Scientia Horticulturae

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1 Scientia Horticulturae 192 (2015) Contents lists available at ScienceDirect Scientia Horticulturae journal h om epage: Optimising crop load and fruit quality of Packham s Triumph pear with ammonium thiosulfate, ethephon and 6-benzyladenine Sally A. Bound Perennial Horticulture Centre, Tasmanian Institute of Agriculture, University of Tasmania, Private Bag 98, Hobart, TAS 7001, Australia a r t i c l e i n f o Article history: Received 3 February 2015 Received in revised form 25 May 2015 Accepted 28 May 2015 Keywords: BA ATS Flesh firmness Thinning Crop regulation European pear TSS a b s t r a c t Trials were conducted at Nubeena in Tasmania (Australia) over a two year period to develop chemical thinning programs for the European pear cultivar Packham s Triumph and to assess the impact of thinning chemicals on fruit quality. Chemicals examined were 80 mgl 1 ethephon and 1.0% v/v ammonium thiosulphate (ATS) applied during the bloom period, and 6-benzyladenine (BA) applied at 100 or 150 mgl 1 from 10 to 40 days after full bloom (dafb). The desiccating agent ATS was an effective bloom thinner, and two applications at 25% and 80% bloom stage would be recommended. The post-bloom thinner BA was a consistent thinner of Packham s Triumph, and can be applied as early as 10 dafb to as late as 40 dafb as a post-bloom thinner after a bloom application of either ethephon or ATS. BA was also an effective thinner when used alone. Two applications of BA did not increase the thinning effect. All chemicals examined maintained or improved fruit quality measured as size, flesh firmness and total soluble solids content, but ATS caused a slight increase in skin russet. BA ameliorated the russeting effect of ATS Elsevier B.V. All rights reserved. 1. Introduction Thinning is one of the major cultural practices influencing yield and fruit quality in pome fruit production. While the principles of pome fruit thinning have been described by Jones et al. (1998) and there are recommendations available for chemical thinning of many apple cultivars, there is little information available on chemical thinning programs for pears. Pear trees can crop well from an early age (van Heek and Issell, 1973), and under Australian conditions pears are much harder to thin with chemicals than apples with cultivars varying in response to thinning agents (Menzies, 1973). Unless properly understood the use of chemical thinners may lead to either over-thinning or under-thinning, either of which represents a commercial risk. The non-availability of reliable thinning programs has resulted in chemical thinning being abandoned by many growers and the resulting high cost for hand thinning is one of the factors limiting the size of the industry in Australia. Hence, the development of recommendations for effective chemical thinning of pear cultivars will result in lower production costs, better fruit quality and increased returns. The move away from a reliance on hand thinning should enable expansion of the industry by removing one of the current limiting factors. Corresponding author. Tel.: address: Sally.Bound@utas.edu.au Early work with ethephon (2-chloroethyl phosphonic acid) on pears gave very unpredictable results. Selimi and Gibbs (1976) experienced either very little thinning or removed practically all the fruit, depending on timing. Later work by Selimi and Gibbs (1978) on Williams Bon Chretien showed that 300 mgl 1 ethephon did thin but 150 mgl 1 did not when applied later than 21 days after blossom. Blossom sprays of ethephon have however, been shown to be more effective than later applications in Winter Cole pear (Bound et al., 1991a). Work with apples has shown that the unpredictable thinning experienced with ethephon was due to poor understanding of the chemical. Timing, particularly early application, was shown to be vital to success (Jones et al., 1992). Jones and Koen (1985) also demonstrated that ethephon was temperature responsive, with increased thinning at higher temperatures. The desiccant ammonium thiosulphate (ATS) has been reported to reduce fruit set in Packham s Triumph (Bound and Mitchell, 2002a) and Conference pear (Maas et al., 2010), but had no effect on the cultivar Clara Frijs (Bertelsen, 2002). In the Pacific Northwest of USA, Schmidt et al. (2011) reported that ATS reduced fruit set to a greater extent than lime sulphur, naphthalene acetic acid (NAA) or urea in 20 pear thinning trials. The synthetic cytokinin, 6-benzyladenine (BA) [N- (phenylmethyl)-1h-purine-6-amine], has shown promise as a post-bloom thinner in several pear cultivars (Bertelsen, 2002; Bound and Mitchell, 2002b; Stern and Flaishman, 2003; Vilardell et al., 2005; Dussi et al., 2008; Dussi and Sugar, 2011; Schmidt / 2015 Elsevier B.V. All rights reserved.

