(Research Paper) Promalin Effect on ‘Imperial Gala’ and ‘Fuji’ Apple Trees

(Research Paper)

Promalin Effect on ‘Imperial Gala’ and ‘Fuji’ Apple Trees

 

G.B. Leite, J.L. Petri and Clori Basso
EPAGRI –Experimental Station of Caçador, P.O. Box 591
89500-000 Caçador, SC
Brazil

Proc. Xth IS on Plant Bioregulators in Fruit
Eds. A.D. Webster and H. Ramirez
Acta Hort. 727, ISHS 2006

 

Abstract

Apples from mild winter regions, such as in Southern Brazil, are small, flattened and russeted, affecting fruit quality and selling value. Experiments were carried out from 2002 to 2004 with the apple cultivars ‘Imperial Gala’ and ‘Fuji’, with the purpose of evaluating the effects of time and concentration of Promalin (GA4 + GA7 + benzyladenine) application on apples growing in the mild winter conditions of Southern Brazil. GA4+7 + BA applied at flowering increased fruit size and reduced russeting. The data showed a strong effect of time of application on fruit set reduction. This effect tended to be less intensive in ‘Fuji’ than in ‘Imperial Gala’. The mean fruit weight of ‘Imperial Gala’ and ‘Fuji’ was always significantly higher in the treated plots. The effects of the treatments on russeting were quite variable. However, the percentage of fruit with russeting, other than in the pedicel cavity, may be considered low in these trials.


INTRODUCTION

Apples from mild winter regions, like those in Southern Brazil, are small, flattened, and russeted, affecting fruit quality and selling value. It is proven that gibberellins and cytokinins may elongate apple fruit (Curry and Williams, 1983; Eccher, 1986). In mild winters, russeting increases on cultivars prone to this physiological disorder. Eccher and Maffi (1986) found that promalin 16 mgL-1 reduced the incidence of russeting and increased the fruit length / diameter (L/D) ratio. Promalin is a growth regulator that contains the gibberellins GA4+7 (1.8%) and benzyladenine (1.8%). It is used to improve apple fruit quality in terms of fruit shape and size, and to reduce the incidence of russeting. The incidence of russeting increases under high air humidity, rain, and
temperature fluctuation at the beginning of the fruit development period. Copper pesticides applied during cell division and excess of nitrogen may also increase this disorder. Since their discovery, a lot of information has emerged regarding the effects of
gibberellins and cytokinins on fruit development and growth (Argenta et al., 1991; Argenta et al., 1993; Bukovak and Nakagawa, 1996; Carbó and Patricay, 1986). GA4+7 + BA applied at flowering have been shown to increase fruit size and the fruit L/D ratio,
and reduce russeting (Jindal et. al., 2004; Greene, 2003; Carbó, 1986). The fruit size increase is a consequence of the induction of cell division and elongation, and the increase in fruit length (Burac and Buyukylmaz, 1977; Looney, 1996). The mode of
action in russeting reduction is related to the control of the epidermis cell elongation, resulting in a fruit cuticle less prone to cracks (Eccher, 1978). Taylor and Knight (1986), examining the effects of gibberellins, observed that they increased the size of the
epidermis cells, giving 25% more plasticity when the cuticle was submitted to a stress. In mild climate regions, where fruit shape is problematic, growth regulators may correct this problem (Looney, 1996). Promalin is used for fruit elongation at 1.17 to 2.34
L ha-1 when the central (king) flower opens, increasing its effect and its thinning capacity if a surfactant is added (Greene, 2003). For russeting control, the Promalin dose may be split into two or more applications, which must be made up to two weeks after petal fall. This research had the purpose of evaluating the effects of time and concentration of Promalin application on ‘Imperial Gala’ and ‘Fuji’ apples growing in the mild winter conditions of Southern Brazil.


MATERIALS AND METHODS

The experiments were carried out from 2002/03 to 2004/05 growing seasons, with the apple cultivars ‘Imperial Gala’ and ‘Fuji’, in Fraiburgo, Santa Catarina State, at latitude 26o46’31”S and longitude 51o00’54”W.

