Slide 1: Environmental influence
on growth, development and yield of vegetable crops By
Dr. P.Syam Sundar Reddy,
Assistant Professor (Hort. Slide 2: The growth and development of plants is dependent on abiotic (physical) and biotic (biological) factors.
Abiotic factors include the physical environmental conditions and biotic factors include animals, insects, and diseases.
Each plant has certain environmental requirements.
To attain the highest potential yields a crop must be grown in an environment that meets these requirements. Slide 3: A crop can be grown with minimal adjustments if it is well matched with its climate or growing condition.
Unfavorable environmental conditions can produce a stress on plants resulting in lower yields.
In such cases the environment can be artificially modified, such as in greenhouses, to meet the crop requirements. Temperature : Temperature Temperature does not supply energy or constituents to the plants but primarily controls the rate of chemical reactions.
Temperature controls plant development including morphogenesis and plant quality.
Temperature is, thus, a major growth factor as it determines climatic zones and controls plant distribution, growth cycles, growth rates and ultimately yield. Slide 5: Biological activity of plants is limited on the lower side by freezing point of water (O°C) and on the upper side by denaturation of protein (50°C).
Plants can only grow and survive within their temperature limits.
In high temperature regime, small leaf, very deep root system, minimum water loss mechanism, orientation of leaf plane, etc., are some of the heat avoiding adaptations. Slide 6: On the other hand, plant can avoid low temperature extreme most commonly through dormancy as in the case of biennial crops like cabbage, onion, European radish and carrot, beet, etc.
In plants, leaves are the main heat absorbing organ.
So, leaf temperature is an important consideration in view of the influence of temperature on crop growth. Slide 7: A leaf may absorb 75 to 90 percent of incident energy in the wavelength of 400-700 nm.
Of the absorbed heat, 20 per cent becomes effective for photosynthesis and the rest 80 per cent must have to be dissipated.
However, light absorption depends on orientation, surface and geometry of leaf.
As for example, vertically oriented leaves minimise the heat load effectively.
Changes of leaf orientation with the response of high temperature and drought as seen in cowpea is termed as 'paraheliotrophy'. Slide 8: Leaf temperature, though correlated positively with atmospheric temperature, is expressed as the result of energy distribution, i.e., heat gain and loss.
Heat gain depends on interception and absorption of light energy along with some adjustments to ambient temperature.
Heat loss from leaf depends on the combination of conduction, convection, re radiation and transpirational cooling. Slide 9: In general, leaf surface temperature is always higher than atmospheric temperature under cool and moderate temperature condition.
In shady condition, however, leaf temperature would be close to atmospheric temperature or slightly below it.
At higher atmospheric temperature, the leaf temperature may be lower than that of atmosphere due to transpirational cooling, provided there would be sufficiently high transpiration.
As a consequence, fully exposed succulent leaves of vegetable and other crops maintain their temperature below ambient. lnfluence of temperature on plant physiology : lnfluence of temperature on plant physiology Temperature is the most important environmental factor for plant growth and development because temperature has unique regulatory influences.
Plants' temperature response curve for growth rises rapidly from 0° to 15°C followed by a steady increase above 15°C to an optimum value between 20° and 30°C.
However, optimum temperature range depends on the particular crop.
In most of the vegetable crops, growth declines above 35°C and thermal death point for most vegetable crops reaches at temperature nearing 50°C. Slide 11: Different metabolic responses, like enzyme activity, membrane permeability, substrate concentration and cumulative reactions, are influenced by temperature.
Plants adopt its physiology according to temperature experience.
Water uptake by roots is greatly affected by temperature
Transpiration which is the driving force for water uptake within the root system is a function of leaf temperature.
The biochemical reactions leading to the metabolic responses do not take place at temperature below the freezing point of water as water changes to solid state and the catalytic action and other properties of water are lost.
At 35°C or above, the molecular structure of the enzymes and protein systems are irreversibly altered leading to stunting of the growth processes. Thermoperiodism : Thermoperiodism Thermoperiodism or diurnal temperature amplitude refers to alternating day and night temperature.
In general, day temperature is higher than night temperature due to presence of sunlight at daytime.