2 188 S.A. Bound / Scientia Horticulturae 192 (2015) et al., 2011; Theron et al., 2011). When applied at the correct time BA is a more consistent thinner of apple than carbaryl (Greene and Autio, 1994). It has no detrimental effects on mite predators (Thistlewood and Elfving, 1992; Elfving and Cline, 1993) and has a low toxicity to mammalian and arthropod species (Thistlewood and Elfving, 1992). Unlike carbaryl, BA is not a persistent chemical and is more likely to meet modern environmental and food quality guidelines. There is limited information on the effect of chemical thinners on pear fruit quality. Most studies on the impact of thinning chemicals on fruit quality have been on apples (Byers, 1997; Bound, 2001; Ferree and Schmid, 2001; Bound and Wilson, 2007). However, McArtney and Wells (1995) reported that ethephon applied 15 days after full bloom at relatively high concentrations (400 mgl 1 ) hastened fruit maturity and reduced the storage quality of pears. These authors also demonstrated that high concentrations of ethephon depressed fruit size compared with trees hand thinned to the same crop load. The aim of this study was to further develop the work undertaken with ATS and BA by Bound and Mitchell (2002a,b) in order to develop chemical thinning programs for the European pear cultivar Packham s Triumph (Packham) and to assess the impact of these chemicals on fruit quality. 2. Materials and methods Five trials were conducted on mature (21 22 year old) regular bearing vase shaped Packham s Triumph pear trees at Nubeena in Tasmania over two consecutive seasons. The thinning chemicals assessed in this work were ethephon (48% a.i., Rhone Poulenc), ATS (782 g L 1 ATS, registered as Culminate by Ferro Corporation (Australia) Pty. Limited), and BA (20 g L 1 6-benzyladenine, registered as CyLex by Valent BioScience) Trial establishment A randomised complete block design was used for all trials with single tree plots blocked on blossom density. Trunk girths were measured on all trial trees in late September of each season and trunk cross-sectional areas (TCSA) were calculated. Blossom clusters were counted and blossom density (number of blossoms cm 2 TCSA) determined. Within each trial, plots were blocked into groups with similar blossom density and treatments allocated at random within each block. Trial 1 examined the time of application and concentration of BA following an initial ethephon treatment which was applied at 80 mgl 1 at full bloom (FB) to all trees in the trial. This was then followed by a single application of 100 or 150 mgl 1 BA, at 10, 15, 20, 25, 30 or 35 days after full bloom (dafb). An ethephon control (no BA) and an untreated control were also included (Table 1). Treatments were allocated across four blocks, giving four replicates per treatment. Trial 2 assessed the effect of two applications of BA. As for trial 1, ethephon was applied at FB to all trees at the rate of 80 mgl 1. Two applications of 100 mgl 1 BA were applied at either 10 and 25 dafb or 20 and 35 dafb. To enable comparison between double and single applications, additional treatments included a single BA application at 10, 20, 25 or 35 dafb. An ethephon control and an untreated control were also included. Treatments were allocated across four blocks, giving four replicates per treatment. Trial 3 examined the effect of BA applied with or without a primary thinner (ethephon). BA was applied at the rate of 100 mgl 1 at 10, 25 or 40 dafb with or without a prior application of ethephon at FB. An unsprayed control treatment was included. The seven treatments were allocated at random within each block, forming 5 single tree replicates per treatment. Trial 4 examined the impact of concentration and number of ATS applications. ATS was applied at three rates (0.7, 1.0 or 1.3% v/v) either twice at 50 and 80% bloom, or three times (50 and 80% bloom and 5 dafb). The third application time was scheduled for 3 dafb, however, inclement weather delayed this application until 5 dafb. An unsprayed control treatment was included to give seven treatments allocated at random within each block, forming 5 single tree replicates per treatment. Trial 5 assessed the effect of BA applied as a post-bloom thinner following one or two applications of ATS at flowering. ATS was applied at 1.0% v/v either once at 25% bloom or twice at 25 and 80% bloom, with or without 100 mgl 1 BA applied 25 dafb. An unsprayed control treatment was included and the five treatments were allocated at random within each block, forming 5 single tree replicates per treatment. All trial trees were subjected to the normal orchard management practices, including commercial spray programs, with the exception of thinning chemicals. Trees in trials 1, 2 and 4 were hand thinned 8 weeks after FB following completion of fruit set counts Treatment application All sprays were applied to drip point by hydraulic hand lance. The wetter Kendeen 20 (polyoxyethylene sorbitan monolaurate, Kendon Chemical & Manufacturing Co. Pty. Ltd.) was included at the rate of 1.25 ml L 1 with all applications Assessments For each trial, fruit set was assessed on each tree 8 weeks AFB and this data used to calculate two crop load variables: number of fruit per 100 blossom clusters and number of fruit cm 2 trunk cross-sectional area (TCSA) for each trial. Trials were harvested 24 weeks AFB, in line with normal commercial practices. At harvest, all fruit was picked and the number and total weight recorded for each individual tree; mean fruit weight was calculated for each tree. A random