Phenology and Yield Efficiency of Early, Mid-, and Late-Maturing Cultivars of Peach in Irrigated Orchards under Mediterranean Climate

ABSTRACT

Productivity of peach cultivars with different ripening seasons was studied under the growers’ conventional conditions of Tunisia. Experiments were performed in northern Tunisia (36° 41ʹ N, 10° 15ʹ E). Performances of Flordastar, Royal Glory, and Carnival as respectively early, mid-season, and late ripening cultivars were evaluated under the grower’s conventional irrigation programs. Fruit growth, yield, water supply, and water productivity were determined through four years. For the three cultivars, Flordastar, Royal Glory, and Carnival, fruit maturity was achieved at 650, 1100, and 2200 GDD, respectively. Average yields were 17.4, 29.8, and 41.1 t ha^–1 and mean values of water productivity were 1.9, 3.1, and 3.6 kg fresh yield m^–3 for early, mid-season, and late cultivars, respectively. Results of agronomic performances evaluation at the farm scale provided a reference on the behavior of early, mid-season, and late cultivars of peach in irrigated orchards in semi-arid conditions.

KEYWORDS:

• Prunus persica
• cultivar
• yield
• water productivity

Introduction

An orchard system is considered as the integration of all of the horticultural factors involved in establishing and maintaining a planting of fruit trees (Barritt, 1987). Vigor potential of scion and rootstock; climatic conditions; soil characteristics; and management factors, such as irrigation, interact in determining the seasonal vigor of shoot, yield, and the eventual size of the mature tree (Webster, 2004).

Peach is a temperate-zone perennial species largely cultivated in Mediterranean regions. In Tunisia, peach yields have significantly increased in the past three decades as a consequence of an improvement of orchard training and pruning systems and the very large numbers of cultivars within farms. Therefore, a peach crop presents high economic value and is considered as a strategic crop with a large extended ripening season (April–September). Consequently, the trend toward high-density orchard systems has increased and revealed growers’ interest. However, peach trees tend to be very vigorous and reach full bearing potential quickly (4–6 years; DeJong et al., 1994). As a result, several training/pruning systems have been developed to accommodate the growth characteristics of peach to high density planting (Chalmers et al., 1978; Day et al., 2005; DeJong et al., 1999). The open vase system, as the conventional orchard system for growing peaches, still accounts for most of the total acreage in Tunisia, although several high density systems were tested and adopted for commercial peach production.

The growers’ orchards of peach can provide references on the agronomic performances, such as the chilling requirement, potential yield, and fruit quality (Giauque and Hilaire, 2002; Hilaire and Giauque, 1994). References issued from cropping systems in situ appear more realistic (Plénet et al., 2009). Assessment of phenological behavior of crops is important to determine the most suitable agronomic techniques to obtain satisfactory production. Geographic location and plant material can influence floral and yield precocity, abundance and time of flowering, the frost sensitivity of the flowers, and the ability of the flowers to set fruits (Campoy et al., 2012; Viti et al., 2010; Webster, 2004). The heat and chilling requirement has a significant impact on growth and yield of woody plants (Egea et al., 2003; Marra et al., 2002; Ruiz et al., 2007). Moreover, the expected increase of temperatures may compromise the ability of many growers of temperate fruits to successfully produce the same array of crops (Luedeling et al., 2009, 2011).

The current cropping patterns use a very large number of peach cultivars with different ripening seasons. The improvement of agronomic performances of peach orchards requires effective control of interventions, which must be well adapted to the behavior of each cultivar (Plénet et al., 2009). Under semi-arid climate with rainfall scarcity, agriculture relies heavily on irrigation. With increasing water scarcity, valuable management of water requires efficient approaches. Better choice of species, cultivars, and drip irrigation systems may improve productivity of water used to define the relationship between yield and supplied water (Ali and Talukder, 2008; Zoebl, 2006).

