s -(+)- abscisic acid is a naturally occurring plant hormone which acts primarily to inhibit growth , maintain dormancy of buds , promote fruit maturation or coloration , activate the defense response against pathogens , induce senescence , and help the plant tolerate stressful conditions . see arteca , r . ( 1996 ), plant growth substances : principles and applications . new york : chapman & amp ; hall ; mauseth , j . d . ( 1991 ), botany : an introduction to plant biology . philadelphia : saunders . pp . 348 - 415 ; raven , p . h ., evert , r . f ., and eichhorn , s . e . ( 1992 ), biology of plants . new york : worth . pp . 545 - 572 . s -(+)- abscisic acid owes its name to early studies with this plant growth regulator that showed abscission of leaves . the chemistry and physiology of abscisic acid and its analogs is described by milborrow , ann . rev . plant physiol . 1974 , 25 , 259 - 307 . the composition of the present invention may contain from about 0 . 01 to about 20 wt % aba or its salts and from about 0 . 01 to about 50 wt . % pbo . the applied concentration of aba or its salts can vary widely and is generally in the range of about 0 . 1 to about 5000 ppm , preferably from about 10 to about 1000 ppm and the concentration of pbo is generally in the range of about 0 . 1 to about 5000 ppm , preferably from about 10 to about 2000 ppm . as used herein , the term “ salt ” refers to the water soluble salts of aba or aba analogs or derivatives , as appropriate . representative such salts include inorganic salts such as the ammonium , lithium , sodium , potassium , calcium and magnesium salts and organic amine salts such as the triethanolamine , dimethylethanolamine and ethanolamine salts . as used herein the term “ stress ” refers to any environmental condition that could adversely effect a plant , as for example , drought , heat , cold , excess water or flooding . the following procedures are utilized in the illustrative examples that follow . cotton was planted and grown at 25 ° c . under a 16 : 8 photoperiod for 14 days . after two weeks , plants were moved to the greenhouse ( 25 ± 2 ° c ., 16 : 8 photoperiod ) for an additional three weeks before treatment . ornamental plants were purchased from local greenhouse retail outlets and allowed to equilibrate to greenhouse conditions for a minimum of 48 hours before experiments were performed . leaf transpiration rate was measured at times 5 , 24 , 48 , 72 or 96 hours after treatment using a li - 1600 steady state porometer ( li - cor , lincoln , nebr .). transpiration rate of each treatment was calculated as the percentage of that of control at each day to eliminate day - to - day variation caused by changes of environmental condition such as light intensity and temperature . to quantify resistance of plants to wilting , a wilt index was developed . the wilt index uses numerical values of 1 - 4 ( 1 = no wilt , 4 = completely wilted and loss of turgor ) to express wilt status . a wilt index was determined for each individual plant assessed daily . when the wilt index was equal to or exceeded 2 . 5 , the plant was considered not salable , and the last day prior to that was considered its last marketable day in cotton , aba , pbo and the combination were applied to evaluate the effect on stomatol conductance . a decrease in stomatal aperture , reflected in the conductance measures , is an immediate and direct effect of applied aba ( finkelstein and rock , 2002 ). in table 1 , plants were drenched treated with 10 percent of their volume ( 20 ml / pot ), and stomatal conductance was measured at the times indicated . drench treatments with 50 ppm aba were only effective at reducing stomatal conductance by 44 % or 22 . 5 % at 5 or 24 hours post drench treatments , respectively . only at 24 hours was the effect of aba drench significantly different than the control . treatments with pbo were not significantly different from the control , at any time point , although numeric decreases in stomatal conductance were observed . combinations with aba did not consistently increase aba activity , and did not statistically differ from the aba only treatment at any time point . in order to determine if spray treatments would be more effective , aba and pbo were spray applied to cotton , as is shown in table 2 . in contrast to the experiment shown in table 1 , pbo effectively reduced stomatal conductance in a dose - dependent manner when spray applied . aba sprays were faster acting than drench treatments , with a significant ( 58 . 9 %) decrease in stomatal conductance observed at 5 hours after spray application . the addition of pbo at 500 ppm to aba sprays significantly increased the effectiveness of the sprays as compared to aba alone . at 5 hours , the addition of pbo increased the effect of aba on stomatal conductance by 27 %. while aba did not significantly affect stomatal conductance at 24 or 48 hours after spraying , the addition of 500 ppm pbo significantly increased aba effectiveness at both times . pbo at 500 ppm alone was less effective at reducing stomal conductance than the combination with aba . in the ornamental plant impatiens , spray applications were made to evaluate the effects of aba , pbo or the combination to increase the number of days until the plants wilted . using a wilt index of 1 - 4 ( 1 = no wilt , 4 = completely wilted and loss of turgor ), plants were evaluated following spray application . as expected , aba application slowed and reduced incidence of wilting . pbo also resulted in a reduction of wilt intensity and slowed wilt incidence . the combination of aba and pbo was superior at controlling plant wilting than either agent alone . the slowing of wilt incidence by the treatments allowed for a comparison of marketability after treatment . when the wilt incidence was less than 2 . 5 , the treated plants were considered saleable . the duration of salability was determined for individual plants and the values averaged ( table 4 ). * days marketable was determined for each individual plant assessed daily . when the wilt index was equal to or exceeded 2 . 5 , the plant was considered not salable , and the last day prior to that was considered its last marketable day . similar to the study shown in table 3 , aba application significantly slowed plant wilting , providing an almost two day increase in shelf life without watering . pbo application resulted in a significant benefit in wilt control over the control spray treatments , although not as good as observed with aba in this study . the combination of aba and pbo was superior to either treatment alone , but was not significantly different from aba using an anova and p = 0 . 05 . a student &# 39 ; s t test showed the difference between the treatments at p = 0 . 06 , indicating that the two means are different , and a difference would be observed in greater than 9 of 10 tests . to better determine the effectiveness of pbo on aba effectiveness , a spatial separation in application methodology was used . that is , water or aba were drench applied at 10 % of the pot volume , followed by a spray application to the foliage of tween 20 ( 0 . 05 %) in water , either alone , or in combination with 1000 ppm pbo . * days marketable was determined for each individual plant assessed daily . when the wilt index was equal to or exceeded 2 . 5 , the plant was considered not salable , and the last day prior to that was considered its last marketable day . the results of the study in table 5 demonstrate that aba and pbo applications are additive for increasing marketable shelf life , even when the applications are made to separate plant tissues . in table 6 , the rate of aba in the drench application is varied in order to determine the effect of pbo sprays on aba rate . * days marketable was determined for each individual plant assessed daily . when the wilt index was equal to or exceeded 2 . 5 , the plant was considered not salable , and the last day prior to that was considered its last marketable day . as shown in the study in table 6 , pbo was additive to aba application , irrespective of aba rate . pbo sprays alone were equal to 50 ppm aba in increasing marketable life of impatiens , while the combination of pbo with 50 ppm aba was statistically equal to a 200 ppm aba drench . the effect of pbo on aba drenches for increasing the market life of impatiens is additive . to determine if the combination of aba and pbo is effective at increasing marketable life of other ornamental plants , viola plants ( violet ) were used . all applications were made by spray to fully hydrated plants . spray solutions were applied as soon as possible after mixing . all spray applications contained tween 20 at 0 . 05 % ( v / v ). * days marketable was determined for each individual plant assessed daily . when the wilt index was equal to or exceeded 2 . 5 , the plant was considered not salable , and the last day prior to that was considered its last marketable day . although pbo and aba were separately able to significantly increase the marketable life of viola , the combination was not significantly superior to aba alone . this finding demonstrates the utility of pbo alone as an anti - wilting compound on violets . moreover , the addition of pbo to the aba spray solution increased the marketable life by nearly half a day . to determine if the aba , pbo , or the combination of aba and pbo is effective at increasing marketable life of other ornamental plants , pansy plants were used . all applications were made by spray to fully hydrated plants . solutions were applied as soon as possible after mixing . all spray applications contained tween 20 at 0 . 05 % ( v / v ). plants were held in a greenhouse without further irrigation . * days marketable was determined for each individual plant assessed daily . when the wilt index was equal to or exceeded 2 . 5 , the plant was considered not salable , and the last day prior to that was considered its last marketable day . although pbo and aba were separately able to significantly increase the marketable life of pansy , the combination was not significantly superior to aba alone . this finding demonstrates the utility of pbo alone as an anti - wilt compound on pansy .
the present invention is directed to the use of piperonyl butoxide , alone or with s -- abscisic acid or its salts to minimize stress to plants .