摘要：

Brushing (40 strokes per 1.5 minutes, twice daily) or moisture stress conditioning (MSC) (daily nonlethal dry-down cycles) reduced seedling growth of two cucumber (Cucumis sativus L.) cultivars in 1991 and three squash (Cucurbita pepo L.) cultivars in 1991 and 1992. In both years, watermelon [Citrullus lanatus Thunb. (Matsum. & Nakai)] cultivars varied in responsiveness to brushing; brushing reduced stem length 0% to 44% over four cultivars in 1992. MSC reduced growth of all cultivars. Brushing increased the rate of water loss from detached leaves of cucumber, squash, and watermelon, whereas MSC decreased water loss from leaves of cucumber and squash. In 1991, under well-watered posttransplant conditions, MSC increased the mean relative growth rate (RGR) of cucumber and watermelon transplants in the greenhouse. Brushing increased the RGR of watermelon transplants. In 1992, MSC increased the RGR of squash and watermelon transplants grown under posttransplant drought-stressed conditions, while brushing had no effect. Both conditioning treatments controlled plant growth in the greenhouse without diminishing subsequent plant performance. To meet the physical limitations of shipping containers and automated transplanters, vegetable transplants must be uniform, short, and sturdy (Cantliffe, 1993; Shaw, 1993). Growth regulation of rapidly growing vegetable transplants during greenhouse pro-duction is a common problem, especially in the southern U.S. climate. Due to restrictions on using chemical growth regulators on vegetable transplants, developing alternative methods of prac-tical growth control during transplant production is necessary. Growers presently are limited to manipulating temperature or restricting water or fertilizer to control transplant growth. The purpose of conditioning greenhouse-grown transplants is to control plant growth in a manner that does not reduce the subsequent growth potential of the plant (Latimer, 1990). Ideally, the conditioning treatments would also improve transplant estab-lishment or stress tolerance in the field or final crop yield. How-ever, acceptance of the conditioning treatment for greenhouse-grown vegetable transplants depends only on the effectiveness of the growth regulation without a negative impact on subsequent plant performance. Moisture stress conditioning (MSC), the con-trolled exposure of plants to nonlethal moisture deficits (Eakes et al., 1991), has been moderately successful as an alternative to daminozide for managing the growth of tomato (Lycopersicon esculentum L.) transplants (Latimer, 1992). Mechanical condi-tioning is a nonchemical means of controlling growth that im-proves plant strength (Heuchert et al., 1983) and overall transplant quality (Latimer, 1991). Brushing effectively controlled growth of commercially grown tomato transplants (Latimer and Thomas, 1991), but growth and conditioning responses of many other crops are unknown. With growing interest in brushing as a mechanical means of controlling height during greenhouse transplant production, our research objectives were to determine the responsiveness of cucur-bit species and cultivars to brushing or MSC and to evaluate the effectiveness of brushing or MSC in increasing the subsequent drought tolerance of the transplants. The following report de-scribes the effect of brushing or MSC on seedling growth in the greenhouse, dehydration resistance of leaves detached from con-ditioned plants, and shoot growth rate of plants grown under cyclic drought conditions after transplanting in the greenhouse. Prelimi-nary results of conditioning effects on subsequent yield of the cucurbit transplants grown in the field also are discussed.

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