THE EFFECT OF PROHEXADIONE-CA ON SHOOT GROWTH AND CROPPING OF YOUNG APPLE TREES OF JONAGOLD CV.

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1 Roczniki Akademii Rolniczej w Poznaniu CCCLXXXIII (2007) ALINA BASAK THE EFFECT OF PROHEXADIONE-CA ON SHOOT GROWTH AND CROPPING OF YOUNG APPLE TREES OF JONAGOLD CV. From Research Institute of Pomology and Floriculture Skierniewice ABSTRACT. The young apple trees cultivar Jonagold/M26 were sprayed with prohexadione-ca during three consecutive years in order to retard shoot growth and improve canopy structure. The trials have been set on three year-old trees. In the first year P-Ca was used at concentrations: 75, 150, mg dm -3. In next two seasons the bioregulator was used at higher doses: 125, 175 and 200 mg dm -3. The effect of different programs of P-Ca use on the number and length of shoots and number and quality of fruits as well as on the subsequent bloom of the trees was evaluated. It was found that on young apple trees some treatments with P-Ca caused reduction of the shoot length as well as the induction of their feathering. As the result of this the tree size was decreased and the structure of canopy was improved. Improved fruit size with no effect on the shape of apples was observed, too. Key words: Prohexadione-Ca, canopy structure, branching apple Introduction It is known that delicate balance exists between vegatative growth and cropping of fruit tree. Frequently, some factors disrupt this balance, resulting in excessive shoot growth. Then, too vigorous shoot growth can negatively influence fruit quality, tree productivity and efficiency of plant protection in orchard. Therefore, there is a need of control of shoot growth in fruit trees. A number of growth control techniques are available (Greene and Authio 1994). Pruning is one of the most popular management practices but also the most time consuming and expensive one. It is necessary to reduce pruning cost by limiting tree growth. It was shown that the inhibitors of gibberellin biosynthesis retard tree growth and, consequently, improve the productivity (Rademacher 1991, 1995, Rademacher and Kober 2003). Cyclohexanediones are the new class of gibberellin biosynthesis inhibitors but prohexadione-ca, one of the compounds Rocz. AR Pozn. CCCLXXXIII, Ogrodn. 41: Wydawnictwo Akademii Rolniczej im. Augusta Cieszkowskiego w Poznaniu, Poznań 2007 PL ISSN

2 262 A. Basak from this group, appears to be particularly effective in shoot growth retardation (Greene 1999). The results of trials conducted in Poland since 1995, confirmed high efficiency of prohexadione-ca in growth control of apple trees (Basak and Rademacher 2000, Basak 2004). In Hungarian trials the increase of branching of apple trees was noticed after use of prohexadione-ca (Buban et al. 2003). The aim of the trials was to determine the effect of use of prohehexadione-ca on the shoot growth and canopy structure in young apple trees. Material and methods The results of trials on growth control in young apple trees cv. Jonagold by use of ProCa will be presented. Prohexadione-Ca, in the form of preparations Regalis, was used by spraying the trees. The experimental trees were grafted on M26 rootstocks and were planted in spacings 4 m between rows and 1 m in the row. The trials had been set on 3-year old trees, and were continued during three consecutive years on the same trees. Thus the 3 experiments were conducted. In the tables the short name of active compound ProCa will be used. The low doses of preparation were used in the first year of trials (in experiment 1) owing to young age of trees. Then, the trees were sprayed with ProCa in doses 75 and 150 mg dm -3 in two terms; first when terminal shoots were about 10 cm long and another group of trees two weeks later. Also, the low dose of ProCa was used twice on the same trees at two weeks interval. In experiment 2, conducted on 4-year old trees, ProCa was used at higher doses; 125 mg dm -3, 150 mg dm -3 and 200 mg dm -3 in one term only, on terminal shoot about 10 cm long. In the third year of trials, in experiment 3, some of the trees were sprayed with ProCa again, while the others were left unsprayed to determine the subsequent effect of retardant use in two previous seasons (Experiment 1 and 2). The following parameters were evaluated: growth of the shoots, intensity of flowering in the year after treatment and quality and quantity of the fruit at harvest. Each of the treatments was tested on one row consisting of 28 trees but only 10 uniform trees were selected from each row for a detailed evaluation. The trees were sprayed with hand gun until run-off. The results were statistically evaluated with the analysis of variance using Duncan s test at P = 0.05 for significance. Results and discussion The effect of ProCa on vegetative growth of Jonagold trees The results of commercial trials have shown low sensitivity of trees cv. Jonagold to ProCa. In orchard, where ProCa was used in the same way on different apple cvs., the shortening of Jonagold terminal shoots by 25% was found, while in Gloster on P22 by 35%, in Gloster on M26, Delikates/M26 or Idared/M26 by about 50% (data are not published). The results of experiment 1, conducted on 3-year old trees, have shown the significant shortening of 1-year old shoots but only after ProCa use early in the season

