In spite of these efforts, relative fruit set is still variable and little improved since the early data reported in 1959 by Kester and Griggs. But, is fruit set the main limiting process for almond productivity? Another approach could be to increase the number of flowers per acre — but that approach demands more information on the eco-physiological basis that regulates flowering of almond spurs . Individual spurs tend to alternate bear with only a small percentage of spurs flowering the year after bearing . The authors have observed tagged spurs in outer canopy– exposed positions to live at least 15 years. To investigate this, an almond spur dynamics research project was initiated by Lampinen and colleagues in 2001. This study was designed to quantify the dynamics of spur renewal, fruitfulness and longevity and to determine how these dynamics are impacted by orchard management practices. Results from the study indicated that the number of flowers borne by individual spurs is a function of spur leaf area in the previous year and whether or not the spur bore a fruit in the previous year.Furthermore, spur mortality was much higher in spurs that had low previous year spur leaf area because fruit bearing competes with leaf growth and decreases the amount of source organ available on bearing spurs . Although there was a strong tendency for individual spurs to not bear fruit in successive years,pot raspberries whole trees or orchards are not strongly alternate bearing because fewer than 20% of the spurs on a tree bear fruit in a given year . In addition, the spur dynamics study documented that the key to ensure the largest flowering over an orchard’s life is to have the largest number of spurs possible with the optimal leaf area for flowering.
Proper irrigation during the previous year vegetative season and even after harvest can help to minimize spur death and has been reported to have a critical impact on subsequent bloom and fruit set . The almond spur dynamics study also provided information regarding the importance of PYSLA in determining subsequent spur flowering, fruit bearing and survival as well as the fact that spur fruit bearing in turn, reduces spur leaf in the same year . Thus, spur flowering and fruiting in two sequential years is relatively rare . However, the total number of flowering spurs on a tree may be of limited significance if greater relative fruit set of the flowers can compensate for decreased flower numbers in the orchard. Thus, understanding the relative impact of flower number and relative fruit set on almond tree yield in commercial orchards is essential for guiding efforts to improve orchard productivity and help growers determine the most profitable practices for almond crop management. To address this question we analyzed flowering and fruit set data recorded during the almond spur dynamics project. The study was conducted in a 145-acre orchard, planted in 1996, at 24 feet between and 21 feet within rows. The orchard planting consisted of rows of ‘Nonpareil’ alternating with pollinizer rows of ‘Monterey’ , and ‘Wood Colony’ . The orchard was located in Kern County on a sandy-loamy soil. Irrigation was carried out by micro-sprinklers and irrigation schedule was based on weekly measurement of midday stem water potential that was maintained between −0.7 and −1.2 MPa. Nitrogen was applied at 110 to 220 pounds per acre and leaf N content was between 1.95% and 2.45% over the period of the experiment. Bee hives were placed at a density of two to three hives per acre prior to bloom.
During the experiment, weather conditions during the pollination period were not limiting for bee activity. The orchard was divided into six equal-sized replicate blocks and 50 spurs were tagged in eight ‘Nonpareil’ trees within each of the six blocks. A total of 2,400 spurs were marked with aluminum tags in late March and early April 2001. Twelve spurs were selected on each of the northeast and northwest quadrants of individual trees and 13 spurs were selected on each of the southeast and southwest quadrants of the same trees. Tagged spurs were located at positions ranging from shaded to exposed portions of the canopy at a height of 3 to 12 feet. During the first 4 years of the study, lost tags or dead spurs were replaced with spurs in close proximity with similar light exposure to the original tagged spurs. The dynamics of annual growth, flowering, fruitfulness and spur mortality were quantified annually. For more detail see Lampinen et al. . The number of flowers produced on each tagged spur was counted in the spring of each year from 2002 through 2007. Multiple year records of PYSLA , previous year bearing, number of flowers in the current year and number of fruit in the current year were used to assess spur behavior in relation to PYSLA in spurs that bore no fruits in the previous year. These analyses involved data from 6,980 spurs spread over the 6 years. Kernel yield of the individual trees with tagged spurs and the kernel yield of the orchard containing those trees were also recorded for 6 years . Statistical analyses were carried out using ANOVA to test the significance at P < 0.01 of relationships between PYSLA and current year spur flower density , current year spur fruit density and current year spur relative fruit set. The same test was also used to test the significance of the relationship between tree yield and tree spur population relative fruit set and spur flower density . The number of flowers differentiated during the previous year is the first component of yield in fruit trees .
