Physiological disorders of cucurbits.

1. Physiological disorders of cucurbits
Kavya D.O.
1st Year PhD (Horticulture)
Department of Vegetable Science,
College of Horticulture, Bagalkot.
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2. • Physiological or abiotic disorders are distinguished from other disorders in that they are not caused
by living organisms (viruses, bacteria, fungi insects etc), but are caused by non- living, abiotic
situations and cause a deviation from normal growth.
• They are physical or chemical changes in a plant from what is normal and generally caused by and
external factor.
• Most of the physiological disorders are not reversible once they have occurred.
• Physiological disorders have a major role in hammering the yield and quality of fresh vegetables.
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3. 1. Nutritional
physiological disorders –
Eg. blossom end rot in
water melon and tomato.
2. Temperature
physiological disorders
(low and high)
Eg. sunburn on the
shoulders of tomato,(high-
temperature injury
occurred prior to harvest).
3. Respiratory
physiological disorders -
low oxygen and or high
carbon dioxide
concentrations in and/or
around harvested produce
in CAS and MAP. Eg. black
heart of potato (low-
oxygen injury).
4. Miscellaneous
disorders- which are
product-specific in terms of
symptoms expressed.
Eg. a) Bitterness
(isocoumarin
accumulation) in carrot.
b) Greening of potatoes
exposed to light
Physiological disorders can be divided into four general categories:
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4. 1. Preharvest environment conditions
– Temperature
– Nutrition
– Water regimes
– Crop development factors (e.g. yield or crop load, position on the
plant and carbohydrate, water and /or nutrient partitioning)
2. Postharvest environment conditions
– Temperature regime
– Gas atmosphere
– Storage time
4
Causes of physiological disorders
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6. Cucumber
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7. Disorder Cause Symptoms Remedy
Crooked fruit or
crooking
Imperfect Pollination
and fertilization
Curved fruit Optimum irrigation
and nutrition
scheduling may prove
to be helpful.
Pillow Ca deficiency Abnormal white
styofoam like porous
textured tissue is
formed in the
mesocarp of the
fruits
Apply calcium
adequately
Fruit splitting or
cracking
Heavy rainfall or rain
after long period of
water stress
The cracking is
mostly vertical
initiated from the
basal part of
the fruit.
Improving moisture
conservation in soil
will help reduce
cracking.
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8. Water Stress and Storage Environment Affect Pillowy Fruit Disorder
in Cucumber
• Pillowy fruit disorder (PFD) was more frequent (110% to 150%) and more severe (59% to 81%) in
freshly harvested fruits from stress plots when compared to controls. No after-storage differences in PFD
were detectable between water stress treatments. Mean PFD ratings of processed fruit following postharvest
storage at 26.5C and either 60% or 75% relative humidity were significantly higher than ratings of fruit stored
at either 10.5 or 15.5C and 85% relative humidity.
• The progressive development of pillowy and the observed enhancement of PFD symptoms following storage
at higher storage temperatures indicated that postharvest changes can occur in fruit mesocarp tissue and that
the development of PFD can be altered, to some extent, during storage. Negative correlations (– 0.18 to –
0.78) between fruit quality and PFD ratings suggested that these changes can affect processed product
quality.
Thomas et al.,1992
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9. Disorder Cause Symptoms Remedy
Light belly
colour
Direct contract of the
fruits with moisture,
soil suppresses
development of
normal fruit colour.
The side of the fruit
touching moist,
cool soil turns to
yellow or whitish
yellow.
Use of plastic
mulch can check
contact of fruit with
moisture soil
helping to avoid
this disorder.
Misshapen fruits Environmental factor
adversely affecting
pollination and
Fertilization.
This refers to
formation of
abnormal- shaped
fruits with reduced
market value.
Keep the optimum
plant population.
Maintain uniform
soil moisture
throughout the crop
period.
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10. Squashes
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11. • It is a physiological disorder of summer squash
(cucurbita pepo)
• This disorder occurs due to moisture scarcity
• The leaves become silver coloured and contain less
chlorophyll
• Photosynthesis is hampered in the silvered leaves
Control:
• Apply adequate and frequent irrigation
LEAF SILVERING
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12. Unfruitfulness in pointed gourd:
• Pointed gourd is a dioecious cucurbit. So, male and female plants are separate.
• A common problem is met where pistillate flowers in female plants are shed due to lack of pollination and
fertilization. In some cases, ovary of the unfertilized flower may flow a bit due to parathenocarpic stimulation
which also abscise after a few days.
Control:
• Male plants must be grown in the field along with the female plants at the rates of 10-12 male plants per 100
female plants to ensure adequate pollination and fruit set.
• Hand pollination may be done successfully to achieve fruit set.
• Hand pollination to the female flowers should be done in the early morning hours because stigma receptivity
decreases with an advancement of the day.
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13. Watermelon
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14. Symptoms:
• The blossom end of the fruit develops a dark leathery
appearance. Symptoms may progress until the entire end of the
fruit turns black and rots
Cause:
• This disorder is associated with insufficient calcium uptake
and alternating periods of wet and dry soil
• Damage to the root system may also account for decreased
calcium uptake and the development of blossom-end rot
Control:
• Minimized by mulching to maintain constant soil moisture,
applying calcium fertilizers and avoiding high levels of nitrogen.
Drip irrigate crop to control water management
BLOSSOM-END ROOT
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15. Blossom-end rot of watermelon in the southern region of Oman
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Blossom-end rot, a non-parasitic disease, was found to occur widely on some
oblong varieties of watermelon, causing much damage in the southern region of
Oman (Dhofar). Fruit contact with soil surface seems to be the major agent of
blossom-end rot of watermelon, especially in the early stage. Incidence of
watermelon blossom-end rot was apparently reduced by mulch using a mixture
of dried grasses or coconut leaves.
Hammouda et al., 1987