Experiment 1:

In 2002, this experiment was carried out in a six-year-old orchard of ‘Gala’/M.9 and ‘Fuji’/M.9. The 4 treatments, with 6 replications of 2 trees per plot, were set in a completely randomized block design. The treatments were: 1 – Promalin 600 ml ha-1 at stage H (petal fall), repeated 10 and 20 days later; 2 – Promalin 500 ml ha-1 at stage H, repeated 7, 14 and 21 days later; 3 – Promalin 1000 ml ha-1 at 40% and at 80% of stage F2 (full bloom); 4 – Control.

Experiment 2:

In 2003, an experiment was carried out with ‘Imperial Gala’ and ‘Fuji’ grafted on Marubakaido rootstocks with M.9 interstocks. A completely randomized block design was used. The 6 treatments, with 10 replicates of single tree plots, were: 1 – Promalin 1.25 L ha-1 at 80% of stage E2 (pink bud), and repeated 14 days later; 2 – Promalin 1.25 L ha-1 at 40% and at 80% of stage E2; 3 -Promalin 0.5 L ha-1 at 80% of stage E2, and repeated 7, 14, 21, and 28 days later; 4 – Promalin 0.5 L ha-1 at stage I (fruit
setting), and repeated 7, 14, 21, and 28 days later; 5 – Promalin 1.25 L ha-1 at stage I, and
repeated 14 days later; 6 – Control.

Experiment 3:

In 2004, another experiment was carried out with ‘Imperial Gala’ and ‘Fuji’ grafted on Marubakaido/M.9 rootstock/interstocks. A completely randomized block design was used. The 7 treatments, with 10 replicates of single tree plots, were: 1 – Control; 2 – Promalin 1.0 L ha-1 at 80% of stage E2 plus 0.5 L ha-1 at stages F2 and H; 3 – Promalin 1.0 L ha-1 at 80% of stage E2, and repeated 3 days later; 4 – Promalin 0.5 L ha-1 at 80% of stage E2, and repeated 4, 8, and 12 days later; 5 – Promalin 0.5 L ha-1 at stage H, and repeated 4 and 8 days later; 6 – Promalin 0.5 L ha-1 at 40% of stage E2 and repeated at stages F2 and H; 7 – Promalin 0.75 L ha-1 at 80% of stage E2, and repeated at stage H.

The variables evaluated were, fruits per cluster, fruit set, fruits per tree, mean fruit weight, fruit length (L), fruit diameter (D), L/D ratio, seeds per fruit, yield per tree, percentage distribution of fruits per size class, and russeting.