The present work investigates the agronomic performances of early, mid-season, and late ripening commercial cultivars of peach trained in an open vase system under Mediterranean climate. It is interesting to determine references on cultivar agronomic performances in the growers’ plots and to analyze the influence of some factors on these performances in peach orchards.

Material and methods

Experimental site

The experiment was conducted in the region of Mornag (36° 41ʹ N, 10° 15ʹ E) in the north of Tunisia. It concerns commercial orchards of peach on a private farm. The production area is characterized by a loamy-clay soil and Mediterranean climate with annual rainfall and Penman-Monteith reference evapotranspiration (ETo) of 450 and 1240 mm, respectively. It is considered as a representative irrigated production area of fruit tree species where peach is successfully cultivated. Average minimum and maximum temperatures were 8 and 18 °C in the winter and 20 and 35 °C in the summer, respectively (Figure 1). Precipitation is characterized by a rainy fall-winter season with low evaporative demand and a prolonged dry season (May–August) with high climatic demand (Figure 1).

Figure 1. Average monthly values of minimum and maximum temperature (Tmin, Tmax), precipitation (P), and Penman-Monteith reference evapotranspiration (ETo) recorded in the experimental area.

Plant material

Five-year-old trees of early ripening cultivar Flordastar, mid-season ripening Royal Glory, and late ripening Carnival cultivars of peach were surveyed. Trees were planted at 3 m × 6 m apart using GF677 as rootstock and trained following the open vase model. A drip irrigated plot of 1 ha was considered for each peach cultivar. One dripper line per row was installed and three drippers of 4 l/h discharge were used to feed each tree. Conventional irrigation was scheduled to seek water requirement of each cultivar based on evaporative demand (ET₀) and cultural coefficient (K_c) (Ghrab et al., 2014).

Measurements

The survey was carried out during 4 consecutive years on the three cultivars of peach—Flordastar, Royal Glory, and Carnival—under conventional irrigation programs applied by the farmer. For each cultivar, full bloom was noted and initial ripening date was registered. Fruit growth and individual yield per tree were determined annually on five trees per cultivar selected consecutively in the same row. Fruit diameter was monitored weekly on 10 fruits per tree and 5 trees per cultivar to establish the growth patterns. Vegetative growth was measured on 30 shoots (6 shoots per tree) only for the late cultivar, Carnival. Fruits were harvested at commercial maturity. Harvest was realized in four picks and total yield (tons ha^–1) was considered. Crop water productivity (W_P) defined as kg of fruits produced or fresh matter (FM) per m³ of total water supply (kg FM m^–3) was determined.

Watering conditions of the experimental orchards were characterized. Daily climatic data (air temperature and relative humidity) were measured using the manual weather station of INA-Tunisia located 15 km from the experimental orchard. Precipitation and irrigation water supply were registered. The reference evapotranspiration ETo (Pennman-Monteith) was calculated from the daily climatic data according to Allen et al. (1998) and used to scale total water supply. Heat and chill accumulations were calculated, respectively, using the growing degree-days (GDD) (Ben Mimoun and DeJong, 1999) and chilling hour (CH) accumulation according to Crossa-Raynaud (1955).

Data analysis

Collected data were subjected to analysis using a one-way analysis of variance with the SPSS statistical package (SPSS Inc., Chicago, IL, USA), using the Duncan test for mean separations (P < 0.05).

Results

Flowering and maturity calendar of peach cultivars

Full bloom and initial ripening dates of three major peach cultivars, Flordastar, Royal Glory, and Carnival, as early, mid-season, and late ripening, respectively, were achieved during 4 successive years. Results showed important annual variations of flowering and ripening dates (Table 1). Full bloom of Flordastar was observed between 2 Feb. and 11 Feb. over the 4 years of study, whereas initial ripening date varied from 5 May to 10 May. However, Royal Glory and Carnival had full bloom dates varying respectively from 7 Mar. to 16 Mar. and 11 Mar. to 23 Mar., which seem to be related to chill accumulation. Delayed flowering was observed during the first and the last year induced by low chilling accumulation (Table 1). Initial ripening date presented significant variation from year to year. It varied between 10 June to 20 June for Royal Glory and 27 July to 15 Aug. for Carnival.

