The Infection of Corsican Pine by Crumenula sororia Karst

For germination ascospores of Crumenula sororia require freemoisture. A temperature range of 20–25 °C was optimal.In these conditions rate of germination was increased by extractsof lodgepole pine bark and extracts of Corsican pine bark andwood. Irrespective of whether spores or hyphae were used, C. sororiaonly Successfully invaded Corsican pine through wounds madewith a scalpel or by removing needle fascicles. Lesions didnot develop when frozen tissues were inoculated. In field inoculation experiments different isolates of the fungusdiffered significantly in pathogenicity. Infections developedmore severely on 4-year-old than on 1-year-old branches, andthis agrees with the incidence of natural branch-infections.     

Winter Frost Hardiness of two Chilean Provenances of Nothofagus procera in Scotland

The frost hardiness of the shoots of individual trees withintwo Chilean provenances of Nothofagus procera (Poepp & Endl.)Oerst. was measured once in each of the months January, February,November and December 1989 and January and February 1990. Therewere significant (P<0.05) differences of frost hardinessbetween provenances but only one tree could be shown to be significantlymore frost hardy than the others within the same provenance.During the winter of 1989/90 both provenances were hardy toabout –14°C (temperature killing 50 per cent of shoots)in December, but the shoots dehardened to about –9°Cin January before hardening again in February. This patternof alternate hardening and dehardening seemed to mirror changesin air temperature and could render N. procera liable to frostdamage where (as happened in 1988/9 in the UK) mild spells occurin winter followed by severe frosts.     

Krebsartige Erkrankung an Pinus contorta-Herkünften

Canker in Pinus contorta provenances . In connection with canker of 9 Pinus contorta provenances the two discomycetous fungi, Crumenulopsis sororia and Lachnellularehmii, were identified. After artificial infections L. rehmii did not produce canker symptoms. Therefore only C. sororia is considered to be the primary parasite. The P. contorta provenances differed in their damage rate.     

Fungi dangerous at Pinus contorta with special reference to pathogens from North Europe

Examples are given of North American fungi potentially dangerous to Pinus contorta plantations in northern Europe. The pathogenicity of North European fungi is discussed. P. contorta was found to be immune or nearly immune to all European rust fungi, more resistant than P. sylvestris to Phacidium infestans and Lophodermium pinastri, but less resistant to Crumenulopsis sororia and Discella strobilina. For other fungi no such clearcut conclusions could be drawn.     

Shading Reduces both Visible and Invisible Frost Damage to Norway Spruce Seedlings in the Field

Two-year-old cuttings of Norway spruce were subjected to nightfrosts in spring on an exposed site in southern Sweden. Shadingwas used to assess the influence of sunlight on the extent ofdamage resulting from night frost. Chlorophyll fluorescencewas measured in needles in flushing shoots, and in shoots atthe stage of bud burst. The F_v:F_m ratio was significantly lowerfor plants exposed to light, compared with shaded plants onthe days following the night frost (minimum temperature –6°C).The effect was similar both in 1-year-old and current year needles.The low F_v:F_m ratios indicate damage to photosystem H, causedby an interaction between sub freezing temperatures and highlight intensity. Shading also increased the survival of flushingshoots. It is suggested that regeneration of Norway spruce onsites exposed to frost should be carried out in partial shade,for example under a shelterwood.     

Frost Hardiness of Subalpine Eucalypts in Britain

Laboratory freezing tests were used to determine seasonal changesin the frost hardiness of detached shoots of young trees ofEucalyptus gunnii (from central Tasmania), and E. niphophilaand E. debeuzevillei (‘snow gums’ from the SnowyMountains, Australian Capital Territory). The trees were growingat the Bush Estate. No difference was found between the speciesor between seedlots, all of which were from high altitudes nearthe tree line. In midwinter (February) the shoots tolerated –16°Cwithout suffering damage, and many shoots survived temperaturesas low as –18°C to –22°C. This result agreedwith Evans' (1986) observation that some trees within theseseedlots survived temperatures in the range –19°Cto –23°C in field planting during the winter 1981/82.In their native habitats the trees rarely experience temperaturesbelow –20°C. The shoots did not harden appreciably before they experiencedfrosts (in late October/early November) and so may be proneto autumn frost damage. By contrast, they were slow to dehardenin late winter and spring and did not seem prone to spring frostdamage. There were no killing air frosts during the period of this study(winter 1985/6), but many trees died, possibly as a result ofground freezing, producing root injury and/or shoot desiccation.In subalpine regions of Tasmania and the Snowy Mountains theground is covered by snow throughout the winter. Variation in frost hardiness within these hardy seedlots couldbe exploited.     

