Material and Methods

This experience was carried out in season 2005/06 in an experimental orchard of 'Algerie' loquat trees located at the Experimental Station of Cajamar Foundation "Las Palmerillas", in Almería (SE, Spain). The area presents a semi-arid subtropical climate with an average rainfall of 231 mm and evaporation from an "A" pan (Epan) of 1922 mm per year. Mean annual temperature and humidity is 18°C and 68%, respectively. Orchard soil is a well-aerated sandy-loam (72.4% sand, 14.6% loam, and 13.0% clay), pH 7.8. Field capacity is 13.4%, while wilting point is 5.1%.

Adult 'Algerie' trees grafted on 'Provence' quince were used for the experiments. The trees are vase-trained and 5 x 5 m spaced. Four irrigation treatments were applied to these trees. First treatment was a control in which trees were fully irrigated with about 40% of Epan measured with a Class A pan placed in the orchard. Next three treatments were different DI strategies in which trees received a 50%, a 25% or 0% of the water applied to controls (treatments W50%, W25%, and W0%, respectively) during a period of six weeks, from mid-June (around 8 weeks after the end of previous harvest) to the end of July. Soil water content in response to treatments was monitored using Watermark (Irrometer Co. Inc.) electrical-resistance blocks. The changes in soil moisture were followed using three sets of sensors, one set per block and treatment, placed at 30, 60 and 90 cm depth. Plant water status in response to the treatments was monitored by measuring stem water potential (Yst) during the period of deficit irrigation using a Scholander pressure chamber. Six mature leaves per treatment were sampled from the outer part of the canopy at 1.75 m height.

Effects of DI treatments on flowering date, length and intensity, and on shoot growth were analyzed following a randomized complete-block design with three replications per treatment. Each replication consisted of one row of trees hydraulically isolated by placing a plastic film 1 m deep, where most quince roots are restricted. The two central trees of the row were chosen for measurements. Tree phenology was followed on these trees from summer rest to bloom using phenological stages described by Cuevas et al. (1997). Flowering date and length and advancement of full bloom with respect to controls were calculated based on observations carried out twice per week. Bloom intensity was estimated on main shoots and secondary late-formed shoots by the percentage of them forming a terminal panicle in ten randomly chosen shoots of each type per tree. The number of flowers per panicle in main and secondary shoots was counted on four panicles per tree.

New growth was followed by counting the new leaves formed from mid-June to the end of September every five days in ten main shoots per tree. Shoot length was also measured with the same periodicity. Plastochron (i.e. days needed between the formation of two consecutive nodes) was calculated along the growing season.

Flower initiation was dated in the most extreme treatments (control versus W0%) by scanning electron and conventional microscopy. To do so, twenty four terminal buds (four per tree) were sampled weekly from mid-July to mid-November. With the aim to process the most representative and uniform samples for each date, the buds once collected at random were taken to the lab and ordered by size. Then, the four intermediate-sized buds were selected for SEM studies and fixed in 3% glutaraldehyde in phosphate buffer, pH 7.2. Before observation, the buds were partially dissected removing most external bracts under binocular, and subsequently dehydrated, critical point dried, sputter-coated with 20 nm gold, and finally observed under a Hitachi S-3000N Scanning Electron Microscopy, mostly operated at 15-20 kV. The remaining twenty buds, also partially dissected, were fixed in a mixture of formalin-glacial acetic acid-alcohol (FAA), dehydrated in tertiary butyl alcohol and ethanol series, and embedded in paraffin wax. The embedded buds were then sectioned at 10 ^m using a Leica RM 2125RT microtome. Finally, preferred sections were stained with safranin, crystal violet and light green (Gerlach, 1969).

Figure 1: Soil matric potential at 0.3 m (top), 0.6 m (center) and 0.9 m depth (bottom) during the six week experimental period in control full irrigated trees and trees suffering different levels of water deficits.
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