Low night temperature between 15° and 21°C for fruit set in tomato, higher temperature in day than night for successful growth in lettuce.
On the other hand, some crops, like cucumber, radish, etc. do not show specific response to day and night temperatures.
However, in general, diurnal differential is beneficial for growth and development Optimum temperature range : Optimum temperature range It may be defined as the temperature range within which maximum photosynthesis and normal respiration takes place throughout the life cycle of the crop, and thus highest marketable yield is realised.
For most crops the optimum functional efficiency occurs mostly between 55 and 75ºF (12 and 24ºC).
Most crops (and especially vegetables) can be classified according to the temperature requirements of their optimum air temperature range. Slide 14: At the temperature range below optimum, both photosynthesis and respiration decrease but rate of decrease is more for photosynthesis.
So, very little carbohydrate will be available for growth and development of the crop.
Further, the rate of protein synthesis in the development of new cells is also low. Hence, yield is reduced markedly.
Immature foliage tissues of the vegetable crops are liable to freezing injury if they are grown persistently in very low night temperature condition. Slide 15: In the upper range of optimum night temperature, vigorous vegetative growth with high rate of photosynthesis and normal rate of respiration during daytime So, little carbohydrate is stored.
On the contrary, at lower range of night temperature, moderately vigorous vegetative growth is induced with consequent storing of more carbohydrate.
This situation is ideally conceived in potato, sweet potato and yam.
So, ideal crop growth and yield may be achieved if upper range of the optimum night temperature in the early vegetative phase and lower range of the optimum night temperature in the late vegetative phase (bulking phase) and reproductive phase of the crop are maintained. Chilling Injury : Chilling Injury Most crops are injured at temperatures at or slightly below freezing.
Tropical or subtropical plants may be killed or damaged at temperatures above freezing but below 50ºF (10ºC).
This latter type of injury is called chilling injury.
Susceptibility to cold damage varies with different species and there may be differences among varieties of the same species.
The susceptibility to cold damage varies with stage of plant development.
Plants tend to be more sensitive to cold temperatures shortly before flowering through a few weeks after anthesis. Heat Stress : Heat Stress When temperatures rise too high, heat destruction of the protoplast results in cell death.
This occurs in the range of 113-122ºF (45-55ºC).
In tomatoes, fruits exposed on vines to high temperatures and high solar radiation can reach 120-125ºF (49-52ºC).
If green fruits are exposed at these temperatures for an hour or more, they become sunburned; and ripe fruits become scalded.
Symptoms of heat injury are the appearance of dead areas in leaves of hypocotyls and young leaves of many plants.
Heat injury occurs over a wide range of plants depending on the species or tissue Vernalization : Vernalization The biennials crops and some of the cool season crops initiate flowering only after extended exposure to low temperature.
The exposure of certain plants to low temp. induces or accelerates flowering (bolting). This is vernalization.
The required length of low temperature exposure varies with species. Influence of temperature on growth and development : Influence of temperature on growth and development Temperatures both of soil and environment, influence all the aspects of growth and development of vegetable crops, viz., seed germination, survivability and growth, development of economic plant parts, flowering and seed production, pollination, fruit set, quality of the produce, seed storage and occurrence of diseases and pests. Soil Temperature : Soil Temperature Soil temperature has direct dramatic effects on microbial growth and development, organic matter decay, seed germination, root development, and water and nutrient absorption by roots.
In general, the higher the temperature the faster these processes occur.
The size, quality, and shape of storage organs are greatly affected by soil temperature.
Dark-colored soils absorb more solar energy than light colored soils.
The capacity of water to move heat from one area to another (conduction) is greater than that of air.
Heat is therefore released to the surface faster in clay soils than in dry sandy soils.
The lower the air temperature, the more rapid the loss.
Although light-colored sandy soils absorb less solar energy, less heat is also released to the atmosphere because of the low water-holding capacity of the soil. Survivability and growth : Survivability and growth Base temperature is the threshold atmospheric temperature level below which the plant cannot develop, and each plant has its own base temperature, e.g., pea (4.4°C), French bean (10°C), asparagus (5.5°C), spinach (2°C), lettuce (4.4°C), pumpkin (13°C), tomato (15°C), etc .
