Apple tree cultivation in Brazil is characterized by being based on two cultivars: Gala and Fuji. The first and its clones represent approximately 60% of Brazilian apple production, estimated at around 1,20 million tons in recent years. Apple trees of the Gala cultivar present rapid maturation during the harvest period and are highly sensitive to fruit drop during pre-harvest, which can result in significant production losses if not harvested at the appropriate time, reducing the post-harvest life of the fruits.
As in most Gala apple orchards and their clones, harvesting must occur in a period of less than 20 days, part of the fruits are picked at an inadequate stage of maturity, two to three weeks after the harvest point. It should also be considered that a large part of Brazil's apple production comes from orchards measuring more than 50ha, which also makes harvesting at the point considered ideal difficult. Furthermore, there are significant production losses resulting from Gala's high sensitivity to pre-harvest fruit fall.
Harvesting fruits after adequate ripeness can lead to poor conservation, low pulp strength and reduced quality. As part of the production of 'Gala' apples is sold after a period of storage, the fruits must be harvested at the appropriate time to have quality fruits at the end of storage. Considering that Gala apple trees present accelerated maturation and are prone to fruit drop during pre-harvest, the management of fruit maturation is of great economic importance in Brazilian conditions.
Figure - Pre-harvest fruit drop on Gala apple trees. Fraiburgo/SC
Fruit maturation management can be carried out through the use of strategies that reduce the formation of ethylene, a plant hormone related to fruit maturation. Among the substances that interfere with the biosynthesis of ethylene is aminoethoxyvinylglycine (AVG). Aminoethoxyvinylglycine (AVG), a compound that was discovered in the early 1970s, inhibits ethylene biosynthesis by blocking the conversion of S-adenosyl-methionine (SAM) to 1-carboxy-1-amino-cyclopropane acid (ACC) , a precursor of ethylene.
The use of AVG in apple production is recent in Brazil, however, it has been widespread. Commercially AVG, marketed under the name Retain, is used to control pre-harvest fruit drop and delay fruit maturation, allowing the harvest to be staggered without losing the characteristics that allow for adequate fruit conservation. The delay in maturation caused by the use of AVG is seen in the delay in the degradation of starch into soluble sugars and in the delay in the loss of firmness. With the delay in maturation provided by the application of AVG, an increase in the average fruit mass can be achieved due to the increase in the period between flowering and fruit maturation. Other substances can be used in apple harvest management, such as naphthaleneacetic acid (NAA), which significantly reduces pre-harvest fruit drop, although its use can increase starch degradation, reduce the firmness of the pulp and, consequently, reduce post-harvest conservation. For this reason, the use of AVG is preferred over naphthaleneacetic acid in reducing pre-harvest drop in apples.
Use of AVG on Gala apples
Application before the point of harvest prevents pre-harvest drop and delays the ripening of apple fruits. AVG applied one, two and four weeks before the harvest point (SAPC) delayed the harvest of Gala apples, where plants treated with the commercial product, regardless of the time of application, delayed the start of harvest by 18 days (Figure 1) , maintaining pulp resistance at levels higher than untreated plants (Table 1).
The increase in the period between flowering and fruit harvest resulted in an increase in the average fruit mass of around 10,2%, considering the average of the three application times evaluated (Figure 2). Regarding the development of the red color of the fruits, the product did not reduce it, but it did delay the development of the red color in proportion to the delay in fruit maturation (Table 2). In harvest management, controlling pre-harvest fruit fall is one of the most important factors, with AVG significantly reducing the loss of fallen fruit. In the present study, the best results regarding the control of pre-harvest fruit falling were obtained with 800g/ha of AVG (1 SAPC), with less than 15,3% of fruit falling at the end of the cycle, while this percentage was greater than 65% in the control treatment (without application) (Figure 1).
Use of AVG on Fuji apples
AVG treatments delayed the development of red fruit color in the same proportion as the delay in fruit maturation occurred. The delay in fruit maturation was accompanied by the maintenance of pulp resistance and starch degradation, as well as an increase in the average fruit mass compared to plants not treated with AVG. The fruit drop before the harvest point was not altered by the concentration and time of application in one or two times. The effects of AVG application on Fuji apple trees are lower than those observed on Gala apple trees, especially with regard to premature fruit drop, as Fuji apple trees are less prone to the occurrence of this disorder. However, all AVG treatments showed less fruit drop before harvest compared to plants that did not receive the treatment (Table 3 and 4).
