Physiological Disorders in Citrus, Growth Regulator Studies

8/3/2019 Physiological Disorders in Citrus, Growth Regulator Studies

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Physiological disorders in Citrus, Growth

regulator studies in Propagation,Flowering and Fruit setting

Mr. Srikantaprasad, DUHS11PGD27

I PhD


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Mandarin

(Citrus reticulata)


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Physiological disorders

Fruit drop

Mandarins: very high initial flowering and

fruiting, heavy fruit drop

the ultimateyield is often low.

In mandarins three distinct waves.

1 soon after fruit setting,

2 during May- June (June drop)

3 drop of mature fruits before harvesting(pre harvest drop).


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Causes: Fluctuating temperature, low atmospheric humidity,

imbalance of soil moisture, lack of proper nutrition,

hormonal imbalance, incidence of insect pests and diseases

Remedy: maintenance of appropriate soil moisture level

during fruit development and application of growth

regulators2,4-D (10 ppm), NAA (5ppm), 2, 4, 5-T (5ppm)

check fruit drop quite effectively. Further, application or

Aureofungain @ 20ppm helps in better retention of fruits

through control of fungal diseases.


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Granulation


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Granulation

Physiological disorder of juice sacs, they become comparatively

hard, grayish color and enlarged. The concentration of pectic

substances increases, reduction in juice content, TSS and acid

content. Because of low sugar and acid content, the granulated

vesicles become rather tasteless and colorless.

.


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Causes:

Young, vigorous trees are more likely to develop granulated

fruits than older ones. Similarly, large fruits have moregranulation than small ones. In addition, granulation

increases as the picking season advances. The incidence of

granulation is highly specific to the type of the mandarin

being cultivated. It is favoured by high relative humidity

and temperature during spring.


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Remedy:

Spraying of lime.

Regulation of irrigation Applications of 2, 4-D (12ppm), zinc and

copper reduces

correct nutrition should be applied,

fruit should be harvested early.


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Decline

After fruitful production for about 15 years, orchards startbearing little crop and become uneconomical.

They show symptoms of ill health and decline. The affected trees

do not die completely but remain in state of decadence and

unproductiveness for a number of years.

Initially, only a few limbs of the plants are involved but later

whole tree is affected. Plants show sparse foliage, stunted

growth, and sickly appearance and in leaves, mid-rib, lateral veins

and intervenal area show diffused yellow color leading to

ultimate shedding of leaves.

As a result of dieback, twigs become short and bear only a few

narrow leaves at their basal ends. Such plants are also

characterized through excessive flowering and very poor fruit

set.


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Unfavourable soil conditions (presence of hard pan, high pH, poor

drainage and high salts), malnutrition, poor orchard management,

indiscriminate use of fertilizers, intercropping, incidence of insect

pests and diseases are major factors contributing to it.

Good cultural practices, improvement in soil fertility and drainage,

control of insect pests, nematodes and diseases may be useful to

minimize its incidence. Use of resistant and compatible rootstocks

and certified budwood for propagation are strongly recommended

for a healthy and productive mandarin orchard.


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Twig dieback

Along with leaves die and dry up on the

tree, gum appears in the wood. Leaves

drop, dry and there is no gum present.

In navel oranges some of the new shoots

developed during the early warm periods

wilt and die back later and stand out

among the green foliage of the tree.Spring twig dieback is often worse on the

western side of the tree.


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Causes:

Damage to the root system by fungi, nematodes,

salt injury, excessive fertiliser application and

periods of excessive dryness (Low soil temperatures, Low soil

moisture, Dry winds and low humidity, Frost injury)

Melanose fungus

If twig dieback has killed young branches, prune them out to avoid

fruit damage. To control twig dieback, maintain optimum soil watercontent, particularly in late autumn and winter.


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Fruit splitting

Fruit splitting is often seen in navel oranges, lemons and othercitrus fruits when temperatures drop and relative humidity

increases with the approach of winter. Splits occur longitudinally

starting at the navel end, where the rind is thinnest.

Causes: great climatic and soil moisture irregularities.

Internal pressure developed by the pulp causes the rind to split.

Regular application of fertiliser and water to provide smooth,

uninterrupted growth might reduce the problem.

foliar spray of potassium fertilizer (Tucker et al. 1994).


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Albedo breakdown or creasing

A major rind disorder of mature navel oranges in particular, but

other fruits can be affected. It shows up as an irregular patternof grooves and furrows in the rind, and is worse on the shaded

side of the fruit. Creasing is caused by excessive loss of

cohesion between albedo cells (the white layer under the skin)

stressed by expansion of the pulp.

Factors that may contribute are rind mineral levels (e.g. low

calcium or high magnesium), rootstock (higher incidence on

rough lemon), water relations, tree age, nutritional conditions

and tree health.

