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Evaluation of growth regulators for transplant size control and earlier maturity of processing tomato

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Title: Evaluation of growth regulators for transplant size control and earlier maturity of processing tomato
Author: Zandstra, J.W.; Dick, J.; Lang, J.
Abstract: Previous work using the triazole paclobutrazol (Bonzi) on processing tomato transplants involved treating the plants with a 5 ppm soil drench at the 2 leaf stage, and subsequently fertilizing heavily (up to 5 times the normal rate) to achieve the desired plant height. This treatment resulted in increased vigor in the field (measures as plant dry and fresh weight), advanced plant development (earlier bloom), advanced fruit maturity and increased yields. However, it is not presently registered on any food crops in North America, so a registration for use on tomato transplants is unlikely. Work in 2005 included other potential growth regulators with greenhouse registrations (uniconazole- Sumagic; Nova) and food crop registrations (Apogee). This approach was continued in 2006.
Description: Up to 8 times the phosphorous, and 2 times the nitrogen and potash were required to produce transplants of marketable size when 10 ppm uniconazole was applied at the 2 leaf stage, when compared to untreated transplants (Table 1). All treatments required additional fertilizer relative to untreated transplants. While plant heights differed significantly from the control in some treatments, all product/rate combinations increased top weights, root weights, total plant weights and stem diameters (Table 2). Total plant weight and stem diameter was the greatest when uniconazole was applied 3 times at a rate of 2.5 ppm; this treatment also required one of the highest rates of 3 fertilizer (Table 2). Applying uniconazole at germination resulted in greater transplant weight and stem diameter compared to applications at the 2nd and 3rd true leaf respectively (Table 2). Multiple applications of uniconazole were no better at improving the plant characteristics (plant weight, stem diameter) of tomato transplants when compared to single 5 ppm application at the 2nd true leaf stage. Apogee and Nova at the rates used were not as effective as the uniconazole treatments. All uniconazole and the paclobutrazol treatments increased seedling fresh weights up to 25 days after transplanting. Early treatments of 5 ppm uniconazole were as effective at increasing plant growth in the field as were high rates of uniconazole (Table 3). The most effective rates/timings of uniconazole were similar to 5ppm paclobutrazol applied at the 2 leaf stage. The growth rates of Nova and Apogee treated plants did not differ from untreated plants. Similar trends were found in the rate of flower development, which was determined up to 40 days after transplanting (Table 4). While total yields did not differ significantly amoung treatments, high rates of uniconazole increased red yields (Table 5). The percent ripe fruit tended to be higher with uniconazole treated plants, but these differences were not significant. All responses reported here were also found in an identical field trial conducted at the CanGro Foods research farm. While uniconazole appears to be a good alternative to paclobutrazol in terms of growth control in the greenhouse and plant establishment in the field, there are still concerns about slight distortions in the growth of uniconazole treated seedlings. All plants treated with uniconazole had a more horizontal leaf orientation and crooked stems, which increased as the rate on uniconazole increased. This made if more difficult to remove the plants from the tray when transplanting, and gave the plants the appearance that they had been handled improperly in the greenhouse. More work is proposed, which will investigate lower multiple applications of uniconazole in an attempt to further reduce these growth distortions.. The application of Nova and Apogee was not as effective at increasing transplant weight and plant growth in the field, and their use will be discontinued.
Date: 2006
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