One of the problems observed with the late harvest of Fuji apples is the increased occurrence of some disorders in the fruits, such as stem cracking and “honey dripping”. Peduncular cracking is characterized by the rupture of the fruit at the insertion of the peduncle, which can contribute to the penetration of pathogenic microorganisms. “Honey drip” is a physiological disorder in which watery areas of tissue are easily distinguished from normal pulp. Both disorders, commonly observed in Fuji apples harvested after the harvest point, can be minimized by the use of AVG, as can be seen in Table 3.
Considerations regarding the use of AVG
The producer who chooses to use AVG in apple harvest management must be guided by the cultivar's cycle, needing to note the date of full flowering observed in the orchard, in addition to knowing the average cycle between full flowering to estimate the harvest date. From the estimated harvest date, the producer will be able to determine the application date, which generally varies from seven to 30 days before the presumed harvest point. The effectiveness of AVG in controlling the ripening of Gala apples varies depending on the season and the dose applied, which can be from 400g/ha to 800g/ha. AVG applications carried out close to the harvest point and in larger doses are more effective in controlling the fall of Gala apples. In conclusion, AVG delays fruit ripening by ten to 20 days, with longer periods requiring higher concentrations.
Figure 1 - Percentage of fruits harvested by date, fruit drop by sampling season and fruit drop accumulated in Gala apple trees depending on the time of AVG application. Fraiburgo, SC
Table 1 - Effect of AVG application at different times on the firmness of Gala apple pulp at different harvest dates. Fraiburgo, SC
Treatments | Pulp firmness (lb/cm2) | ||||
13/02 | 02/03 | 13/03 | 21/03 | 29/03 | |
Witness | 19,2 b | 16,9 b | 15,5 b | 15,6 to | 13,9 b |
AVG 800g/ha – 4 SAPC* | 21,8 to | 18,7 to | 17,3 to | 16,0 to | 15,8 to |
AVG 800g/ha – 2 SAPC | 21,4 to | 18,4 to | 17,4 to | 16,0 to | 15,7 to |
AVG 800g/ha – 1 SAPC | 21,9 to | 18,3 to | 17,8 to | 15,9 to | 15,4 to |
Treatments
Pulp firmness (lb/cm2)
13/02
02/03
13/03
21/03
29/03
Witness
19,2 b
16,9 b
15,5 b
15,6 to
13,9 b
AVG 800g/ha – 4 SAPC*
21,8 to
18,7 to
17,3 to
16,0 to
15,8 to
AVG 800g/ha – 2 SAPC
21,4 to
18,4 to
17,4 to
16,0 to
15,7 to
AVG 800g/ha – 1 SAPC
21,9 to
18,3 to
17,8 to
15,9 to
15,4 to
*SAPC - Weeks Before Collection Point. Means not followed by equal lowercase letters differ significantly using the Tukey test, at a 5% probability of error.
Figure 2 - Average mass of Gala apples depending on the application of AVG. Fraiburgo, SC
Table 2 - Effect of AVG application, percentage of fruits according to the red color of the epidermis in Gala apples. Fraiburgo, SC
Treatments | Percentage of fruits according to epidermis color | ||
#/b### | ≥50e >80>#/b### | ≥ 80>#/b### | |
Witness | 9,4 to | 45,9 to | 44,7 b |
AVG 800g/ha – 4 SAPC* | 6,1 b | 43,0 to | 50,9 ab |
AVG 800g/ha – 2 SAPC | 3,9 b | 34,9 to | 61,1 to |
AVG 800g/ha – 1 SAPC | 6,7 b | 50,9 to | 42,3 b |
Treatments
Percentage of fruits according to epidermis color
#/b###
≥50e >80>#/b###
≥ 80>#/b###
Witness
9,4 to
45,9 to
44,7 b
AVG 800g/ha – 4 SAPC*
6,1 b
43,0 to
50,9 ab
AVG 800g/ha – 2 SAPC
3,9 b
34,9 to
61,1 to
AVG 800g/ha – 1 SAPC
6,7 b
50,9 to
42,3 b
*SAPC - Weeks Before Collection Point. Means not followed by equal lowercase letters differ significantly using the Tukey test, at a 5% probability of error.
