59Bonofiglio et al.—Influence of principal meteorological parameter

Tommaso BonofIglIofaBIo orlandICarlo sgromoBruno romanomarCo fornaCIarI

department of applied Biologyuniversity of PerugiaBorgo XX giugno 74-061Perugia, Italyemail: fabor@unipg.it

abstract  This study concerns the flowering of the olive (Olea europaea) in a large southern Italian area. It was carried out using the “volumetric” method of pollen sampling and the analysis of the meteorological parameters of temperature and rainfall. The results show that flowering occurs mainly in may, with the maximum values in the second half of the month. meteorological analysis showed that the biological cycle of the olive was greatly influenced by the temperature. The relationship between an increase of temperature before the beginning of flowering and the advance of flowering was 2.5 days/°C. another important result concerns the value of the mean temperature which by the beginning of flowering was 16°C at all monitoring stations, even if the growing degree day (gdd) requirements were different. The temperature accumulation evidenced the homogeneity of plant behaviour in dependence of latitude, except for the province of Taranto. also, our study showed that rainfall determined a considerable decline of pollen concentration in the atmosphere, until the maximum of 80% when the value of 8 mm of rainfall/day was reached.

Influence of temperature and rainfall on timing of olive (Olea europaea) flowering in southern Italy

Keywords  pollen; Olea europaea; phenology; flowering

INTRODUCTION 

Italy occupies second place internationally among the countries which produce olive oil. It has c. 2 million ha of olive (Olea europaea l.) groves, which are situated mainly in the southern Italian regions. The economic importance of this cultivar, especially in the mediterranean basin, has induced studies aimed at the realisation of innovative agronomic techniques for optimisation and improvement of productive processes. olive growing presents some important problems such as production alternation, ovarian abortion and intraspecific self-incompatibility, phenomena which considerably influence the pollination process and consequently the potential production. according to some important studies, self-incompatibility is genetically determined (Bradley & griggs 1963), though the genetic expression greatly depends on environmental and growing conditions. This has already been observed in many species considered as self-sterile in one country or region, whereas the same species were self-fertile in others and vice versa (morettini & Valleggi 1940; morettini & Benetti 1942; gerarduzzi 1958). moreover, the best fruit set results (potential production) have been obtained through free pollination, which is cross-pollination (Cimato 1980; Bini 1984; Quero et al. 2002; sgromo et al. 2006). Besides the genetic characteristics, the pedo-climatic condition is also important, because it influences an olive grove’s potential production (fornaciari et al. 2005; orlandi et al. 2005a). Today, these characteristics are of particular importance because the olive cultivars are diffused beyond the traditional growth zone (fernàndez-Escobar 1993). Indeed, in the last few decades olive cultivation has had considerable diffusion in areas outside the mediterranean basin, such as California, argentina, australia, and others. Before introducing a certain cultivar in a new agrarian ecosystem, it is therefore

H06116; Online publication date 11 March 2008 Received 19 December 2006; accepted 28 January 2008

New Zealand Journal of Crop and Horticultural Science, 2008, Vol. 36: 59–690014–0671/08/3601–0059 © The royal society of new Zealand 2008

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important to know its pedo-climatic requirements and the physiological characteristics that favour its introduction. for example, although in new cultivation areas the climate may be quite similar, the atmospheric circulation in the eastern parts of the climatic zones is rather variable and may cause damage to the cultivation because of excessive temperatures and frosts (Bongi 2004). of all the biological phases, flowering is the critical phase of every fructiferous plant and, in particular, the olive, because most cultivars are self-sterile and therefore must be cross-pollinated (maracchi et al. 1994). Hence, it is important that during the flowering phase the atmospheric conditions which may heavily damage the flower’s opening and the pollination process not occur (morettini 1972). rainfall and wind during the flowering period may disturb pollen emission and reduce its diffusion (lavee 1996; ribeiro et al. 2003). as has been documented (griggs et al. 1975; fernandez-Escobar et al. 1983), temperatures above 30°C cause growth inhibition of the ovary pollen tube. When

the temperature exceeds 32°C the plant’s vegetation ceases and when it exceeds 44°C the first cellular damage can be seen (mancuso et al. 2002). also, dry wind during flowering, although rare, may cause a withering of the stigma and growth inhibition of the pollen tube on the style. Besides meteorological factors, there are other elements, both anthropic and phytopathologic, which may influence the olive pollination process. among them, the most important are those which act directly on the plant’s nutritional state and, in the final analysis, on the flower’s quality, determining its capacity to become a mature fruit (fernandez-Escobar 1993). In recent years, research on olive flowering has been carried out with the use of air palynology (studies on pollen emission and dispersion in the atmosphere) as a tool for indirect evaluation of the anthesis phenophase (la Torre et al. 1997; orlandi et al. 2005a). using air-biological sampling techniques, it is possible to analyse the anthesis phenomenon through the determination of mean daily pollen concentration per cubic metre of air, that is the direct consequence of the anthesis