16. HOLLOW HEART
Symptoms:
• Cracks in internal watermelon fruit flesh can occur due to
accelerated growth in response to ideal growing conditions.
Cause:
• There is a genetic component to this disorder, but growing
conditions can account for much of the variation observed.
• It appears to be associated with conditions that result in poor
pollination followed by rapid fruit growing conditions.
Control:
• Avoid watermelon varieties with a tendency to exhibit hollow heart.
Implement best practices for irrigation and fertilization programs.
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Maynard et al., 1999
Watermelon Fruit Disorders

18. Symptoms:
• Papery white areas develop on fruit
Cause:
• Develops during hot summer weather when fruit
are suddenly exposed to direct sunlight
Control:
• Minimized by maintaining strong vine growth to ensure
the fruit is covered
SUNSCALD
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19. Delay in fruit ripening
• This problem is particularly important in muskmelon and watermelon. Delay in repining is
sometime associated with less sweetness and cracking of fruits which occur due to high moisture
level and temperature fluctuation at ripening stage
Control:
• Irrigation should be stopped at the ripening stage to hasten ripening
• Sowing time should be adjusted in such a way that fruits ripe in hot and rainless condition which
hastens ripening and at the same time improve sweetness of the fruits
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Fruit disorders Leaf / plant disorders of cucurbits
Poor pollination
Bitterness
Frost or Low Temperature Injury
Drought stress
Yellowed foliage due to flooding.
Magnesium deficiency
Manganese toxicity
Molybdenum deficiency
Nitrogen deficiency
Stem splitting
General disorders of cucurbits

21. With the exception of parthenocarpic cucumbers, cucurbits require pollination to produce fruit.
Several visits from pollinators on the day that a flower is open are often required to ensure appropriate
fruit development. Many fruits will appear misshapen and small when pollination is poor. Fruits will be
reduced in size at the stem end. Very high and low temperatures can also affect pollen viability,
resulting in poor pollination. If too much nitrogen is used (resulting in excessive vegetative growth) or
plants were improperly spaced, bees may have difficulty locating the flowers.
Management:
• Provide pollinators to ensure good fruit set and high yields.
• Do not spray insecticides during morning hours when flowers are open and insects are actively
pollinating plants.
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Poor pollination

22. Drought stress
Cucurbits are particularly sensitive to drought. Fruit are typically 85% to 90% water and can suffer
under drought conditions. Pumpkins often produce long vines with many leaves and can transpire
large quantities of water during hot summer days. Severe drought stress affects fruit development,
resulting in unmarketable produce. Affected fruit may appear curled, distorted, or tapered at the
blossom end; pumpkins become soft and wrinkled.
Management:
• Irrigate when necessary.
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23. Bitterness
All cucurbits produce a group of chemicals called cucurbitacins, which cause the
vegetables to taste bitter, and the higher the concentration of cucurbitacin the more bitter the
vegetable will taste. Mild bitterness is fairly common in cucumbers resulting from higher
levels of cucurbitacin triggered by environmental stress, like high temperatures, wide
temperature swings or too little water. Uneven watering practices (too wet followed by too
dry), low soil fertility and low soil pH are also possible stress factors. Over mature or
improperly stored cucurbits may also develop a mild bitterness.
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24. Frost or Low Temperature Injury
Air temperatures at or slightly below freezing (depending on the extent of radiational cooling) can severely
damage all cucurbits seedling stages may be severely stunted or killed by low, but non freezing
temperatures because they are "chilling sensitive crops. Damage progresses from a water-soaked
appearance of affected leaf tissue or fruit surface immediately after exposure, to a grayish-green scorched"
appearance of leaves.
Overhead irrigation applied during the low temperature exposure may provide partial protection
against a light frost
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Yellowed foliage due to
flooding.
Leaf / plant disorders of cucurbits
Magnesium deficiency on
muskmelon leaves.
Manganese toxicity on a
muskmelon leaf.

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Molybdenum deficiency of
cucurbit crops.
Nitrogen deficiency on
pumpkins.
Stem splitting on watermelon
transplants.

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