Table 3 - Percentage of pre-harvest fruit drop, percentage of fruit with stem cracking and percentage of fruit with “honey drip” disorder in Fuji Suprema apple trees in response to AVG application. Fraiburgo, SC
Treatments | Pre-harvest fruit drop | Fruits with stalk crack | Fruits with a drop of honey |
| ###P# | |||
1. Witness | 8,9 to | 8,1 to | 8,3 to |
2. AVG 800 g/ha 2 SAPC1 | 2,3 b | 3,2 b | 1,9 b |
3. AVG 400g/ha 2 SAPC + AVG 400g/ha 1 SAPC | 3,0 b | 3,7 b | 1,9 b |
4. AVG 800g/ha 1 SAPC | 1,8 b | 2,3 b | 1,3 b |
5. AVG 400g/ha 1 SAPC | 4,3 b | 2,0 b | 3,1 b |
6. AVG 400g/ha 1 SAPC + AVG 400g/ha PC2 | 1,8 b | 2,7 b | 1,7 b |
7. AVG 400g/ha PC | 3,0 b | 2,9 b | 2,3 b |
Treatments
Pre-harvest fruit drop
Fruits with stalk crack
Fruits with a drop of honey
###P#1. Witness
8,9 to
8,1 to
8,3 to
2. AVG 800 g/ha 2 SAPC1
2,3 b
3,2 b
1,9 b
3. AVG 400g/ha 2 SAPC + AVG 400g/ha 1 SAPC
3,0 b
3,7 b
1,9 b
4. AVG 800g/ha 1 SAPC
1,8 b
2,3 b
1,3 b
5. AVG 400g/ha 1 SAPC
4,3 b
2,0 b
3,1 b
6. AVG 400g/ha 1 SAPC + AVG 400g/ha PC2
1,8 b
2,7 b
1,7 b
7. AVG 400g/ha PC
3,0 b
2,9 b
2,3 b
1SAPC – Weeks before harvest point. 2 PC – harvest point. ns – not significant by the F test at 5% probability of error. Means followed by the same letter do not differ from each other using the Tukey test at a 5% probability of error.
Table 4 – Percentage of harvested fruits, pulp resistance (lb/cm2) and percentage of fallen fruits 20 days after the harvest point of the control treatment as a function of the concentration and time of application of AVG in Gala. Fraiburgo, SC
Treatment | Lb/cm2 | >b#< fallen fruits | |
1 – control | 100,00a | 15,20 c | 6,14 to |
2 – AVG 830g/ha – 30 DAPC | 45,80 b | 16,50 b | 1,46 b |
3 – AVG 415g/ha – 30 + 15 DAPC | 33,50 bc | 17,00 b | 0,48 b |
4 – AVG 600g/ha – 15 DAPC | 28,30 c | 18,70 to | 0,64 b |
5 – AVG 830g/ha – 7 DAPC | 32,90 bc | 17,40 b | 0,50 b |
6 – AVG 600g/ha – 7 DAPC | 33,60 bc | 16,80 b | 0,88 b |
Treatment
Lb/cm2
>b#< fallen fruits
1 – control
100,00a
15,20 c
6,14 to
2 – AVG 830g/ha – 30 DAPC
45,80 b
16,50 b
1,46 b
3 – AVG 415g/ha – 30 + 15 DAPC
33,50 bc
17,00 b
0,48 b
4 – AVG 600g/ha – 15 DAPC
28,30 c
18,70 to
0,64 b
5 – AVG 830g/ha – 7 DAPC
32,90 bc
17,40 b
0,50 b
6 – AVG 600g/ha – 7 DAPC
33,60 bc
16,80 b
0,88 b
DAPC – Days after the harvest point. Means followed by the same letter do not differ from each other using the Tukey test at a 5% probability of error.
Check out the article in issue 84 of Cultivar Hortaliças e Frutas magazine.
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