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Thomas Gradziel, Noreen Mahoney, and Ashraf Abdallah

Genetic differences were observed in levels of aflatoxin production following controlled inoculations of California almonds [Prunus dulcis (Mill.) D.A. Webb, syn. P. amygdalus, Batsch.; P. communis (L.) Arcangeli, non Huds.]. Genetic variation was also observed in kernel oil composition, and in susceptibility to Aspergillus flavus Speare as indicated by rate of mold expansion on the surface of cut kernels. Several almond lines resulting from the introgression of peach [P. persica (L.) Batsch] germplasm had very low aflatoxin levels relative to commercial cultivars tested. Peach-derived almond breeding lines and cultivars also produced some of the highest oil quality as determined by the proportion of oleic acid, and by the oleic to linoleic acid balance. The proportion of linoleic acid to total oil ranged from 16% to almost 30%. No correlations were detected between aflatoxin production in inoculated almond kernels and either kernel oil composition or mold growth rate on injured kernel tissue.

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Marc van Iersel

Uprooting and transplanting seedlings can cause root damage, which may reduce water and nutrient uptake. Initiation of new roots and rapid elongation of existing roots may help minimize the negative effects of transplant shock. In this study, seedlings with four true leaves were transplanted into diatomaceous earth and the plants were transferred to a growth chamber, where they were treated with NAA (0, 0.025, 0.25, and 2.5 mg·L-1; 36 mL/plant). The effects of drenches with various amounts of 1-naphthaleneacetic acid (NAA) on the posttransplant CO2 exchange rate of vinca [Catharanthus roseus (L.) G. Don] were quantified. Whole-plant CO2 exchange rate of the plants was measured once every 20 minutes for a 28 day period. Seedlings treated with 0.025 or 0.25 mg·L-1 recovered from transplant shock more quickly than plants in the 0 and 2.5 mg·L-1 treatments. Naphthaleneacetic acid drenches containing 0.025 or 0.25 mg·L-1 increased whole-plant net photosynthesis (Pnet) from 10 days, dark respiration (Rdark) from 12 days, and carbon use efficiency (CUE) from 11 days after transplanting until the end of the experiment. The increase in CUE seems to have been the result of the larger size of the plants in these two treatments, and thus an indirect effect of the NAA applications. These differences in CO2 metabolism among the treatments resulted in a 46% dry mass increase in the 0.025 mg·L-1 treatment compared to the control, but shoot-root ratio was not affected. The highest rate of NAA (2.5 mg·L-1) was slightly phytotoxic and reduced the growth rate of the plants.

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How-Chiun Wu and Chun-Chih Lin

conditions. Low photosynthetic ability of plantlets cultured in vitro has been found to be the cause of low survival rate and poor growth during acclimatization ( Kubota et al., 2001 ). Xiao et al. (2005) showed that during acclimatization, the survival

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J.A. Larrinaga-Mayoral, E. Troyo-Dieguez, M. Toyota, and B. Murillo-Amador

Salt and water stress affect in a significant way most common horticultural crops in northwest Mexico, where bell pepper, hot pepper, and tomato are the most important vegetable crops. Growth rate (GR) and physiological traits in bell pepper were analyzed under salt and drought stress. Two cultivars of bell pepper, `Hungarian Yellow' (HY) and `Sta. Fe Grande' (SG), were evaluated. GR in both cultivars was decreased by salt and drought stress interaction. Salt concentration in the irrigation water affected the amount of dry matter in the plant tissue. Relative growth ratio (RGR), net assimilation ratio (NAR), leaf area ratio (LAR), and photosynthesis rate (Pn) decreased in a correlated amount to the salt NaCl content in the experiment (0, 80, and 160 mm). Differences in the RGR under salt and drought stress between SG and HY were significant. The observed decrease in RGR was explained by NAR and LAR, where RGR was more affected by NAR than LAR. Similarly, the decrease in NAR was explained by C/F and Pn, indicating that NAR was more affected by Pn than C/F. The difference in observed NAR between both cultivars was understood by difference in C/F. Finally, a high relation of C/F in SG cultivar under salt and drought stress was caused by a physiological use of photosynthetic products, causing a significant decrease in NAR in the cultivar HY. This difference in NAR was found to be the factor that affected RGR in both cultivars.

