Chemical thinning programs for vigorous ‘Maxi Gala’ apple trees under black anti-hail netting in Southern Brazil

Marchioretto, Lucas De Ross; Rossi, Andrea De; Marodin, Gilmar Arduino Bettio

doi:10.1590/0034-737X202471000005

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Crop production • Rev. Ceres 71 • 2024 • https://doi.org/10.1590/0034-737X202471000005 copy

Chemical thinning programs for vigorous ‘Maxi Gala’ apple trees under black anti-hail netting in Southern Brazil¹ 1 This work is part of the doctoral thesis of the first author.

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

Hail netting increases natural fruitlet drop. Mixing lower concentrations of Plant Growth Regulators (PGRs) and spraying on more advanced fruitlets could promote adequate crop load management and improve fruit quality. The objective of this study was to evaluate thinning programs with low concentrations of PGRs sprayed at advanced fruitlet size looking for reducing crop load, enhancing fruit quality, and preserving yield. On 2020/21 and 2021/22, in an orchard covered with hail netting in Bom Jesus-RS, eight programs were tested on vigorous ‘Maxi Gala’: Benzyladenine (BA)+Gibberellic acid₄₊₇ (BA-GA) at full bloom (FB) and BA+Ethephon (ETH) at 15mm; BA-GA at FB and Naphthalene acetic acid+Carbaryl (CB) at 7 mm; BA-GA at FB and BA+CB at 15 mm; ETH+CB at 15 mm and Metamitron (MM)+ETH at 20 mm; BA-GA at FB and BA at 7 mm and MM at 20 mm; MM at 7 mm and MM at 20 mm; Manual Thinning Only; Untreated Control. The treatments containing CB reduced fruit set, although diminished yield unsustainably. All PGR programs improved fruit quality. In conclusion, BA-GA at FB and BA+ETH at 15 mm, and MM at 7 mm and MM at 20 mm reduce crop load, preserve yield and improve fruit quality.

Keywords
(CLM) crop load management; Malus domestica Borkh; fruit set; semi-vigorous rootstock; fruit weight

Treatments	Growth stages
Treatments	Full Bloom	7 mm	15 mm	20 mm
T1	Untreated Control (UTC)
T2	Manual Thinning Only (MTO)
T3	Promalin^®, 2 L.ha^-1		Maxcel^®, 3 L.ha^-1 + Ethrel 720^®, 1.5 L.ha^-1
T4	Promalin^®, 2 L.ha^-1	ANA Técnico^®, 20 g.ha^-1 + Sevin 480 SC^®, 0.6 L.ha^-1
T5	Promalin^®, 2 L.ha^-1		Maxcel^®, 3 L.ha^-1 + Sevin 480 SC^®, 0.6 L.ha^-1
T6			Ethrel 720^®, 1.5 L.ha^-1 + Sevin 480 SC^®, 0.6 L.ha^-1	Goltix WG^®, 280 g.ha^-1 + Ethrel 720^®, 1.5 L.ha^-1
T7	Promalin^®, 2 L.ha^-1	Maxcel^®, 3 L.ha^-1		Goltix WG^®, 280 g.ha^-1
T8		Goltix WG^®, 170 g.ha^-1		Goltix WG^®, 280 g.ha^-1

		Fruit set (fruits/flower clusters)¹
Treatments		Growing seasons
Treatments		20/21	21/22	Mean
UTC 1 (T3, T4, T5, T7)	-	0.54	0.54	0.54
UTC 2 (T6)	-	0.97	1.01	0.99
UTC 3 (T8)	-	0.82	0.64	0.73
T3	BA+GA,FB / BA+ETH,15	0.45	0.35	0.40
T4	BA+GA,FB / NAA+CB,7	0.29	0.29	0.29
T5	BA+GA,FB / BA+CB,15	0.37	0.39	0.38
T6	ETH+CB,15 / MM+ETH,20	0.56	0.54	0.55
T7	BA+GA,FB / BA,7 / MM,20	0.47	0.58	0.52
T8	MM,7 / MM,20	0.57	0.61	0.59
Mean		0.56	0.55
		p-value
Growing season (GS)		ns
Treatment (T)		< 0.0001
GS*T		ns
C.V. (%)		46.72
Contrasts				p-value
T3 vs UTC 1				0.0766
T4 vs UTC 1				0.0006
T5 vs UTC 1				0.0624
T6 vs UTC 2				< 0.0001
T7 vs UTC 1				0.8929
T8 vs UTC 3				0.2481