sample of 100 fruit per tree was graded for size and the percentage of fruit 180 g or larger was determined as a measure of fruit size. In trials 3 and 5, the 100 fruit sample was also visually assessed for skin finish (russet) after size grading, with a three point scale used to determine the amount of russet: 1. Slight (<5%); 2. Moderate (5 10%); and 3. Severe (>10%). In all trials, a second sub-sample of 30 randomly selected fruit from each tree was examined for seed numbers, flesh firmness, and total soluble solids (TSS). Flesh firmness was measured on pared flesh with a Mecmesin AFG250 force gauge fitted with an Effegi 11 mm penetrometer probe. Juice expressed from the fruit during the firmness measurements was collected and TSS assessed with an Atago PR-1 digital refractometer. The pears were sliced horizontally through the core and the number of viable seeds counted. In trials 3 and 5, the calyx end half of each fruit was dipped in iodine solution and the six point index for the starch staining pattern as described by Little (1999) used to determine the amount of starch present in the fruit. The higher the starch index the lower the percentage of starch present. Return bloom was assessed in trials 1, 2 and 4 in the spring following treatment and related to tree size by expressing the data as number of blossom clusters cm 2 TCSA Data analysis Data was subjected to analysis of variance using Genstat 12.1 (VSN International Ltd). Main effects and interactions were ana-

3 S.A. Bound / Scientia Horticulturae 192 (2015) Table 1 Treatments applied in trials 1, 2 and 3. Trial 1 (season 1) Trial 2 (season 1) Trial 3 (season 2) Untreated control Untreated control Untreated control 80 mgl 1 ethephon at FB (E) 80 mgl 1 ethephon at FB (E) 100 mgl 1 BA at 10 dafb E mgl 1 BA at 10 dafb E mgl 1 BA at 10 dafb 100 mgl 1 BA at 25 dafb E mgl 1 BA at 10 dafb E mgl 1 BA at 20 dafb 100 mgl 1 BA at 40 dafb E mgl 1 BA at 15 dafb E mgl 1 BA at 25 dafb E mgl 1 BA at 10 dafb E mgl 1 BA at 15 dafb E mgl 1 BA at 35 dafb E mgl 1 BA at 25 dafb E mgl 1 BA at 20 dafb E mgl 1 BA at 10 and 25 dafb E mgl 1 BA at 40 dafb E mgl 1 BA at 20 dafb E mgl 1 BA at 20 and 35 dafb E mgl 1 BA at 25 dafb E mgl 1 BA at 25 dafb E mgl 1 BA at 30 dafb E mgl 1 BA at 30 dafb E mgl 1 BA at 35 dafb E mgl 1 BA at 35 dafb BA = 6-benzyladenine; FB = full bloom; dafb = days after full bloom. lysed, and appropriate orthogonal contrasts were examined for each data set. Data are presented as mean values for each treatment combination. Treatment means were compared using Fishers protected LSD. Unless specified, all results quoted as significant are at probability level of Where appropriate, regression analyses were performed and significant treatment effects plotted using Sigmaplot for Windows Version Results 3.1. Trial 1: (Ethephon and BA) Ethephon alone had no effect on crop load (number of fruit cm 2 TCSA or number of fruit per 100 blossom clusters) compared with the untreated control (Table 4). However, application of BA reduced crop load by approximately 50%. There was no effect on mean fruit weight or size, or on return bloom (results not presented). Compared with the untreated control, ethephon treatment resulted in higher fruit flesh firmness (Table 4); but there was no additional effect following application of BA. Application of BA significantly increased fruit soluble solids content compared with the untreated control. Seed number was not affected by either ethephon or BA treatments (results not presented). Concentration of BA had no effect on crop load, mean fruit weight, size, flesh firmness or return bloom (results not presented), but TSS increased with increasing concentration of BA (R 2 = 0.93) (Fig. 1). There were no significant interactions between BA concentration and application time for crop load or fruit quality Trial 2: (Double BA applications) Application of BA reduced crop load by approximately 50% (Table 5), however, two applications of BA gave no further thinning effect over one application. Fruit soluble solids content, flesh firmness and seed number were higher with BA application (Table 2), however, two applications did not show any improvement over one application. Compared with treatments without BA, neither one or two applications of BA had any effect on mean fruit weight or return bloom (data not presented). Examining the individual treatment differences, ethephon had no effect on crop load, fruit TSS or seed number compared with the untreated control, however, it did increase flesh firmness (Table 5(ii)). Compared with the ethephon only treatment, addition of BA reduced crop load at all application times, both single and double. In the single BA application treatments there were no significant differences between the various application times for most variables examined, nor were there any differences between the 10 and 35 or 20 and 35 dafb double applications with the exception of TSS. The 10 and 25 dafb treatment showed higher TSS than the corresponding 10 or 25 dafb single applications; while the 20 and 35 dafb treatment was lower in TSS than the corresponding single applications Trial 3: (Effect of BA with or without ethephon as a primary thinner) All treatments reduced crop load and improved mean fruit weight and fruit size (Table 6). The inclusion of ethephon as a blossom thinner prior to the application of BA had no additional effect on either crop load or on fruit weight or size. Regression analysis of BA application time showed a significant linear increase in thinning effect (reduction in crop