The minimum and maximum temperatures for growth and development of most of the vegetable crops lie within the range of 7 to 35°C Slide 24: According to the temperature requirement for proper growth and development, vegetable crops are broadly categorised into two groups :
cool and warm season vegetable crops COOL SEASON VEGETABLE CROPS : These vegetable crops, hardy or weak, are frost insensitive.
Among these crops, rhubarb, horse radish, sorrel, etc., are frost resistant and can stand subzero temperature.
Crops like cabbage, onion, garlic, Brussels sprouts, knol khol, pea, turnip, radish are more tolerant to cold temperature than cauliflower, carrot, celery, beet, palak, etc.
According to the relative insensitivity to weak frost, the cool season vegetable crops can be classified into hardy (more tolerant to cold temperature) and half hardy (comparatively less tolerant to cold temperature).
Chilling causes bolting in some of these crops. COOL SEASON VEGETABLE CROPS Cool season vegetables : Hardy crops
Broad bean ,Brussels sprouts , Broccoli, Cabbage ,Garlic, Kale ,Horse radish ,Leek ,Knolkhol, Onion ,Mustard, Peas ,Parsley, Rhubarb ,Radish, Turnip, Spinach, Pak-choi, Sorrel
Half hardy crops
Asparagus ,Carrot , Rutabaga ,Cauliflower, Beet ,Celery Chard, Chicory, Chinese cabbage, Globe artichoke Parsnip, Potato Cool season vegetables WARM SEASON VEGETABLE CROPS : WARM SEASON VEGETABLE CROPS These tropical vegetable crops cannot withstand prolonged cold weather, and are best suited in relatively high temperature condition.
Among these crops, tomato, brinjal, sweet pepper, pumpkin, cucumber, etc., are heat-loving crops, while, muskmelon, watermelon, sweet potato, winged bean, cluster bean, etc., are heat-resistant crops.
Heat-resistant crops can be grown in very high temperature (40°C) condition.
These warm season vegetable crops are called tender crops which are sensitive to weak frost. Warm season vegetables : Warm season vegetables Tender crops Cowpea, New Zealand spinach, French bean, Soybean, Sweet corn, Tomato, Sweet potato, Sweet pepper, Summer squash, Pumpkin
Very Tender crops Cucumber, Brinjal, Lima bean, Cluster bean, Winged bean, Amaranthus, Hyacinth bean, Okra Chilli, Bottle gourd, Bitter gourd, Watermelon, Ridge gourd, Muskmelon, Cassava, Pointed gourd, Indian spinach, Elephant-foot yam TEMPERATURE REQUIREMENT FOR SUCCESSFUL CULTIVIATION OF DIFFERENT VEGETABLE CROPS : TEMPERATURE REQUIREMENT FOR SUCCESSFUL CULTIVIATION OF DIFFERENT VEGETABLE CROPS Development of vegetative plant parts of economic use : Development of vegetative plant parts of economic use Development of the modified vegetative plant parts, in particular, are greatly influenced by the prevailing atmospheric temperature. Slide 31: CAULIFLOWER :
Curding is initiated in the plant under wide range of temperature from 5° to 28°C depending on the cultivars.
This transformation to curding, however, requires certain amount of vegetative growth in all the cultivars.
The tropical or Indian cauliflowers initiate curding at much higher temperature condition than required for temperate type cultivars.
Accordingly, the cauliflowers grown, in lndia are classified as Group I (early), Group II (mid), Group III (mid-late) and Group IV (late).
They are also named by the month in which the curd mature, such as : Group lA (Kanwari, Sept-Oct), Group IB (Kartiki, Oct-Nov.), Group II (Aghani, November), Group III (Pousi, December), Group IV (Maghi, January).
Optimum temperature ranges for curd initiation and development of the different cauliflowers grown in India are :
Group IA- 20-270C; Group IB- 20-25°C; Group II- 16-19°C; Group III- 12-16°C; Group IV-10-12°C. CABBAGE : CABBAGE There is no such Indian group of cabbage as in cauliflower.
The European cultivars which are mostly grown in India require 15-18°C temperature for the growth and heading.
Most of the traditional European cultivars under mild and short span of winter condition of eastern and western India do not form tight heads.