3 The effect of prohexadione-ca on shoot growth and cropping in higher dose (150 mg dm -3 ) and after sequential, two sprayings of the same trees with low dose of preparation (75 mg dm -3 ). Both treatments reduced shoot length by about 16% in comparison to control unsprayed trees (Table 1). Then, the significant reduction of the long shoots number (longer than 40 cm) and, on the other hand significant increase of the number of short shoots (less than 20 cm long) was found (data are not shown). The reduction of vegetative growth had no influence on the number of 1-year old shoots. Only, low dose of ProCa, applied late, induced branching in young Jonagold trees, in spite of no effect on shoot length. Early spraying with low dose of retardant decreased the total shoot length per tree. All treatments of retardant caused less or more evident increase of the trunk diameter but only trees treated twice with low dose of retardant and with high dose but applied late, differed significantly in this respect from the control untreated trees. Only, treatment with ProCa at low dose 75 mg dm -3 caused increase of the spurs number per tree. No subsequent effect of Prohexadione-Ca on flowers number in next spring was found. In the second year of trials (Experiment 2) no reduction of shoot length was observed (Table 2). In all trees, independently of the treatment, the shoots were short, nearly 20 cm of long as an average. In spite of no reduction of shoot length, significant increase of the shoot number was noticed. As the result, total shoot length per tree was increased significantly (most often), independently of the dose of retardant. Only, in trees sprayed in experiment 1 with high dose of retardant, no reduction of spur number was found in experiment 2. But trees treated with low dose of retardant in 1 experiment responded with reduction of spur number in experiment 2. Great increase of flower clusters number was noticed in the trees sprayed with with ProCa in experiment 2 except the trees sprayed with retardant in dose 200 mg dm -3. Summarizing the results of two first experiments we can conclude that the effect of retardant on spur formation depended on the degree of vegetative growth reduction. Too high doses of ProCa can influence negatively these features. As the result of experiment 3, conducted on 5-year old trees it was shown: No subsequent effect was observed of ProCa use in two consecutive seasons on the shoot growth in the third year (Table 3). Use of ProCa for the third time on the same trees, inhibited shoot growth by about 12% only, in spite of higher dose of preparation. The effect was not proved statistically. None of the treatments with ProCa increased the number of shoots and their total length per tree. Some treatments with retardant increased the number of spurs but none of them improved the intensity of flowering in spring next year. It means the efficiency of ProCa in the third year of trials was very low. The effect of ProCa on cropping of young apple trees cv. Jonagold In the first year of trials, when the trees were 3-years old, ProCa used early in dose 150 mg dm -3 increased fruit set significantly. The yield was increased then, too. All treatments with ProCa caused the increase of mean fruit weight by about 13%. However, the largest apples were harvested from trees sprayed twice with low dose of the preparation (Table 1). In the second year of trials, where the trees were 4-years old, all treatments with retardant increased fruit set in comparison to control unsprayed trees. However, it was found that significant growth retardation in previous season by ProCa at 75 mg dm -3 used twice worsened the fruit set next year. Then, the sprayings with ProCa caused increase of mean

4 264 A. Basak The results of prohexadione-ca used in Jonagold trees in 1997 (Experiment 1) Wyniki po zastosowaniu proheksadionu-ca na jabłonie odmiany Jonagold w roku 1997 (doświadczenie 1) Table 1 Effect on vegetative growth Wpływ na wegetatywny wzrost drzew Effect on the number and apple quality Wpływ na liczbę i jakość jabłek Treatments concentration Sposób traktowania Stężenie (mg dm -3 ) shoot length shoots/tree / total length shoots (cm tree -1 ) całkowita (cm -1 ) increase of trunk diameter przyrost średnicy pnia spurs/tree krótko/ flower clusters/tree next year kwiatostanów/ w następnym roku fruit set zawiązane owoce (%) yield (kg tree -1 ) plon (kg -1 ) mean fruit weight przeciętna masa jabłka (g) Control untreated Kontrola nietraktowana 27.6 bc 49 ab d 1.9 a 44 cd 185 a 11.9 a 2.4 abc 204 ab ProCa 75 T ab 43 a a 2.4 ab 62 e 200 a 12.0 a 1.9 a 244 bc 150 T a 56 bc c-f 2.2 ab 42 bc 166 a 18.2 b 3.4 c 208 abc 75 T1+75 T a 50 ab abc 2.6 b 62 e 186 a 13.4 a 2.9 ab 248 c 75 T bc 61 c d 2.3 ab 58 de 180 a 12.5 a 2.6 abc 238 bc 150 T c 52 abc a-d 2.6 b 51 cde 188 a 13.8 a 2.4 abc 204 ab Means in columns signed with the same letter do not differ significantly; t Duncan s test at P = Wartości w kolumnach oznaczone tą samą literą nie różnią się istotnie; test t Duncana, przy prawdopodobieństwie 95%.