load) following application of BA from 10 to 40 dafb (Fig. 2). Both mean fruit weight and size also decreased with later application times of BA (Fig. 3). There were no significant interactions between treatment regime and BA application time for crop load, fruit weight or size (results not presented). Fruit quality was affected by both ethephon and BA (Table 7). Compared with the untreated control, total soluble solids content was reduced in all treated fruit, but the BA alone treatments showed lower levels than ethephon followed by BA. Compared with the untreated control, flesh firmness was also reduced by all treatments, but BA alone increased flesh firmness compared with the ethephon plus BA treatments. Starch index was higher in the ethephon plus BA treatments. All treatments reduced seed number, but there was no difference between the two treatment regimes. Russet was higher in the ethephon plus BA treatments, but BA alone had no effect compared with the untreated control. While there were differences in fruit quality parameters with time of BA application (Table 7), there was no discernible pattern over time, with the exception of flesh firmness, which decreased with increasing time after full bloom. Application time had no effect on fruit russet. There were no significant interactions between regime and BA application time on TSS, flesh firmness, starch index, seed number, or russet index (results not presented) Trial 4: (Impact of concentration and number of applications of ATS) Treatment with ATS reduced crop load by approximately 40% (Table 8). There was a negative linear relationship between concentration of ATS and crop load (Fig. 4). Compared with the untreated control, application of ATS had no effect on mean fruit weight or fruit size (Table 8). Concentrations of 1.0 and 1.3% ATS resulted in heavier fruit and a greater percentage of fruit 180 g or larger than the 0.7% treatments. There were no significant interactions

4 190 S.A. Bound / Scientia Horticulturae 192 (2015) Table 2 Treatments applied in trials 4 and 5. Trial 4 (season 1) Trial 5 (season 2) Untreated control Untreated control 0.7% ATS at 50 and 80% bloom 1.0% ATS at 25% bloom 1.0% ATS at 50 and 80% bloom 1.0% ATS at 25% bloom mgl 1 BA 25 dafb 1.3% ATS at 50 and 80% bloom 1.0% ATS at 25 snd 80% bloom 0.7% ATS at 50 and 80% bloom and 5 dafb 1.0% ATS at 25 and 80% bloom mgl 1 BA 25 dafb 1.0% ATS at 50 and 80% bloom and 5 dafb 1.3% ATS at 50 and 80% bloom and 5 dafb ATS = ammonium thiosulphate; BA = 6-benzyladenine; FB = full bloom; dafb = days after full bloom. Table 3 Some climatological characteristics in the orchards on the treatment application dates. Chemical Blossom stage Date of application Max daily temperature Relative humidity a Cloud cover ( C) (%) (%) (i) Season 1 Trials 1, 2 and 3 ATS 50% bloom 27-September nil ATS 80% bloom 30-September Ethephon FB 30-September ATS 5dAFB 05-October nil BA 10 dafb 10-October BA 15 dafb 15-October BA 20 dafb 20-October nil BA 25 dafb 25-October BA 30 dafb 30-October BA 35 dafb 04-November (ii) Season 2 Trials 4 and 5 ATS 25% bloom 22-September ATS 80% bloom 25-September nil Ethephon FB 25-September BA 10 dafb 05-October nil BA 25 dafb 20-October BA 40 dafb 03-November nil ATS = ammonium thiosulphate; FB = full bloom; dafb = days after FB; BA = 6-benzyladenine. a Relative humidity taken at time of treatment application. between concentration of ATS and number of applications for crop load, fruit weight or size (results not presented). Fruit from treated trees showed reduced TSS content and seed number following ATS application (Table 9). Fruit firmness was higher in fruit treated with ATS. Both higher concentration of ATS and greater number of applications resulted in a greater reduction in seed number. A significant negative relationship (R 2 = 0.95) was observed between crop load and flesh firmness (Fig. 5). There were no significant interactions between ATS concentration and number of applications on TSS, flesh firmness or seed number (results not presented) Trial 5: (Impact of ATS and BA) Compared with the untreated control, all treatments reduced crop load and improved mean fruit weight and fruit size (Table 10). Fig. 1. The relationship between 6-benzyladenine (BA) concentration and total soluble solids content of fruit of Packham s Triumph pear (Trial 1).

5 S.A. Bound / Scientia Horticulturae 192 (2015) Table 4 The effect of (i) treatment regime, and (ii) application time of 6-benzyladenine (BA) on crop load, fruit soluble solids content and flesh firmness of Packham s Triumph pear (Trial 1). No. fruit cm 2 TCSA No. fruit per 100 blossom clusters Total soluble solids ( Brix) Flesh firmness (N) (i) Treatment regime Untreatedcontrol 4.8 b 82 b 13.5 a 52.9 a Ethephon a control 5.81 b 98 b 13.8 ab 71.5 b Ethephon + BA treated 2.46 a 46 a 13.9 b 70.6 b LSD (p = 0.05) (ii) Applicationtime of BA 10 dafb 2.98 bc 52 bc 13.6 b 67.6 a 15 dafb 1.53 a 30 a 14.9 e 73.5 b 20 dafb 2.13 ab 39 ab 14.1 cd 69.6 a 25 dafb 2.08 ab 42 ab 13.8 bc 75.5 b 30 dafb 3.65 c 72 c 12.9 a 67.6 a 35 dafb 2.38 ab 40 ab 14.4 d 68.6 a LSD (p = 0.05) Means with the same letter within each column and contrast set are not significantly different at the 5% level. TCSA = trunk cross-sectional area; dafb = days after full bloom. a 80 mgl -1 ethephon applied at full bloom. Table 5 The effect of single and double applications of the post-bloom thinner 6-benzyladenine (BA) on crop load and fruit quality parameters of Packham s Triumph pear (Trial 2). Treatment/contrast No. fruit cm 2 TCSA No. fruit per 