For the last several years, research in my laboratory has been focused on studying the developmental and environmental control of dry matter partitioning in peach trees based on the concept that plants grow as collections of semi-autonomous, but interacting, organs. This concept assumes that plant genotype, triggered by developmental and environmental signals, determines current organ specific growth potentials and that environmental conditions dictate conditional growth capacity and respiration (both growth and maintenance) requirements of each organ at any specific time. Dry matter partitioning at any given time is then determined by the availability of resources to be partitioned, the conditional growth capacity and maintenance requirements of each organ, and the relative ability of each organ to compete for the resources. In this presentation, I will demonstrate how developmental patterns of various organs influence dry-matter partitioning within the tree over time, how organ number can influence the amount of dry-matter partitioned collectively to an organ type, and propose an hypothesis for how environmental conditions may influence partitioning on a diurnal basis.
T.M. DeJong and K.R. Day
The relationships between shoot light exposure in one year and the flower and fruit production characteristics of those shoots the following year were indirectly investigated in summer pruned and nonsummer pruned peach [Prunus persica (L.) Batsch.] trees by evaluating leaf characteristics (leaf N and dry matter content per unit leaf area; Na and Wa, respectively) on tagged shoots during one season and the flowering and fruiting characteristics during the subsequent season. There were significant positive linear relationships between leaf Na and Wa on shoots in one year and flower and fruit production per unit shoot length during the subsequent year. Summer pruning had relatively little influence on these relationships. There was no apparent relationship between percent fruit set in the spring and light exposure of the shoots the previous summer. Following dormant pruning and commercial thinning, trees summer-pruned the previous year had higher yields than nonsummer pruned trees because of less shoot mortality and more fruit per tree.
E.W. PAVEL and T.M. DEJONG
The fruit growth of three peach (Prunus persica (L.) Batsch cvs. `Spring Lady', `Flamecrest', `Cal Red') and two apple cultivars (Malus domestica Borkh. cvs. `Cox Orange', `Golden Delicious') was measured weekly during the 1988 growing period. Seasonal patterns of fruit relative growth rate calculated on a dry weight basis were very similar for both species. Changes in nonstructural carbohydrate composition of peach mesocarp and apple pericarp were correlated with the two physiological phases of sink-activity of the relative growth rates Changes in sucrose concentrations seemed to coincide with increasing dry matter accumulation for both species, even though fructose was a dominant sugar in apples.
Y.L. Grossman and T.M. DeJong
Plant dry matter production is proportional to light interception, but fruit production does not always increase with increased light interception. Vegetative growth potential, the effect of cropping on vegetative growth, light interception and cropping efficiency of a clingstone peach [Prunus persica (L.) Batsch `Ross' on `Nemaguard' rootstock] were assessed in four production systems differing in tree density and training system. The four systems were a perpendicular V (KAC-V) system, a high-density perpendicular V (HiD KAC-V) system, a cordon system, and an open vase system. Vegetative growth potential, assessed on defruited trees, was higher in the cordon system and lower in the open vase system compared to the V systems. Cropping reduced leaf growth on the V and cordon systems and stem growth on the KAC-V and cordon systems. On a ground area basis, the HiD KAC-V system had the highest crop yields and the open vase system had the lowest. The cordon and HiD KAC-V systems intercepted more light and produced more fruit, stem, and leaf biomass than the open vase system. However, the modified harvest increment, the ratio of fruit dry mass to the sum of fruit, leaf, and stem dry mass, was lower in the cordon system than in the other systems. Thus, on this basis, the cordon system was the least efficient. On a trunk cross-sectional area basis, there were no significant differences in fruit production among any of the four training systems. For current year production, crop production per unit ground area is the best measure of economic efficiency. However, when planning the spacing, training and pruning of orchard trees, the most appropriate goal seems to be a system that increases light interception without increasing vegetative growth potential, such as the HiD KAC-V system.
E.W. Pavel and T.M. DeJong
Dry weights of whole fruit and of different fruit tissues, such as the mesocarp (with exocarp) and the endocarp (with seed), were accumulated on early (`Spring Lady'), midseason (`Flamecrest'), and late-maturing (`Cal Red') peach [Prunus persica (L.) Batsch] cultivars during the 1988 growing season. Seasonal relative growth rate (RGR) patterns of whole fruit showed two distinct phases for `Flamecrest' and `Cal Red'; however, `Spring Lady' did not exhibit two distinct RGR phases. The shift from phase I to phase II of the whole fruit RGR curve was related to an intersection of mesocarp and endocarp RGR curves, indicating a change of physiological sink activities in those fruit tissues in the later-maturing cultivars, but not in the early cultivar. Nonstructural carbohydrate compositional changes in concentration or content were similar in the three peach cultivars. Sucrose accounted for most of the seasonal increase in mesocarp nonstructural carbohydrate concentration. A sudden rise of sucrose was associated with the phase shift of the fruit RGR curves of the midseason and late-maturing cultivars, but not of the early maturing cultivar; however, in the early maturing cultivar, mesocarp compositional carbohydrate changes and, particularly, the sucrose increase, indicate that the physiological processes normally associated with the two phases exist in very early maturing fruit but are not associated distinctly with two separate RGR phases.