Table 1. Chilling hour accumulation (CH), full bloom (FB), and initial ripening (IR) dates of three major peach cultivars (Flordastar, Royal Glory, and Carnival as respectively early, mid-season, and late ripening) cultivated in the region of Mornag (36° 41ʹ N, 10° 15ʹ E) in the north of Tunisia during four successive years.

		Flordastar		Royal Glory		Carnival
	CH	FB	IR	FB	IR	FB	IR
Year 1	81	2 Feb.	5 May	16 Mar.	21 June	23 Mar.	15 Aug.
Year 2	306	3 Feb.	6 May	7 Mar.	13 June	18 Mar.	5 Aug.
Year 3	166	11 Feb.	5 May	9 Mar.	10 June	15 Mar.	27 July
Year 4	85	2 Feb.	10 May	7 Mar.	12 June	11 Mar.	07 Aug.

Growth pattern of peach cultivars

Terminal shoots growth presented two main stages for the late ripening cultivar Carnival. An active vegetative growth was noted until 1000 degree-days (GDD), which coincided with the two first stages of fruit growth (Figure 2). Shoot growth started approximately after an accumulation of 200 GDD and ended when degree-days accumulation reached 1600 GDD.

Figure 2. Trend of fruit and vegetative growth of late ripening cultivar of peach (Carnival).

Fruit growth presented a clear double sigmoid pattern (Figure 3). Timing of the different phases within double-sigmoid fruit development depended on the ripening season. The lag phase of fruit growth was more distinct for late cultivars than early ones. Initial fruit ripening of the late cultivar of peach Carnival was observed from 2000 to 2200 GDD. Fruit maturity was recorded at 650 and 1100 GDD for early and mid-season ripening cultivars. Under Mediterranean conditions, the gap between the earliest flowering cultivars and the latest flowering ones was more than 1 month.

Figure 3. Fruit growth curves of early (Flordastar), mid-season (Royal Glory), and late (Carnival) ripening cultivars of peach in the region of Mornag.

Water supply and fresh yield

The average total amount of water supplied to early, mid-season, and late ripening cultivars was 490, 538, and 684 mm, respectively (Table 2). Annual climatic demand (ET_o) was ranged between 1125 and 1387 mm. Significant annual variations of precipitation occurred. It was ranged between 306 and 631 mm.

Table 2. Climatic demand (ETo, mm), precipitations (P, mm), and supplied water (I, mm) for Flordastar, Royal Glory, and Carnival as respectively early, mid-season, and late ripening cultivars of peach during four successive years.

			I (mm)
	ETo (mm)	P (mm)	Flordastar	Royal Glory	Carnival
Year 1	1387	306	565	627	749
Year 2	1125	631	555	577	721
Year 3	1212	450	389	394	533
Year 4	1287	378	451	553	733
Average	1246	468	490	538	684

With the growers’ conventional irrigation program the commercial peach cultivars had different and variable yields during the 4 years of study. A progressive increase of yield with tree age was observed for Flordastar as early-maturing cultivar from 11 to 22 tons ha^–1 (Table 3). However, pronounced fluctuations of yield were observed for mid-season (Royal Glory) and late ripening (Carnival) cultivars. Average yields were 17, 30, and 41 tons ha^–1, respectively, for early, mid-season, and late ripening cultivars. Early and mid-season cultivars produced 43% and 73% of the total production of the late cultivar and permitted an average of water saving of 150 and 200 mm, respectively.

Table 3. Fruit yield (t/ha) of Flordastar, Royal Glory, and Carnival as respectively early, mid-season, and late ripening cultivars of peach during four successive years.