Fig. 1  distribution of the 15 observational sites in southern Italy: 1, ribera (ag); 2, Castelvetrano (TP); 3, Termini I. (Pa); 4, ficarra (mE); 5, Palmi (rC); 6, stalettì (CZ); 7, spezzano a. (Cs); 8, avetrana (Ta); 9, squinzano (lE); 10, Pezze di greco (Br); 11, Bitonto (Ba); 12, san severo (fg); 13, Campagna (sa); 14, ariano I. (aV); 15, solopaca (Bn).

61Bonofiglio et al.—Influence of principal meteorological parameter

phenomenon intensity (fornaciari et al. 2001). our present study was carried out from 1999 to 2006 in 15 areas situated in four regions of southern Italy, optimal for olive growing (sicily, Calabria, Puglia, and Campania). The aim of the research was to obtain further information about the phenological characteristics of the O. europaea cultivars present in the 15 study areas and the interaction between plants and climate. In particular, the study objectives were: (1) to determine the flowering periods; (2) to investigate the relationships between plant development and temperature in southern Italy, based on the study observation period; and (3) to evaluate the effect of the climate factors of temperature and rainfall on pollen release and its dispersion in the atmosphere.

MaTERIaLS aND METHODS

Description of the study areaThe study area is situated in four regions (Puglia, Calabria, sicily, and Campania) in southern Italy at 37°–42°n (fig. 1). The total area is 73 141 km2, 10% of which (7382 km2) is cultivated in olives. This cultivation is particularly widespread in the region of Puglia, where it occupies c. 3600 km2 with c. 40 million olive plants. The overall study area represents more than 90% of the productive Italian olive groves which provide c. 25% of world olive oil production. The climate is influenced by the mediterranean sea and is characterised by relatively mild winters and

hot, dry summers. The average yearly temperature during the study period was 18.9°C. on a seasonal basis, rainfall mostly occurred outside the summer period. during the study period, median annual rainfall values ranged from 210 mm in 2000 at the foggia station to 992 mm in 2005 at the Benevento station. at the study stations, which represent the olive cultivation of the entire area, different cultivars of autochthonous olive plants are present (Table 1).

Pollen monitoring and phenology The sampling of pollen emitted in the atmosphere was preceded by a thorough study of agro-meteorological conditions of the considered regions and by the analysis of the cultivar’s distribution and consistency. This preliminary analysis was necessary to identify the most typical olive growing areas so as to concentrate our studies there. In the monitoring areas the presence of several different cultivars was found, evidence of the traditional cultivation of olive species in Italian territories partially owing to the typical self-sterility problem (Table 1). sampling was carried out by the “volumetric” method, which is based on the possibility of capturing pollen and other biological and non-biological particles present in the atmosphere using the principle of depression impact (fornaciari et al. 1997). The classic instrument that works on this principle is the Hirst spore trap (Hirst 1952). The VPPs 2000 lanzoni model was created in Italy and used for this research. The volume of air sampled in 24 h is 14.4 m3 and the instrument

Table 1  list of the selected monitoring stations with their olive (Olea europaea) cultivars.

region Province station latitude Principal cultivars

Puglia foggia (fg) s. severo 41°41′n Provenzale, Coratina Bari (Ba) Bitonto 41°02′n Coratina, ogliarola B. Brindisi (Br) Pezze di g. 40°52′n ogliarola B., Coratina Taranto (Ta) avetrana 40°21′n Coratina, ogliarola B. lecce (lE) squinzano 40°26′n ogliarola l., CoratinaCalabria Cosenza (Cs) spezzano a. 39°43′n grossa di C., Carolea Catanzaro (CZ) stalettì 38°46′n Carolea reggio C. (rC) Palmi 38°21′n ottobratica, sinopolesesicilia messina (mE) ficarra 38°06′n nocellara messinese Trapani (TP) Castelvetrano 37°41′n nocellara del Belice agrigento (ag) ribera 37°29′n Biancolilla Palermo (Pa) Termini I. 37°59′n BiancolillaCampania Benevento (Bn) solopaca 41°11′n ortice, ortolana avellino (aV) ariano I. 41°08′n ogliarola, ravece salerno (sa) Campagna 40°15′n Pisciottana, rotondella