In this situation, early short duration cultivars and tropical cultivars perform well.
The tropical cultivars of Japan and some high temperature hybrids are capable of forming tight heads even at an average temperature of 25°C.
For this reason, such imported cultivars are gaining popularity in India. Slide 33: KNOLKHOL : The European cultivars that are grown in India require 15° to 18°C for good growth and stem tuber formation, although the. quality of tuber becomes better at comparatively low temperature of 10-15°C.
BRUSS,ELS SPROUTS : It requires a temperature of 10-15°C for the successful development of miniature heads in the leaf axil.
SPROUTING BROCCOLI: Development of flower heads require 1 0-12°C temperature.
For proper development of flower head, night/day temperature regime of 10-15°C is optimum, Warm weather condition makes the bud clusters loose.
CHINESE CABBAGE : High quality produce can be obtained under moderate to cool temperature (15.5° to 21°C).
Below 15°C seed stalks may form before good heads are produced Slide 34: ONION : Photoperiod seems to have major role in bulbing, but influence of temperature to bulbing and bulb development cannot be ignored.
In the long day cultivars (rabi onion) that are widely grown in India during December-January to April-May, temperature above 15°C is necessary for bulbing and bulb development, 19-20°C being the optimum.
In the Short-day cultivars (kharif onion) that are mostly grown in Maharashtra during mid-August to November-December,20-220 C is optimum for bulbing.
Rapid bulb growth-20-220 C
Bulbing retarded->400 C
Favourable for vegetative growth-10-150 C Slide 35: GARLIC : Low temperature is the pre-requisite for higher yield in garlic. Cool and moist condition is required for proper vegetative growth.
During bulbing and bulb development, cool temperature of 10-15°C helps in producing larger bulbs. However, cool and dry period favour the production of best quality bulbs.
POTATO: Relatively high temperature of 20-25°C is optimum for stem and leaf growth.
Optimum night temperature for tuberisation is 18-20°C and tuberisation is inhibited above 21°C night temperature.
High night temperature decreases tuber yield more than high day temperature.
This optimum night temperature for tuberisation, however, varies with the prevailing photoperiod.
At 12-hour photoperiod, night temperature of 20°C is optimum. Slide 36: RADISH: Radish, in general, is best suited to cool or moderate climate. The Asiatic or tropical cultivars are more adapted to high temperature condition than European or temperate cultivars.
Relatively high temperature of 20-25°C for early root growth and low temperature of 10-18°C in the later part are required for proper root development. Slide 37: CARROT : Very high or low temperature is not conducive to proper growth and colouration of the roots. So, it requires moderate climate."
However, the Asiatic or oriental types are well adapted to comparatively high temperature condition than the European types.
A temperature range of 16-21°C is ideal for root development and good colouration.
In the temperature regime below 15°C, roots become slender with inadequate colour development.
At higher temperature condition around 24-25°C, roots become shorter, thicker and less coloured. Slide 38: BEET : Beet is fairly hardy and can tolerate freezing temperature for some time.
It can be grown in warm weather but best quality roots are produced at the temperature regime of 15° to 21°C.
In warm weather (above 25°C), zoning of beet marked by alternate white and coloured circles in the root tissue is pronounced.
At temperature between 10° to 15°C, seed stalks are produced prematurely. Slide 39: TURNIP: It is best suited to cool or moderate climate (15-20°C).
At temperature below 10°C, flower stalks may emerge.
Though it can be grown in warm weather (25° to 26°C), yet its quality is affected.
The roots become tough and bitter in taste in high temperature condition.
TARO : It is best suited in swampy tropical climate with a temperature range of 25° to 30°C. In moist environment, it can be grown at a temperature of 20° to 21°C. Slide 40: SWEET POTATO: The plant is tender and requires long, warm growing season. A temperature range of 20-2YOC is best suited to vine growth.
A slightly lower temperature regime of 20° to 25°C is ideal for tuberisation.
Tuberisation is hampered at very high temperature (35-40°C) and low temperature (15°C). However, tuberisation is greatly influenced by short-day condition.