	Crop load (Fruits.cm^-2 TCSA)¹ 1 Data transformed through √y.					Number of fruits removed at the manual thinning per tree³ 3 Treatment means followed by different letters in a column are significantly different according to the Tukey-Kramer-Nemenyi test (p ≤ 0.05).						Yield (t.ha^-1)¹ 1 Data transformed through √y.
	Growing season						Growing season					Growing season
Treatments² 2 Treatment means followed by different letters in a column are significantly different according to the Tukey’s HSD test (p ≤ 0.05).		20/21		21/22		Mean	20/21		21/22		Mean	20/21	21/22	Mean
T1	UTC	10.24	a	5.77*	a	8.00	-		-		-	79.1	44.4	61.7	A
T2	MTO	7.89	ab	4.15*	ab	6.02	41	a	5	a	23	85.9	33.3	59.6	AB
T3	BA+GA,FB / BA+ETH,15	6.21	bc	4.11*	ab	5.16	9	b	3	a	6	63.9	34.1	48.9	ABC
T4	BA+GA,FB / NAA+CB,7	3.74	d	4.19^ns	ab	3.97	6	b	2	a	4	50.4	35.1	42.7	BC
T5	BA+GA,FB / BA+CB,15	5.42	cd	3.29^ns	b	4.35	10	b	1	a	6	55.0	26.3	40.7	C
T6	ETH+CB,15 / MM+ETH,20	5.29	cd	4.15^ns	ab	4.72	10	b	2	a	6	50.2	34.0	42.1	C
T7	BA+GA,FB / BA,7 / MM,20	5.13	cd	3.61^ns	b	4.37	15	ab	1	a	8	60.1	26.5	43.3	BC
T8	MM,7 / MM,20	5.41	bcd	4.45^ns	ab	4.93	12	ab	3	a	8	60.3	33.7	47.0	ABC
Mean		6.17		4.22			15		2			63.1	33.4*
		p-value					p-value					p-value
Growing season (GS)		0.0125					-		-				0.0008
Treatment (T)		< 0.0001					0.0013⁴ 4 Significance according to the Kruskal-Wallis test (p ≤ 0.05). TCSA: trunk cross-sectional area; UTC: Untreated Control; MTO: Manual Thinning Only; BA+GA4+7: Benzyladenine+Gibberellic Acid4+7; BA: Benzyladenine; ETH: Ethephon; NAA: Naphthalene Acetic Acid; CB: Carbaryl; MM: Metamitron. FB: Full Bloom; 15: Fruitlet Ø 15 mm; 20: Fruitlet Ø 20 mm. Non-bold lowercase data: simple effects; Bold uppercase data: main effects.		ns⁴ 4 Significance according to the Kruskal-Wallis test (p ≤ 0.05). TCSA: trunk cross-sectional area; UTC: Untreated Control; MTO: Manual Thinning Only; BA+GA4+7: Benzyladenine+Gibberellic Acid4+7; BA: Benzyladenine; ETH: Ethephon; NAA: Naphthalene Acetic Acid; CB: Carbaryl; MM: Metamitron. FB: Full Bloom; 15: Fruitlet Ø 15 mm; 20: Fruitlet Ø 20 mm. Non-bold lowercase data: simple effects; Bold uppercase data: main effects.				0.0003
GS*T		0.0017					-		-				ns
C.V. (%)		21.89					159.56						25.24