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captures particles from the surrounding area within a range of c. 50 km. The samples taken from the traps were subdivided in daily units and prepared for further morphological identification and microscopic counting. The laboratory phase was considerably simplified as samples were not chemically treated; microscopic examination was carried out directly on prepared adhesive melinex tapes taken from the trap, where the pollen was captured during the sampling. The results of microscopic analysis were elaborated through mathematical calculations to obtain pollen concentration values per cubic metre of air per time unit. We thus obtained the “pollination curves” which represent a trend of daily pollen concentrations in the atmosphere during the flowering period. since the presence of pollen in the atmosphere is a direct consequence of the process of flower opening, the data on pollen concentrations permitted us to calculate exactly the dates of the beginning, maximum, and end of flowering of anemophilous species in a certain area (galan et al. 1995; recio et al. 1998; fornaciari et al. 2000; orlandi et al. 2003). Therefore, the interpretation of flowering with the use of this kind of sampling permitted us to reduce and even eliminate subjectivity in interpretation, which does not always occur in classical phenological observational methods.

Climatic analysisTo carry out a climatic analysis, the values of temperature and rainfall were used. These values were obtained at the meteorological stations which are situated near the monitoring areas and are part of the military aviation network and national agro-meteorological network. In all the stations the mean temperatures of the pre-anthesis period (registered in the 30 preceding days) were analysed using the running averages with a 10-day basis. The running averages were calculated to verify what kind of influence temperature exerts on the beginning of flowering. according to some studies, the influence of meteorological conditions on flowering in this period is rather significant. However, once anthesis begins, it continues more or less rapidly depending on the cultivar’s characteristics (Bini 1984). Climatic analysis was also carried out during the anthesis phase. for every studied area a percentage of days during the “effective pollination period” (Bini 1984) in which the temperature exceeded 30°C was calculated. Temperature above 30°C inhibits growth of the pollen tube and favours an ovary abortion. This kind of observation is particularly important because

in the period of may–June when olive flowering occurs, high temperature values above 30°C are frequent in the mediterranean area. at each monitoring station the temperature requirements (effective ΣT°C values) of the most representative cultivars were calculated, taking as a parameter the values of the mean temperatures registered every year from 1 January until the date showing the maximum value of pollen concentration. generally, this date corresponds to the full flowering date of the most diffuse and representative cultivar of the studied area. The quantity of “biothermic units” necessary for completing a certain phenological phase was defined as “requirements”; it represents a specific characteristic for each cultivar (anderson et al. 1986; motisi et al. 1998; Valentini et al. 2001). The initial date of accumulation (1 January) was set up arbitrarily, taking into consideration the olive’s low requirements at cold temperatures, which within this date was considered to be satisfactory in the southern Italian areas. To make calculations, the following formula was used: gdd (i.e., growing degree days) = Σ(T m – T threshold), where “T m” is the daily mean temperature and “T threshold” is the minimum temperature below which biothermic accumulation stops or is reduced to the lowest terms. for the olive, the T threshold value considered was 7.5°C given that all the study areas are characterised by a meso-mediterranean climate where optimum threshold ranges are indicated between 5°C and 7°C whereas other studies indicated the higher correlation values from 6°C to 9°C (mancuso 2000; Bongi et al. 2002; orlandi et al. 2006; ribeiro et al. 2006). using the same method, the gdd values were calculated until the start date of flowering to verify possible behaviour differences of various cultivars between initial and maximum intensity of the anthesis phenomenon. The other meteorological parameter influencing the pollination process of the anemophilous species is rainfall, which may obstruct the process of pollen release and dispersion in the atmosphere in two different ways. The first is directly, by causing pollen to fall to earth; the second is indirectly, by making pollen heavier and less transportable because of water absorption. To determine the influence of rainfall on pollen distribution, the correlation between daily pollen concentrations and amount of rainfall in the same day was analysed. This analysis was made on a series of data, gathered in all study areas and regarding different quantities of rainfall. The data are grouped by classes of 1 mm of rainfall and analysed separately to determine the decrease of pollen concentration in the atmosphere.

