Báo cáo khoa học: "Variation in the phenology of shoot elongation between geographic provenances of maritime pine (Pinus pinaster) - implications for the synchrony with the phenology of the twisting rust fungus"

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article Original Variation in the phenology of shoot elongation between geographic provenances of maritime pine (Pinus pinaster) - implications for the synchrony with the phenology of the twisting rust fungus, Melampsora pinitorqua ML F Desprez-Loustau, Dupuis INRA, Centre de Bordeaux, Station de Pathologie Végétale, BP 81, F-33883 Villenave-d’Ornon cedex, France 1993; accepted 17 December 1993) 18 March (Received Summary — The phenology of shoot elongation was monitored for 2 or 3 years at 4 sites in France with 6 maritime pine geographic provenances. Within each provenance, the onset of phenological stages, especially the earlier ones, was better predicted by heat sums than by calendar days. The accuracy of prediction could be increased by about 50% for the earliest studied stage (from 19 to 10 d). However, temporal and, to a greater extent, site effects were still observed for heat sums. These may be attributed in part to stressful environmental conditions for pine. The geographic provenances used represent a range of significantly different heat requirements, the Tamjout (from Morocco) and the Leiria (from Portugal) provenances representing the earliest and the latest, respectively, with a difference of approximately 100 degree-days (for a threshold temperature of 0°C). A positive correlation was observed between precocity and vigour though this could not explain differences in precocity between provenances. A comparison of pine and rust (Melampsora pinitorqua) phenologies, monitored at the same sites in south-west France, revealed that synchrony between the host-susceptible stages and the parasite-spore-producing stages did not always occur. The earliness of the Tamjout provenance pre- disposed it to greater rust infection than other provenances due to better synchrony with basidiospore production. Variations in host-parasite synchrony are discussed from an evolutionary perspective and in relation to the prediction of infection risk. pine / rust / phenology / susceptibility period / infection risk maritime Résumé — Variabilité phénologique de l’élongation des pousses entre provenances géogra- phiques de pin maritime. Conséquences sur la synchronisation avec la phénologie du cham- pignon responsable de la rouille courbeuse, Melampsora pinitorqua. La phénologie d’élonga- tion des pousses a été suivie pendant 2 ou 3 ans dans 4 sites pour 6 provenances géographiques de pin maritime. Pour chaque provenance, les sommes de températures et les dates ont été comparées en tant que variables prédictrices de l’apparition des stades phénologiques, par la méthode du coef-
ficient de variation et de l’erreur standard de prédiction. Les sommes de températures se sont révélées les meilleures variables prédictrices, surtout pour le stade le plus précoce, avec une erreur de prédiction réduite d’environ 50% (de 19 à 10 j). Toutefois, il reste une variation entre années et surtout entre sites. Cette dernière pourrait provenir en partie de conditions défavorables pour la croissance des pins dans 2 des sites étudiés. Les provenances étudiées ont manifesté des exigences thermiques significativement différentes, les provenances Tamjout (Maroc) et Leiria (Portugal) représentant la plus précoce et la plus tardive respectivement, avec une différence d’environ 100 degrés/jours (pour un seuil de 0°C). La précocité et la vigueur sont corrélées positivement. Toutefois les différences de précocité entre provenances sont maintenues après ajustement à la vigueur. La sensibilité des pins et la phénologie du champignon responsable de la rouille courbeuse (Melampsora pinitorqua) ont été sui- vies dans le même site dans les Landes. La coincidence entre les stades sensibles chez les pins et la production de basidiospores par le champignon n’est pas toujours observée, même pour la prove- nance landaise de pin maritime. La précocité de la provenance Tamjout se traduit par une plus grande prédisposition aux infections que pour les autres provenances, du fait de la coincidence entre la période de sensibilité et la production de basidiospores. Une discussion est proposée sur les variations de la coincidence phénologique hôte-parasite, du point de vue de l’évolution et en relation avec la pré- vision des risques d’infection. pin maritime / rouille / phénologie / période de sensibilité / risque d’infection INTRODUCTION infections are produced only for a short in spring (approximately 1 month), period after the breaking of teliospore dormancy Maritime pine (Pinus pinaster Ait) shoot (Kurkela, 1973; Desprez-Loustau and elongation has been studied extensively Dupuis, 1992). Therefore, variations in pine with respect to seasonal pattern (Illy and phenology may affect the synchrony Castaing, 1968), genetic control (Kremer, between susceptible stages and basid- 1982), and morphogenetic components