Kevin R. Day

Partitioning of leaf nitrogen with respect to within canopy light exposure and nitrogen availability in peach (Prunus persica)

SummaryRelationships between leaf nitrogen content and within canopy light exposure were studied in mature nectarine peach trees (Prunus persica cv. Fantasia) that had received 0, 112, 196, 280 or 364 kg of fertilizer nitrogen per hectare per year for the previous 3 years. The relationships between light saturated leaf CO2 assimilation rates and leaf nitrogen concentration were also determined on trees in the highest and lowest nitrogen fertilization treatments. The slope of the linear relationship between leaf N content per unit leaf area and light exposure was similar for all nitrogen treatments but the y-intercept of the relationship increased with increasing N status. The slope of the relationship between leaf N content per unit leaf area and light saturated CO2 assimilation rates was greater for the high N trees than the low N trees, but maximum measured leaf CO2 assimilation rates were similar for both the high and low N treatments. A diagrammatic model of the partitioning of leaf photosynthetic capacity with respect to leaf light exposure for high and low nitrogen trees suggests that the major influence of increased N availability is an increase in the photosynthetic capacity of partially shaded leaves but not of the maximum capacity of highly exposed leaves.

Girdling of early season ‘Mayfire’ nectarine trees

The effect of four times of limb girdling on fruit and tree response was examined on ‘Mayfire’ nectarine (Prunus persica (L.) Batsch). Girdling prior to Stage II of fruit growth reduced the lag phase associated with Stage II, and caused peak fruit growth rates to occur earlier in the season than on later girdled or ungirdled trees. Optimum response was obtained by girdling prior to Stage II, when fruit seed length was approximately 10 mm. Girdling at this time increased fruit weight by 22.5% and more than doubled the percentage of fruit in the largest three size categories. Maturity, measured as soluble solids concentration, was increased by 42%. Shoot extension growth was reduced only by early girdling. Leaf weight per unit area was increased, and leaf nutrient concentrations were decreased by all girdling treatments. Leaf conductance to water vapour (g,) was not affected when measured 8 days prior to and 78 days after harvest. Fifteen days after harvest, g, was decreased in all girdling treatments.

Postharvest water stress of an early maturing plum

Postharvest water stress was imposed on a May harvested plum (Primus salicina Lindl. cv. Red Beaut) over a three year period. Control trees were irrigated at approximately 100% ET. One stress treatment (Tl) received 50% of the water applied to the control. The second stress treatment (T2) was subjected to cycles of on-and-off irrigation which varied from year to year. All treatments were fully irrigated at about 100% ET through harvest. Treatment Tl received about 30 cm less irrigation water than the control and showed no decrease in yield, fruit weight or fruit quality over all three years. Treatment T2 received about the same amount of water as Tl in the first two years of the experiment and also showed no decrease in productivity. In the third year, T2 was irrigated only for a single three week period after harvest which saved over 60 cm of applied water. The trees were extensively defoliated by the end of the season, showed some shoot and scaffold dieback, and had reduced yields in the following year....

Interactions between rootstock, inter-stem and scion xylem vessel characteristics of peach trees growing on rootstocks with contrasting size-controlling characteristics.

This paper documents that while characteristics of the xylem anatomy and calculated hydraulic conductance of peach rootstock genotypes differ according to their effects on vigour of the scion they do not strongly influence the xylem characteristics of the scion. Furthermore xylem characteristics of a dwarfing rootstock genotype used as an inter-stem do not substantially influence anatomical characteristics of a vigorous rootstock below the inter-stem or the scion above it.

10 Stone Fruit

Peaches and nectarines Peaches and nectarines are classified from the horticultural point of view as stone fruits or drupes. They are soft fleshed with a pit, contain a high level of antioxidant but are highly perishable with a limited market life potential (Lill et al. 1989). The total antioxidant capacities of peaches and nectarines are about 15% and 20% of the total antioxidant capacity relative to that of 100 ml of red wine and 100 ml of green tea, respectively (USDA 2007a). Potential opportunities for export marketing, combined with the desire to store some late-season cultivars to extend the marketing season, have increased interest in understanding fruit physiology and extending postharvest life. Peach, Prunus persicae, is native to China and Persia (Iran); at one time it was called ‘Persian apple.’ Chinese literature dates its cultivation in China to 1000 bce. Probably carried from China to Persia, the peach quickly spread from there to Europe. In the sixteenth century, it was established in Mexico probably by the Spanish missionaries who introduced the peach to California in the eighteenth century. Nectarine (Prunus persicae var. nectarina) has been reported for nearly as long as peach, but its origin is unknown. Because they may have arisen from peach seeds, most peach-growing areas world-wide have also introduced nectarine cultivars.