63Bonofiglio et al.—Influence of principal meteorological parameter

RESULTS aND DISCUSSION

Phenological analysisafter 8 years of study the mean trend of flowering for each examined olive growing area was constructed by means of pollination graphs indicating the beginning, duration, and end of flowering (fig. 2). This permitted us to make a comparison among different olive growing areas, both within one region and in general, highlighting similarities in olive behaviour. It was observed that in all the years of monitoring the first pollen was captured at the Palermo station, whereas the latest day was registered at the avellino station. These results reflect the differences in latitude and consequently the differences in environment which influence the start date of flowering (Bonofiglio et al. 2005). on average, comparing these two sites, flowering delay was 23 days (Palermo: 25 april; avellino: 18 may). It is evident that the trend observed at the Puglia stations on average was rather homogeneous, particularly regarding the beginning of anthesis (fig. 2). Therefore, it can be noted that even in the large agricultural areas, such as Puglia, olive

flowering occurred in all the stations at the same time, generally between 2 may and 8 June. The homogeneity of plant behaviour during the flowering period observed in the Puglia region was not confirmed in the other regions. for example in sicily, the olive growing area of the messina Province showed a delay of flowering that averaged 10 days compared to the Palermo area, where the first pollen was registered. In the regions of Calabria and Campania, the “scale-like” pattern of flowering was observed, considering the mean values of 8 study years, with differences which are not greater than 4 days between one station and another. olive pollen is present in the atmosphere for an average of 2 months, with the maximum concentration value in may. The avellino station is an exception; this value was registered on average on 4 June.

Relationship between  plant development and temperatureThe mean temperature trend for the 15 monitoring stations was calculated using the running averages with a 10-day basis and registered in the period before the beginning of flowering (fig. 3). for

Fig. 2 mean olive (Olea europaea) flowering periods based on the 8-year study results. (aV, avellino; Bn, Benevento; sa, salerno; rC, reggio C.; Cs, Cosenza; CZ, Catanzaro; Ta, Taranto; lE, lecce; fg, foggia; Br, Brindisi; Ba, Bari; TP, Trapani; Pa, Palermo; mE, messina; ag, agrigento.)

64 new Zealand Journal of Crop and Horticultural science, 2008, Vol. 36

a clear and synthetic representation of the trend the Box-Plot (Tukey 1977) technique was used. average temperature values increased until reaching a median value of 16°C the day before flowering (fig. 3). Variability and distribution of data obtained before flowering are included. average temperatures increased and there was also a decrease in variability with standard deviation (sd) values from 1.77 to 1.37. also to be noted is the reduction in range which, together with the skewness index, shows a more uniform temperature trend in correspondence with the day preceding the flowering start date. all these phenomena occurred despite the monitoring stations being situated at different latitudes, and present a maximum shifting of flowering of 23 days between the Palermo and the avellino stations. “Heat requirements” of different cultivars in reaching the flowering phase at the 15 monitoring stations vary: from a minimum of 437 gdd at the avetrana station to a maximum of 1005 gdd at the Palmi station (fig. 4). from the comparison of these different areas, except for avetrana, some homogeneity in plant behaviour in function of latitude can be seen. The major heat requirements were observed at the lowest latitudes, in particular in the areas of Palmi and ficarra, whereas in general the least heat requirements were observed at the highest latitudes. This kind of behaviour can be attributed to the genetic characteristics of the autochthonous cultivars of the study areas. In each

one, these cultivars are present from 50% to 90% of the local olive groves as a result of co-evolution of the original genetic material with the environment. Heat requirement values are calculated for the start date (sf) and the maximum date (mf) of flowering for each monitoring station (fig. 5). The differences of accumulation between these dates are constant (190 gdd) except for the Benevento area. This result is particularly important because it confirms the hypothesis that once the heat requirements for starting the anthesis phase are satisfied, O. europaea needs a more or less constant quantity of “biothermic units” for completing the flowering process (Bini 1984). This behaviour is independent from the latitude and genetic characteristics of various cultivars. The other result of particular interest is the mean temperatures in each area during the period before the beginning of flowering (1 January—the mean start date of flowering) and the start dates of flowering in Julian calendar days (fig. 6). from the equation it can be seen that an increase of Julian days (i.e., a delay of the beginning of flowering) corresponds to a decrease of a mean temperature. This behaviour of O. europaea was observed in all studied regions. Therefore, the higher values of mean temperature anticipate the satisfaction of the olive’s heat requirements. from the data obtained, the olive flowering seems to be determined by meteorological and genetic parameters, though it is independent

Fig.  3 mean temperature trend before the beginning of flower-ing.