iospore occurrence. The prediction of phe- (Kremer and Roussel, 1982, 1986; Kremer nological stages in maritime pine may pro- and Lascoux, 1987). However, most studies vide a risk assessment of rust infection, when have focussed on quantitative aspects since related to the prediction of basidiospore dis- they have concerned breeding for higher persal. growth rates. The phenology of elongation The present study was undertaken with 2 has been given little attention as it often objectives. The first was to confirm and appears unrelated to total shoot growth define the extent of phenological variation in (Cannell et al, 1976). maritime pine: our previous data (Desprez- Our interest in phenological variation in Loustau and Baradat, 1991) were limited to maritime pine originates from an observa- a few measurements at a single site. We tion that such variation appeared to be asso- thus compared provenances originating from ciated with differences in susceptibility to the whole natural distribution area of P twisting rust, caused by Melampsora pini- pinasterat 4 locations in France represent- torqua Rostr (Desprez-Loustau and Bara- ing a wide range of environmental condi- dat, 1991). Pine shoots show different tions. As air temperature has been shown to degrees of susceptibility to M pinitorqua be a major determinant of shoot growth in according to their elongation stage, the maxi- many species including conifers (Lavender, mum susceptibility being observed between 1980; Perala, 1985), we analysed thermal bud-scale disjunction and needle emergence requirements at the onset of the different (Kurkela, 1973; Desprez-Loustau, 1990). phenological stages for each maritime pine Furthermore, the basidiospores causing provenance. Pines were monitored from 3 to
the combined pollen from 10 paternal trees of the 5 years old, at an age of fixed growth pattern other. Reciprocal crossings were made by in- (ie elongation of preformed units, Lanner, versing maternal and paternal trees. All families 1976) and with a high susceptibility to twist- obtained from the various crossings were used ing rust. The second objective was to give [Corsica x Landes] hybrids. as further biological support to the previously Seedlings were grown in nursery for 1 year, observed relationship between phenology and then transplanted in the experimental sites. and rust infections in maritime pine. This The general features of the 4 experimental part of the study was restricted to 1 site in sites are given in table II. Sixty plants per popula- the Landes area, where the fungus has a tion (provenances or hybrids) were used at each site. The [Corsica x Landes] hybrids were not used natural occurrence and the pine twisting rust at the Lagnereau site. Completely randomized disease is endemic. Rust phenology and designs with unit plots of 3-6 trees were used. rust susceptibility of 3 contrasting maritime pine provenances were monitored. Monitoring shoot elongation MATERIALS AND METHODS Weekly observations were performed in spring (March-June) for 2 successive years at each site (3 years at the Ruscas site). On each observa- tion date, shoot length and phenological stage Experimental design recorded for each tree on the leader shoot. were The phenological stages were defined according Sixgeographic provenances of P pinaster were to Debazac (1966) (fig 1), as follows: The main ecological characteristics compared. B0: dormant buds; ofthe seed collection sites are given in table I. B1: buds swollen; In additon, ’hybrids’ were created between the B2: buds elongating, disjunction of bud scales Landes and the Corsica provenances by pollina- making the shoot surface visible; tion of 5 maternal trees from 1 provenance with
B3: emergence of Vivario) on 5 dates in 1989 and 1990 at the brachyblasts; Lagnereau experimental site. Inoculations were B4: emergence of needles; performed on excised shoots under controlled B5: disjunction of the needles from the fas- same conditions, using basidiospore producing aspen cicle leaf discs, as described previously (Desprez-Lous- Owing to the acropetal development of shoots, tau, 1990). Mean basidiospore numbers per inoc- observations were made at approximately the U3 ulated shoots were approximately 10 000 (350 level from the shoot base; L is defined as the shoot per mm in 1989 and 5 000 (180 per mm in ) 2 ) 2 length on the observation date. The date of occur- 1990. Successful inoculations (ie shoots bearing rence of a phenological stage was considered to pycnia and/or aecia) were assessed after 3 weeks. be the date when this stage was first observed. Meteorological data Phenology of M pinitorqua Minimum and maximum daily temperatures Samples of infected aspen leaves, the over- recorded at the nearest standard climatological wintering host of M pinitorqua, were collected on station (National Meteorological Network) were each observation date near the Lagnereau and used for each site. Heat sums (HS), in degree- Ruscas sites in 1989 and 1990. The develop- days, were calculated according to the following mental stage of the fungus was