100 blossom clusters Total soluble solids ( Brix) Flesh firmness (N) Average seed no. (i) Number of BA applications No BA 5.31 b 90 b 13.6 a 62.4 a 6.2 a Single BA application 2.6 a 47 a 14.2 b 70.9 b 6.7 b Multiple BA applications 2.32 a 43 a 13.8 a 73.6 b 6.1 a LSD (p = 0.05) (ii) Treatment interactions Control 4.8 bc 82 cd 13.5 b 52.9 a 5.8 a Ethephon a at FB (E) 5.81 c 98 d 13.8 b 71.5 c 6.4 ab E + BA b 10 dafb 3.48 ab 59 bc 12.9 a 65.7 b 7.3 c E + BA 20 dafb 2.7 a 51 ab 14.3 c 72.5 c 6.4 ab E + BA 25 dafb 1.69 a 34 a 13.7 b 79.4 d 6.1 a E + BA 35 dafb 2.51 a 43 ab 14.8 d 64.7 b 6.9 bc E + BA 10 and 25 dafb 2.51 a 47 ab 14.6 cd 75.4 cd 5.7 a E + BA 20 and 35 dafb 2.03 a 39 ab 13 a 71.5 c 6.3 ab LSD (p = 0.05) Means with the same letter within each column are not significantly different at the 5% level. TCSA = trunk cross-sectional area; dafb = days after full bloom. a Ethephon applied at 80 mgl 1. b BA applied at 100 mgl 1. Table 6 Comparison of thinning treatment regimeson crop load and fruit size of Packham s Triumph pear (Trial 3). No. fruit cm 2 TCSA No. fruitper 100 blossom clusters Mean fruit weight (g) % fruit 180 g or larger (i) Treatment regime contrasts Untreatedcontrol 4.75 b b 144 a 13 a 100 mgl 1 BA a 3.43 a 83.1 a 158 b 30 b Ethephon b + BA 3.44 a 83.1 a 164 b 38 b LSD (p = 0.05) Means with the same letter within each column are not significantly different at the 5% level. TCSA = trunk cross-sectional area. a BA applied at 10, 25 or 40 dafb. b 80 mgl 1 ethephon applied at full bloom. Table 7 The effect of the post-bloom thinner 6-benzyladenine (BA) applied with or without a primary thinner (ethephon) on fruit quality of Packham s Triumph pear (Trial 3). Total soluble Solids ( Brix) Flesh firmness (N) Starch index Average seed no. Russet index (i) Treatment regime Untreatedcontrol c c 5 a 8.9 b 1.72 a BA a b 5.1 a 7.5 a 1.71 a ethephon a + BA b a 5.3 b 7.1 a 1.85 b LSD (p = 0.05) (ii) BA application time 10 dafb 13.9 c c 5.1 a 8.4 c dafb 12.8 a b 5.5 b 6.2 a dafb b a 5.1 a 7.4 b 1.8 LSD (p = 0.05) ns Means with the same letter within each column are not significantly different at the 5% level dafb = days after full bloom. a 80 mgl 1 ethephon applied at full bloom.

6 192 S.A. Bound / Scientia Horticulturae 192 (2015) Fig. 2. The relationship between time of application of the post-bloom thinner 6-benzyladenine (BA) and crop load of Packham s Triumph pear (Trial 3). Fig. 3. The relationship between time of 6-benzyladenine (BA) application and (i) mean fruit weight, (ii) fruit size of Packham s Triumph pear (Trial 3). Applying BA as a post-bloom thinner after ATS at flowering further reduced the number of fruit cm 2 TCSA, but had no statistically significant effect on fruit weight or size. Increasing the number of ATS applications from one to two resulted in a significant reduction in crop load, but there was no effect on fruit weight or size. (Table 10). There were no significant interactions between regime and number of ATS applications for crop load, fruit weight or size (results not presented). There was a negative linear relationship between number of ATS applications and crop load (Fig. 6). All treatments increased TSS compared with the untreated control (Table 11). There was no effect on flesh firmness. Starch index was higher in fruit treated with both ATS and BA. Seed number was reduced by ATS compared with the untreated control, while addition of BA reduced seed number further. ATS resulted in increased russet compared with the untreated control, but the addition of BA Table 8 The impact of concentration and number of applications of ammonium thiosulphate (ATS) on crop load of Packham s Triumph pear(trial 4). TCSA = trunk cross-sectional area. No. fruit cm 2 TCSA No. fruit per 100 blossom clusters Mean fruit weight (g) % fruit 180 g or larger (i) Untreated versus treated Untreatedcontrol 4.74 b 80.1 b ATS 2.76 a 49.8 a LSD (p = 0.05) ns ns (ii) ATS concentration 0.7% ATS 3.43 b 59.6 b a 1.0% ATS 2.69 ab 52.6 b b 1.3% ATS 2.17 a 37 a b LSD (p = 0.05) (iii) Number of ATS applications Two (50 and 80% bloom) Three (50 and 80% bloom and 5 dafb) LSD (p = 0.05) ns ns ns ns Means with the same letter within each column are not significantly different at the 5% level.

7 S.A. Bound / Scientia Horticulturae 192 (2015) Fig. 4. The relationship between concentration of ammonium thiosulphate (ATS) and crop load of Packham s Triumph pear (Trial 4). Table 9 The effect of concentration and number of applications of ammonium thiosulphate (ATS) on fruit quality of Packham s Triumph pear (Trial 4). Total soluble Solids ( Brix) Flesh firmness (N) Average seed no. (i) Untreated vs treated Untreated control b 97 a 6.3 b ATS a b 4.6 a LSD (p = 0.05) (ii) ATS concentration 0.7% ATS b a 5.2 b 1.0% ATS c b 4.8 b 1.3% ATS a b 3.8 a LSD (p = 0.05) (iii) Number of ATS applications Two (50 and 80% bloom) 12.4 a b Three (50 and 80% bloom and 3 dafb) b a LSD (p = 0.05) 0.14 ns 0.4 Means with the same letter within each column are not significantly different at the 5% level dafb = days after full bloom. to the program reduced russet compared with ATS alone. Number of ATS applications had no effect on fruit weight, size, TSS, flesh firmness, starch index, seed number or russet index (results not presented). There were no significant interactions between treatment regime and number of ATS applications for TSS, flesh firmness, starch index, seed number or russet index (results not presented). Fig. 5. The relationship between crop load and fruit flesh firmness of Packham s Triumph pear (Trial 4).