CASSAVA: Cassava is only suited in places where average annual temperature lies above 20°C. Ideal temperature for the crop ranges between 25° to 32°C. Slide 41: ELEPHANT-FOOT YAM: It requires fairly high temperature (30°C) with adequate moisture for shoot emergence and vegetative growth. Wide fluctuation in day and night temperatures during growth stage is not desirable.
Tuberisation requires comparatively less temperature (20-25°C) and dry weather condition.
YAM: Warm climate (25° to 30°C) and adequate moisture are ideal for vegetative growth and tuber bulking. Growth is adversely affected below 20°C temperature condition. Slide 42: MONOECIOUS CUCURBITS : In cucumber, pumpkin, bitter gourd, ridge gourd, bottle gourd, etc., yield is increased under moderate temperature (20-25°C) and short day condition because more female flowers are developed under this condition.
YAM BEAN: Warm (25-30°C) and humid climate is needed for initial vegetative growth, but cool night temperature of 18-20°C along with dry sunny days are required for tuber bulking and development.
MELONS: Lower night temperature increases sugar content in the fruit.
For this reason, sweetest melons are produced in the arid climate where very hot day is followed by cool night. Slide 43: ASPARAGUS: It requires a temperature range of 15° to 24°C, 16-18°C being the optimum throughout the growing season for good spear production.
During dormancy, low. temperature below 10°C is required for 2-3 months.
ARTICHOKE : The plants are killed by freezing temperature.
On the other hand, hot weather causes the buds to open thereby reducing the tenderness of the edible portion.
So, mild winter and cool summer are ideally suited for its growth and production Slide 44: PALAK : It can be grown in a wide range of temperature condition.
However, mild temperature condition of 16-21°C is best suited.
High temperature condition (25°C and above) leads to bolting, causing reduction in leaf yield.
SPINACH : It thrives best during relatively cool weather and can withstand frost.
It cannot do well in hot weather. Favourable temperature for best yield ranges between 16° and 21°C under Short-day condition. Slide 45: LETTUCE: It is best grown in a relatively cool growing season with a temperature range of 13° to 18°C. More precisely, day temperature of 20°C with 18°C night temperature is the best.
CELERY : Optimum temperature condition for successful growth is 15° to 18°C. Low temperature range of 10-15°C causes bolting.
High temperature causes bitterness in the leaves. Flowering, pollination and fruit set : Flowering, pollination and fruit set Photoperiod and temperature are the most important environmental factors in the induction of flowering.
Photo thermal flowering responses, though common, yet influence of photoperiodism is more strong.
The photothermal control of the timing of flowering is especially important with regard to adaptation. Slide 47: PEA: It thrives best in cool weather, optimum monthly average temperature being 10-18°C.
High temperature (above 25°C) hastens the maturity, lowers pod set and adversely affects the quality.
FRENCH BEAN : Short-day condition and a moderate temperature range of 18- 25°C are ideal for its cultivation.
High temperature (27-32°C), though increases flower number per plant, yet decreases pod set markedly. Slide 48: LIMA BEAN : High temperature (26-30°C) drastically affects fruit set.
OTHER BEANS: All other beans excepting broad bean, viz., cowpea, hyacinth bean, cluster bean, winged bean, etc., are typical warm season crops.
They are also adapted to subtropical conditions.
ldeal temperature for most of the cultivars of these beans ranges between 18° and 25°C.
However, very high temperature above 35°C adversely affects fruit set, particularly in reduced relative humidity condition. TOMATO : Critical factor in setting of fruits of the tomato is the night temperature, the optimum range being 15° to 21°C.
Fruits fail to set at 13°C or below.
Fruit set is also reduced markedly when average maximum day temperature goes above 32°C and average minimum night temperature goes above 21°C.
However, some cultivars which can set fruit above and below the critical temperature are called high-temperature-tolerant and cold set cultivars, respectively. TOMATO BRINJAL : It requires long and warm growing season with a temperature range of 17-25°C for successful growth, fruit set and yield.
However, fruit set is mostly influenced by the genotype.
In low temperature condition (10°C and below), sometimes ovary in the bud stage splits and deformed fruits are developed. BRINJAL CHILLI : Both chilli and sweet pepper are tropical crops but sweet pepper requires somewhat moderate temperature.
Night temperature of 18- 20°C is ideal for fruit set and fruit development in chilli.