65Bonofiglio et al.—Influence of principal meteorological parameter

Fig.  4 relationships between latitude and temperature amounts related to the flowering dates (start and max.).

Fig.  5 Heat requirement values of the principal cultivars at 15 monitoring stations. growing de-gree days (gdd) calculated to the start (sf) and the maximum (mf) of flowering. (ribera, ag; Cas-telvetrano, TP; Termini I., Pa; fi-carra, mE; Palmi, rC; stalettì, CZ; spezzano a., Cs; avetrana, Ta; squinzano, lE; Pezze di greco, Br; Bitonto, Ba; san severo, fg; Campagna, sa; ariano I., aV; solopaca, Bn.)

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Fig.  6 relationship between start flowering date and the mean temperature (T mean) values in the four regions (Calabria, Puglia, Campania, sicilia) during 1996–2006.

Fig.  7 Percentage of days with a maximum temperature (T max.) above 30°C. (ribera, ag; Cas-telvetrano, TP; Termini I., Pa; fi-carra, mE; Palmi, rC; stalettì, CZ; spezzano a., Cs; avetrana, Ta; squinzano, lE; Pezze di greco, Br; Bitonto, Ba; san severo, fg; Campagna, sa; ariano I., aV; solopaca, Bn.)

from the effects of daylight duration (photoperiod). The linear trend lines for each regional chart and the related equations are shown (fig. 6). The slopes of the equations confirm the relationship between temperature values and dates of flowering for each geographical area.

Effect of the environment on pollen dispersionClimatic analysis during the flowering period mainly concerned the maximum temperature and the effects of rainfall on the pollen concentration in the atmosphere. a maximum temperature of over 30°C causes an ovary abortion and during the effective pollination period the quantity of days with the higher values are rather significant (fig. 7). In particular, the highest mean value was registered at

the Trapani station with 13.5% of days during the effective pollination period. This phenomenon was observed in different areas, including those situated at high latitudes, such as the avellino station. Probably, temperatures during the flowering period that occurs mainly between the last 10 days of may and the first 10 days of June exceed 30°C more easily. These temperatures should not be considered unreachable, because they refer to the inflorescences exposed to the sun; therefore, it is normal that this temperature is 4–5°C higher than that of the atmosphere. rainfall quantity determines a decline in pollen concentration in the atmosphere (fig. 8). The entity of influence is proportional until a value of 8 mm of rainfall, after which the decrease in concentration levels out to values c. 80%, even for values greater

67Bonofiglio et al.—Influence of principal meteorological parameter

Fig. 8  Influence of rainfall on pollen concentration in the atmosphere.

than 10 mm. usually precipitation during the flowering period (may–June) is stormy, intense, and of short duration and does not influence the pollination process, because some hours after the ending of this meteorological event the pollen concentration level returns. on the contrary, the processes of dispersion and pollination are hindered and in some instances compromised when rainfall exceeds 8 mm and lasts for several days during flowering.

CONCLUSIONS

The present study allowed us to explain some aspects of the anthesis phenophase in the olive species observed in the certain mediterranean olive growing areas. above all, it seems evident that the flowering period in different areas presented more or less a scale-like pattern of flowering, depending on diverse endogenous and exogenous factors. The results of 8 years of pollen monitoring study showed that the early flowering registered in the region of sicily compared with that of the other areas was caused not by the major precocity of the present cultivars, but by diverse climatic characteristics that altogether anticipate the satisfaction of temperature requirements. This is confirmed by most present cultivars in the regions of sicily and Calabria (at the lower latitudes) needing higher temperatures to reach the anthesis phase. moreover, the climatic conditions seem to influence particularly the start date of flowering, whereas the opening of flowers is determined principally by the cultivar’s endogenous characteristics. This statement is strengthened by the analysis of the gdd differences between the two dates of flowering, which are practically constant in

