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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.

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Johannes Daniel Scharwies, Eckhard Grimm and Moritz Knoche

fruits are particularly sensitive to russeting ( Knoche et al., 2011 ; Wertheim, 1982 ). From this we hypothesize that the incidence of russeting will be higher on surfaces subjected to high relative growth rates and vice versa. Pear fruit is a

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Martin P.N. Gent

included different minimum temperatures of 10 compared with 20 °C, harvested on 1 Apr. 2007 and 30 Nov. 2007. Otherwise, average temperatures varied from 14 °C in winter to 27 °C in summer. Table 2. Statistics for variables related to relative growth rate

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Theodore M. DeJong

The growth and development patterns of fruit have been studied for many years and it has become traditional to think of peaches as having a double sigmoid pattern with three main stages fruit growth. This concept is primarily based on analyses of fruit absolute growth rates An alternative approach is to express growth on a relative growth rate (RGR) basis which is simply the weight increase perg of fruit weight per day. This analysis applied to dry-weight peach fruit growth results in a two-phase curve that is known mathematically as a Gompertz function. During the first growth phase the RGR decreases logarithmically and during the second phase the RGR remains relatively stable. Expressing fruit growth on a RGR basis is advantageous for fruit growth carbon budget modelling because RGR is directly related to respiration rates and for physiological studies because most analyses for physiologically active substances are expressed on a weight basis. There is obviously not only one “right” way to express fruit growth but it may be instructive to use the RGR approach particularly when studying factors that may be associated with “sink” activity.

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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.

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David F. Graper and Will Healy

Abbreviations: DW, dry weight; FW, fresh weight; HPS, high pressure sodium; IR, infrared; PPF, photosynthetic photon flux; RGR, relative growth rate. 1 Currently Assistant Professor, Dept. of Horticulture, Forestry, Landscape and Parks, South Dakota

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Toshio Shibuya, Ryosuke Endo, Yoshiaki Kitaya and Saki Hayashi

. The relative growth rate (RGR), relative leaf expansion rate (RLER), net assimilation rate (NAR, dry weight basis), leaf area ratio (LAR), specific leaf area (SLA), and leaf weight ratio (LWR) of cucumber seedlings grown under light with a high red to

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Douglas D. Archbold

Abbreviations: AGR, absolute growth rate; DW, dry weight; RGR, relative growth rate; SAR, sorbitol accumulation. The investigation reported in this paper (no. 91-10-86) is in connection with a project of the Kentucky Agricultural Experiment Station

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Hideaki Yamaguchi, Yoshinori Kanayama, Junichi Soejima and Shohei Yamaki

Seasonal changes in the amounts of the NAD-dependent sorbitol dehydrogenase (NAD-SDH) (enzyme code, 1.1.1.14) protein in developing apple (Malus pumila Mill var. domestica Schneid) fruit were determined by immunoblotting analysis. The amounts of the enzyme protein were very low in young fruit and rose as fruit matured. The weak correlation between enzyme protein and NAD-SDH activity and also the changes in NAD-SDH specific activity suggested that there could be posttranslational modification to the pre-existing enzyme or isoenzyme(s) of NAD-SDH. The changes in the amounts of NAD-SDH protein did not show the same pattern as those in relative growth rate, which is used to express sink activity, especially in young fruit. The role of NAD-SDH on sink activity in apple fruit, therefore, could not be explained simply by the amount and activity of the enzyme. In young fruit, it seems that enzymes other than NAD-SDH would be more directly related with fruit growth.

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Jean-Pierre Privé and J. Alan Sullivan

Growth rates for two types of tissue-cultured plant stock for `Heritage', `Ruby', and `Redwing' red raspberry (Rubus idaeus L.) were examined. Actively growing plantlets from the greenhouse (G) were compared to cold-treated (CT) plantlets from cold storage. The greatest differences between these two occurred during the first 6 weeks after planting. At 4 weeks, CT plants for all cultivars had longer canes and internodes, sometimes twice that of G plants. Although `Heritage' had greater total plant dry weights following chilling, `Ruby' and `Redwing' had less. Chilling had no effect on `Heritage' root growth but did reduce root dry weight for `Redwing' and `Ruby'. Relative growth rate (RGR) and leaf area ratio (L-AR) were more effective variables for analyzing growth as they considered differences in initial biomass and cane number and provided a better representation of the data during the initial 6 weeks of growth. All cultivars showed a greater total plant RGR and LAR for the CT plants at 6 weeks. During the first 4 weeks, the G plants were more efficient producers of root dry matter while the CT plants were more efficient producers of cane dry matter. By 6 weeks, the G plants had partitioned a greater percentage of their assimilates into cane growth while the leaves, canes, and roots of the CT plants contributed equally to total RGR. No difference in total or individual component RGR was observed after 6 weeks.