Physiological Disorder of Root Crops

Deepali Tewari

GBPUAT, Pantnagar

Physiological disorder can be defined as:

• Any kind of abnormality in economically important part of vegetables or other parts that contribute to yield and quality of vegetable is termed as physiological disorder.

 Reasons of physiological disorders are environmental /a biotic factors. Physiological disorders are caused because of:

• Deficiency of micronutrient
• Sudden fluctuation in temperature
• Poor soil conditions and
• Improper moisture availability during cultivation.

 

Why it is important to study physiological disorders?

This aspect is more important in vegetables as quality and marketable yield is very a key factor in vegetable market. If a farmer has a uniform, healthy and good-looking product, he will get higher prices.

Major Physiological Disorders in Root crops:

Name of disorder:       Pore extent, Pore development or Pithiness
Crop:                           Radish

Damage: Symptoms:

• Pores are formed in the root. The quality of radish is reduced, destroying its commercial value. 
• It is caused by excessive root growth in comparison with the corresponding assimilation ability of leaf tissue. Physiologically, parenchymatous cells in root tissue are collapsed.   Pore development is a sign of senescence and its degree varies from variety to variety. Varieties forming early pores have larger parenchymatous cells in roots, more tender basal tissue and lower starch content. 
• Varieties showing early maturity, earlier enlargement of root and rapid reduction in T/R ratio (ratio of the root weight R to the top weight T) have a tendency to form large pores. 

Reasons:

• When harvesting is delayed, this disorder is more pronounced.
• There is no particular gene is identified which directly controls pore development, but genes indirectly influence these physiological characteristics.

Control:

• To avoid the pore extent, harvesting should be done at appropriate time.
• As long term strategy, it is suggested that a variety with early root enlargement and late pore development might be bred by crossing between varieties that had high assimilation ability and early growth.

Name of disorder:       Elongated root or Forking
Crop:                           Radish, Carrot

Damage: Symptoms:

There is secondary elongating growth in the roots that gives a look of fork like structure to the root.

Reasons:

• Inter varietal variation are being considered to result from the degree of secondary elongating growth.  Elongated root relates closely to soil adaptation. Varieties with vigorously elongated root, short root or round root have been selected in areas of shallow arable soil and varieties with poorly elongated root, long root and huge root have been cultivated in areas with deep soil conditions.
• The disorder is due to the excess moisture during the root development of radish and carrot.
• It also occurs in heavy soil due to the soil compactness.
• Un-decomposed organic manure favours elongated root in radish.

Control:

• It can be corrected by reducing the moisture from the field, by balanced irrigation and also by sowing the radish and carrot in sandy loam or light soil having soils of loose and friable in nature.

 

Name of disorder:       Bolting
Crop:                           Radish

Symptom:

• Development of seed stalk without proper development of economically important / edible vegetative part is termed as bolting.
• Radish is a seed vernalizing crop in response to low temperature. 
• The degree of bolting ability has been studied because of its disadvantage in cultivation, and breeding research has been directed toward late bolting. 

Name of disorder:       Pungency
Crop:                           Radish

Damage / Symptom:

• The taste of radish for fresh eating is one of the most important quality traits.
• The pungent component of radish is 4-methylthio-3-butenyl isothiocynate (MTB-ITC).
• It was confirmed that many varieties (temperate) were low in contents of 4-methylthio-3-butenyl glucosinolate (MTB-GSL) (100-200 mmol per 100 g fresh weight) preferred in Europe and USA.
• As a disorder roots become more pungent.

Reasons:

It happens due to high temperature and water stress condition.

Control:

• Proper water management.
• Selection of variety as per season.

Name of disorder:       Root splitting
Crop:                           Carrot

• Splitting or cracking of carrot roots is a major problem in many carrot growing areas.  It is reported that this tendency towards is controlled by genetic factors but a number of other factors are also involved.
• As clear by its name, roots get splitted making it unfit for market.
• Earlier cultivars split more readily than late ones (Moravec, 1961).
• In soils with high content of N, splitting of roots is increased. High soil concentrations of ammonium compounds caused more serious splitting than by other forms of nitrogen.  Heavy side-dressings with NH4NO3 when the roots were 6.5 cm in diameter increased splitting, especially when nitrogen applied to widely spaced roots.
• Wider the spacing, the greater chance of splitting
• If roots are large, there are chances of splitting as compared to small ones.

Control/ Management

• Follow proper management practices like right spacing and optimum amount of N application.
• Prefer other forms of N fertilizer source than ammonium compounds.

 

Name of disorder:       Cavity spot
Crop:                           Carrot

Symptoms:

This disorder appears as a cavity in the cortex, in most cases the subtending epidermis collapses to from a pitted lesion. 

Reasons:

• The cavity spot disorder is induced by deficiency of Ca. 
• This is associated with an increased accumulation of K which leads to a decreased accumulation of Ca. 
• Maynard et.al., 1963 reported that the cavity spot disorder of carrot roots is a manifestation of Ca deficiency, which may be induced by excess K uptake during the ontogeny of carrot plants. 

Control:

• Increase in Ca level in the growing medium leads to significant reduction in the incidence of cavity spot.
• Jakobsen and Jorgensen (1986) suggested that application of fertilizer should be kept minimum and only be done in spring or early summer when the crop requires it the most .This would avoid a build up of K in the plant.

Name of disorder:       Internal black spot or brown heart
Crop:                           Garden beet

Symptoms

• Boron deficient plants usually remain dwarf or stunted.
• The leaves are smaller than normal.  The roots do not grow to full size and under conditions of severe boron deficiency they remain very small and distorted, and have a rough, unhealthy, grayish appearance instead of being cleans and smooth.  Their surface often is wrinkled and cracked.  Within the fleshy roots hard or corky spots are found scattered throughout the roots.
• Discolouration of cell walls and granulation of protoplasts of meristematic cells appear first.  In the cambium, cell division continues with little differentiation into xylem and phloem and many cells are abnormally large. 
• This leads to disturbed trans-location and eventually distorted growth follows necrotic black spots.

Reasons:

• Boron deficiency is more common in a dry season, particularly when a long dry spell is followed by a wet period favouring rapid growth, most probably because the root system in the upper soil layer ceases to function during the dry period and thus intake of boron is reduced. 

Control:

• The quantity of borax needed for satisfactory control of boron deficiency varies with the nature of the soil, the soil reaction and soil moisture.
• An application of 10-15 kg of borax per hectare is recommended.