			Fruit weight (g)				Ratio Length:DiameterGrowing season						Yield of fruits Ø > 60mm (%)¹ 1 Data transformed through.
			Growing season				Growing season						Growing season
Treatments² 2 Treatment means followed by different letters in a column are significantly different according to the Tukey’s HSD test (p ≤ 0.05).		20/21		21/22		Mean	20/21		21/22		Mean	20/21	21/22	Mean
T1	UTC	94.8	c	91.1^ns * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05).	a	93.0	0.94	b	1.03^* * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05).	b	0.98	70	37	54A
T2	MTO	98.8	bc	92.8^ns * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05).	a	95.8	0.94	b	1.03^* * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05).	b	0.99	73	45	59A
T3	BA+GA,FB / BA+ETH,15	120.7	a	90.5^* * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05).	a	105.6	0.96	ab	1.03^* * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05).	b	0.99	87	45	66A
T4	BA+GA,FB / NAA+CB,7	116.1	a	88.0^* * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05).	a	102.0	0.99	a	1.03^ns * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05).	b	1.01	78	40	59A
T5	BA+GA,FB / BA+CB,15	120.2	a	93.6^* * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05).	a	106.9	0.96	ab	1.07^* * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05).	a	1.02	79	45	62A
T6	ETH+CB,15 / MM+ETH,20	105.6	abc	88.2^ns * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05).	a	96.9	0.95	b	1.03^* * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05).	b	0.99	66	40	53A
T7	BA+GA,FB / BA,7 / MM,20	115.8	a	94.9^* * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05).	a	105.4	0.97	ab	1.05^* * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05).	ab	1.01	86	48	67A
T8	MM,7 / MM,20	112.0	ab	90.0^* * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05).	a	101.0	0.95	b	1.03^* * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05).	b	0.99	82	39	60A
Mean				110.6		91.1			0.96		1.04	78	*42^ * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05).**
						p-value					p-value		p-value
Growing season (GS)						0.0157			0.0004				< 0.0001
Treatment (T)						0.0002			0.0003				ns
GS^* * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05). T						0.0004			0.0029				ns
C.V. (%)						15.96			5.09				22.25

		Seed number per fruit¹ 1 Data transformed through.			Flesh firmness (N)			Total soluble solids (°Brix)			Skin russet 10-30% of fruit surface area (%)
		Growing season			Growing season			Growing season			Growing season
Treatments² 2 Treatment means followed by different letters in a column are significantly different according to the Tukey’s HSD test (p ≤ 0.05).		20/21	21/22	Mean	20/21	21/22	Mean	20/21	21/22	Mean	20/21	21/22	Mean
T1	UTC	5.47	3.17	AB	67.48	78.94	73.21A	10.42cd	11.62^* * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05). b	11.02	46	64	55A
T2	MTO	5.54	3.86	A	66.01	76.90	71.46A	10.40d	12.11^* * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05). ab	11.26	48	64	56A
T3	BA+GA,FB / BA+ETH,15	4.63	2.45	CD	68.53	76.45	72.49A	11.21abc	12.00^* * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05). ab	11.61	40	61	51AB
T4	BA+GA,FB / NAA+CB,7	4.58	3.00	BCD	68.08	74.74	71.41A	10.83bcd	11.89^* * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05). ab	11.36	28	56	42B
T5	BA+GA,FB / BA+CB,15	4.14	2.32	D	68.74	80.19	74.47A	10.77bcd	12.43^* * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05). a	11.60	37	55	46AB
T6	ETH+CB,15 / MM+ETH,20	5.13	2.83	ABC	70.35	77.94	74.14A	11.70a	12.19^nsab	11.94	45	70	58A
T7	BA+GA,FB / BA,7 / MM,20	4.99	3.16	ABC	70;73	77.74	74.23A	11.24ab	11.71 ^nsab	11w.48	41	59	50AB
T8	MM,7 / MM,20	5.32	3.59	AB	67.63	78.20	72.91A	10.62bcd	12.04^* * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05). ab	11.33	42	69	56A
Mean		4.98	*3.05^ * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05).**		68.44	*77.64^ * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05).**		10.90	12.00		41	*62^ * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05).**
			p-value			p-value			p-value			p-value
Growing Season (GS)			0.0345			0.0001			0.0003			0.0005
Treatment (T)			< 0.0001			0.0257			0.0001			0.0009
GS^* * and ns in a row are significant and non-significant, respectively according to confidence intervals (p ≤ 0.05). T			ns			ns			0.0014			ns
C.V.(%)			19.06			7.91			7.25			21.29

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[1] * Corresponding author: lucasdeross@hotmail.com

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Chemical thinning programs for vigorous ‘Maxi Gala’ apple trees under black anti-hail netting in Southern Brazil1 1 This work is part of the doctoral thesis of the first author.

ABSTRACT

Chemical thinning programs for vigorous ‘Maxi Gala’ apple trees under black anti-hail netting in Southern Brazil¹ 1 This work is part of the doctoral thesis of the first author.