defined as its formula: potential to produce basidiospores under optimal conditions in the laboratory, as described previ- ously (Desprez-Loustau and Dupuis, 1992). The period extending from maximum production to the end of production under these conditions was for days with Tm> Tt; = i Tmmean daily temper- i shown to coincide with basidiospore dispersal ature, calculated Tm = (Tmin + Tmax)/2 or as under field conditions. assuming a sinewave diurnal fluctuation between Tmin and Tmax; Tt= threshold temperature. Each degree from 0 to 5°C was tested, as this Shoot susceptibility tests range includes values commonly used for shoot growth studies (Cannell and Smith, 1983; Osawa Shoots from the last whorl level were collected et al, 1983; Perala, 1985; Volney and Cerezke, from 3 provenances (Landes, Tamjout and 1992).
The cummulative degree-day values were predicted values and examining the distribution of always calculated from January 1 of each year. intra-group variances. Infection percentages were analysed using a generalization of the analysis of variance adapted to categorical data analysis (CATMOD procedure Statistical analysis of SAS). A log-linear model, with a maximum- likelihood estimation of the parameters, was used. Calendar days and the different heat sums, obtained with the aforementioned formula, were compared as predictors of the onset of pheno- RESULTS logical stages. Two statistical approaches, the coefficient of variation and the standard error of prediction were used (Castonguay et al, 1984). Pine phenology First, the mean of individual tree values was cal- culated for the different tested variables in each of the 9 [site x year] combinations of the study, for The dates of occurrence, all prove- mean each stage and each provenance. The coefficients being pooled, of the different phe- nances of variation (CV), ie the ratio of the mean to the nological stages for the 9 [site x year] com- standard deviation of these 9 values, were then calculated. The approach using the standard error binations are given in table III. The of prediction is based on the comparison between phenological evolution of the Landes prove- observed and predicted dates of the onset of nance at the Lagnereau site in 1989 and phenological stages. Predicted dates were 1990 is presented in figure 2 as an example. obtained as follows. For calendar days, the pre- A range of about 40 d was observed dicted value, taken for 1 given provenance and 1 between sites for the same stage. As given stage, was the mean date observed over expected, pine development occurred much the 9 [site x year] combinations. For heat sum later in the northern site (Orleans) than in variables, the predicted dates were obtained by determining, in each of the 9 [site x year] combi- the 3 southern ones. Variation within any nations the date corresponding to the mean heat given site over the 2- to 3-year observation sum value previously calculated from the 9 period was less than between sites. observed values from their respective meteoro- logical data. The error of prediction was calcu- lated as the difference between the predicted and actual dates. The mean value of these errors over the 9 [site x year] combinations should be null. The standard deviation represents the standard error of prediction (Castonguay et al, 1984). The best predictor variables should present low val- ues of both coefficient of variation and the standard error of prediction. Phenological data were analysed by analysis of variance with the SAS package (SAS Institute, 1988). Means per unit plot, comprising 3-6 trees, were considered as elementary data. As the same trees were observed in the successive years (resulting in an inherent correlation of measure- ments between years), repeated measures anal- ysis of variance were performed, using a multi- variate approach (Moser et al, 1990). The non-violation of the assumptions of the analysis of variance, particularly the adequacy of the model and the homogeneity of residual variances, were checked graphically by plotting residuals against
For the B2 stage, heat sums always pre- Results on coefficients of variation and sented a lower CV than calendar days. For standard errors of prediction of the differ- all stages, a regular decreasing trend of CV ent variables tested as predictors of phe- was observed for threshold values de- in nological stages figure 3. presented are creasing from 5 to 0°C. The heat sum cal- As similar trends were observed for all culated with a threshold value of 0°C gave provenances, only mean values are pre- a lower CV than calendar days for all stages, sented. In preliminary calculations, CV val- except B5. Standard errors of prediction cal- ues using the sine curve reconstitution of culated for heat sums (with Tm (Tmin + daily temperatures were slightly higher than = Tmax)/2) were always much lower than for those obtained with the simpler formula calendar days, the difference being maxi- Tm (Tmin + Tmax)/2. The latter formula = mum for the B2 stage (about 9 d). Very little was therefore used for the threshold study.
