Effects of plant growth regulator (2,4-D) treatments on fruit development and chemical content in the kiwifruit plant (Actinidia chinensis)

Abstract

As a dioecious fruit tree, Kiwifruit requires pollination for female plants to bear fruit. This study used 2,4-Dichlorophenoxyacetic acid (2,4-D), a plant growth regulator, to induce fruit set, improve quality and increase kiwifruit yield in Actinidia chinensis var. 'Donghong' without pollination. Exogenous application of 2,4-dichlorophenoxyacetic acid (2,4-D) effectively triggered parthenocarpic fruit development in 'Donghong' kiwifruit (Actinidia chinensis var. 'Donghong'), while significantly improving fruit quality. The fruit set rate of parthenocarpic fruits reached 16.95% with 2,4-D treatment at 140 days after flowering; female flowers treated with 2,4-D showed differences in pollen structure compared to those treated with water. Also, no viability was detected in female flower pollen treated with 2,4-D. At the maturity stage, the fruits from the 2,4-D treatment were slightly smaller than those from the control group. The 2,4-D treatment group showed significant differences from the control group in skin hardness, flesh firmness and core hardness. There was no significant difference in the soluble solids content between the fruits treated with 2,4-D and those from the control group at maturity. However, the dry matter content of the 2,4-D treated fruits was lower than that of the pollinated fruits. The soluble sugar content of mature fruits from 2,4-D treatment reached 18.59 g/kg, and organic acid content was 18.10 g/kg, resulting in a significantly higher sugar-acid ratio than the control group. The seeds from 2,4-D treated fruits failed to germinate normally. This technology can facilitate the induction of fruit sets in actual production, which has significant practical value and potential in kiwifruit processing. From these results, important data were obtained regarding the establishment and production of kiwifruit orchards without including pollinator varieties, which take up a significant amount of space in the orchard establishment and cause a decrease in the yield obtained from the total area.

Keywords: 2,4-D; Fruit quality, germination; Kiwifruit; Parthenocarpy.

Fig. 1

Morphological diagram of flower development stage after pollination treatment and 2,4-D treatment of ‘Donghong’ kiwifruit. (A) Control treatment groups; (B) 2,4-D treatment groups; (a) intact flower morphology in F1; (b) intact flower morphology in F2; (c) intact fruit-sitting morphology in 3 DAF; (d) flower longitudinal cut morphology in F1; (e) flower longitudinal cut morphology in F2; (f) fruit-sitting longitudinal cut morphology in 3 DAF

Fig. 2

Pollen morphology and pollen viability of Actinidia chinensis (A), Pollen grain size (B). (a) male pollen grains of Actinidia chinensis; (b):'Donghong'kiwifruit pollen (water control group); (c):'Donghong'kiwifruit pollen grains (2,4-D treatment group); (d): Pollen tube germination of male flowers of Actinidia chinensis; (e):'Donghong ‘kiwifruit pollen tube germination (water control group); (f): ‘Donghong ‘kiwifruit Pollen tube germination (2,4-D treatment group); the statistical methods used One-way ANOVA; * represent significant difference at p<0.05. ** represent extremely significant difference at p<0.01

Fig. 3

Histological observation of different treatments at various stages of flower development of ‘Donghong’ kiwifruit. (A) ‘Donghong’ kiwifruit ovary microscopic transverse section; (a) ovary microscopic transverse section in control group at F1; (b) ovary microscopic transverse section in control group at F2; (c) ovary microscopic transverse section in control group at 3 DAF; (d) ovary microscopic transverse section in 2,4-D treatment group at F1; (e) ovary microscopic transverse section in 2,4-D treatment group at F2; (f) ovary microscopic transverse section in 2,4-D treatment group at 3 DAF; (B) the microscopic transverse section of the ovary wall cells; (g) control group F1 period; (h) control group F2 period; (i) control group 3 DAF period; (j) 2, 4-D treatment group F1 period; (k) 2,4-D treatment group F2 period; (l) 2,4-D treatment group 3 DAF period; (C) ovary wall thickness; (D) cell size; (E) number of cells; water treatment was control at F1 and F2, pollination treatment was control at 3 DAF; C: water treatment; P: pollination treatment; 2,4-D: 2,4-D Treatment; 1: ovules; 2: ovary; the statistical methods used One-way ANOVA; * represent a significant difference at p<0.05. ** represent extremely significant difference at p<0.01

Fig. 4

Morphological map of parthenocarpy of ‘Donghong’ kiwifruit in different periods and fruit transverse diameter, longitudinal diameter, lateral diameter, fruit shape index and single fruit weight. (A) Appearance figure; (B) cross-section morphological map; (C) fruit transverse diameter; (D) fruit lateral diameter; (E) the fruit longitudinal diameter; (F) fruit shape index; single fruit weight(G); P: pollination treatment; 2,4-D: 2,4-D treatment; the statistical methods used One-way ANOVA; * represents a significant difference at p<0.05. ** represents extremely significant difference at p<0.01

Fig. 5

Single fruit weight, dry matter, soluble solids (a) and texture analysis (b-e). P: pollination treatment; 2,4-D: 2,4-D treatment; the statistical methods used One-way ANOVA; * represents a significant difference at p<0.05. ** represents extremely significant difference at p<0.01

Fig. 6

Determination of soluble sugar (A) and organic acid (B) content and ratio of sugar to acid (C) at mature stage. P: pollination treatment; 2,4-D: 2,4-D treatment; the statistical methods used One-way ANOVA; * represents a significant difference at p<0.05. ** represents extremely significant difference at p<0.01.

Fig. 7

Seed germination rate (A) and seed germination morphology (B)