Testing CPPU for improving fruit quality in Bartlett pear, Kitren Glozer 1 and Chuck Ingels 2

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1 Testing CPPU for improving fruit quality in Bartlett pear, 2006 Kitren Glozer 1 and Chuck Ingels 2 1 Plant Sciences Department, U.C. Davis 2 Farm Advisor, Sacramento County Summary: CPPU (2-chloro-4-pyridyl)-N=-phenylurea) applied at petal fall + 2 weeks doubled the percentage of the crop that was #1 fruit, significantly increased weight of both #1 and #2 fruit, and advanced maturity based on firmness. Effects appear to be due to a direct effect on size increase during Stage I growth; fruit set on individual limbs was increased, but number of fruit per half tree was decreased. Problem and Its Significance: Bartlett pear in the leading European pear variety grown in California. Bartlett pears are grown for both fresh and processing markets. A premium price can be obtained for large sizes in most years and if the majority of the crop is above minimum size at an early harvest timing, multiple harvests might be reduced or eliminated, thereby reducing hand labor costs and enabling rapid harvest over the large acreages that are typical for California s growers. Harvest timing is by size and soluble solids, rather than color, as this crop is harvested green, unripe, and stored for shipping and later ripening if destined for fresh consumption. Fruit quality for fresh market is of great importance, and although fruit are harvested green, storage potential can be improved with fruit that are firmer at a soluble solids index appropriate for harvest timing. CPPU has been shown to improve the conversion of starch to sugars, and indicator of advancing maturity, yet fruit storage quality has not been affected (Antognozzi et al., 1996). Plans and Procedures: , The experimental site was near Courtland and consisted of approximately 40-year old >Bartlett=/=Winter Nelis= trees planted on a 10 x19 spacing and microsprinkler-irrigated. Three treatments were compared using 4 trees per treatment, in a single row with treatment group trees contiguous and separated from other treatment groups by 2-4 guard trees. No randomization was used in this small-scale, pilot study. An untreated control was compared to two treatment timings of 10 ppm CPPU + 0.1% Regulaid applied at approximately 200 gallons per acre using a Stihl mistblower; applications were made at petal fall + 2 weeks (11 May) when small fruit were just starting to drop, and at petal fall + 4 weeks (25 May). Fruit diameter at the second treatment timing averaged 25.2 mm (range was 20.4 to 29.6 mm). Two bearing limbs per treated tree were tagged prior to the first treatment and number of fruitlets counted. Fruit set was determined at harvest (1 August) by adding the number of fruit on both tagged limbs per tree as set was quite low. Fruit size (diameter) and weight at maturity, firmness and soluble solids (combined sample) were determined by treatment at commercial harvest timing. Fruit were examined for evidence of shape abnormalities (knobbing at calyx end). Fruit were counted on the west half of each tree for estimation of crop load and yield was calculated from this number and the weight of 20 fruit selected at random from the counted half of the tree. This 20-fruit sample was used to determine percentage of undersized fruit (#2, less than 2 1/2" in diameter), and weight and diameter of a 10-fruit subsample was used to determine soluble solids, firmness, fruit size and weight of #1 fruit. Firmness was measured by UC pressure tester on opposite cheeks after removal of peel. Ten fruit per treated tree were stored for approximately 1 month at F, brought to room temperature for a week, then re-evaluated for physiological disorders: senescent scald, superficial scald, watery