variation was observed in relation to thresh- site, provenance (6 levels corresponding to old temperature values. From the above the 6 geographic provenances), time (2 results, the heat sum calculated with Tm levels corresponding to the third and fourth = (Tmin + Tmax)/2 and with a threshold value year after plantation) and interaction effects of 0°C was chosen as the best predictive was first tested. Adjusted sums of squares variable for the onset of phenological stages (type III of SAS) were used owing to the dif- and used for further analysis (expressed in ferent numbers of unit plots at the 4 sites. degree-days above 0°C DD ). 0 These results are given in table V. For all = phenological stages, provenance, site The heat sum means at the onset of the [provenance x site] and [time x site] effects different stages for the 4 sites, all prove- were significant at the 5% level. HS values nances being pooled, are presented in table IV. HS values per tree (all provenances and at the onset of the different phenological sites pooled together) reached at 2 different stages were always significantly lower at phenological stages within the same year the Truncat and Orleans sites than at the were highly significantly correlated (r= 0.61 Lagnereau and Ruscas sites (interactions to 0.92, according to stage and year). with time or provenance did not affect this major distinction). A significant effect of time appeared only at the B3 and B4 stages with Variation in phenology between maritime either no interaction or only a slightly sig- pine provenances nificant interaction with provenance. No def- inite trend was observed between succes- sive years. analysis of variance with HS as the An dependent variable was performed for each Owing to the significant [provenance x phenological stage. A general model with site] effect, and also to include [Corsica x
Landes] hybrids, an analysis of variance ited a contrasting behaviour with a delay of then performed for each site with a about 100 DD as compared to Tamjout. 0 was restricted model without site and [site x other Other provenances showed an intermedi- ate behaviour. The [Corsica x Landes] sources] effects. A significant provenance hybrid appeared to show lower heat require- effect observed in 22 out of the 36 was ments, on average, than its 2 parent popu- [site year x stage] analyses (table VI). A x lations. few [year x site] combinations did not allow a discrimination between provenances, mainly in 1990 at the Truncat site and in Relation between phenology 1991 at the Orleans site. In most cases with and shoot elongation a provenance effect (19 out of 22), the Tamjout provenance exhibited a significantly higher precocity (ie lower heat sum values) For all pairs of shoot length measurements than the Leiria provenance, the other prove- single tree, at 2 different dates within on a nances being intermediate (same results the same year, highly significant correla- obtained with Student Newman Keuls, tions were observed (r= 0.6-0.99). The last Scheffe’s and Tukey’s tests). The [Corsica x measurement of length (when most pines Landes] hybrid always fell within the same had reached the B5 stage) was considered homogeneous group as its parent popula- further for the study of the relations between tions. In order to generate data for all sites, phenology and shoot growth. It was shown to be highly correlated with tree height (r= years and stages, the provenance means 0.73 and 0.67 for 1989 and 1990, respec- (in DD for each analysis were replaced by ) 0 tively) at the Ruscas site, where these data the difference with the overall mean for all were available. provenances. The mean of these deviations was then calculated for each provenance significant effect of provenance for A (cf table VII). The earliness of the Tamjout shoot length was observed only at the provenance was clearly indicated by a large Lagnereau site (results not shown), the negative deviation in DD from the mean of 0 Leiria provenance presented the lowest provenances. The Leiria provenance exhib- growth for both years. Significant differences