Performance and Frost Hardiness of Picea sitchensis x Picea glauca Hybrids in Scotland

The growth of seven Picea sitchensis x Picea glauca hybridswas compared with the growth of two P. sitchensis provenancesand Picea glauca var.albertiana at two sites in northern Scotland.The sites were at Aultmore (an exposed, dry site with a mineralsoil) and Shin (a frosty, wet site with deep peat). They wereof the type considered more suited to Pinus contorta than P.sitchensis. At age 10, in 1984, most of the hybrids, at both sites, wereabout 10 and 20 per cent taller than P. sitchensis of Masset(Q.C.I.) and Ketchikan (Alaska) provenance, respectively. P.glauca var. albertiana grew very poorly, especially at Aultmore. At Aultmore, the frost hardiness of three of the tallest hybrids,the two P. sitchensis provenances, and P. glauca var.albertiana,was tested at about 3-weekly intervals throughout 1982 and 1983.Detached shoots were subjected to artificial frosts in a programmablechamber. P. glauca var. albertiana was frost susceptible atbudburst, but at all other times it was relatively very frosthardy (eg. to^–10°C in mid-August). Also, the hybridswere consistently more hardy than P. sitchensis of even Ketchikan(Alaska) provenance from July onwards. However, the hybridswere less frost hardy than P. sitchensis of Masset (Q.C.I.)provenance in early spring (they dehardened a week earlier inMarch-April) and their buds were equally as frost susceptibleat the time of budburst. In 1983, trees of P. glauca var. albertianaburst their buds about a week sooner than P. sitchensis. It was concluded that P. sitchensis x P. glauca hybrids canperform better than P. sitchensis at sites considered ‘marginal’for P. sitchensis, and that their good performance may be partlyattributed to, or associated with, their greater summer andautumn frost hardiness. A programme of inter-specific hybridizationis being pursued.     

Forest characteristics affecting the rate of shoot pruning by the pine shoot beetle (Tomicuspiniperda L.) in Pinus radiata D. Don and P. sylvestris L. plantations

Different variables, such as altitude and presence of defoliators,were studied in Bizkaia (northern Spain) in order to assessthe susceptibility of Pinus radiata (D. Don) and P. sylvestris(L.) stands to Tomicus piniperda (L.) (Coleoptera: Scolytidae).Altitudes higher than 400 m, presence of logs, degree of thinningand incidence of fires, all increased the susceptibility ofP. radiata monocultures to shoot attack by T. piniperda. P.sylvestris plantations were more affected at alti tudes lowerthan 400 m and by poor forest hygiene. The presence of the processionarymoth (Thaumetopoea pityocampa Den and Schiff.) had a significanteffect on the rate of shoot pruning on the trees; vigorous treesand those with bare leader were more affected by the bark beetleattack if T. pityocampa larvae were feeding on their needles,while trees with dominance taken by the side shoots were lessattacked when moth larvae were present.     

The effect of roots and litter of Calamagrostis canadensis on root sucker regeneration of Populus tremuloides

Marsh reed grass (Calamagrostis canadensis (Michx.) Beauv.)is a common, highly competitive grass native to the boreal mixedwoodforest. This grass increases in abundance after clear-cut loggingbut little is known about its effects on trembling aspen (Populustremuloides Michx.) sucker regeneration. The effects of Calamagrostissod and its litter on aspen regeneration were studied in twoseparate greenhouse studies. Calamagrostis sod did not affectthe initiation of suckers, but resulted in 30 per cent fewersuckers emerging above the soil that were smaller and had 40per cent less leaf area. Calamagrostis litter had little effecton the initiation and number of emerged suckers; however, itdelayed emergence by 10 days. The physical barrier by rootsand litter of Calamagrostis reduced or delayed the expansionof suckers and therefore prolonged their dependence on rootreserves. By the time the suckers reached the surface, theyhad to compete for light with Calamagrostis shoots that hademerged a week earlier. This, coupled with low soil temperaturesassociated with Calamagrostis in other experiments, will significantlyreduce the number and growth of suckers. Any reduction and delayin sucker emergence will decrease aspen regeneration and productivitysince the growing season in the boreal forest region is short.     