High night temperature of 24°C and above causes flower drop.
High day temperature condition (above 30°C) coupled with low light intensity leads to flower drop. CHILLI SWEET PEPPER : SWEET PEPPER In sweet pepper, optimum day and night temperature regime for ideal fruit set and development is 20-25°C (day) and 15-16°C (night).
High day temperature of 30°C and above causes flower drop.
Low night temperature of 10° to 15°C reduces pollen viability leading to parthenocarpic development of fruits (seedlessness) in both chilli and sweet pepper. POTATO : POTATO Flowering and subsequent fruit set in potato is the result of interaction between photoperiod and temperature.
Long day length (longer than 12 hours) coupled with cool temperature (10-12°C) induces the emergence of inflorescence and results in subsequent fruit set. INDIAN CAULIFLOWER : INDIAN CAULIFLOWER Indian cauliflowers (Group I & II) are tropical annual in nature and do not require varnalisation (specific cold temperature treatment) for the emergence of flower stalks.
However, during curd formation and development stage, the temperature should be uniformly cool with moderate humidity to avoid development of different disorders like riceyness, fuzziness, etc. BIENNIAL AND TEMPERATE ANNUAL CROPS : BIENNIAL AND TEMPERATE ANNUAL CROPS In the crops, like cabbage, Group III and IV cauliflower, knolkhol, Brussels sprouts, sprouting broccoli, kale, Chinese cabbage, rabi onion, leek, beet, turnip, European radish and carrot, parsley, parsnip, celery, Swiss chard, rutabaga, etc.,
exposure of the plants to low temperature of 4-70C for 6-8 weeks (vernalisation) is required after they have passed the juvenile phase for the production of flower stalks. Slide 56: Promotive effect of low temperature on flowering is called vernalisation.
Vernalisation is common in species which are adapted to temperate and Mediterranean climates.
This response may be found in winter annuals, biennials and perennials, but it is particularly important in biennials.
A general explanation of vernalisation is based on the suppression of vegetative growth, but this explanation does not hold good in all the cases.
In most of the cases, the plants require vernalisation to flower in long-day condition.
In fact, the temperate vegetable crops often tend. to bolt, i.e., elongate their stems and then flower in response to cool temperatures followed by long days. Slide 57: In cauliflower and broccoli, because of the nature of storage organ), flowering does not involve vegetative stem elongation, instead peduncles and flower buds elongate.
But this photoperiodic requirement is not critical as low temperature exposure may replace photoperiodic requirement.
In onion, appearance of scape is solely a function of subsequent temperature but floral initiation at the apex is affected by both temperature and photoperiod.
Vernalisation stimulus is received by the apical meristems and expanding leaves.
Some of the vernalisation stimulus is related to natural gibberellin substances in the plants.
This proposition is based on two main observations:
(a) gibberellin plays a role in the flowering of many long-day plant, (b) vernalisation effect could be obtained with gibberellin application in some crops, like cabbage, carrot, etc. Slide 58: vernalisation has some crop specific considerations, like
(a) juvenile stage for low temperature exposure varies with the crops (in cabbage and cauliflower it is after 10-12 weeks of planting while in Brussels sprouts, it is after 12-16 weeks),
(b) sometimes very low temperature shortens the vernalisation period,
(c) low temperature requirement varies with the crop and cultivars of the crop (tropical cabbage requires 10-13°C for 6-8 weeks, rabi onion varieties of India generally need 1 0-12°C for 5-6 weeks, beet, turnip, etc., require 8-10°C). CUCURBITS : CUCURBITS In cucumber, pumpkin, summer squash, muskmelon, watermelon and bitter gourd, pollination and fruit set take place in the morning hours at the optimum temperature range of 12.8° to 18.3°C.
On the other hand, fruit set in bottle gourd and ridge gourd occurs at comparatively high temperature condition (above 25°C) of midday.
In snake gourd and pointed gourd, anthesis occurs at night with the influence of night temperature.
Anthesis in these two crops hastens with the rise in night temperature and fruit set occurs in moderate temperature condition of morning hours. Slide 60: PALAK: Temperature above 25°C coupled with long-day condition leads to bolting in the plants.