between sites were apparent, pines in the Truncat and Orleans sites showing poor growth (approximately 10 cm for the last measure of shoot length for both years) Rust phenology - variation in the timing compared with the Lagnereau site (approx- of susceptibility between 3 provenances imately 20 cm) and more so the Ruscas at the Lagnereau site (30-50 cm) site. Within each site, the HS accumulated at Periods of potential basidiospore dispersal each phenological stage were negatively (ie from the date of maximum production to correlated with shoot length for the same the date of the end of production under opti- year, ie the more vigorous trees had an ear- mal conditions) occurred throughout April lier development (table VIII). Similar trends for both years and sites: April 4-17, 1989 were observed for each provenance in the and April 5-23, 1990 at the Truncat site; Lagnereau and Ruscas experiments and April 4-24, 1989 and April 5-23, 1990 at more variation between provenances was the Lagnereau site. observed in the Orleans and Truncat experi- The evolution of susceptibility, expressed ments. An analysis of covariance was thus infection percentage after artificial inoc- performed for the first 2 sites, for each phe- as ulation, of the Corsican, Moroccan and nological stage, with HS as the dependent Landes provenances for spring 1989 and variable, provenance as the independent 1990 is presented in figure 4, where poten- variable and shoot length as the covariable. tial basidiospore dispersal is also shown. Provenance effects observed in the analysis Only the Moroccan provenance in 1989 of variance (table VI) were always main- appeared to show a significant degree of tained after adjustment with the covariable. susceptibility before the end of the basid- Tamjout and Leiria remained the earliest iospore production period. For both years, and latest provenances, respectively. Rank- the 3 provenances did not differ significantly ings of intermediate provenances were in their overall susceptibility throughout weakly affected.
could account for factors other than air tem- spring (table IX). However, the significant perature which have not been included in [provenance x date] effect in 1989 indicated a difference in the timing of susceptibility the model. Soil temperature may be a better predictor of shoot growth than air temper- between the 3 provenances. This was mainly due to the earlier receptivity of the ature (Lavender, 1980). Soil water poten- Moroccan provenance compared with the tial has been shown to be a contributing fac- other 2 provenances. Differences in infection tor in red pine shoot growth (Jones et al, percentages were highly significant in 1989 1991).Site effects may also result in part for the 2 first observation dates, though this from differences in the accuracy of weather was not the case in 1990. station data in reflecting the experimental site microclimate. HS for the Orleans and Truncat sites may have been underesti- DISCUSSION mated owing to their particular location (ie a forest clearing in the former and a coastal dune in the latter case). In addition, there Our results have defined the phenological was no clearance of the indigenous vege- development of maritime pine. In agreement tation at these 2 sites, with a consequence with previous work on other species (Per- that the proliferation of blackberry bushes ala, 1985; Ramesh and Gopalaswamy, may have provided shelter for the pines. 1991),air temperature degree-days were Finally, the Orleans and Truncat sites shown to have a better predictive value of appeared to be inferior sites for pine growth, the onset of phenological stages, particu- probably due to sub-optimal soil conditions, larly the earlier ones, than calendar days. possibly combined with the presence of The accuracy of prediction was increased blackberry bushes (competition effects for by approximately 50% for the B2 stage, from nutrients and/or water). The interaction of 19 d, with calendar days as predictor, to water stress and plant phenology has been 10 d, with HS. This is most interesting from emphasized by ldso et al (1978). Water an epidemiological point of view as the B2 stress has been shown to result in earlier stage corresponds to the beginning of pine flushing in young Cedrus saplings (Finkel- susceptibility to twisting rust (Desprez-Lous- stein, 1981). Results obtained at the tau, 1990). The lower adequacy of HS in Lagnereau and Ruscas sites are possibly predicting later stages may be partly arte- more representative of the average factual, arising from an increase in the error behaviour of maritime pine under silvicul- HS calculations with time, related to sea- on tural conditions. With a view to predicting sonal warming, whereas the error on cal- the phenological stages, the aforementioned endar days remains constant (weekly obser- factors should be taken into account. The vations). The threshold temperature of 0°C number of observation years employed was has been chosen for statistical considera- too few for detecting any age