Creasing can be reduced with pre-harvest

sprays of gibberellic acid as well as

calcium sprays


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Sunburn

Sunburn of fruit is worse in varieties which produce their fruit on the

outside of the trees such as Murcott tangor, Afourer and Satsumamandarins. It can affect citrus trees in various ways, burning the

fruit, leaves and bark. It may be due to direct sunlight or hot drying

winds coupled with inadequate moisture uptake.To minimise sunburn, do not over-prune citrus trees and paint the

stems of young trees or exposed limbs with a white, water-based

paint.

navel orange with sunburn


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Winter yellowsWinter yellows is a disorder of citrus trees which is

common when good growing conditions continue

late into autumn.

Immature foliage goes yellow at the onset of cold weather, but re-

greens and develops normally with the return of warm weather in

spring. In some seasons it affects mature, functional leaves.

Winter yellows usually begins between late March and early April and

develops rapidly as the days shorten.

In severe cases the leaves may fall and there may be some out-of-season blossoming.


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Physiologically, the yellowed leaves have excess starch and the

root system is depleted of starch and parts of it may die.Once warmer temperatures and longer days set in, the tree

gradually recovers but it will be retarded if the root system has

been damaged.

Cause:

Unknown (may be the depleted carbohydrate reserves of the

root system)

Hickson mandarin and Eureka lemon are particularly susceptible

to winter yellows.

Remedy: discouraging late autumn growth of two to five year old trees

(reduce water and fertiliser)

leaving a few fruit on young trees to avoid excess vegetative

growth


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Use of growth regulators

Degreening: application of Ethrel (50ppm) one week before

the actual date of harvesting

Further, fruits dipped in 50 ppm Ethrel after harvesting

develop golden yellow color within 5 days of the treatment.


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New degreening treatments to improve the quality of citrusfruit combining different periods with and without ethylene

exposure Clemenules variety good colour with the lowest incidence

of calyx alteration, the optimum degreening treatment wasbased on 72 h with ethylene and 48 h without ethylenewhen fruit were harvested with a color index of between

9 and 3. Another treatment of 24 h with ethylene plus 48 h without

ethylene is recommended for fruit with an external colorindex higher than 2.

Navelina oranges, highly sensitive to calyx senescence

during degreening, a treatment consisting of 24 h withethylene plus 48 h without ethylene is recommended,which involves harvesting the fruit with a color index ofover 0.

Sdiri, et al., 2011


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Citrus clementine cv.Nules (a seedless mandarin) excellentquality for consumption as fresh fruit

Poor fruit set small-sized fruits.

gibberellic acid (GA3) as a foliar spray environmental

issues A trial with bioregulator containing methyl-xanthine,

Fruit yield was significantly increased in treated trees from17.4 to 25.7% for GA3 and MX treatments, respectively,compared to untreated control trees,

A single foliar application of MX was enough to increasefruit set.

Spray application of MX on clementine mandarins at theend of the flowering period, when all petals have fallen.

Ana Quiones, et al., 2011


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Methyl jasmonate and salicylic acid dips can

enhance the resistance of fruit to chilling

injury probably through an increase in

antioxidant levels.

Siboza et al., 2011


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Cropping system Sweet orange (Citrus sinensis (L) Osbeck Cv. Agege) on alfisol

in Nigeria.

Sweet orange + pineapple no fruits. (pH decreased by 2.17)

There was a build up of nitrogen (N) and organic carbon in the

soil for all the intercrops after the third year of the study. The cropping mixture with legumes highest N value of 0.70 g

N/kg soil as compared to 0.30 g N/kg pre-planting.

Sweet orange leaf analysis for N in all the treatments showed

that leaf N was higher than the 2.5-2.7% optimum level,except for citrus intercropped with cassava, which had a leaf

N concentration of 2.36%.

Olanyan and Fagbayide, 2007


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Sweet orange intercropped with maize/cowpea had thehighest phosphorus (P) level of 0.17%, , while sweet orangeintercropped with cassava or pineapple had the lowest Pvalues.

Potassium (K) was in the adequate range in the sweetorange leaves for all the cropping systems, but the Zncontent was below the satisfactory range of 20-50 ppm.

The nutrient dynamics were results of the interactionamong cropping systems, soil depth, and croppingcycle.

Maize intercropped in the early planting season followed bycowpea in the late season was the most compatible cropwith sweet orange in terms of fruit yield.

Olanyan and Fagbayide, 2007


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The results of 4 year study at coorg

there will be staggered income spread over 10

months in a year when coffee is grown withpepper, cardamom and coorg mandarin.

Mixed cropping also had a higher benefit-cost

ratio of3.10 as against 1.99 in case of mono-

cropping of robusta coffee


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Mites on lemonsshowingfruit bronzing symptom;

mealybugs

iron deficiencyleaf miner


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Scab symptoms on fruit Canker symptoms on leaves and fruit

Documents

Physiological Disorders in Citrus, Growth Regulator Studies