PhysiologicalPhysiological Disorder Disorder ofof SquashSquash

Presented to :Dr. Nihad Alsmairat Done by: Eman R. Al-Junaidi

What physiological disorder What physiological disorder means??means??

Physiological plant disorders :

Refer to the breakdown of tissue that is not caused by invasion by disease causing organisms or by mechanical damage .

Squash are susceptible to several physiological and

environmental disorders that limit production or affect fruit quality.

Most of the disorders are poorly understood and can be induced by many conditions related

to nutrition, environments, or cultural practices.

We can classified disorders into many types ..

But the most important disorders are:

1.Physiological and physical disorder .

2.Pathological disorder .

Physiological Disorders

1. Chilling injury :Summer squash are chilling sensitive at temperatures below 5°C (41°F) if held for more than a day or two. Varieties vary in their chilling sensitivity (see table under special considerations). Consequences of chilling injury are water-soaked pitting, discoloration, and accelerated decay. Chilling injury is cumulative and may be initiated in the field prior to harvest.

Optimum Relative Humidity is 95%

Rates of Respiration Production :

Temperature

0°C (32°F) 5°C (41°F) 10°C (50°F) 15°C (59°F) 20°C (68°F)

ml

CO2/kg·hr6-7 7-10 17-18 37-45 42-48

2. Freezing Injury. Freezing injury will be initiated at -0.5°C (31.1°F). Symptoms of freezing injury include water soaked patches on the soft rind or an outer ring of water soaked pulp becoming brown and gelatinous in appearance over time.

Physical Injury : Harvesting should be done by cutting free of the vine rather than by snapping. A poorly trimmed stem-end is a quality defect because it promotes decay.

Summer squash are very susceptible to water loss. Shriveling may become evident with as little as 3% weight loss. Pre-cooling and storage at high RH will minimize weight loss.

Squash can be waxed, but only a thin coating should be applied. Waxing provides some surface lubrication that reduces chaffing in transit.

Summer squash skin is very tender ; skin breaks and bruises can be a serious source of water loss and microbial infection.

Oedema

This is a physiological disorder that affects cucurbits during fruit enlarging when moisture availability is uneven.

The stress causes raised, circular shaped lesions that are corky or crusty on the fruit surface.

These lesions may be irregularly spaced or just on the side exposed to sunlight.

Blossom-End Rot Disease Blossom-end rot is a summer disease very

common in tomatoes and fruit vegetables such as peppers, eggplant, and sometimes melons and summer squash.

It is a non-pathogenic disease, a physiological disorder, It is a symptom of calcium deficiency in the fruit. Calcium deficiency may be caused by low soil calcium, low calcium in maturing fruit, or fluctuating soil moisture. It is usually severe following extremes in soil moisture conditions--either too dry or too wet.

Calcium is required in large amounts by fruits for normal cell growth. When a rapidly growing fruit is calcium-deficient, normal cell growth is interrupted and the tissues start breaking down. This leaves a characteristic dry, sunken lesion at the blossom end of the fruit.

"Blossom-end rot is induced when calcium demand exceeds supply. This may come as a result of low calcium levels or competition for calcium uptake with other mineral nutrients in the soil.

"The other factors that can predispose plants to blossom-end rot are very little moisture in the soil caused by drought stress, excessive soil moisture fluctuations which reduce uptake and movement of calcium into the plant, or rapid vegetative growth due to excessive nitrogen fertilization."

"Blossom-end rot usually causes the fruit to ripen prematurely and it then becomes inedible, "Sometimes the affected areas become infected with secondary pathogens which appear black on the affected areas. The affected area can be small or may cover most of the fruit.’’

"Blossom-end rot appears as tan in color and should not be confused with sunburn that appears whitish in color mainly away from the blossom end. It appears mainly on the first cluster of fruits."

How we will control this disease??!The disease can be controlled by selecting sites with

deep, well-drained soils where plants will develop well-formed root systems for optimal uptake of calcium and other mineral nutrients.

"Test your soil after every three years and lime it if needed. "Avoid use of ammoniacal nitrogen fertilizers such as ammonium nitrate as the ammonium inhibits calcium uptake. Do not over fertilize the plants at planting.

"Provide adequate moisture throughout the growing season and mulch the plants. Avoid severe pruning of the plants, and when controlling weeds, do not dig deep closer to the base of the plant. Foliar sprays can be used as a short-term measure but their absorption by the fruit is very poor. Calcium chloride can be used as a foliar spray only in tomatoes and should be sprayed when it is not too hot to avoid burning the leaves."

Blossom-end rot

Boron deficiency

Calcium blossom end rot

Sunken pit