all the monitoring areas, except for the Benevento station. The climatic analysis in the pre-flowering period demonstrated that the olive flowering generally starts when the mean temperature (calculated with running averages on a 10-day basis) reaches values close to 16°C. These results also confirm that the olive phenological phases are principally affected by the temperature and not by the photoperiodic phenomenon (osborne et al. 2000). Therefore, it is probable that the different cultivars for starting the flowering process, besides the satisfaction of heat requirements (Cu, chilling units; gdd), need also the fulfilment of other conditions such as the mean temperature above 15°C during the week before the anthesis. moreover, the dependence of the vegetative-reproductive development on the temperature trend characterises the olive as an indicator species of climatic changes in the mediterranean area (osborne et al. 2000; orlandi et al. 2005b). The results related to the flowering periods are of considerable practical importance in the projection of a new system for choosing the pollinators. The usefulness of these results is that the pollinators’ full flowering should coincide with the beginning of flowering of the most diffuse olive cultivar in each area studied. Indeed, the first and second order flowers as the most fertile and characterised by the highest fruit set capacity are the first to open in an inflorescence (Cimato 1980; Cuevas et al. 2004). It is also important, especially in the “new” cultivation areas, to consider the maximum temperature limit (30°C) and the rainfall values during the flowering period, because they may seriously interfere with the pollination process and successive fertilisation. If the conditions during the flowering phenophase are not optimal, the consequence will be a considerable decrease of potential production. It is necessary to guarantee good agronomical practises for improving flower quality (fernandez-Escobar 1993). It is also obvious from the above research that suitable pollinators are required, since the olive species is predominantly self-sterile, and an appropriate evaluation of the climatic conditions of the cultivation area is needed. It should be remembered that the olive’s metabolic range is rather narrow, with an optimal temperature interval of only 10°C (20°–30°C). Therefore, when new cultivars are introduced in the new cultivation areas, it is important to consider the results of this study to obtain good production, particularly as regards climatic requirements and flowering periods of different cultivars.

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aCKNOWLEDGMENTS

We thank the staff of the unaPol (national union of olive Producers’ associations) for their collaboration.

REFERENCES

anderson Jl, richardson Ea 1986. Validation of chill unit and flower bud phenology models for “montmorency” sour cherry. acta Horticulturae 184.

Bini g 1984. fioritura e impollinazione nell’olivo: Indagini sul periodo d’impollinazione, recettività dello stigma ed evoluzione del gametofito femminile. rivista ortoflorofrutticoltura Italiana 68: 120–125.

Bongi g 2004. modelli produttivi in olivicoltura. olivo e olio 9: 8–15.

Bongi g, Berichillo l, Calducci V, Pannelli g 2002. la fioritura dell’olivo come strumento indicatore delle variazioni climatiche. Proceedings of “Convegno Internazionale di olivicoltura”. spoleto: 183–187.

Bonofiglio T, sgromo C, orlandi f, ruga l, romano B, fornaciari m 2005. Indagine fenologica sulla fenofase antesica di Olea europaea l. nel meridione d’Italia. Informatore Botanico Italiano 37(1): 680–681.

Bradley mV, griggs WH 1963. morphological evidence of incompatibility in Olea europaea l. Phytomorphology 13: 141–156.

Cimato a 1980. osservazioni su alcuni aspetti della biologia fiorale e di fruttificazione della cultivar di olivo “frangivento” in impianti ad elevata densità. rivista ortoflorofrutticoltura Italiana 64: 73– 82.

Cuevas J, Polito Vs 2004. The role of staminate flowers in the breeding system of Olea europaea (oleaceae): an andromonoecious, wind-pollinated taxon. annals of Botany 93: 547–553.

fernández-Escobar r 1993: Tecniche colturali per il controllo della fruttificazione dell’olivo. olIVÆ 46: 38–41.

fernández-Escobar r, gomez-Velledor g, rallo l 1983. Influence of pistil extract and temperature on in vitro pollen germination and pollen tube growth of olive cultivars. Journal of Horticultural science 58: 219–227.

fornaciari m, Pieroni l, Ciuchi P, romano B 1997. a statistical model for correlating airborne pollen grains (Olea europaea l.) and some meteorogical parameters. agricoltura mediterranea 127: 134–137.

fornaciari m, galan C, mediavilla a, dominguez E, romano B 2000. aeropalynological and phenological study in two olive mediterranean areas: Cordoba (spagna) and Perugia (Italy). Plant Biosystems 134(2): 199–204.

fornaciari m, lanari d, orlandi f, Polinori P, Tedeschini E, romano B 2001. P.o.m. a31 “due anni di attività della rete multiregionale per le previsioni di raccolta della produzione olivicola”—anno 2000.