5 The effect of prohexadione-ca on shoot growth and cropping The results of prohexadione-ca used in Jonagold trees in 1998 (Experiment 2) Wyniki po zastosowaniu proheksadionu-ca na jabłonie odmiany Jonagold w roku 1998 (doświadczenie 2) Table 2 Effect on vegetative growth Wpływ na wegetatywny wzrost drzew Effect on the number and apple quality Wpływ na liczbę i jakość jabłek Treatments concentration Sposób traktowania Stężenie (mg dm -3 ) mean shoot length shoots/tree / total shoots length (cm tree -1 ) całkowita (cm -1 ) spurs/tree krótko/ flower clusters/tree next year krótko/ fruit set zawiązane owoce (%) yield (kg tree -1 ) plon (kg -1 ) mean fruit weight przeciętna masa jabłka (g) the percentage of apples with red colour > 75% surface procent jabłek z rumieńcem na > 75% powierzchni Control untreated Kontrola nietraktowana 17.9 a 41 a 762 a 141 bc 261 a 28.5 a 9.7 a 195 a 99.9 b ProCa 125 T1 in 1998 (75 T2 in 1997) 17.6 a 61 b ab 110 a 417 bc 38.8 c 8.6 a 216 a 92.7 ab 175 T1 in 1998 (75T1+75 T2 in 1997) 19.4 a 70 b b 131 abc 427 bc 27.9 ab 8.8 a 215 a 98.9 ab 200 T1 in 1998 (75 T1 in 1997) 18.7 a 67 b b 114 ab 287 ab 47.0 c 10.9 a 214 a 88.4 a 125 T1 in 1998 (150 T1 in 1997) 17.4 a 64 b b 145 c 451 c 36.1 bc 9.4 a 210 a 99.8 b 175 T1 in 1998 (150 T2 in 1997) 18.3 a 74 b b 146 c 422 bc 38.5 c 9.7 a 217 a 97.9 ab Explanations as in Table 1. Objaśnienia jak w tabeli 1.

6 266 A. Basak The result of prohexadione-ca use in Jonagold trees in 1999 (Experiment 3) Wyniki po zastosowaniu proheksadionu-ca na jabłonie odmiany Jonagold w roku 1999 (doświadczenie 3) Table 3 Treatments concentration Sposób traktowania Stężenie (mg/dm 3 ) mean shoot length shoots/tree szt/ Effect on vegetative growth Wpływ na wegetatywny wzrost drzew total shoots length (cm tree -1 ) całkowita (cm -1 ) increase of trunk diameter przyrost średnicy pnia spurs/tree krótko/ bloom intensity in 5 scale next year intensywność kwitnienia drzew wg 5-stopniowej skali w roku następnym Effect on the number and quality of apple Wpływ na liczbę i jakość jabłek fruit set zawiązane owoce (%) yield (kg tree -1 ) plon (kg -1 ) mean fruit weight przeciętna masa jabłka (g) Control untreated Kontrola nietraktowana 20.5 a 66 a a 1.79 a 169 a 3.1 a 48.1 a 17.5 a 164 a ProCa 125 T1 in 1999 (125 T1 in 1988; 75 T2 in 1997) 18.5 a 61 a a 1.94 a 304 d 3.0 a 37.3 a 20.6 a 174 ab 175 T1 in 1999 (175 T1 in 1998; 75T1+75T2 in 1997) 19.7 a 81 a a 2.31 a 184 ab 2.7 a 32.6 a 21.2 a 180 ab 200 T1 in 1999 (200 T1 in 1998; 75 T1 in 1997) 18.1 a 64 a a 2.21 a 259 cd 3.9 a 30.9 a 17.3 a 191 b unsprayed in 1999 (125 T1 in 1998; 150 T1 in 1997) 19.4 a 72 a a 2.24 a 224 bc 2.8 a 30.4 a 19.7 a 180 ab unsprayed in 1999 (175 T1 in 1998; 150 T2 in 1997) 20.0 a 52 a a 1.67 a 207 ab 3.3 a 31.2 a 22.4 a 176 ab Explanations as in Table 1. Objaśnienia jak w tabeli 1.