SPINACH : Normally, long days in combination with warm weather (above 25°C) are favourable for seed stalk formation.
But photoperiodic response in spinach can be altered by low temperature treatment.
Exposure of the plants to 10-15°C for a month can induce flowering in short-day condition.
LETTUCE: Temperature above 22°C accelerates seed stalk development. Product Quality : Product Quality TOMATO: Colour development is one of the important quality criteria of tomato.
At temperature below 10°C, both red and yellow colours do not develop. Ideal temperature range for the development of both red and yellow colours is 10-25°C.
At high temperature above 30°C, red colour is suppressed but it redevelops when 30°C temperature is restored.
At 40°C, Lycopene pigment is destroyed and no red colour is developed further resulting in yellow shoulders.
High temperature also causes scalding in fruits.
CHILLI : High night temperature is responsible for the higher capsaicin content in the fruit. Slide 62: CAULIFLOWER: Occurrence of riceyness (development of small flower buds over curd) is often related to fluctuation in temperature both high and low than the optimum required for curding in a particular cultivar.
However, high temperature is mostly responsible for riceyness.
High temperature exposure after curd formation can cause loose or leafy curd along with yellowing of the curds.
CABBAGE : Traditional European cultivars do not form tight heads resulting in loose heads in the temperature above 18-20°C.
However, tropical cultivars of Japan are capable of forming tight heads at temperature regime of 25°C. Slide 63: CARROT : In the European or temperate cultivars, proper orange colouration in the root is the prime quality consideration.
A temperature range of 16-21°C is the best for colour development.
Synthesis of carotene (proportional to orange colouration) is decreased at temperature below 15°C and above 24°C.
However, intensity of colour increases with the age of the root. So, effect of temperature is to be considered with the age of the root in view.
RADISH: Hot weather condition makes the root tough and pungent before reaching edible size, particularly, in temperate radish cultivars (Japanese radish and summer radish of temperate region). Slide 64: BEET : Good quality roots having high sugar content and dark internal colour throughout the root are produced under cool weather condition (15-18°C).
In warm weather (above 25°C) during growth period, the roots show alternate white and coloured rings when sliced which is called zoning of beet.
This disorder reduces the quality.
TURNIP: Best quality root is developed in moderate climate.
In temperature above 25°C, the roots become tough and bitter in taste.
In low temperature condition (below 100C), bolting occurs before good roots are formed. Slide 65: PEA : Quality of pea is associated with tenderness (less starch content) and high sugar content.
High temperature of 30°C and above sharply reduce the quality by toughening the peas.
At high temperature, enzymatic conversion of sugar to starch and sugar to CO2 + H20 + heat is more, resulting in less sugar content.
MELONS: High day temperature followed by cool night, i.e., wide day and night temperature differential enhances translocation of sugars in fruits and thus becomes more sweet. Slide 66: PALAK : Hot weather condition (above 25°C) reduces leaf quality by triggering early bolting and by decreasing leaf succulence quickly.
SPINACH : In moderate temperature (16-21°C), the leaves become lush green in colour, contain more sugar and dry matter which mark good quality.
In temperature condition of 25°C and above, leaves become yellow and contain less sugar and dry matter due to bolting tendency.
Leaf succulence is also hampered due to high temp.
LETTUCE : It requires cool temperature condition of 20/18°C day and night for best quality produce, like solid head, leaf crispyness, etc.
Temperature above 22°C reduces the quality of the head and leaves. Slide 67: POTATO : Plant tissue commonly shows increase in sugar concentration at temperature below 10°C.
For this reason, potatoes become undesirably sweeter when stored in cold storage at 4-5°C temperature condition.
Such sweetness is developed because in low temperature condition, enzymatic conversion of sugar to starch and sugar to CO2 + H20 + heat is reduced drastically in comparison to enzymatic conversion of starch to sugar. Incidence of diseases and pests : Incidence of diseases and pests Incidence of some diseases and insect pests are highly correlated with the prevailing atmospheric temperature and relative humidity.
LATE BLIGHT OF POTATO AND TOMATO: The fungus (Phytopthora infestans) rapidly multiplies under cool temperature (10-20°C) and high humidity (above 80% relative humidity) condition. