Burns, Jackie :

Abscission compound screening Introduction and scope Olive abscission compound screening trials were conducted at three locations in Central California from mid September to mid November , 2006 . The objective of these trials was to determine if compounds , previously shown to loosen mature Florida citrus fruit when applied to canopies ( Burns et al , 2006 ; Burns et al , 2005 ; Pozo et al , 2004a ; Burns et al , 2003a ; Hartmond et al , 2000 ) , would accelerate olive fruit abscission . The long - term goal of this project is to adapt table olives to mechanical harvesting . Identification of a suitable abscission agent is viewed as a key to industry adoption of mechanical harvesting , as mechanical harvesting could be performed less aggressively and fruit damage could be minimized . George Martin and others ( eg Denney and Martin 1994 ) have worked extensively in this area and focused primarily on ethylene - releasing compounds . Conclusions 1 . Fifteen abscission compounds or effectors were screened alone or in combination . 2 . Compounds releasing ethylene or inducing ethylene biosynthesis loosened olive fruit . However , these compounds also caused moderate defoliation . 3 . Components of â?? Harvaid â?? loosened olive fruit but also caused moderate defoliation . 4 . Additional work must focus on managing application of these agents to maximize fruit loosening but minimize unwanted leaf loss . Materials , methods and results Kearney Agricultural Center trials Trials were initiated on 4 separate dates in late September to mid October 2006 . Three uniform olive trees with adequate fruit load were selected within a block of trees located at the northeast corner of the Kearney Agricultural Center , Parlier , CA . Overall , yield was low in this block , but trees appeared to receive normal horticultural care for the crop load present . For each trial , six replicate branches were selected for each treatment . Each branch contained at least 8 fruit and 25 leaves . Treatments were randomly assigned to the branches , and the number of fruit on each branch was recorded . Abscission compounds were dissolved in water containing 0.05 % Kinetic organosilicate adjuvant . A water control containing adjuvant was included in all trials . Treatments were applied between 10 : 30 am and 2 : 00 pm with a hand - held 1.5L pressurized sprayer until run - off . Fruit detachment force ( FDF ) in grams - force was measured 7 or 12 days after application using an Imada DPS - 11 digital force gauge . Treatment branches were removed and brought to the laboratory . Olive fruit were clipped from branches to include at least 1 cm pedicel , inserted into the gauge , and the pedicel pulled parallel to the fruit axis until it separated from the fruit . The force necessary to remove fruit from the pedicel was measured in grams - force . Percentage fruit drop was computed by counting the number of fruit that dropped from the branch , dividing by the total number of fruit at the beginning of the trial , and multiplying by 100 . Data were analyzed as a completely randomized design . Analysis of variance and Duncanâ??s mean separation were used to test significance and display means . Percentage data were transformed using arcsin transformation when necessary to stabilize variance . Trial 1 . On September 21 , 2006 , a trial was initiated using methyl jasmonate ( 2 , 10 and 20 mM ) and a Valent BioSciences proprietary compound VBC 20050 ( 200 , 1000 and 2000 ppm ) . Maximum , minimum and average temperatures on the day of application were 85 , 54 and 69 ºF , respectively . On October 3 , 2006 , FDF and % fruit drop were measured . After 12 days FDF and % fruit drop were no different than the control ( table 1 ) . Maximum , minimum and average temperatures for the duration of the trial were 83 , 53 and 67 ºF , respectively . Trial 2 . On September 25 , 2006 , a trial was initiated using MAXCEL ( 200 , 1000 and 2000 ppm ) , VBC 30069 ( 500 and 1000 ppm ) , and coronatine ( 200 ppm ) . Maximum , minimum and average temperatures on the day of application were 92 , 48 and 69 ºF , respectively . On October 7 , 2006 , FDF and % fruit drop were measured . After 12 days , FDF in all treatments were no different than the control , but significantly more fruit dropped when VBC 30069 was used ( table 2 ) . Maximum , minimum and average temperatures for the duration of the trial were 79 , 52 and 65 ºF , respectively . Trial 3 . On September 27 , 2006 , a trial was initiated using traumatic acid ( 1000 ppm ) , Ethrel ( 500 and 1000 ppm ) , and traumatic acid + Ethrel ( 1000 + 1000 ppm ) . Maximum , minimum and average temperatures on the day of application were 90 , 53 and 69 ºF , respectively . On October 9 , 2006 , FDF and % fruit drop were measured . Ethrel at 1000 ppm significantly reduced FDF compared to the control ( table 3 ) . Combining traumatic acid with Ethrel numerically reduced FDF , but loosening was no different than the control . Significantly more fruit dropped in all Ethrel treatments . More fruit dropped when 1000 ppm Ethrel was used alone or in combination with traumatic acid . Excessive leaf drop was noted in Ethrel treatments exceeding 500 ppm . Maximum , minimum and average temperatures for the duration of the trial were 78 , 52 and 64 ºF , respectively . Trial 4 . On October 8 , 2006 , a trial was initiated using VBC 30030 ( 1000 ppm ) , VBC 30030 + Ethrel ( 1000 + 1000 ppm ) , dikegulac ( 200 , 1000 and 2000 ppm ) , and 5 - chloro - 3 - methyl - 4 - nitro - 1H - pyrazole ( CMNP ; 1000 and 2000 ppm ) . Maximum , minimum and average temperatures on the day of application were 78 , 49 and 62 ºF , respectively . On October 15 , 2006 , FDF and % fruit drop were measured . No differences were seen in FDF or % fruit drop between any treatments ( table 4 ) . Increased time from application to analysis may be needed to improve efficacy of these compounds . Maximum , minimum and average temperatures for the duration of the trial were 78 , 52 and 64 ºF , respectively . Lindcove Research and Extension Center trials A trial was initiated on October 11 , 2006 in a block of olive trees located on the north perimeter of the Lindcove Research and Extension Center , Exeter , CA . The purpose of this trial was as stated above , and to provide another geographic location for screening . Three uniform â?? Manzanillo â?? trees with good fruit load were selected , and 4 replicate branches for each treatment were tagged . Fruit number was recorded . Treatments were randomly assigned to the branches . Abscission compounds were dissolved as indicated and applied between 9 : 00 am and 12 : 30 pm . Applications were made as described above . Treatments were Ethrel ( 750 , 1125 and 1500 ppm ) with and without 5 mM 1 - methylcyclopropene ( 1 - MCP ) or 2 mM guanfacine . 1 - MCP and guanfacine were selected to mitigate Ethrel - induced leaf loss ( Pozo et al , 2004b ; Burns et al , 2003b ) . 1 - MCP and guanfacine controls were included . Maximum , minimum and average temperatures on the day of application were 77 , 44 and 61 ºF , respectively . On October 18 , it was decided that efficacy and leaf drop could not be adequately evaluated because of excessive shrivel in treatment trees . Visual assessment indicated little or no fruit loosening or leaf drop . Maximum , minimum and average temperatures for the duration of the trial were 74 , 49 and 61 ºF , respectively . Tehama trials A trial was initiated on October 24 , 2006 , in a commercial olive orchard located in Tehama north of Corning , CA . In two rows , 47 uniform â?? Manzanillo â?? trees were selected and treatments randomly assigned . Fifteen treatments were applied to three trees each , whereas two treatments were applied each to a single tree because of lack of material . All spray treatments included 0.05 % Silwet adjuvant . Spray applications were done using a pressurized hand - gun until run - off . Treatments were Ethrel ( 500 , 1000 , 1500 and 2000 ppm ) , Ethrel + 1 - MCP ( 1000 ppm + 5 mM , 1500 ppm + 5 mM , and 2000 ppm + 5 mM ) , 5 mM 1 - MCP , VBC 30069 ( 500 , 1000 and 2000 ppm ) , 4 % MPK with and without 1000 ppm Ethrel , 50 ppm MAXCEL + 500 ppm VBC 30069 ( single tree ) , 500 ppm VBC 30050 + 500 ppm VBC 30069 ( single tree ) , a water control and an untreated control . Maximum , minimum and average temperatures on the day of application were 86 , 46 and 63 ºF , respectively . After 3 , 6 , 10 , 13 and 17 days following application , a representative branch from each replicate tree was removed . In the case of single tree applications , three representative branches were removed . Each branch contained at least 8 fruit and numerous leaves . Branches were transported to the Glenn County Cooperative Extension Office in Orland . FDF was determined as described above . Defoliation was evaluated in the orchard using a subjective leaf abscission score of 0 ( no defoliation ) , 1 ( light defoliation ) , 2 ( moderate defoliation ) , and 3 ( severe defoliation , greater than 50 % canopy volume ) . Maximum , minimum and average temperatures for the duration of the trial were 74 , 49 and 61 ºF , respectively . No significant difference was measured between the untreated , adjuvant and 1 - MCP control treatments , so these values were pooled ( data not shown ) . Ethrel reduced FDF over the 17 day evaluation period ( figure 1 ) . Application of 1500 and 2000 ppm reduced FDF greater than 50 % of the control . VBC 30069 was also effective , especially at concentrations of 1000 and 2000 ppm . However , both compounds increased defoliation as time after application increased , especially at the highest concentrations . When 500 and 1000 ppm of Ethrel and VBC 30069 were compared , greater reduction in FDF occurred with VBC 30069 17 days after application ( figure 2 ) . At 2000 ppm , however , both compounds reduced FDF similarly . Little difference in leaf abscission score was measured when Ethrel and VBC 30069 were compared at similar concentrations . No change in FDF or leaf abscission score was measured when trees were sprayed with MAXCEL + VBC 30069 or VBC 30050 + VBC 30069 ( data not shown ) . However , color change likely associated with anthocyanin production was noted where excess spray pooled on the blossom end of fruit . MPK at 4 % had little effect on FDF or defoliation ( figure 3 ) . Similar reduction in FDF was measured when 1000 ppm Ethrel was compared with 1000 ppm Ethrel + 4 % MPK . However , FDF was lower after 17 days when trees were sprayed with Ethrel + MPK . Ethrel and Ethrel + MPK increased the leaf abscission score in a similar fashion . 1 - MCP was used in an attempt to reduce Ethrel - induced defoliation . At 1000 and 1500 ppm Ethrel , combining 1 - MCP in the spray tank had little effect on Ethrel - induced reduction in FDF , but defoliation was delayed ( figure 4 ) . Although defoliation was delayed and reduced with 2000 ppm Ethrel + 1 - MCP compared with 2000 ppm Ethrel alone , Ethrel - induced fruit loosening was negatively impacted . After 17 days , however , FDF was similar in both treatments . A final evaluation was performed 24 days after application in all treatments . In all cases , FDF either did not change or began to increase ( data not shown ) . This increase is viewed as a re - tightening of a partially loosened abscission zone as a process of wound healing occurs . Maximum , minimum and average temperatures for the duration of the trial were 68 , 44 and 55 ºF , respectively . Although we do not know the full impact of temperature in trials reported herein , lower temperatures are expected to reduce efficacy ( Yuan and Burns , 2004 ) . Warmer temperatures at the time of application and through the duration of trials may increase efficacy and reduce the time necessary to achieve adequate loosening . Literature cited Burns JK , Roka FM , Li KT , Pozo L , Buker RS ( 2006 ) Late season â?? Valencia â?? orange mechanical harvesting with an abscission agent and low frequency harvesting . HortSci 41 : 660 - 663 . Burns JK , Buker RS , Roka FM ( 2005 ) Mechanical harvesting capacity in sweet orange is increased with an abscission agent . HortTechnol 15 : 758 - 765 . Burns JK , Pozo LV , Arias CR , Hockema B , Rangaswamy V , Bender C ( 2003a ) Coronatine and abscission in citrus . J Amer Soc Hort Sci 128 : 309 - 315 . Burns JK , Pozo LV , Yuan R , Hockema B ( 2003b ) Guanfacine and clonidine reduce defoliation and phytotoxicity associated with abscission agents . J Amer Soc Hort Sci 128 : 42 - 47 . Denney JO , Martin GC ( 1994 ) Ethephon tissue penetration and harvest effectiveness in olive as a function of application time , and BA or NAA addition . J Amer Soc Hort Sci 119 : 1185 - 1192 . Hartmond U , Yuan R , Burns JK , Grant A , Kender WJ ( 2000 ) Citrus fruit abscission induced by methyl jasmonate . J Amer Soc Hort Sci 125 : 547 - 552 . Pozo L , Redondo A , Hartmond U , Kender WJ , Burns JK ( 2004a ) â?? Dikegulac â?? promotes abscission in citrus . HortSci 39 : 1655 - 1658 . Pozo L , Yuan R , Kostenyuk I , Alferez F , Zhong GY , Burns JK ( 2004b ) Differential effects of 1 - methylcyclopropene on citrus leaf and mature fruit abscission . J Amer Soc Hort Sci 129 : 473 - 478 . Yuan R , Burns JK ( 2004 ) Temperature factor affecting the abscission response of mature fruit and leaves to CMN - pyrazole and ethephon in â?? Hamlin â?? oranges . J Amer Soc Hort Sci 129 : 287 - 293 . Table 1 . Abscission compound screening trial applied on 9 - 21 - 06 at the Kearney Agricultural Center , Parlier , CA . Compounds were applied to six replicate branches . Fruit detachment force ( FDF in grams - force ) and % fruit drop were evaluated 12 days after application . Compounds evaluated were methyl jasmonate and VBC 30050 at the concentrations indicated , and a water control . All treatments contained 0.05 % Kinetic . No significant differences in FDF or % fruit drop were found between treatments . treatment FDF ( g - force ) % fruit drop control 466 4.6 methyl jasmonate 2 mM 461 3.4 10 mM 437 4.8 20 mM 488 4.0 VBC 30050 200 ppm 439 3.1 1000 ppm 453 4.8 2000 ppm 427 3.3 Table 2 . Abscission compound screening trial applied on 9 - 25 - 06 at the Kearney Agricultural Center , Parlier , CA . Compounds were applied to six replicate branches . Fruit detachment force ( FDF in grams - force ) and % fruit drop were evaluated 12 days after application . Compounds evaluated were MAXCEL , VBC 30069 and coronatine at the concentrations indicated , and a water control . All treatments contained 0.05 % Kinetic . treatment FDF ( g - force ) % fruit drop * control 555 3.5 c MAXCEL 200 ppm 515 3.2 c 1000 ppm 512 0.0 c 2000 ppm 525 3.2 c VBC 30069 500 ppm 515 28.4 b 1000 ppm 561 54.3 a Coronatine 200 ppm 538 1.5 c * Means followed by the same letter are not significantly different , P < 0.05 . Table 3 . Abscission compound screening trial applied on 9 - 27 - 06 at the Kearney Agricultural Center , Parlier , CA . Compounds were applied to six replicate branches . Fruit detachment force ( FDF in grams - force ) and % fruit drop were evaluated 12 days after application . Compounds evaluated were traumatic acid , Ethrel and traumatic acid + Ethrel at the concentrations indicated , and a water control . All treatments contained 0.05 % Kinetic . treatment FDF ( g - force ) * % fruit drop * control 490 a 2.5 c Traumatic acid ( TA ) 1000 ppm 431 a 0.0 c Ethrel 500 ppm 436 a 12.9 b 1000 ppm 342 b 46.4 a TA + Ethrel 1000 + 1000 ppm 394 ab 44.9 a * Means followed by the same letter are not significantly different , P < 0.05 . Table 4 . Abscission compound screening trial applied on 10 - 8 - 06 at the Kearney Agricultural Center , Parlier , CA . Compounds were applied to six replicate branches . Fruit detachment force ( FDF in grams - force ) and % fruit drop were evaluated 7 days after application . Compounds evaluated were VBC 30030 , VBC 30030 + Ethrel , dikegulac and 5 - chloro - 3 - methyl - 4 - nitro - 1H - pyrazole ( CMNP ) at the concentrations indicated , and a water control . All treatments contained 0.05 % Kinetic . No significant differences in FDF or % fruit drop were found between treatments . treatment FDF ( g - force ) % fruit drop control 525 2.8 VBC 30030 1000 ppm 524 3.7 VBC 30030 + Ethrel 1000 + 500 ppm 483 4.2 Dikegulac 200 ppm 468 0.0 1000 ppm 506 1.3 2000 ppm 439 2.6 CMNP 1000 ppm 469 0.0 2000 ppm 487 0.0 Figure 1 . The effect of various concentrations of Ethrel and VBC 30069 on fruit detachment force ( FDF in grams - force , upper panels ) and leaf abscission score ( 0 , no abscission ; 3 , severe abscission , lower panels ) in olive . Trial was initiated on October 24 , 2006 in Tehama , CA . Data plotted are the means + SE . Figure 2 . A comparison of equivalent concentrations of Ethrel and VBC 30069 on fruit detachment force ( FDF in grams - force , upper panels ) and leaf abscission score ( 0 , no abscission ; 3 , severe abscission , lower panels ) in olive . Trial was initiated on October 24 , 2006 in Tehama , CA . Data plotted are the means + SE . Figure 3 . The effect of 4 % MPK 1000ppm Ethrel , and 4 % MPK + 1000 ppm Ethrel on fruit detachment force ( FDF in grams - force , left panel ) and leaf abscission score ( 0 , no abscission ; 3 , severe abscission , right panel ) in olive . Trial was initiated on October 24 , 2006 in Tehama , CA . Data plotted are the means + SE . Figure 4 . The effect of various concentrations of Ethrel and Ethrel + 5 mM 1 - MCP on fruit detachment force ( FDF in grams - force , left panel ) and leaf abscission score ( 0 , no abscission ; 3 , severe abscission , right panel ) in olive . Trial was initiated on October 24 , 2006 in Tehama , CA . Data plotted are the means + SE .