-term storage of acorns J Guthke W Spethmann Universität Hannover, Institut für Obstau und Baumschule, Am 3203 Sarstedt, Steinberg 3, Germany Summary — The development of a seedlot of oak has been followed over a period of 32 months. During the observation period, the absolute starch content of acorns and the exploitation of starch reserves at germination decreased with increasing duration of storage. Ageing processes are prob- ably impairing the availability of food reserves. After 12 months, a marked decrease in germination capacity appeared, caused by a fungal disease. However, the low storage temperature and high CO content seem to have stressed the acorns which has probably predisposed them to infection 2 with the weak pathogen, Cylindrocarpon didymum. Under natural conditions, the acorns developed typical frost hardiness. storage/ germination / food reserves / frost hardiness acorn Résumé — Aspects physiologiques et pathologiques de la conservation des glands à long terme. Le développement d’un lot de glands a été observé pendant une période de 32 mois. Pen- dant la période observée, la teneur absolue en amidon et l’utilisation des réserves d’amidon des glands ont diminué avec l’augmentation de la durée de conservation. Il est possible que le proces- sus de vieillissement réduise la disponibilité des réserves nutritives. Après 12 mois, une diminution nette de la faculté germinative s’est manifestée, causée par une infection fongique. Il semble que la température basse et les teneurs en CO élevées constituent des facteurs de stress sur les glands, 2 qui pourraient favoriser l’infection par le champignon Cylindrocarpon didymum. Dans les conditions naturelles, les glands manifestent une résistance au gel. germination/ réserves nutritives / résistance au gel conservation des glands /
0.25 Another 200 acorns were sown for a INTRODUCTION mm. test at each sampling date. When germination the first leaves on the epicotyl began to appear, Knowledge of physiological processes in a sample of 50 seedlings/treatment was taken to determine the consumption of food reserves and seeds is a prerequisite for the develop- build-up of shoot and root dry matter. ment of seed-storage methods. The cur- development of To the winter- investigate rent rule of thumb is that a water content in forest and a hardiness, acorns were sown a of 40% and a temperature of -4 °C are the nursery seedbed. Every 30 days, samples were minima acorns require to survive (Holmes taken for analyses (as above) and laboratory and Buszewicz, 1956; von Schönborn, frost-hardiness test were run for about 20 days 1964; Bonnet-Masimbert et al, 1977; Susz- at specific temperatures. ka and Tylkowski, 1980; Muller and Bon- The great variability within the acorn popula- net-Masimbert, 1984). tion contrasted with a variance-analytical inter- pretation of the results. The observed pathologi- Nevertheless, traditional but also cur- cal disintegration of the population also impeded rent methods are not up to the high stan- statistical evaluations. dards required for seed storage today and in the future. Above all, for gene conserva- tion, improved methods will be necessary. RESULTS In the context of a long-term storage project at the University of Hannover, the The temperature of -2 °C proved not to be physiological development during storage low enough to prevent germination in stor- and germination of different oak seedlots age. Within 12 months, epicotyls began to observed from November 1988. Ad- were appear. ditional investigations were concerned with A specific aim of the study was to deter- the ecophysiological behavior during the mine the influence of CO on stored 2 development of winter-hardiness (Guthke acorns (fig 1). This aim failed because of and Spethmann, 1991a,b). fungal invasion but, nevertheless, it was possible to assess the physiological and pathological aspects of acorn ageing. MATERIALS AND METHODS Although thermotherapy was reason- ably effective against attack by Ciboria The long-term storage trial started in November batschiana, it failed to protect against other kg of Quercus petraea acorns 1988 with 250 microorganisms. After 12 months, there from Lüß. After thermotherapy (2 h in 42 °C hot water; Delatour, 1978) and surface-drying, the distinct-wide decrease in germina- was a acorns were placed in boxes with dry peat and tioncapacity caused by another fungal dis- put into a jacket cooling at -2 °C. At this stage, ease, possibly Cylindrocarpon didymum. the had water content of 54%. Differ- acorns a At higher CO concentrations the fungal in- 2 (0.5, 1, 3 and 5%) 2 CO ent contents were ap- fection was even worse. plied. The dry matter of sound acorns (after Every 4 months, a sample was taken. Fresh the cutting test) fluctuated and a relation- weight, germination and fungal infection were for 700-1200 determined - 2 acorns/CO ship could not always be shown with the treatment. 200-300 obviously sound acorns dry matter residue after the germination were taken from each group for a cutting-test. test. Therefore, different dry weights were The fresh matter of the really sound acorns was calculated in comparison to the original instantly deep frozen and later dried to constant fresh weight of the whole samples and to weight over about 1 week at 70 °C. The cotyle- the acorn residues after germination. It don dry matter was ground for analysis to <
