Growth and Development of Horticultural Crops (1+1)

Regulation of fruit drop

FRUIT DROP
Causes

• The fruit lost are those they have not been completely pollinated.
• Competition between the fruits for food, water and nutrients
Fruit drop and growth regulators

• The application of plant growth regulators can re-enforce hormone balance in the peel, reducing or retarding this precocious fall and the losses at harvest (Primo et al., 1966).
• Monselise and Goren (1978) reported that the spraying of auxins prevented the dropping of fruit by maintaining the cells at the zone of abscission, preventing the synthesis of hydrolitic enzymes, such as cellulase, which decomposed the cell walls.
• Citing Riov (1974), the same authors reported that hormone balance acted on the polygalacturonase activity, which, together with cellulase, was responsible for the degradation of the two important components of cell walls, cellulose and pectin.
• The use of 2,4-D as a growth regulator to promote size and to control fruit and leaf drop was reported by Hield et al. (1964)
• According to El-Otmani (1992), the combined application of GA3 and 2,4-D reduces the precocious drop of fruit through the action of auxin and retards the softening and senescence of the peel, by the longer harvest time, and more economical storing in areas where stocking capacity is limited and cost is high.
• Prevention of pre-mature drop of fruits: 2,4,D,IAA,IBA, 2,4,5-T, are used to prevent pre-harvest deep of sweet oranges( 100 to 500 ppm)
• The effects of NAA application, cincturing and shoot-tip removal on the incidence of premature fruit
• A single, post-anthesis application of NAA (1 ppm) increased (P < 0.05) the final set of macadamia fruit by 35%.
Hormonal changes during fruit development

• The gibberellin content in seed increased rapidly during early seed growth and declined as growth decreased. The seed was the major source of gibberellin in the fruit, the pericarp containing only traces. Cytokinins were present both in pericarp and seed. During the single period of rapid growth in fruit and seed, cytokinin concentrations increased rapidly at two periods .The first rapid increase in cytokinin concentrations precedes the period of rapid cell division and cell enlargement and the second increase coincides with the period of rapid cell enlargement only. The level of ABA-like inhibitor was high in the first 21 d preceding pollination which corresponded with the period of slow growth in fruit and heavy fruit drop. During the rapid period of fruit growth, the level of inhibitors decreased and that of promoters increased. However, in maturation and slow fruit growth period, the levels of both the growth promoters and inhibitors were low. Thus all the growth promoters play their role in the growth of the fruit. Deficiency of auxins, gibberellins and cytokinins coupled with high level of inhibitors appear to cause fruit drop in mango cv Dashehari.
PARTHENOCARPY

• In botany, the formation of fruits without seeds. This phenomenon, of no obvious benefit to the plant, occurs naturally in some plants, such as bananas. It can also be induced in some fruit crops, either by breeding or by applying certain plant hormones.
GA3

• Gibberellic acid application (10 µmol pistil 1) caused development similar to that in pollinated pistils, while benzyladenine (1 µmol pistil 1) and naphthylacetic acid (10 µmol pistil 1) treatment produced shorter siliques. Naphthylacetic acid primarily modified mesocarp cell expansion.
Auxins

• Parthenocarpy: IBA, NAA produces seed less/fruits - smaller sized fruits, but more in number, hence yield not affected.
A Summary of growth regulator treatments used around the world.

Growth Regulators	Effect	Timing	Concentration	Extent of Effect
GA	Reduce flower number to increase fruit size.	Early June and at bud break.	One, (or for greater effect) two sprays of 25 ppm two weeks apart. Ralex® at label rates	Proportional to crop size, variety and tree vigour. 20% reduction in flowering in Australian trials. Registration of Ralex® due 2002, restricted use trial permit currently used
GA	Improve fruit set.	70-90% petal fall (October).	10 to 25 ppm	Proportional to crop size, variety and tree vigour.
Ethephon	Thin crop load	When fruitlets are 10 to 15mm in diameter	50-70ml/100Lat about 3500L/ha	Cost effective thinning agent. Good application techniques required.
3,5,6-TPA	Thin crop load especially smaller fruitlets.	When fruitlets are 15 to 17 mm in diameter	15ppm	Proportional to crop size, variety and tree vigour.
3,5,6-TPA	Expand cell size to increase fruit size.	When fruitlets are 20 to 30 mm in diameter	15ppm	Proportional to crop size, variety and tree vigour.
2,4,-D	Expand cell size to increase fruit size.	When fruitlets are 5 to 19 mm in diameter	57-110g/ha@ 5000L/ha.	Proportional to crop size, variety and tree vigour. Isopropyl ester formulation.
Dichlorprop (2,4,DP)	Expand cell size to increase fruit size.	Mandarins: 15 to 20 mm in diameter Oranges: 22 to 25 mm in diameter	50 to 100 ppm.	Proportional to crop size, variety and tree vigour. A 4 to 5 mm increase in fruit diameter for mandarins and a 5 to 10 mm increase for oranges.
NAA	Crop thinning	When fruitlets are 15 to 20 mm in diameter	200-350ppm	Temperature dependant (rates vary to ambient temperatures)