Incidence and importance of Crumenula sororia on Lodgepole pine

In stands of Lodgepole pine over 6 years old, 68% of stems in Climatic Zones A and B, characterised by a relatively short growing season, and 63 % of stems in Climatic Zone C were infected by Crumenula sororia. On individual trees, the number of stem whorls showing C. sororia infection increased significantly with increasing stand elevation and with decreasing exposure in crops on Alberta and Shuswap Lake provenances over 30 years old, whereas in Shuswap, Long Beach and Vancouver Island stands less than 30 years old, increasing elevation and decreasing exposure had little effect on numbers of infected whorls. The numbers of infected whorls were not related to compartment aspect in crops of Alberta provenance, whereas in stands of Shuswap Lake, Long Beach and Vancouver Island provenances, W, SW and S-facing compartments showed fewer infections. In contrast the numbers of active cankers showed a positive correlation with increasing compartment elevation and exposure. In Zones B and C, cankers were concentrated on Northerly and Westerly aspects of individual stems. The evidence suggests that particular climatic regimes in different zones of the tree and in different ages of crop may be critical in determining the success of failure of infection by C. sororia.     

Effects of nitrogen fertilization and temperature on frost hardiness of Aleppo pine (Pinus halepensis Mill.) seedlings assessed by chlorophyll fluorescence

In a 14-week study, 1-year-old Aleppo pine seedlings were grownin two growth chambers. Seedlings were artificially hardenedby decreasing photoperiod and temperature. In each chamber halfof the seedlings were fertilized with nitrogen (8.4 mg seedling^–1).In order to determine the relative importance of the hardeningenvironment versus fertilization, each chamber was programmedto decrease night temperatures down to a low of 8 or 4°C.Chlorophyll fluorescence and frost hardiness was measured fivetimes during the experiment. A sample of seedlings from eachtreatment was exposed to an artificial frost at –5°Cand the freezing effects were assessed by measurements of chlorophyllfluorescence and visual evaluation of needle damage. Seedlingsincreased their frost hardiness during the experiment in allthe treatments but the ratio of variable to maximal chlorophyllfluorescence (F_v/F_m) measured before freezing did not vary duringthe experiment. This indicates that Aleppo pine maintains itsphotosynthetic ability during hardening in contrast to otherconiferous species from colder climates. The effect of nitrogenfertilization on frost hardiness was small in comparison withchamber effect. Nitrogen fertilization slightly delayed theacquisition of hardening in the coldest chamber. Seedlings inthe warmest chamber did not become fully resistant to –5°C,but in the coldest chamber, where night temperature reached4°C, all the seedlings were resistant to the frost. Severedamage caused by frost could be related to a rapid rise of minimalfluorescence (F₀) but the best index of damage was the dropof F_v/F_m after freezing.     

A Study on the Mode of Infection of Pinus sylvestris L. by Peridermium pint (Pers.) Lev.

Inoculations by Peridermium pini (Pers) Lev. aeciospores ofscalpel wounds 2 mm deep on current year's Pinus sylvestrisL. shoots gave more numerous infections than shallower wounds.Some lesions resulting from these infections developed pycnidialdroplets and a few also produced aecial blisters within thefirst year after infection. Infection of P. sylvestris by P.pini can take place by direct stomatal penetration. This wasobserved only inside the needle sheaths of trees with previousnatural infections and was not observed on healthy trees. Thehyphae that developed from these penetrations passed intercellularlythrough the mesophyll to the vascular tissue where they proliferated.     

The status of Crumenula sororia infections in crops of Corsican pine

Nodal cankers caused by C. sororia on Corsican pine were three times as common as internodal cankers. Natural infections reached maximum incidence on the fourth internode from the apex in branches and stems, but on stem internodes only on the ninth internode down. The longitudinal rate of canker spread was approximately 4 times that of the tangential rate. Crops of Corsican pine on N-facing slopes were more severely infected than those on S-facing slopes or flat areas, but in all cases the frequency of infection increased progressively with crop age. Cankers on individual stems showed a highly significant concentration on Northerly and Easterly aspects. Evidence is presented which suggests that the temperature differentials observed on different sectors of tree trunks may influence the duration of water films and hence limit the time period during which spore germination is possible.     

A Study of Some Factors of Resistance of Pinus sylvestris L. to Peridermium pint (Pers.) Lev.

External needle extracts from an infected and a healthyPinussylvestris L. did not adversely affect the germination of aeciosporesof Peridermium pini (Pers.) Lev.Internal extracts and juicesexpressed from needles and shoots showed a fungistatic effecton spores. The effect was more pronounced when extracts and juices werederived from needles of a healthy tree than from an infectedone. In the former case, the germ tubes were invariably deformed.The significance of these differences in relation to resistanceis discussed.     