2 breakdown, pink calyx (Mitcham et al.). Fruit were evaluated for reduced quality of skin yellowing, mealy flesh and the inability to ripen. Statistical analyses: Analyses of variance were performed with Proc GLM in SAS (SAS Institute Inc., Cary, NC) and mean separations tested by Duncan=s Multiple Range Test, P = All data was normal and did not require transformation (Adler and Roessler, 1964). Results and Discussion: Fruit set as measured on two limbs per tree indicates more than double the set on trees treated with 10 ppm CPPU 2 weeks after petal fall (Table 1), however, this result should be treated cautiously because it is in contradiction to actual fruit count per half tree (Table 2). While the fruit count per half tree does not directly count fruit set (flowers per half tree were not counted, nor were initial fruit numbers), it does represent crop load on a larger scale. Thus, a conclusion as to whether fruit set was increased by CPPU applied 2 weeks after petal-fall, or was decreased by this treatment is unclear. CPPU has been found to induce parthenocarpic set (set without pollination, such as occurs in Bartlett pear in the Sacramento Delta) in kiwifruit (Iwahori et al., 1988). Crop load was not limiting in 2006 as trees lost potential fruit to a freeze prior to bloom and number of inflorescence buds was reduced as a result. Thus, an increase in fruit set could still be possible even with increased fruit size (Table 1) and percentage of the crop that was #1 fruit increased (Table 2) by treatment with CPPU at petal-fall + 2 weeks. CPPU has been shown to improve fruit size by at least 50% in early applications on apples in Israel (Stern et al., 2003) without any fruit thinning, when applied at 10 ppm at 2 weeks after full bloom. CPPU increased fruit size of Spadona pear when applied at two weeks after full bloom, when fruitlets were 10 mm in diameter, and fruit shape and seed number were not affected (Flaishman et al., 2005). This size increase was due to an increased number of cells along the fruit radius. Thus, fruit size can be increased with early treatment of CPPU, whether fruit set is affected or not. Crop load, fruit size, and yield were unaffected by later treatment with CPPU in this trial. We did not find any evidence of abnormal shapes in fruit, as has been found with later applications (25 days after full bloom) in apple; this is likely because the apple study applied 20 ppm at that timing, which also delayed harvest (Tartini et al., 1993). Maturity of pears treated with 10 ppm CPPU was advanced, using firmness as a maturity index, although soluble solids were not different from the control. No treatment differences in firmness, skin color, appearance of abnormalities or ability to ripen were found (data not shown). The issue of fruit set increase or decrease is one that is an important point to clarify in future work, as growers seek to reduce labor costs and increase profitability. A chemical thinner for pears has been sought for decades; in 1995 and 1996, Southwick and Glozer evaluated Accel (Abbott Laboratories now replaced by MaxCel, Valent BioSciences), containing a cytokinin (6-benzyladenine) and 2 gibberellins (GA 4 and GA 7 ), purported to be an effective thinner and fruit sizing agent for several apple varieties. In those studies, we did not obtain a thinning effect at either petal fall or small fruit stages of application timing. Fruit set was increased by 15 g a.i. Accel applied at petal fall, compared to the untreated control for both Bartlett and Red Sensation varieties. Application at 11 mm diameter fruit size did not affect fruit set. The increase in fruit set has been explained as Accel (benzyladanine and gibberellins A 4 A 7 ) applied at petal fall enhancing by parthenocarpic set 2

3 References: Antognozzi, E., A. Battistelli, F. Famiani, S. Moscatello, F. Stanica and A. Tombesi Influence of CPPU on carbohydrate accumulation and metabolism in fruits of Actinidia deliciosa (A. Chev.). Sci. Hort. 65: Botelho, R.V., S. Kerniski, R.M. Mercer, C.A. Pott and M.M.L. Müller. The effects of CPPU on the fruit development of kiwi cv. Bruno in the region of Guarapuava, State of Paraná, Brazil. Maringá 27: Flaishman, M.A., A. Shargal, L. Shlizerman, R.A. Stern, S. Lev-Yadun and G. Graft. The synthetic cytokinins CPPU and TDZ prolong the phase of cell division in developing pear (Pyrus communis L.) fruit. Acta Hort. (ISHS) 671: Iwahori, S., S. Tominaga and T. Yamasaki Stimulation of fruit growth of kiwifruit, Actinidia chinensis Planch., by N-(2-chloro-4-pyridyl)-N -phenylurea, a diphenylurea-derivative cytokinin. Sci. Hort. 35: Kupferman, E Controlled atmosphere storage of apples and pears. Washington State University. Postharvest Information Network Article. Mitcham, E.J., C.H. Crisosto and A.A. Kader. Pear: Bartlett. Recommendations for maintaining postharvest quality. Stern, R.A., R. Ben-Arie, O. Neria and M. Flaishman CPPU and BA increase fruit size of Royal Gala (Malus domestica) apple in a warm climate. J. Hort. Sci. Biotech. 78: Tartini, S., S. Sansavini and M. Ventura CPPU control of fruit morphogenesis in apple. Sci. Hort. 53:

4 Table 1. Effects of 10 ppm CPPU applied at petal fall (PF) + 2 weeks or PF + 4 weeks (11 and 25 May, respectively) on Bartlett pear in 2006: fruit set. Treatment Control CPPU 11 May CPPU 25 May %Fruit set on 2 limbs per tree, combined 10.9 b x 26.8 a 12.9 b x Mean separation within columns by Duncan s Multiple Range Test, P =

5 Table 2. Effects of 10 ppm CPPU applied at petal fall (PF) + 2 weeks or PF + 4 weeks (11 and 25 May, respectively) on Bartlett pear in 2006: harvest evaluation. Treatment Diameter of #1 fruit (cm) #Fruit per half tree %Crop = #1 fruit Weight (g) Estimated yield (kg) #1 fruit #2 fruit #1 fruit #2 fruit total %Soluble solids Firmness (lb) Control 2.60 b x a 38.0 b b 105.5b 52.0a 33.7a 85.8a 11.4 a 17.6a CPPU 11 May 2.68 a a 79.0 a a 117.5a 93.2a 9.5b 102.7a 11.8 a 16.6b CPPU 25 May 2.65 ab a 48.5 b a 112.5ab 63.4a 28.4a 91.8a 11.3 a 16.7b x Mean separation within columns by Duncan s Multiple Range Test, P = 0.05.