	Yield (t/ha)
	Year 1	Year 2	Year 3	Year 4	Average
Flordastar	11.0	16.5	20.0	22.0	17.4
Royal Glory	16.0	36.0	39.0	28.0	29.8
Carnival	35.6	60.8	40.9	27.1	41.1

Water productivity

Water productivity (W_P) varied depending on ripening season within peach cultivars (Table 4). For the early ripening cultivar, W_P increased significantly from 1.263 to 2.622 kg FM m^–3. However, W_P values were better for the mid-season cultivar in spite of the weak difference in water supply (about 50 mm). It reached a value of 4.621 kg FM m^–3 with an average of 3.073 kg FM m^–3 (Table 4). While, in spite of the important amount of water supplied, Carnival as the late ripening cultivar had an average W_P of 3.614 kg FM m^–3. The weak values of W_P found for the early cultivar can be explained by the imperfect irrigation management and the low potential of production.

Table 4. Water productivity (kg of fruit production m^–3 of water supply) for Flordastar, Royal Glory, and Carnival as respectively early, mid-season, and late ripening cultivars of peach during four successive years.

	Flordastar^z	Royal Glory	Carnival
Year 1	1.263c	1.715b	3.379a
Year 2	1.391c	2.980b	4.499a
Year 3	2.384b	4.621a	4.164a
Year 4	2.622a	2.976a	2.415a
Average	1.915	3.073	3.614

^zMeans with different letters in a line are significantly different according to Duncan’s test (P ≤ 0.05).

Discussion

The main aspect of expanding peach adaptability is the accurate evaluation of cultivar responses to different growth conditions. Adaptation is related to the capacity to grow and produce in a specific environment. Thus, the study of the phenological behavior of a crop is important both to obtain satisfactory production and to determine the most suitable agronomic techniques.

Flowering and ripening dates of commercial peach cultivars, grown in the Mediterranean climate of Tunisia with well differentiated seasons, were achieved. They revealed extended flowering and ripening seasons (Table 1). However, a delayed flowering and an earlier fruit maturity of peach cultivars were observed in comparison to other production areas (Giauque and Hilaire, 2002; Hilaire and Giauque, 1994; Johnson and LaRue, 1989). This can be explained by the effect of climatic conditions especially of chill and heat accumulations. In fact, important differences between cultivars in chilling and heat requirements have been reported (Egea et al., 2003; Erez and Fishman, 1998). Fruit maturity of the late cultivar of peach, Carnival, was achieved by 5 Aug. in our experiment, whereas it occurred the 2nd week of September in the Fresno area (Johnson and LaRue, 1989). In the region of Rhône-Alpes (France), fruit maturity was observed the 2nd week of July for Royal Glory (Giauque and Hilaire, 2002), while it was 2 weeks earlier in the region of Mornag in the north of Tunisia. Under our conditions, heat requirements were satisfied quickly with the high temperatures of spring and summer seasons. Fruit maturity is dependent on spring temperatures (Edwards et al., 1970) and heat unit or degree-day accumulation is used to measure developmental time (DeJong, 1999; DeJong and Goudriaan, 1989; Grossman and DeJong, 1995). Fruit maturity is reached after having accomplished a fixed amount of degree-days (GDD) since bloom (Ben Mimoun and DeJong, 1999; Lopez et al., 2007).

The productivity of an orchard depends in part on equilibrium between vegetative and fruit growth. Vegetative growth presented different trends depending on peach cultivar. One main peak of shoot growth was observed for the late cultivar, Carnival (Ghrab et al., 1998), which ended at 1600 GDD. Similarly, Grossman and DeJong (1995) indicated that active vegetative growth of the late cultivar was observed until 500 GDD then declined slowly to stop at 1500 GDD. The peak in shoot growth occurs during the lag phase of fruit growth for the late ripening cultivars (Figure 2) but a second peak of vegetative growth was often stimulated after harvest for early ripening cultivars of peach (DeJong and Johnson, 1989; DeJong et al., 1987; Ghrab et al., 1998; Johnson et al., 1992; Mounzer et al., 2008). Growth of the different organs is not only determined by environment but also by the interaction among them. The seasonal pattern of fruit, root, and shoot growth rates suggest that these organs compete with each other, since their peak rates do not occur at the same time (DeJong and Johnson, 1989; Mounzer et al., 2008).