Development of the fungus Ceratocystis fimbriata in shoots of poplar clones with differing resistance1

Differences in the development and rate of spread of C. fimbriata hyphae between susceptible, moderately resistant and resistant clones were observed. Conidia of various shapes and ascospores appeared in necrotic parts of shoots of susceptible and moderately resistant clones while in the resistant one only cylindrical conidia were present.     

The Effect of Gravity on Root Emergence from Cuttings of Some Tree Species

Poplar shoots trained horizontally and normally growing shootswere used to compare the effect of horizontal and vertical orientationin summer on the subsequent rooting of terminal cuttings; asignificantly greater number of preformed roots emerged fromcuttings of vertical shoots. This difference in rooting abilitymay be due to the lower concentration of indolyl-acetic acidin the upper than in the lower half of horizontal poplar stemsas shown by Leach and Wareing (1967). Decapitation of a seriesof these poplar cuttings (Populus ? robusta Schn.) showed thatwound-root production was influenced by the larger terminalbuds on vertical than on horizontal shoots. From a comparison of horizontal and vertical storage of applerootstock cuttings at 45 ?F in the autumn, 29 per cent moreof the horizontal cuttings than the vertical ones had a basalcallus in the following February. Of these cuttings which madesatisfactory shoot growth (over 5 cm) in the following summer,horizontal cuttings exceeded vertical ones by 80 per cent; aresult which was correlated with root production. In a second experiment with M II apple rootstocks in which cuttingswere both stored and grown at the same angle more roots occurredon cuttings placed horizontally rather than vertically, andthis orientation also induced the rootings of a greater proportionof leafy Worcester Pearmain apple cuttings.     

Seasonal Changes in the Frost Hardiness of Provenances of Picea sitchensis in Scotland

Changes in the natural level of frost hardiness of shoots offour provenances of Picea sitchensis were monitored over twogrowing seasons by detaching shoots from 7 to 10-year-old treesgrowing in a nursery in Scotland, and subjecting them to freezingtemperatures under conditions which simulated night frosts. Six seasonal phases of frost hardiness were identified (Fig.3).

1. During each autumn, killing temperatures (the level of hardiness)decreased from –5°C to below –20°C, beginningseveral weeks after shoot elongation ceased. Alaskan provenanceshardened in September, apparently in response to shorteningday lengths alone, whereas an Oregon provenance did not hardenuntil November, after repeated frosts. Queen Charlotte Islandsprovenances were intermediate.
2. From November to March allprovenances were hardy to below –20°C,which is adequateto prevent direct freezing injury at mostplantation sites.
3. In March-April, several weeks before bud-burst, old shootsdehardenedto killing temperatures of about –10°Cin responseto warm temperatures, and southerly provenancesdid so beforenortherly ones.
4. During bud-burst the newly-emergingshoots were hardy to only–3°C to –5°C untilthey were about 3.5 cmlong. All provenances burst bud at thesame time and were equallyfrost susceptible at this time.
5. DuringMay-July the elongating shoots fluctuated in hardinessbetween–5°C and –10°C apparently in responsetofluctuating ambient temperatures.
6. In August 1980 there wasa period of late summer dehardeningto killing temperaturesof about –3°C.

Seasonal changes in hardiness are discussed in relation to changesin shoot growth and environmental factors. The main opportunitiesfor selecting frost hardy genotypes seem to be in the rate ofautumn hardening, the time of pre-bud burst dehardening, andthe time of bud-burst.     

A Study Undertaken in Southern Britain to Investigate the Late-Flushing of Hedgerow Ash in Spring 1987

Following the abnormally late flushing of many ash (Fraxinusexcelsior) in 1987 a study on their condition was initiated.An investigation of 19 trees at 12 sites in England and Waleswas carried out in June with a second inspection later in thesummer. For comparison, another full survey of the same treeswas undertaken the following year. Information collected onmore than 4000 bud positions showed that in 1987 significantlyfewer buds flushed to produce healthy shoots than in 1988 (18per cent compared with 34 per cent respectively). Although nodifference was detected between the two years in the numbersof buds killed or damaged by ash bud moth (Prays fraxinella)or invaded by fungi (principally Fusarium lateritium) therewere significantly more buds killed by unknown causes in 1987than in 1988 (13 per cent and 4 per cent respectively). Thetrees were fully recovered by mid-summer 1987 and went on tofoliate normally in 1988. There was thus no reason to considerthat the late flushing marked the onset of any serious dieback. Received 22 May 1990.