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Douglas D. Archbold and Ann M. Clements

Several components of whole-plant growth were compared among accessions of Fragaria chiloensis (FC) and F. virginiana (FV) grown at 23 and 31 °C daytime temperatures. The accessions loosely represented North American (NA) and South American (SA) provenances of FC and Kentucky (KY) and eastern Canadian (CN) provenances of FV. Differences in component values between species and by provenance and accession within species were observed at each temperature. Using the ratio of the component value at 31 °C to that at 23 °C as a basis for comparisons, whole-plant relative growth rate (RGR), leaf net assimilation rate (NAR), root RGR, and root: shoot ratio were reduced relatively more by high temperature in FC than FV, while crown RGR, leaf RGR, and leaves produced per day were not consistently affected by temperature or and did not differed significantly between species. While the SA FC exhibited higher values for nearly all components than the NA FC at both temperatures, both were affected similarly by high temperature. The CN FV exhibited somewhat greater sensitivity to high temperature than the KY FV, with significantly lower leaf NAR, crown RGR, and leaves produced per day in the former group.

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Mario Pérez-Grajales, Víctor A. González-Hernández, Ma. Carmen Mendoza-Castillo, Cecilia Peña-Valdivia, Aureliano Peña-Lomelí, and Jaime Sahagún-Castellanos

Six manzano hot chile pepper landraces (Capsicum pubescens R & P) were evaluated to identify genotypes which might contribute toward obtaining superior hybrids by providing the following characteristics: low height, short internodes, rapid biomass accumulation, high harvest index, high fruit quality, and high photosynthetic rate. The landraces studied were `Chiapas', `Huatusco I', `Huatusco II', `Perú', `Puebla', and `Zongolica'. Plants were grown in a shaded glasshouse for 9 months, with drip irrigation. Growth, biomass distribution, fruit quality and yield were determined. All varieties exhibited advantageous characteristics, i.e., large fruit (60 mL) with thick pericarp (4.2 mm) in `Puebla'; short internodes (10 cm) in `Zongolica' and `Huatusco II'; high harvest index (0.24), high yield (18 to 19 t·ha−1) and high relative growth rates (0.12 g·g−1·d−1) in `Perú' and `Puebla'; and high dry mass accumulation (450 g/plant) in `Chiapas'. The highest photosynthesis rate in manzano hot pepper was 7.7 μmol of CO2/m2/s at 500 μmol photons/m2/s, in `Zongolica' and `Puebla'.

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Paul T. Wismer, J.T.A. Proctor, and D.C. Elfving

Benzyladenine (BA), carbaryl (CB), daminozide (DM), and naphthaleneacetic acid (NAA) were applied postbloom, as fruitlet thinning agents, to mature `Empire' apple trees. Although fruit set and yield were similar for BA, NAA, and CB, BA-treated fruit were larger, indicating BA increased fruit size beyond the effect attributable to thinning. BA applied at 100 mg·liter–1 increased the rate of cell layer formation in the fruit cortex, indicating that BA stimulated cortical cell division. The maximum rate of cell division occurred 10 to 14 days after full bloom (DAFB) when fruit relative growth rate and density reached a maximum and percent dry weight reached a minimum. Cell size in BA-treated fruit was similar to the control. Cell division ended by 35 DAFB in the control and BA-treated fruit when percent dry weight and dry weight began to increase rapidly and fruit density changed from a rapid to a slower rate of decreased density. These data support the hypothesis that BA-induced fruit size increases in `Empire' apple result largely from greater numbers of cells in the fruit cortex, whereas the fruit size increase due to NAA or CB is a consequence of larger cell size.