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Takeshi Suzuki, Hiroshi Amano, and Toyoki Kozai

The two-spotted spider mite (Tetranychus urticae Koch.) has a worldwide distribution and is one of the most harmful agricultural pests for a variety of plant species. To reveal a visible light wavelength that reduces the population growth rate (as r m, unit: d–1) of the mite, we investigated the r m under wavelength peaks of 468, 515, and 658 nm with half bandwidths of 23, 44, and 22 nm using blue, green, and red light-emitting diodes, respectively. In all treatments, light intensity was set at 2.3 W·m–2 with a light period of 16 h·d–1, and air temperature was set at 25 °C. The survival percentage (l x) and the number of eggs deposited per female (m x) on each age (x, unit: d) were determined to calculate the r m by the following equation: ∑exp(–r m · xl x /100 · m x = 1. The r m and the total m x decreased with increasing wavelength. This result shows that the population growth rate can be reduced under red light (658 nm).

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Peter R. Hicklenton and Kenneth G. Cairns

Nutrient release from Nutricote Type 100 (100-day N release; 16N-4.4P-8.1K), and from a 1:3 mixture of Nutricote Type 40 (40-day N release; 16N-4.4P-8.1K) and Type 100 was affected by time and temperature. The Type 40/100 mixture released nutrients more rapidly over a 5 to 35C range in laboratory studies. Seasonal growth of containerized cotoneaster (Cotoneaster dammeri C.K. Schneid `Coral Beauty') and juniper (Juniperus horizontalis Moench. `Plumosa Compacta') increased with increasing application rates of either Nutricote Type 100 or a 1:3 mixture of Type 40/100 over the range 2-10 kg·m-3. Between 25 June and 27 July, cotoneaster grew more rapidly in media with Type 40/100 Nutricote, but by the end of the season (27 Sept.), fertilizer type showed no effect on plant dry weight. Shoot N was higher in cotoneaster plants grown with Type 40/100 Nutricote than with the Type 100 formulation during the first 2 months of growth, reflecting the more rapid release and uptake of N from the mixture. During the last month the situation was reversed, as nutrients from the Type 40/100 mixture were depleted. Potassium and P shoot concentrations were not affected by fertilizer type. Juniper growth and shoot concentrations of N, K, and P were not affected by fertilizer type at any time during the season. The results provided no evidence that seasonal growth could be enhanced in either cotoneaster (grows rapidly) or juniper (slower growing) by mixing rapid and more slowly releasing types of Nutricote.

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Riccardo Lo Bianco, Mark Rieger, and She-Jean S. Sung

Terminal portions of `Flordaguard' peach roots [Prunus persica (L.) Batsch] were divided into six segments and the activities of NAD+-dependent sorbitol dehydrogenase (SDH), sorbitol oxidase (SOX), sucrose synthase (SS), soluble acid invertase (AI), and soluble neutral invertase (NI) were measured in each segment 10, 15, and 20 days after seed germination. The same type of experiment was conducted with terminal portions of `Flordaguard' and `Nemaguard' peach shoots except that one of the six segments consisted of the leaflets surrounding the apex. Independent of the age of individual roots, activities of SDH and AI were consistently highest in the meristematic portion and decreased with tissue maturation. In shoots, AI was the most active enzyme in the elongating portion subtending the apex, whereas SDH was primarily associated with meristematic tissues. A positive correlation between SDH and AI activities was found in various developmental zones of roots (r = 0.96) and shoots (r = 0.90). Sorbitol and sucrose contents were low in roots regardless of distance from tip, while sucrose showed a decreasing trend with distance and sorbitol, fructose, and glucose increased with distance from the meristem in shoots. Activity of SDH in internodes, but not apices, correlated with shoot elongation rate of both cultivars, whereas activities of other enzymes did not correlate with shoot elongation rate. We conclude that AI and SDH are the predominant enzymes of carbohydrate catabolism and the best indicators of sink growth and development in vegetative sinks of peach.

Open access

Yuqi Li and Neil S. Mattson

germination rate, seedling survival rate, and seedling related indices. Transplant growth. The growth of cucumber transplants was affected by organic fertilizer sources and rate ( Table 2 ). The stem length, leaf number, DW, RI, and SPAD readings increased

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Rebecca L. Darnell, Nicacio Cruz-Huerta, and Jeffrey G. Williamson

LNT or high source-sink ratio has also been correlated with increased ovary carbohydrate concentration ( Aloni et al., 1999 ). Under LNT, pepper plants exhibit slower growth rates, resulting in decreased shoot dry weight (DW) compared with plants grown

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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.