8 194 S.A. Bound / Scientia Horticulturae 192 (2015) Table 10 The effect of ammonium thiosulphate (ATS) and 6-benzyladenine (BA) on crop load and fruit size of Packham s Triumph pear (Trial 5). TCSA = trunk cross-sectional area. No. fruit cm 2 TCSA No. fruit per 100 blossom clusters Mean fruit weight (g) % fruit 180 g or larger (i) Untreated vs treated Untreated 4.75 b 109 b 145 a 13 a Treated 3.02 a 72 a 170 b 43 b LSD (p = 0.05) (ii) Treatmentregime ATS 3.52 b ATS plus BA 2.51 a LSD (p = 0.05) 0.86 ns ns ns (iii) Number of ATS applications one (25% bloom) two (25 and 80% bloom) LSD (p = 0.05) 0.72 ns ns ns Means with the same letter within each column are not significantly different at the 5% level. Fig. 6. The relationship between number of applications of ammonium thiosulphate (ATS) and crop load of Packham s Triumph pear (Trial 5). Table 11 The effect of ammonium thiosulphate (ATS) and 6-benzyladenine (BA) on fruit quality of Packham s Triumph pear (Trial 5). Total soluble solids ( Brix) Flesh firmness (N) Starch index Average seed no. Russet index (i) Treatment regime Untreated a a 8.9 c 1.72 a ATS b a 8.2 b 1.98 c ATS plus BA b b 6 a 1.86 b LSD (p = 0.05) 0.12 ns Means with the same letter within each column are not significantly different at the 5% level. 4. Discussion and conclusions Fruit thinning and the subsequent effects on fruit size, fruit quality and regular cropping are dependent on having a predictable thinning program, and this study demonstrates that there are several options available for thinning of Packham s Triumph pear. The use of both blossom and post bloom thinners in a program reduces the risks involved in thinning, rather than relying on a one-hit thinning policy which can be high risk. Results from this study show that the thinning program can be structured to include the use of more than one application of thinning chemical, as recommended by Jones et al. (1998). Full bloom ethephon applications have been reported to thin Winter Cole pear effectively at concentrations as low as 50 mgl 1 (Bound et al., 1991a), so the lack of thinning observed in this study with 80 mgl 1 ethephon was surprising. It is possible that the efficacy of ethephon as a thinner may be cultivar specific as Maas et al. (2010) saw no thinning effect on Conference pear following application of 200 mgl 1 ethephon at full bloom. However, another explanation for the lack of thinning may the relatively low temperatures at the time of application (16.8 C in season 1 and 14.0 C in season 2). Application timing is important in determining the effectiveness of BA. The results of this study suggest that the time span for effective thinning with BA on Packham s Triumph pear extends from 10 through to 40 days after full bloom, which is considerably longer than the recommended period for apples. Greene and Autio (1989) found dafb to be the period of maximum thinning on McIntosh apple. In a detailed study on time of application, Bound et al. (1993) found that the most effective time of application of BA on Fuji apple is dafb, while Bound et al. (1997) recommended an application timing of dafb for red Delicious and Golden Delicious apples. Initial work on Packham s Triumph pear by Bound and Mitchell (2002b) found that BA was an effective thinner from 8 to 26 dafb, while Stern and Flaishman (2003) reported variation in thinning effect of BA between cultivars, with light thinning in Spadonia and a heavy thinning effect in Coscia following application of BA 2 weeks AFB.

9 S.A. Bound / Scientia Horticulturae 192 (2015) There are varying reports on the optimal concentration of BA for thinning, the concentrations of mgl 1 used in this study were effective on Packham. This is confirmed by the findings of Bertelsen (2002), Bound and Mitchell (2002b), Stern and Flaishman (2003) and Dussi et al. (2008) in studies on a range of pear cultivars; although Greene (2012) saw no thinning effect on Bartlett pears with 150 mgl 1 BA. Greene and Autio (1989) reported that BA would thin apples at concentrations as low as 25 mgl 1, and Greene et al. (1990) achieved good results with mgl 1, Bound et al. (1991b, 1993),) reported that rates of BA less than 100 mgl 1 were ineffective for apples under Australian conditions. As a thinning agent, BA is extremely temperature dependent, lacking efficacy at cooler temperatures, when used as a post-bloom thinner in apples (Bound et al., 1997). In this study, all application temperatures for BA were in the range recommended for apples (Bound et al., 1997). Greene and Autio (1994) also noted that Accel, another formulation of BA, should be applied only when the temperature is 65 F (18 C) or higher. Bound and Mitchell (2002b) demonstrated that this temperature dependency was not as critical in pears where BA thinned at temperatures as low as 11 C. BA can be safely applied after either ethephon at full bloom or the desiccant ATS at 25% bloom. It also appears to be an effective thinner of pears when used alone. Although Dussi et al. (2008) reported additional thinning with two applications of BA, multiple applications of BA were not effective in this work. Stern and Flaishman (2003) concluded that the response of pears to BA is cultivar dependent. Multiple applications of desiccants during the flowering period provide the most effective thinning results in apples (Bound, 2001), and previous work on Packham s Triumph pear by Bound and Mitchell (2002a) supported these findings. The results of this work are in agreement, with increased thinning observed with increasing number of applications. It is important to note that the effectiveness of desiccating chemicals may be indirectly influenced by temperature, with cooler temperatures often resulting in fewer