Results

Deficit Irrigation Effects on Soil and Plant Water Content

Controls trees received circa of 6800 m3 per ha of water along the season; 990 of them applied during the six-week experimental period. During this time, W50%, W25% trees 450 and 259 m3 per ha, respectively, while W0% trees were not irrigated at all. Rainfall during the season accounted for a total of 229 mm; there was no rain during the DI period. DI treatments progressively diminished soil water content during this period (Figure 1). The rest of the year water soil content did not differ among treatments (data not shown). At the end of the period of water shortage, soil around W0% trees had values of -172 kPa, -127 kPa and -123 kPa at 30, 60 and 90 cm depth, respectively while in W25% soil reached ¥m values of -26 kPa at 30 cm, -57 kPa at 60 cm and -83 kPa at 90 cm. Water content of soil around W50% trees was kind of similar to that observed for W25% (-17 kPa, -77 kPa and -97 kPa, for 30, 60 and 90 cm depth, respectively). In contrast, soil around control fully irrigated trees was close of field capacity showing records between -10 and -20 kPa, along the season. The reduction of soil water moisture in moderate and severe DI treatments translated into the plant, but seemed not to affect to W50% trees. Controls and W50% presented similar Yst values at the end of July (Yst=-1.07 MPa for controls versus -1.37 for W50%). More negative records were reached at the end of the water shortage period in W25% and W0% (Yst=-1.74 and -2.07 MPa, respectively). Differences were significant between these two groups.

Deficit Irrigation Effects on Flowering

The alteration of soil and plant water status modified reproductive phenology of 'Algerie' loquat. At this regard, all deficit irrigation treatments promoted earlier flowering. However, the more severe the water stress was, the earlier the blooming resulted. Therefore, the earliest blooming took place in W0% trees (October 22nd, 27 days ahead of control trees). A noticeable advancement in full bloom also occurred in W25% trees, which flowered on October 28th, 21 days before than controls. W50% reached full bloom on November 8th, ten days before control trees (Figure 2). Control trees bloomed on November 18th. The average full bloom date of these trees is November 23rd (9 years controlled). Water-stressed trees not only reach full bloom date earlier than control trees, but they also opened their first flowers before (Figure 2).

21-Sep 1-Oct 11-Oct 21-Oct 31-Oct 10-Nov 20-Nov 30-Nov

Figure 2: Blooming course of control full irrigated trees and trees suffering different levels of water deficits.

21-Sep 1-Oct 11-Oct 21-Oct 31-Oct 10-Nov 20-Nov 30-Nov

Figure 2: Blooming course of control full irrigated trees and trees suffering different levels of water deficits.

Control

17-ago 27-ago 6-sep 16-sep 26-sep 6-oct 16-oct 26-oct 5-nov 15-nov

Figure 3: Loquat phenology from dormancy to visible floral buds in control full irrigated trees and trees suffering different levels of water deficits.

Figure 3: Loquat phenology from dormancy to visible floral buds in control full irrigated trees and trees suffering different levels of water deficits.

Figure. 4. First stages of panicle initiation and development. A and B. Vegetative meristem. C and D. Panicle raising. E and F. Bracteoles formation. FD: Floral dome. LP: leaf primordia. B: bracteole.

The advancement in full bloom and bloom break dates for water-stressed trees basically coincided with the advancement observed in prior-to-bloom phenophases. In effect, bud dormancy release and panicle differentiation phenophases occurred before in W0% trees followed by W25% and W50% trees (Figure 3). Furthermore, flower initiation date determined by scanning electron and conventional microscopy confirmed that the changes within the bud associated to flower initiation occurred before in samples of water-stressed trees (Figure 4). In these samples, anatomical changes compatible with the initiation of the panicle were recognizable on July 7th in water-stressed trees, while similar stage of development was reached by well-watered trees three weeks later (25th July). The subsequent stages of panicle elongation and individual flower bud initiation were seen in control trees samples during the first weeks of August, and between 12 and 18 days before in water-stressed trees (Figure 4).

On the other hand, no clear pattern in the duration of the phenophases can be inferred from the comparison of treatments. In control trees, 36 days were needed to take a bud from dormancy release to anthesis, while 33 days passed in W50% trees between bud break and bloom, and no less than 39 days in W0% trees (Figure 3). Only W25% trees exhibited a little faster developmental rate during panicle formation phenophases (30 days), also expressed in a more compact blooming period.

Finally, DI only caused minor effects on flowering intensity. The percentage of bearing shoots was slightly enhanced by DI (Table 1). The differences were not significant in main shoots. However, the differences in secondary late-formed shoots, although small, reached statistical significance. No differences were observed in the number of flower per panicle in main shoots, while in secondary shoots the most severe DI treatments (W0%) had a reduced number of flowers per panicle (Table 1).

Table 1: Effects of Regulated Deficit Irrigation treatments on bloom intensity and shoot growth
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