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C.R. Clement and R.M. Manshardt

The pejibaye (Bactris gasipaes Kunth) is being evaluated in Hawai'i for its fresh heart of palm, a gourmet vegetable. Seven half-sib progenies of the Putumayo land race were planted in a split-plot design, with densities (3333, 5000, 6666 plants/ha) as the main plots, progenies as the sub-plots, three replications, and nine plants/plot. Precocity was defined as “days from planting to harvest”; relative growth rate (RGR) and unit leaf rate (Ea) are possible causes of precocity and were estimated for the period from 6 months after planting to harvest. Density effects were never significant, suggesting that competition is not significant before harvest. Mean precocity ranged from 610 to 712 days; Va accounted for 14% of the phenotypic variance (Vp), with h2 = 0.57, similar to fruiting precocity in African oil palm (Elaeis guineensis Jacq.). Mean Ea ranged from 1.89 to 2.21 g/m2 per day, Va accounted for 8% of Vp, with h2 = 0.33 Mean RGR ranged from 0.0086 to 0.0102 d–1; Va accounted for 9% of Vp, with h2 = 0 35 Neither RGR (r = 0.20) nor Ea (r = 0.19) are significantly correlated with precocity. Heart, edible stem, and total edible product weights did not present significant progeny effects, probably because of the criterion used to determine harvest (height = 1.3 m). Precocity is easiest to work with and should give acceptable genetic gains.

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J. R. Potter

A method was developed to rapidly screen genotypes for capacity of leaves to export photosynthate, with the expectation that rapid export should promote growth. Vegetative plants of 13 cultivars of Pisum sativum L. (pea) were screened based on changes in specific leaf weight (SLW) at dawn before and after exposing plants to CO2-enriched air (1200 ppm) for one diurnal cycle. Three cultivars (Nofila, Little Marvel, Sugar Daddy) had relatively little increase in SLW and were designated rapid exporters; based on this criterion `Alaska', `Oregon Sugar Pod II', and `Manoa' were slow exporters. The increase in SLW was due to starch and sugars. Neither single leaf net photosynthetic nor dark respiration rates consistently differed among cultivars when measured at 1200 or 350 ppm CO2 (normal air). The difference between rapid and slow exporters persisted after plants were grown for 2 weeks at 1200 vs. 350 ppm CO2. However, the relative growth rate (RGR) of whole-plant dry mass did not differ consistently among cultivars at either CO2 level, except it was high for `Alaska', a slow exporter. The high RGR for `Alaska' was due in part to a high ratio of whole plant leaf area to dry mass early in the growth period. Thus, although the rapid exporters accumulated relatively low levels of starch and sugars, this trait did not dominate other growth determining traits.

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Douglas D. Archbold

Plants of a diverse collection of Fragaria clones from a range of native habitats representing F. chiloensis, F. virginiana, F. virginiana glauca, and F. vesca, were grown in a controlled environment at one of three day/night temperatures, 15/15, 23/15, or 31/15°C. Relative growth rate (RGR) and net assimilation rate (NAR) were estimated from plant leaf areas and total dry weights. At 23/15°C, the species mean RGR and NAR values were comparable although clones within species exhibited significant variation. At 15/15 and 31/15°C, RGR and NAR for species were lower than at 23/15°C. At 31/15°C, chiloensis and vesca mean values were reduced more than the others, to less than 50% the 23/15°C values. Also, NAR declined most for chiloensis, to 45% the 23/15°C value. At 15/15°C, virginiana had much higher RGR and NAR values than the other species, and its NAR mean value was greater than at 23/15°C. Although the species means would suggest that there are interspecific differences in temperature response, intraspecific variability was also large. Thus, classifying Fragaria species by temperature response may be an over-generalization.

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Ted M. DeJong

Previous research using relative growth rate models indicates that under normal cropping conditions peach fruit growth and yield is alternately source and sink limited during different phases of fruit growth. An experiment was designed to test this concept on whole trees in the field. Shortly after bloom central leader trees of `Spring Lady' and `Cal Red' peaches, were thinned to various crop loads ranging from -50 to -400 fruit per tree. At specific intervals trees representing the full range of crop loads were harvested to determine mean individual fruit weight/total crop weight relationships for whole trees. Then, assuming that fruit on low cropped trees grew at their maximum potential growth rate (sink demand) and that total crop growth on unthinned trees represented the maximum dry matter available for fruit growth (source supply), the relative source and sink limitation between each harvest interval was calculated. With `Cal Red', fruit growth appeared to be primarily source limited early and late in the season but primarily sink limited during the mid-period (Stage II) of fruit growth. At normal commercial crop loads, `Spring Lady' was less source limited than `Cal Red'.