flowers open and susceptible to the desiccating action. The lack of effect on fruit weight and size in trials 1, 2 and 4 in this work, is most likely attributable to the fact that trees in these trials were hand thinned eight weeks after flowering, following completion of the fruit set counts. In Australia, hand thinning in commercial pear orchards is often not completed until around 16 weeks after bloom, potentially leading to considerable loss in fruit size at harvest. Working with apples, Greene and Miller (1984) and Greene et al. (1990) found that increased thinning with BA resulted in larger fruit size, and the results of trials 3 and 5 in this study (where no hand thinning was undertaken) confirm this. Theron et al. (2011) reported increased fruit size in Early Bon Chrétien with increasing concentration of BA. In earlier studies on Packham s Triumph pear, Bound and Mitchell (2002b) also concluded that the increase in fruit size was a function of thinning level. Several authors have demonstrated that BA can increase apple fruit size independently of its effects on crop load (Greene et al., 1992; Bound et al., 1997). The results of this study support this conclusion for Packham s Triumph pear as two applications of BA resulted in improved fruit size in the absence of further thinning. This work also indicates that, although BA may be an effective thinner as late as 40 dafb, later applications result in reduced fruit weight, most likely due to resources being directed to fruit which later drops. If thinning is completed earlier there is less wastage of photosynthate into fruit which will ultimately be removed by the thinning treatments. The effect of ATS on fruit soluble solids content was variable in this work, with a decrease observed in trial 4 but an increase in trial 5. Bound and Wilson (2007) reported increased soluble solids content in apples following treatment with ATS. The desiccant endothal has also been reported to increase TSS in apples (Bound, 2001). Application of BA increased soluble solids in two of the four trials using BA in this study, however, it had no effect in one trial and reduced soluble solids in another. Bound and Wilson (2007) reported increased soluble solids in apple with BA, but Dussi et al. (2008) saw no effect on Williams pear. The variation in results is difficult to explain but may be related to seasonal effects or variation in harvest maturity between seasons. The positive effect on fruit firmness in this study supports the findings of Bound and Wilson (2007), who reported increased firmness in apples following thinning with ATS. Bound (2001) also reported increased firmness in apple fruit treated with the desiccant endothal. Previous studies with BA on apple have shown that BA tends to increase fruit firmness (Bound et al., 1997; Bound, 2001; Bound and Wilson 2007), but Dussi et al. (2008) reported a lack of effect on fruit firmness in Williams pear. Fruit firmness was increased in this study in two of the four BA trials. Link (2000) stated that thinning generally increases fruit firmness, but in some circumstances a decrease is observed. This effect was observed in Trial 3 of this study, but only in the later thinning treatments, supporting the recommendations of Jones et al. (1998) that the earlier that thinning is completed the greater the benefits for fruit quality. The slight reduction in seed numbers with ATS in this work was similar to that observed in initial work with ATS in apples (Bound and Jones, 2004) and is seen as having little biological significance. The effect of BA on seed numbers appears to be related to time of application. McArtney et al. (1995) found early BA treatments had only a minor effect on apple seed numbers compared with late applications which halved seed numbers in some cultivars. This work on Packham s Triumph pear found the greatest reduction in seed number was at 25 days after bloom, with a smaller reduction seen at 40 days, but there was no reduction at 10 days. However, BA treatment following ethephon had no effect on seed number. Low seed numbers can contribute to senescent breakdown (Bramlage et al., 1990). Bound and Wilson (2007) concluded that the positive effect of BA often seen on fruit size, sugar content and firmness usually counteracts any negative effects of reduced seed numbers. Chemically induced russet can be a serious problem, as russeted fruit is normally downgraded or discarded. The increase in russet caused by both ATS and ethephon in this study suggests caution. Maas et al. (2010) also observed increased russet in Conference pears following bloom applications of ATS. Although Greene (2012) reported fruit russeting on Bartlett pears following BA application, in this study the addition of BA to the thinning program ameliorated the russeting effect of ATS. This study has demonstrated that the post-bloom thinner BA is a consistent thinner of Packham s Triumph providing weather conditions are suitable, and it can be applied as early as 10 dafb to as late as 40 dafb, several days later than previously reported. While BA can be used as a stand alone thinner of Packham s Triumph, it is risky to rely on one spray application in case weather conditions are unsuitable for application. Two applications of BA did not increase the thinning effect, hence, would not be recommended. The blossom thinner ATS proved to be an effective thinner, and two applications during the flowering period would be recommended. It can also be effectively combined in a program with the post-bloom thinner BA, thus, giving growers increased options when determining their thinning programs. Acknowledgments Funding for this project was provided by the Horticultural Research and Development Corporation through the Apple and Pear Levy. Thanks are due to Jeff and Scott Hansen, Nubeena, Tasmania for use of their orchard; Shenan Daniels for technical support and Steve Wilson for review of the manuscript. Thanks are also due