RESULTS AND DISCUSSION

The effects of time of application and concentration of Promalin on the fruit set of ‘Gala’ and ‘Fuji’ are presented in Tables 1 to 4. Data in Tables 1 and 3 show a strong effect of time of application on fruit set reduction. Promalin applied when flowers were at
pink bud stage (E2) or at full bloom (F2), independently of its concentration or number of applications, reduced fruit set in relation to the control and to Promalin application after bloom, at stages H or I. The fruit set reduction was greater in 2004 than in 2005. In 2005, even the control treatment had low fruit set. Similar results were obtained for ‘Fuji’ (Tables 2 and 4), although the effects seemed to be lower because ‘Fuji’ had higher fruit set than ‘Gala’. In 2004, all Promalin applications at bloom had numerically lower fruit set than in the control, but only Promalin at 1.25 L ha-1 applied at 40% and again at 80%
of stage E2 was significantly different from all other treatments (Table 2). Promalin strongly reduced fruit set in 2005, although it had no effect when applied at stage H (Table 4). This research confirmed previous results regarding the thinning effect of
Promalin applied at bloom (Petri, 2003). Promalin also reduced the number of fruit per cluster. Numbers of fruit per tree and yields of ‘Imperial Gala’ and ‘Fuji’ were quite variable, although they tended to be reduced by Promalin application, in a similar way to the aforementioned reductions of the fruit set. In 2005, independently of time of application, all Promalin treatments significantly reduced the numbers of fruit and yields per tree of ‘Imperial Gala’ (Table 3). In 2004 (Table 1), only those treatments with Promalin applied at bloom significantly reduced yield, although all them had numerically
less production than the control. There was less reduction of the production of ‘Fuji’ following Promalin applications. For ‘Fuji’, in 2005, there was no significant difference between Promalin treatments and the control, except for the treatment Promalin 0.5 L ha-1 applied at 40% of stage E2 plus at stages F2 and H, which had higher production per tree
than the other treatments (Table 4). There was no effect of the concentration of Promalin on the production per tree. In
2005, the lowest production per tree of ‘Imperial Gala’ was found with the treatment of Promalin at 0.5 l ha-1 at stage E2 and repeated 4, 8, and 12 days later (Table 3). The mean fruit weights of ‘Imperial Gala’ and ‘Fuji’ were always significantly
higher in the plots treated with Promalin (Tables 1 to 5). The increase in fruit weight may be related to the reduction of yield per plant observed in the Promalin treated plots. However, the gain in mean fruit weight was maintained even when the production was similar to that of the control, such as in the plots treated with Promalin at the stages E2 or F2. This confirms the results of Curry and Williams (1983), who observed an increase in mean fruit weight of the apple ‘Delicious’ treated with Promalin at full bloom (F2). In relation to the control, the increase in mean fruit weight resulting from Promalin treatment increased the percentage of high caliper sized and reduced the percentage of low caliper sized fruit (Tables 6, 7, and 8). As an example , in 2005, fruit sized 120 in ‘Imperial Gala’ represented 5.8% in the control and 31.1% in the trees treated with Promalin 0.5 L ha-1 at stage E2 plus reapplications at stages F2 and H, while yields of fruit sized 198 were 31.4% and 17.3% respectively (Table 7). The greater percentage of apples found in the top classes due to Promalin application may economically compensate for
the yield reductions, since these fruit realize better selling prices. Promalin increased the fruit L/D ratio, especially for ‘Imperial Gala’ in the growing seasons 2004 and 2005 (Tables 9 and 10). On ‘Fuji’, the greatest L/D ratio was obtained with Promalin 0.5 L ha-1 at stage H and repeated 4 and 8 days later, showing a tendency for greater efficiency in L/D ratio when applied at petal fall.
Time of application and concentration of Promalin did not affect the number of seeds per fruit. Also, the effects on russeting were quite variable. The percentage of fruit with russeting other than in the peduncle cavity (grade 2) may be considered low in these trials (Table 11).


CONCLUSIONS

Promalin had thinning effect, reducing the fruit set on ‘Imperial Gala’ and ‘Fuji’ apple trees. The mean fruit weight increased from 5% to 15% due to Promalin applications. Promalin promoted fruit elongation in ‘Imperial Gala’, improving its
marketable form.


Table 1. Effect of Promalin on ‘Imperial Gala’ apple fructification in 2003/04.


Table 2. Effect of Promalin on ‘Fuji’ apple fructification in 2003/04.


 

Table 3. Effect of Promalin on fruit set, fruit per tree, yield per tree, and mean fruit weight
of ‘Imperial Gala’ in 2004/05.


 

Table 4. Effect of Promalin on fruit set, number of fruits per plant, yield per plant, and
mean fruit weight of ‘Fuji’ in 2004/05.


 

Table 5. Effect of Promalin on fruit size and shape of ‘Gala’ and Fuji apples in 2003.


 

Table 6. Effect of Promalin in the percentage of fruit of ‘Imperial Gala’ and ‘Fuji’ sized
<135 and >180 in 2004.


 

Table 7. Effect of Promalin on ‘Imperial Gala’ fruit distribution per size class in 2005.


 

Table 8. Effect of Promalin on ‘Fuji’ fruit distribution per size class in 2005.

 


 

Table 9. Effect of Promalin on fruit L/D ratio and on the number of seeds per fruit of
‘Imperial Gala’ and ‘Fuji’ apples in 2004.

 


 

Table 10. Effect of Promalin on fruit L/D ratio and on the number of seeds per fruit of
‘Imperial Gala’ and ‘Fuji’ apples in 2005.

 


 

Table 11. Effect of Promalin on the percentage of fruit with different intensities of
russeting in ‘Fuji’ apples in 2005.

 


ORIGINAL DOCUMENT

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