turned out that the sound acorns analyzed centage of starch consumed at germina- were heavier than the mean of the whole so that exploitation of food reserves tion, could be population and the germinated acorns impaired. were even heavier than the sound acorns, An additional investigation was explored especially in the last year. as to how acorns survive the winter under Another feature observed was the de- natural conditions. Even during the quite velopment of starch (%) during storage (fig warm winter of 1989-1990, acorns showed 2). While the starch weight decreased con- typical development of frost hardiness (fig tinuously, the percentage did not change 3). About 50% of the acorns survived at la- but fluctuated around 35%. Since only boratory tests -8 °C in January. sound acorns were analyzed, it seems Unexpectedly, water content increased probable that not only heavier acorns but from 49% in October to 62% in March. also acorns with a higher percentage of Sugar content increased with the develop- starch were more viable. ment of frost hardiness. Sugars exhibited a After prolonged acorn storage, seed- distinct reaction to cold, especially in the showed gradual reductions in shoot cell sap. Cutting tests showed, by the natu- lings and root dry matter. It is not yet clear if the ral browning reaction of frost damaged tis- decrease in shoot and root dry matter was sues, that frost hardiness of the acorn was higher around the embryo axis and in inner only associated with decreased acorn dry matter before the germination test. A dis- tinct decrease also appeared in the per-
of shoot and root dry matter development at germination, the exploitation of starch at germination was reduced and may have availability resulted from a reduced of food reserves. In respect to these ageing pro- cesses and the more obvious physiological and pathological disintegration of the popu- lations, it also seems to be necessary to in- vestigate the genetic development of fur- ther storage trials. New methods must be found to solve the old problem of acorn storage. A prom- ising way may be a controlled hardening treatment of acorns. REFERENCES Bonnet-Masimbert M, Muller C, Morelet M (1977) De nouveaux espoirs pour la conservation des glands. Bull Tech Off Nat For 9, 47-54 Delatour C (1978) Recherche d’une méthode de lutte curative contre le Ciboria batschiana (Zopf) Buchwald chez les glands. Eur J For Pathol 8, 193-200 Guthke J, Spethmann W (1991 a) Abhärtung von Eicheln an ihrem natürlichen Standort. Wis- than in outer and (Guthke areas ones senschaftliche Arbeitstagung des BDGL, Uni- Spethmnn, 1991a, b). versität Hannover 27/02-01/03/1991, BDGL- Schriftenreihe 9, 78 Guthke J, Spethmann W (1991b) Frost hardi- of acorns is induceable! INRA- DISCUSSION ness Congress Génétique des Chênes, Nogent- sur-Vernisson, 01-06 Sept 1991, Poster One aim of this storage trial was to investi- Holmes GD, Buszewicz G (1956) Reports on re- gate the influence of elevated CO content sults of individual investigations. III. Longevi- 2 ty of acorns with several storage methods. which seemed to be a suitable way of re- Report on Forest Research 1955. Ann Rep ducing the metabolism of acorns. This ef- Forestry Comm 1956 fect cannot be excluded, but it was impos- Muller C, Bonnet-Masimbert M (1984) La con- sible to prove because, simultaneously, servation des glands. In: Bilan des Essais infection with Cylindrocarpon increased Menés entre 1976 et 1982. INRA Centre de with the CO concentration. It is possible 2 Recherches d’Orléans that Cylindrocarpon infection is stimulated Von Schönborn A (1964) Die Aufbewahrung des by elevated CO but this was not investi- , 2 der Waldbäume. Saatgutes BLV- gated. Apart from this obvious pathological Verlagsgesellschaft, Münich development, some symptoms of physio- Suszka B, Tylkowski T (1980) Storage of acorns logical ageing of the acorns were also evi- of the English oak (Q robur L) over 1-5 win- dent. In addition to the gradual reduction ters. Arbor Kórnickie 25, 199-229