10 196 S.A. Bound / Scientia Horticulturae 192 (2015) to Valent BioScience for provision of the CyLex used in this work and to Ferro Corporation (Australia) Pty. Ltd. for supply of the ATS. References Bertelsen, M.G., Benzyladenine and other thinning agents for pear cv. Clara Frijs. J. Am. Pomol. Soc. 56, Bound, S.A., The influence of endothal and 6-benzyladenine on crop load and fruit quality of red Delicious apple. J. Hortic. Sci. Biotech. 76, Bound, S.A., Jones, K.M., Ammonium thiosulphate as a blossom thinner of Delicious apple, Winter Cole pear and Hunter apricot. Aust. J. Exp. Agric. 44, Bound, S.A., Jones, K.M., Graham, B., Oakford, M.J., Tichon, M., Modelling the effects of timing and rates of application of benzyladenine as a secondary thinner of Fuji after ethephon. J. Hortic. Sci. 68, Bound, S.A., Jones, K.M., Koen, T.B., 1991a. Ethephon concentration and timing effects on thinning Winter Cole pears. Aust. J. Exp. Agric. 31, Bound, S.A., Jones, K.M., Koen, T.B., Oakford, M.J., 1991b. The thinning effects of benzyladenine on Red Fuji apple trees. J. Hortic. Sci. 66, Bound, S.A., Jones, K.M., Oakford, M.J., Post-bloom thinning with 6-benzyladenine. Acta Hortic. 463, Bound, S.A., Mitchell, L., 2002a. The effect of blossom desiccants on crop load of Packham s Triumph pear. Acta Hortic. 596, Bound, S.A., Mitchell, L., 2002b. A new post-bloom thinning agent for Packham s Triumph pear. Acta Hortic. 596, Bound, S.A., Wilson, S.J., Ammonium thiosulphate and 6-benzyladenine improve the crop load and fruit quality of Delicious apples. Aust. J. Exp. Agric. 47, Bramlage, W.J., Weis, S.A., Greene, D.W., Observations on the relationships among seed number fruit calcium, and senescent breakdown in apples. Hortsci. 25, Byers, R.E., Effects of bloom-thinning chemicals on apple fruit set. J. Tree Fruit Prod. 2, Dussi, M.C., Giardina, G., Reeb, P., Gastiazoro, J., Thinning programs in pears cv Williams. Acta Hortic. 800, Dussi, M.C., Sugar, D., Fruit thinning and fruit size enhancement with 6-benzyladenine application to Williams pear. Acta Hortic. 909, Elfving, D.C., Cline, R.A., Benzyladenine and other chemicals for thinning Empire apple trees. J. Am. Soc. Hortic. Sci. 118, Ferree, D.C., Schmid, J.C., Chemical thinning Gala apple in the midwest. J. Am. Pomol. Soc. 55, Greene, D.W., Influence of abscisic acid and benzyladenine on fruit set and fruit quality of Bartlett pears. Hortsci. 47, Greene, D.W., Autio, W.R., Evaluation of benzyladenine as a chemical thinner on Mcintosh apples. J. Am. Soc. Hortic. Sci. 114, Greene, D.W., Autio, W.R., Suggestions for use of the new postbloom thinner Accel. Fruit Notes Spring 1994, Greene, D.W., Autio, W.R., Miller, P., Thinning activity of benzyladenine on several apple cultivars. J. Am. Soc. Hortic. Sci. 115, Greene, D.W., Autio, W.R., Erf, J.A., Mao, Z.Y., Mode of action of benzyladenine when used as a chemical thinner on apples. J. Am. Soc. Hortic. Sci. 117, Greene, D., Miller, P., Uses of 6-benzyladenine as a chemical thinner for apples. HortSci. 19, 52. Jones, K.M., Koen, T.B., Temperature effects on ethephon thinning of apples. J. Hortic. Sci. 60, Jones, K.M., Bound, S.A., Oakford, M.J., Identifying the optimum thinning time for Red Fuji apples. J. Hortic. Sci. 67, Jones, K.M., Bound, S.A., Miller, P., Crop Regulation of Pome Fruit in Australia. Tasmanian Institute of Agricultural Research, University of Tasmania. Link, H., Significance of flower and fruit thinning on fruit quality. Plant Growth Regul. 31, Little, C.R., A manual of procedures for assessing apple and pear maturity for specific storage schedules. In: Little, C.R. (Ed.), Scientific Horticultural Consultant. Sherbrooke, Victoria, Australia, 118 pages. Maas, F.M., Kanne, H.J., van der Steeg, P.A.H., Chemical thinning of Conference pears. Acta Hortic. 884, McArtney, S.J., Wells, G.H., Chemical thinning of Asian and European pear with ethephon and NAA. N. Z. J. Crop Hortic. Sci. 23, McArtney, S.J., Tustin, D.S., Seymour, S., Cashmore, W., Looney, N.E., Benzyladenine and carbaryl effects of fruit thinning and the enhancement of return flowering of three apple cultivars. J. Hortic. Sci. 70, Menzies, R., Chemical thinning of some fruit, Australian Fruit Research Conference, Working Papers 3(c) 3 3(c), 4. Selimi, A., Gibbs, J.F., Temperate tree fruit, Annual Report of the Horticultural Research Station, Tatura ( ), 13. Selimi, A., Gibbs, J.F., Ethrel as a fruit thinner of pears, Biennial Report of the Irrigation Research Station, Tatura ( ), 23. Schmidt, T.R., Auvil, T.D., Hanrahan, I., Castillo, F., McFerson, J.R., Crop load management of tree fruits in the Pacific Northwest of USA. Acta Hortic. 903, Stern, R.A., Flaishman, M.A., Benzyladenine effects on fruit size, fruit thinning and return yield of Spadona and Coscia pear. Sci. Hortic. 98, Theron, K.I., Chabikwa, T.G., Lötze, G.F.A., Evaluation of 6-benzyladenine (BA) and naphthylacetamide (NAD) as post-bloom thinning compounds for Early Bon Chrétien pear. Acta Hortic. 909, Thistlewood, H.M.A., Elfving, D.C., Laboratory and field effects of chemical fruit thinners on Tetranychid and predatory mites (Acari) of apple. J. Econ. Entomol. 85, van Heek, L., Issell, L., Early and continuous heavy cropping of pears by pruning, manipulation of tree shape closer planting and rootstocks, Australian Fruit Research Conference, Working Papers 3(b) 5 3(b),6. Vilardell, P., Carbo, J., Casala, M., Bonany, J., Asin, L., Dalmau, R., Effect of 6-BA and NAA as thinning agents of Conference pear. Acta Hortic. 671,