fornaciari m, orlandi f, romano B 2005. Yield forecasting for olive trees: new appoach in a historical series (umbria, central Italy). agronomy Journal 97: 1537–1542.

galan C, Emberlin J, dominguez E, Bryant rH, Vllamandos f 1995. a comparative analysis of daily variations in the gramineae pollen counts at Cordoba, spain and london, united Kingdom. grana 34: 189–198.

gerarduzzi JB 1958. determination de l’autocompatibilitè et de l’auto-incompatibilite des varieties d’olives entre elles dans la republique argentine. Premier Conference internationale des Techniques oleicoles, Tangeri. Pp. 106–113.

griggs WH, Hartmann HT, Bradley mV 1975. olive pollination in California. Califorina agricultural Experimental station. Bulletin 869.

Hirst Jm 1952: an automatic volumetric spore trap. annals of applied Biology 39: 257–265.

la Torre f, Perez C f 1997. one year airborne pollen sampling in mar del Plata (argentina). grana 34: 49–53.

lavee s 1996. Biology and physiology of the olive. In: Plaza and Janes ed. World olive Encyclopaedia. Barcelona. Pp. 61–105.

mancuso s 2000: Electrical resistance changes during exposure to low temperature measure chilling and freezing tolerance in olive tree (Olea europaea l.) plants. Plant, Cell and Environment 23: 291–299.

mancuso s. azzarello E 2002. Heat tolerance in olive. advances in Horticultural science 16(3–4): 125–130.

maracchi g, Pittalis f, Bindi m, sillari B 1994. la produzione dell’olivo ed i fattori meteorologici “studio Preliminare”. olIVÆ 52: 30–37.

morettini a 1972. olivicoltura. ramo Editoriale degli agricoltori (rEda), rome.

morettini a, Benetti a 1942. ricerche sull’autofertilità e sull’autosterilità delle varietà di olivo coltivate nelle province di roma. l’olivicoltore 19(10): 3–9.

morettini a, Valleggi m 1940. ricerche sull’autofertilità e sull’autosterilità delle varietà di olivo nel Pesciatino. l’olivicoltore 17(3): 12–17.

69Bonofiglio et al.—Influence of principal meteorological parameter

motisi a, marra fP, Perini l, Caruso T 1998. I modelli fenoclimatici come supporto alla scelta varietale del pesco. l’Informatore agrario 32: 59–63.

orlandi f, ferranti f, romano B, fornaciari m 2003. olive pollination: flowers and pollen of two cultivars of Olea europaea l. new Zealand Journal of Crop and Horticultural science 31: 159–168.

orlandi f, romano B, fornaciari m 2005a. relationship between flowering and heat units to analyze crop effiency of olive cultivars located in southern Italy. Hortscience 1, 40: 60–68.

orlandi f, ruga l, romano B, fornaciari m 2005b. olive flowering as an indicator of local climatic changes. Theoretical and applied Climatology 81(3–4): 169–176.

orlandi f, lanari d, romano B, fornaciari m 2006. new model to predict the timing of olive (Olea europaea l.) flowering: a case study in central Italy. new Zealand Journal of Crop and Horticultural science 34: 93–99.

osborne CP, Chuine I, Viner d, Woodward fI 2000. olive phenology as a sensitive indicator of future climatic warming in the mediterranean. Plant, Cell and Environment 23: 701–710.

Quero a, Pinillos V, Cuevas J 2002. reduced ovule longevity increases cross-pollination response in olive. acta Horticulture 586: 469–471.

recio m, Cabezulo B, mar Trigo m, Toro fJ 1998. Pollen calendar of malaga (souther spain), 1991–1995. aerobiologia 14: 101–107.

ribeiro H, Cunha m, abreu I 2003. airborne pollen concentration in the region of Braga, Portugal, and its relationship with meteorological parameters. aerobiologia 19: 21–27.

sgromo C, reale l, orlandi f, fornaciari m, ferranti f, romano B 2006. autoincompatibilità e produttività in tre cultivar di olivo (Olea europaea l.). Proceedings of “101° Congresso nazionale della società Botanica Italiana”. 146 p.

Tukey JW 1977. Exploratory data analysis. addison-Wesley, reading, massachusetts, united states.

Valentini n, me g, ferrero r, spanna f 2001. use of bioclimatic indexes to characterize phenological phases of apple in northern Italy. International Journal of Biometeorology 45: 191–195.