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J.C. Palumbo and C.A. Sanchez

Imidacloprid is a new, chloronicotinyl insecticide currently being used to control sweetpotato whitefly [Bemisia tabaci Genn, also known as silverleaf whitefly (Bemisia argentifolii Bellows and Perring)]. Large growth and yield increases of muskmelon (Cucumis melo L.) following the use of imidacloprid have caused some to speculate that this compound may enhance growth and yield above that expected from insect control alone. Greenhouse and field studies were conducted to evaluate the growth and yield response of melons to imidacloprid in the presence and absence of whitefly pressure. In greenhouse cage studies, sweetpotato whiteflies developed very high densities of nymphs and eclosed pupal cases on plants not treated with imidacloprid, and significant increases in vegetative plant growth were inversely proportional to whitefly densities. Positive plant growth responses were absent when plants were treated with imidacloprid and insects were excluded. Results from a field study showed similar whitefly control and yield responses to imidacloprid and bifenthrin + endosulfan applications. Hence, we conclude that growth and yield response to imidacloprid is associated with control of whiteflies and the subsequent prevention of damage, rather than a compensatory physiological promotion of plant growth processes. Chemical names used: 1-[(6-chloro-3-pyridinyl)methyl]-4,5-dihydro-N-nitro-1-H-imidazol-2-amine (imidacloprid); [2 methyl(1,1′-biphenyl)-3yl)methyl 3-2-chloro-3,3,3-trifluoro-1-propenyl]-2,2-dimethylcyclopropane carboxylate (bifenthrin); 6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodiaxathiepin 3-oxide (endosulfan).

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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.

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Marc van Iersel

Container size can affect the growth and development of bedding plants. The effects of widely differing container sizes on growth and development of salvia (Salvia splendens F. Sellow ex Roem. & Schult.) were quantified. Plants were grown in a greenhouse in 7.3-, 55-, 166-, and 510-mL containers. Container volume affected plant growth as early as 18 days after planting. Growth was positively correlated with pot size and differences increased throughout most of the growing period. Growth of the plants in the 7.3-mL cells was reduced because of a low net assimilation rate (4.34 g·m-2·d-1), compared to the plants in the 55-, 166-, and 510-mL pots (≈5.44 g·m-2·d-1). Plants in 510-mL containers grew faster than those in 55- and 166-mL containers because of a higher leaf area ratio. Both lateral branching and leaf expansion were suppressed by root restriction and flowering was delayed. The growth rate of plants in 166-mL pots declined after the onset of flowering, and final plant size was comparable for plants in 55- and 166-mL pots. Although water deficit stress or nutrient deficiencies cannot be excluded as contributing factors, these were probably not the main reason for observed differences.

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Marjorie Reyes-Díaz, Claudio Inostroza-Blancheteau, Rayen Millaleo, Edgardo Cruces, Cristián Wulff-Zottele, Miren Alberdi, and María de la Luz Mora

different Al treatments in the same conditions mentioned above. At the end of the experiment (20 d), the Al-treated plants were harvested for fresh and dry weight determinations (W 2 ). Growth was expressed as the relative growth rate (RGR) from the mean

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Edgar L. Vinson III, Kaitlyn J. Price, J. Raymond Kessler, Elina D. Coneva, Masuzyo Mwanza, and Matthew D. Price

weights were combined to determine plant weight. Relative growth rate (RGR) was calculated using the following equation ( Fernandez et al., 2001 ): R G R   =  l n P D W 2 − l n P D W 1 T 2 − T 1 , where lnPDW2 is the natural log of plant dry weight 2

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Haiyan Zhang

than continuous light, and large seeds than small seeds in the early seedling stage. Table 3. Shoot height (SH), average growth height (AGH), and relative growth rate (RGR) of large and small seeds in C. bungei at 15 (T15), 20 (T20), and 25 °C (T25

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Jer-Chia Chang and Tzong-Shyan Lin

) characterized fruit growth of ‘73-S-20’, an irregular bearing line of ‘No Mai Tsz’ litchi found in JiJi, Nantou, central Taiwan (lat. 23°N) ( Yen et al., 1984 ) and documented that during the peak periods of the fruit, relative growth rate (RGR in dry weight

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Anke van der Ploeg, Ranathunga J.K.N. Kularathne, Susana M.P. Carvalho, and Ep Heuvelink

in SD. With the dry weight and leaf area observations collected in Expt. 2, relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR), specific leaf area (SLA), and leaf weight ratio (LWR) were calculated over the LD period

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Ming Li and Wei-tang Song

treatment. These results coincide with those of Yelle (1990) . Hence, the change in plant responses to eCO 2 can be detected with these methods. Fig. 10. Relative growth rate ( RGR ) of Angelica transplants calculated based on the estimated dry weight of

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Augusto Ramírez-Godoy, María del Pilar Vera-Hoyos, Natalia Jiménez-Beltrán, and Hermann Restrepo-Diaz

applications of synthetic elicitors on stomatal conductance ( g S ), leaf temperature, chlorophyll content, and PSII efficiency in Tahiti lime trees. Fig. 3. Effect of foliar applications of synthetic elicitors on the relative growth rate in flush shoots of