In almond spurs, flower formation was closely related to spur leaf area in the previous year . Thus, if the leaf area of each spur on a tree were known, the number of flowers that a tree would bear in the following year could be estimated, and, if spur relative fruit set were constant, spur fruit bearing and yield of that tree could be predicted. However, although the relationship between spur fruit density and PYSLA was significant, it was weaker than the relationship between spur flowering and PYSLA . This was because fruit set was highly variable in almond across years. Relative fruit set varied from 19% to 36% . These data apparently support the large effect of season, and particularly weather conditions, on the fruit set process. In almond, rainfall during the bloom period has been reported to affect pollinator activity and to wash pollen off stigmas . Anther dehiscence also can be affected by rain and high relative humidity . Temperature affects pollen germination, pollen tube growth , ovule degeneration and pollinator activity in the field . Wind can also affect pollinator activity. On the basis of this information, some have hypothesized that yield fluctuations can be explained mainly by variations in climatic factors . Actually, large relative fruit set variability also occurred among individual trees . This fluctuation could be a result of “on-trees” and “off-trees” occurring in the same orchard and season . On the other hand, fluctuations of relative fruit set of spur populations in different trees exposed to the same climatic conditions suggest that climatic conditions are not the major factor influencing tree spur population fruit set. In this experiment, at the spur level, there was no correlation between the PYSLA and relative fruit set in the current year . Thus, whereas previous year conditions are fundamental for flower formation on spurs , previous year leaf area did not appear to influence current year spur relative fruit set. Furthermore, spur fruiting was associated with reduced spur leaf area in the current season, suggesting that current year spur leaf area does not exert any influence on spur relative fruit set . In this experiment, the number of nuts borne by individual trees was significantly correlated with the number of nuts borne by the tagged spur populations in those trees . This suggests that our spur sample was relatively representative of the spur population of the trees. On a whole tree basis,plastic garden pots tree yield was not correlated with mean relative fruit set measured on tree spur populations. Instead, tree yields appeared to be more closely correlated with flower density on the tagged spur population. Thus, while relative fruit set is obviously important, it was not the primary yield limiting factor in this orchard situation, and increased relative fruit set when floral densities were low did not compensate for lower numbers of flowers . There were significant correlations between spur flower density and tree yield over years ; for individual years, the relationship was significant in 4 of the 6 years of our experiment . On the other hand, the relationship between tree relative fruit set and tree yield was not significant in any of the 6 years of the experiment.
However, it should be noted that the coefficients of determination were low due to the large number of points and the limited size of the spur sample compared with the total number of spurs borne by each tree; only 5.3% of the variability in tree yield can be explained by spur flower density. These results support the validity of flower density as an important parameter in the evaluation of almond cultivars . These data support the importance of total flower production for obtaining large crops. As a result of these spur dynamics studies, it is clear that the key to optimizing yields in commercial almond orchards is to focus on maximizing healthy populations of productive spurs. Some spur mortality is unavoidable and linked to insufficient spur leaf area associated with spur bearing and spur shading . Thus, continued productivity is dependent on spur renewal that is achieved by ensuring that there is annual growth of as many existing spurs as possible and new shoots that provide sites for new spurs . Health of spurs is also a function of total canopy light interception and good light distribution with the tree canopy . It is clearly important to select cultivars with the ability to produce large numbers of flowers and have crop management practices aimed at limiting abiotic stresses during the vegetative season . In an experiment not potentially biased by experimental manipulation , these results support the assertion of Kester and Griggs that reductions in total number of flowers due to adverse orchard conditions are not likely to be compensated for by increased relative fruit set when adequate pollinizers and pollinators are present and can result in some measure of crop reduction. Such was the case in this study since it was conducted in an orchard in which the ‘Nonpareil’ trees were flanked by two pollinizer cultivars selected for bloom overlap with ‘Nonpareil’ and relatively high populations of bee pollinators were placed in the orchard each year to facilitate pollination. Had such factors not been present in the orchard during bloom, it is likely that relative fruit set would have varied even more among years and measured tree yields would have been more dependent on variations in relative fruit set.Refrigeration can lead to post harvest loss and waste , although it is the most effective strategy to maintain the quality and prolong the shelf-life of horticultural products. The rates of metabolic reactions increase 2–3-fold for every 10°C rise in temperature, and low-storage temperature delays deterioration by slowing down respiration and ethylene production, and by reducing pathogen growth and water loss. Commodities such as apples, blackberries, blueberries, cherries, and grapes benefit from refrigeration, however, in produce originating from tropical and subtropical regions, such as tomato, banana, pineapple, potato, and basil, refrigeration may lead to injury. Postharvest chilling injury is initiated when the tissues of cold-sensitive species are stored between 0 and 15°C, but becomes apparent after transfer to warmer conditions. Because the affected species are taxonomically diverse and the organs affected vary, for example, fruit, tuber, root, leaf, and stem, PCI symptoms can be variable . However, some common phenotypes include tissue browning or blackening, pitted surfaces, shriveling, negative changes in texture, carbohydrates and aroma volatiles, and fungal infection. PCI severity is determined by many factors with temperature and storage time being the most important. If low temperatures are mild and exposure istransient, many metabolic functions will resume after rewarming, and visible symptoms may not develop.