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Meriam G. Karlsson and Royal D. Heins

The relative progression of lateral shoot elongation from pinch to flower of chrysanthemum [Dendranthema grandiflora (Ramat.) Kitamura `Bright Golden Anne'] plants grown under 2 to 22 mol·day-1·m-2 photosynthetic photon flux and 10 to 20C was modeled using Richards function. Parameters for the function were determined by first transforming data of shoot length and time from pinch (start of short photoperiods) to flower to a relative scale of 0.0 to 1.0 by dividing all intermediate shoot lengths and measurement dates by final shoot length and number of days to flower, respectively. Data used for parameter estimation originated with plants grown at a daily average of ≤20C, since those grown at a daily average above 20C exhibited delayed morphological flower induction and reached 50% of the final shoot length earlier in development. Relative shoot elongation was described by Richards function in the following form: Relative shoot length = SF × {1 + [(SF/SO)N-1] e-SF Kt}-1/N where t (relative time) = 0.0 to 1.0, SF (maximum relative shoot length) = 1.018, SO (relative shoot length at t = o) = 0.0131, N (model parameter related to the shape of the curve) =0.3923, and K (model parameter related to mean relative growth rate) = 5.8138.

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Nader Soltani, J. LaMar Anderson, and Alvin R. Hamson

`Crimson Sweet' watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] plants were grown with various mulches and rowcovers and analyzed for relative growth rate (RGR), net assimilation rate (NAR), specific leaf area (SLA), leaf area index (LAI), and crop growth rate (CGR). Spunbonded polyester fabric (SB-PF) and perforated polyethylene film (PCP) rowcovers generally showed greater mean RGR, SLA and CGR than spunbonded polypropylene polyamide net (SB-PP), black plus clear combination plastic mulch and black plastic mulch alone. Plants on mulches and under rowcovers showed significant increases in RGR, NAR, and SLA over plants grown in bare soil. Carbon dioxide concentration inside the transplanting mulch holes was nearly twice the ambient CO, concentration. Growth analysis of sampled watermelon plants during early stages of development under various treatments was predictive of crop yield. Plants under SB-PF and PCP rowcovers produced the earliest fruit and the greatest total yield. An asymmetrical curvilinear model for watermelon growth and development based on cardinal temperatures was developed. The model uses hourly averaged temperatures to predict growth and phenological development of `Crimson Sweet' watermelon plants grown with and without rowcovers. Early vegetative growth correlated well with accumulated heat units. Results indicate a consistent heat unit requirement for the `Crimson Sweet' watermelon plants to reach first male flower, first female flower and first harvest in uncovered plants and plants under rowcovers. Greater variability was observed in predicting date of first harvest than first bloom.

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Maria A. Macias-Leon and Daniel I. Leskovar

Onions (Allium cepa L.) are easily outcompeted by weeds because of slow germination and relative growth rates. Therefore, high percentage of seed germination and root vigor are important traits to improve field performance. The effects of exogenous plant growth regulators (PGRs), 2-chloroethylphosphonic acid (ethephon, Eth), indole-3-acetic acid (IAA), trans-zeatin (tZ), and 1-aminocyclopropane-1-carboxylic acid (ACC) were evaluated on the germination and root growth of ‘Don Victor’ (yellow) and ‘Lambada’ (red) onion seedlings. Seeds were soaked for 10 hours in hormonal solutions and water (hydro-priming). Seed germination improved with Eth (30 and 100 μm), Eth (100 μm) + IAA (10 μm), and IAA (3 μm) treatments. Root surface area (RSA) increased in response to Eth at 30 and 100 μm, Eth + IAA, and 3 μm IAA. Root length (RL) and root diameter (RD) were enhanced by 1 μm tZ and 100 μm ACC. Eth reduced RL and RD, whereas IAA showed no effects. A subsequent experiment evaluated synergistic effects of different PGRs. Treatment of seeds with ACC (250 μm) + tZ (0.5 μm) and ACC (250 μm) + tZ (0.5 μm) + Eth (20 μm) enhanced RL and RD. RSA was unaffected by ACC + tZ + Eth. The results suggest that exogenous PGRs could be useful to enhance germination, RL, and RSA of onion seedlings.