7 The effect of prohexadione-ca on shoot growth and cropping fruit weight by about 10% in comparison to the control. Lower dose of ProCa (120 and 175 mg dm -3 ) had no influence on red colour of apples and their internal quality at harvest expressed by firmness and refraction values (data not shown). However, the high dose 200 mg dm -3 worsened red colour of apples and decreased their firmness and refraction values (data not shown). In third year of trials (Experiment 3) no effect on fruit set and yield was observed, but mean fruit weight increased by about 10%. The dose 200 mg dm -3 worsened red colour of apples, similarly as in experiment 2. Conclusions It was found that ProCa can be used not only for reduction of vegetative growth of apple trees but, in the case of very young apple trees, also to improve canopy structure. To improve canopy structure young apple trees should be sprayed with ProCa during two consecutive years. In the first year the preparation causes above all the shortening of shoot length (as the result of two from five treatments) but applied on the same trees in the second year induces their branching (concerning long shoots but not spurs) and improves flowering next spring. ProCa used in young apple trees in dose 200 mg dm -3 worsened red colour apples and decreased firmness and refraction value of apples at harvest. Also, it did not improve flowering of the trees. Thus, the dose lower than 200 mg dm -3 should be used in young trees. In the experimental orchard the trees were sprayed in the first year with ProCa in dose 150 mg dm -3, but in the second year with dose 175 mg dm -3 differed from the others in: the highest number of shoots per tree (74 shoots as compared to 41 in the control trees), the highest total shoot length per tree (1384 cm as compared to 762 cm in the control trees), abundant flowering in the third year, the canopy of the tree was compact, good effect on mean fruit weight. Literature Basak A. (2004): Growth and fuiting of Elstar apple trees in response to prohexadione calcium depending on the rootstock. Acta Hort. 653: Basak A., Rademacher W. (2000): Growth regulation of pome and stone fruit trees by use of prohexadione calcium. Acta Hort. 514: Buban T., Foldes L., Kormany S., Hauptmann S., Stammler G., Rademacher W. (2003): Prohexadione-Ca in apple trees: Control of shoot growth and reduction of fire blight incidence in blossoms and shoots. J. Appl. Bot. 77: Greene D.W. (1999): The growth management and fruit quality of apple trees treated with prohexadione-calcium (BAS 125). Hort. Sci. 34, 7: Greene D.W., Authio W.R. (1994): A rewiev methods to control vegetative growth apple trees. The Moutaineer Grower 524:

8 268 A. Basak Rademacher W. (1991): Inhibitors of gibberellins biosynthesis; Application in agriculture and horticulture. In: Gibberellins. Eds N. Takahashi, B.O. Phinnley, J.Mc. Millan. Springler Verlag, New York. Rademacher W. (1995): Growth retardants biochemical features and applications in horticulture. Acta Hort. 394: Rademacher W., Kober R. (2003): Efficient use of prohexadione-ca in pome fruits. Eur. J. Hort. Sci. 68, 3: EFEKT STOSOWANIA PROHEKSADIONU-CA (REGALISU) NA WZROST ORAZ OWOCOWANIE MŁODYCH JABŁONI ODMIANY JONAGOLD Streszczenie Młode jabłonie odmiany Jonagold/M26 opryskiwano Pro-Ca przez 3 kolejne lata w celu zahamowania wzrostu i poprawy struktury korony. Badania rozpoczęto na 3-letnich drzewach. W pierwszym roku Pro-Ca zastosowano w stężeniach: 75, 150, mg dm -3, w dwóch kolejnych latach w wyższych dawkach: 125, 175, i 200 mg dm -3. Oceniano wpływ Pro-Ca na liczbę i oraz liczbę i jakość owoców, a także na następcze kwitnienie drzew. Stwierdzono, że niektóre sposoby traktowania Pro-Ca spowodowały u młodych jabłoni redukcję długości, a także lepsze ich rozgałęzianie. Wynikiem opryskiwań Pro-Ca było zmniejszenie rozmiaru drzew, poprawa struktury korony oraz przyrost plonu i wielkość owoców.