effect, though tions though its biological significance is it is likely that this effect occurs, as men- unknown. This value is lower than those tioned for other species (Nienstaedt, 1974). commonly found in literature concerning pine shoot elongation and may be partly The demonstration of a variation in phe- related to the fact that we studied earlier nology between maritime pine provenances stages (Castonguay et al, 1984). confirms earlier results (Desprez-Loustau and Baradat, 1991).The Tamjout prove- However, differences were still observed nance appears to require significantly lower between sites, and to a much lesser extent HS than the Leiria provenance to complete between years, when considering HS at the the early stages of growth. Other prove- of phenological stages. This occurrence
found to be intermediate, but years may be the result of a good synchrony nances were might have been better discriminated with a between host and parasite phenologies due more precise notation of phenological to particular weather conditions. The impor- tance of pine phenology in relation to M stages, on bi-weekly basis for example. This pinotorqua infection has also been empha- study also confirms that the precocity of the sized in the case of P nigra (Longo et al, inter-provenance hybrid is greater than that 1970, 1980). In contrast to maritime pine, of its parent populations. The provenance M pinitorqua appears better adapted to the effect for phenology is not a result of differ- P sylvestris host. In P sylvestris, annual vari- ences in vigour, as evidenced by the covari- ations in infection were attributed mainly to ance analysis. However, differences climatic conditions during pine growth; syn- between provenances were less often chrony between host and parasite phe- observed at the inferior sites. nologies is generally observed (Kurkela, In contrast to pine phenological data, the 1973). As previously hypothesized by period of M pinitorqua basidiospore same Moriondo (1957) considering the occurrence production was observed at the 2 Landes of M pinitorqua in Italy, this fungus, which sites and for the 2 years of observation, sug- is better adapted to rather cold climates, gesting that pine and rust phenologies are may have moved from northern to south- driven by different factors. This resulted in a ern Europe during the glaciary and post- variation of pine-rust synchrony between glaciary periods, in association with P sites and years. At the Lagnereau site, for sylvestris. It may then have passed to other both years of observation, shoot elongation, susceptible pine species such as P pinaster. on average for all provenances, took place Indeed, P pinaster is thought to have when basidiospores were no longer pro- appeared in the northern Landes area duced. This was also observed for the local approximately 8 000 years ago, at a time (Landes) provenance. The earlier develop- when P sylvestris was the dominant species ment of the Tamjout provenance resulted (Baradat and Marpeau-Bezard, 1988). The in a higher susceptibility to rust than the presence of M pinitorqua in the Landes area other provenances at the time when basidio- may therefore represent a relic of this period, spores were still being released. This is in which may explain the partial lack of adap- agreement with previous data from another tation to present climatic conditions. Syn- Landes site where the higher field suscep- chronization of the M pinitorqua life cycle tibility of the Tamjout provenance was with that of pine is not critical for the sur- though to be due to its higher precocity vival of this rust as it can maintain itself upon (Desprez-Loustau and Baradat, 1991). the telial host (ie aspen). Moreover, pine The observation that shoot susceptibil- infection can occur over a much longer ity in the Landes provenance was out of period on seedlings and young saplings, phase with the basidiospore production with a free growth pattern, which are sus- period in the same area for the 2 years of ceptible during all the growing season. Rust the study, is remarkable. This observation is synchronization with maritime pine phenol- in agreement with most of our data for the ogy, therefore, may not have been subjected Landes area, where M pinitorqua basidio- to a high selection pressure. In contrast with spores are often produced before or at the the maritime pine-rust system, a good syn- very beginning of maritime pine shoot sus- chronization between host and parasite phe- ceptibility (unpublished results). This may nologies has been reported for other pine explain the very irregular pattern of rust rusts (Merrill and Kistler, 1976; Hollis and damage in the area between years and Schmidt, 1977), which may reflect a longer sites. The ’rust explosions’ observed in some coevolution process. Synchronization with