Fruit growth studies are usually based on measurements of fruit diameter or fresh weight (Austin et al., 1999). Fruit growth is commonly analyzed fitting curves, which allow for the calculation of absolute and relative growth rates. These growth rates permit prediction and forecasting of fruit size, and also identifying the time of critical stages, which allow the optimization of crop management. A clear double sigmoid pattern was observed for the late ripening cultivars of peach (Chalmers and van Den Ende, 1975; DeJong and Goudriaan, 1989). Timing of the different phases within double-sigmoid fruit development is more distinct for the late cultivars than the early ones (Figure 3) as previously reported (Johnson and Handley, 1989; Pavel and DeJong, 1993). Under our conditions the gap between the early and late flowering cultivars was more than 1 month, whereas it does not exceed 10 to 15 days for other reports (Bretaudeau and Fauré, 1991).

With the grower’s irrigation program, the late cultivar received 150–200 mm of irrigation water more than the early and mid-season ones (Table 2). Otherwise, early and mid-season ripening cultivars produced 43% and 73%, respectively, of total yield of the late cultivar (Table 3). These differential performances between early and late-maturing cultivars were similar with other reports on peach (Chalmers et al., 1981; Day et al., 2005; Johnson and Handley, 2000; Larson et al., 1988). However, mid-season and late ripening cultivars presented pronounced fluctuation of yield. Carnival and Royal Glory trees consistently had higher crop yields than Flordastar trees, coinciding with previous reports that yield increased in late-maturing cultivars (Johnson and Handley, 1989; Plénet et al., 2009; Vera et al., 2013). Smaller yield in early-maturing cultivars may be associated with resource limitations that cannot support high fruit growth rates and within-fruit sink competition (Grossman and DeJong, 1995; Pavel and DeJong, 1993; Mounzer et al., 2008). Furthermore, warm conditions seem to affect peach production mainly for mid-season and late maturing cultivars. The lowest yields obtained the first and the last year of study have the low chilling accumulation. Insufficient winter chill severely reduces yield and fruit quality (Luedeling et al., 2009).

The report of fruit yield to total water supply revealed interesting values of water productivity (W_P) for the late ripening cultivar in spite of the important supplied water (Table 4). The early cultivar presented a progressive increase of W_p over the experimental period, whereas mid-season and late cultivars had variable W_p values. W_p seems to be affected by irrigation management and climatic conditions mainly with late cultivars of peach.

Conclusion

Peach is a very interesting crop in the semi-arid Mediterranean climate of Tunisia. With an extended maturity season, it offers a great opportunity to market demand. However, it needs an all-important water supply and, with the increasing scarcity of water, an improvement of the water use efficiency is necessary. Late cultivars perform an interesting yield with high fruit quality under semi-arid conditions of Tunisia (Ben Mechlia et al., 2002; Ghrab et al., 1998). Their fruit growth stages coincided with the period of high evaporative demand, which require an important amount of irrigation water. Otherwise, shifting for early and mid-season ripening cultivars may improve water saving in an orchard. Furthermore, severe climatic changes observed over the last several years affect the magnitude of flowering and production of peach cultivars—mainly mid- and late-maturing ones. The use of low chilling cultivars is considered as a very interesting and competitive method.

Acknowledgment

We wish to thank the SADIRA Company for providing the experimental field.

Funding

This research was financially supported by the Tunisian Ministry of Higher Education and Scientific Research (Laboratoire d’Amélioration de la Productivité de l’Olivier et des Arbres Fruitiers, Institut de l’Olivier), and the EU research project WASIA (“Water Saving in Irrigated Agriculture”).