E.W. Pavel and T.M. DeJong
Peach [Prunus persica (L.) Batsch] fruit thinning was used to reduce the competition for assimilates among peach fruits and to identify periods of source- and sink-limited growth during development. Individual fruit size, based on diameter or calculated dry matter accumulation, increased in trees with lower crop loads compared to fruits of unthinned trees in three peach cultivars. Relative growth rate analysis indicated that peach fruit growth was apparently limited by the assimilate supply (source-limited) or by its genetic growth potential (sink-limited) during specific growth periods. In stage I and at the beginning of stage III of the double-sigmoid growth curve, periods of source-limited growth occurred in the later-maturing cultivars Flamecrest and Cal Red. Peach fruit growth was apparently sink-limited during stage II of the growth curve when fruit relative growth rates were similar for the thinning treatments. Fruit growth in `Spring Lady', an early maturing cultivar, appeared to be primarily source-limited during the season. Although total fruit dry matter production was reduced by thinning, individual fruit dry weight on thinned trees was higher than that on trees with a heavy crop load. This typical thinning response was apparently caused by the differences in the amount of time that fruits grew under sink-vs. source-limited conditions with different crop loads. Final crop yield depended on fruit count per tree and on the available assimilate supply, and was affected by the individual fruit growth potential.
F.J.A. Niederholzer, S.A. Weinbaum, and T.M. DeJong
The interrelationships were studied between local soil N availability, tree N status, and
J.L. Saenz, T.M. DeJong, and S.A. Weinbaum
This study was designed to characterize the mechanisms of N-stimulated peach Prunus persica (L.) Batsch productivity. The effects of N fertilization on potential assimilate availability (source capacity) and on the growth capacity of individual fruit (sink capacity) were assessed. On heavily thinned trees, fertilization did not stimulate fruit growth rates relative to those on nonfertilized trees, suggesting that fruit growth rates were not assimilate-limited throughout the period of fruit development. However, N fertilization resulted in a longer fruit development period and increased the growth potential of individual fruit by 20% (fresh mass) and 15% (dry mass) vs. controls. In unthinned trees, N fertilization increased total fruit yield by 49% (fresh mass) and 40% (dry mass) compared to the unthinned, nonfertilized controls. N fertilization increased total fruit yield per tree in unthinned peach trees by extending the fruit development period and thus increasing the amount of assimilate accumulated for fruit growth. The fruit development period was prolonged both by assimilate deprivation associated with increasingly higher crop loads and by N fertilization. Thus, the prolongation of the peach fruit development period by N-fertilization appears inconsistent with the role of N in increasing assimilate availability for fruit growth. We conclude that N fertilization stimulates peach yields by increasing the period for fruits to use assimilates (sink capacity). The effect of N on assimilate availability was not directly evaluated. The timing of fertilizer N availability did not influence fruit growth potential.
W.A. Retzlaff, L.E. Williams, and T.M. DeJong
Nursery stock of plum (Prunus salicina Lindel., `Casselman') was planted 1 Apr. 1988 in an experimental orchard at the Kearney Agricultural Center, Univ. of California, near Fresno. The trees were enclosed in open-top fumigation chambers on 1 May 1989 and exposed to three atmospheric ozone partial pressures (charcoal-filtered air, ambient air, and ambient air + ozone) from 8 May to 15 Nov. 1989 and from 9 Apr. to 9 Nov. 1990. Trees grown outside of chambers were used to assess chamber effects on tree performance. The mean 12-hour (0800-2000 hr Pacific Daylight Time) ozone partial pressures during the 2-year experimental period in the charcoal-filtered, ambient, ambient + ozone, and nonchamber treatments were 0.044, 0.059, 0.111, and 0.064 μPa·Pa-1 in 1989 and 0.038, 0.050, 0.090, and 0.050 pPa·Pa-1 in 1990, respectively. Leaf net CO2 assimilation rate of `Casselman' plum decreased with increasing atmospheric ozone partial pressure from the charcoal-filtered to ambient + ozone treatment. There was no difference in plum leaf net CO2 assimilation rate between the ambient chamber and nonchamber plots. Trees in the ambient + ozone treatment had greater leaf fall earlier in the growing season than those of the other treatments. Cross-sectional area growth of the trunk decreased with increasing atmospheric ozone partial pressures from the charcoal-filtered to ambient + ozone treatment. Yield of plum trees in 1990 was 8.8, 6.3, 5.5, and 5.5 kg/tree in the charcoal-filtered, ambient, ambient + ozone, and nonchamber treatments, respectively. Average fruit weight (grams/fruit) was not affected by atmospheric ozone partial pressure. Fruit count per tree decreased as atmospheric ozone partial pressure increased from the charcoal-filtered to ambient + ozone treatment. Decreases in leaf gas exchange and loss of leaf surface area were probable contributors to decreases in trunk cross-sectional area growth and yield of young `Casselman' plum trees during orchard establishment.