the host pènes pour la connaissance et l’amélioration de l’e- plant has also been shown to be spèce. Thèse d’Etat de l’Université Bordeaux I, critical, and of great evolutionary signifi- France cance, for several phytophagous insects, Cannell GR, Smith RI (1983) Thermal time, chill days especially those which feed on newly and prediction of budburst in Picea sitchensis. JAppl emerged foliage (Du Merle, 1983, 1988; Ecol 20, 951-963 Hunter, 1992). Cannell GR, Thompson S, Lines R (1976) An analysis of inherent differences in shoot growth within some Overall, this study has emphasized the north temperate conifers. In: Tree Physiology and link between maritime pine phenology and Yield Improvement (MGR Cannell, FT Last, eds) predisposition to rust infections. Academic Press, New York, USA Castonguay Y, Boisvert J, Dubé PA (1984) Comparaison 1. Annual and spatial variations in rust infec- de techniques statistiques utilisées dans l’élaboration tion on maritime pines are likely to result de modèles prévisionnels phénoclimatiques. Agric mainly from differences in synchrony For Meteorol 31, 273-288 between host and parasite, resulting from Debazac EF (1966) Les modalités de la croissance en hauteur chez les pins. Bull Soc Bot Fr, 3-14 weather (and microclimatological) condi- tions. Changes in climate, such as warm- ML (1990) A cut-shoot bioassay for Desprez-Loustau assessment of maritime pine susceptibility to twisting ing, may affect pine-rust synchrony, as pre- rust. Eur J For Pathol 20, 386-391 dicted for plant-insect interactions (Dewar Desprez-Loustau ML, Baradat P (1991) Variabilité inter- and Watt, 1992). Modelling of pine and rust raciale de la sensibilité à la rouille courbeuse chez le phenologies with respect to climatological pin maritime. Ann Sci For 48, 497-511 factors is essential in order to predict spatio- Desprez-Loustau ML, Dupuis F (1992) A time-course study of teliospore germination and basidiospore temporal patterns of infection risks. release in Melampsora pinitorqua. Mycol Res 96, 2. Differences in precocity between geno- 442-446 types may result in differences in predispo- Dewar RC, Watt AD (1992) Predicted changes in the sition to infection. Changes in vigour (higher synchrony of larval emergence and budburst under climatic warming. Oecologia 89, 557-559 growth) may also affect the infection risk in Du Merle P (1983) Phénologies comparées du chêne relation to higher precocity. This factor pubescent, du chêne vert et de Tortrix viridana L should be taken into account in maritime (Lep Tortricidae). Mise en evidence chez l’insecte pine breeding. Selection for higher growth de deux populations sympatriques adaptées cha- has been shown to result in earlier flushing cune à l’un des chênes. Acta &OElig;col &OElig;col Applic 4, 55- 74 in several species (Kleinschmit and Sauer, Du Merle P (1988) Phenological resistance of oaks to the 1976; Rehfeldt, 1992). Fertilization effects green oak leafroller, Tortrix viridana L (Lep Tortrici- should also be considered. dae). In: Mechanisms of Woody Plant Defenses against Insects - Search for Pattern (WJ Mattson, J Levieux, C Bernard-Dagan, eds) Springer-Verlag, New York, USA, 215-226 ACKNOWLEDGMENTS Finkelstein D (1981) Influence des conditions d’alimen- tation hydrique sur le débourrement et la croissance We thank the technical staff of INRA Experimental des jeunes plants de Cèdre (Cedrus atlantica Stations at Le Ruscas, Orleans and Bordeaux, Manetti) cultivés en serre. Ann Sci For 38, 513-530 especially D Vauthier, M Vallance and P Paz- Hollis CA, Schmidt RA (1977) Site factors related to tuzka, for their technical assistace; H Jactel and fusiform rust incidence in north Florida slash pine A Kremer for their helpful comments on the plantations. For Sci 23, 69-77 manuscript; and M Guye for reviewing the English. Hunter MD (1992) A variable plant-insect interaction: the relationship between tree budburst phenology and population levels of insect herbivores among trees. Ecol Entomol 16, 91-95 REFERENCES Idso SB, Jackson RD, Reginato RJ (1978) Extending the ’degree day’ concept of plant phenological devel- Baradat P, Marpeau-Bezard A (1988) Le pin maritime opment to include water stress effects. Ecology 59, Pinus pinaster Ait. Biologie et génétique des ter- 431-433
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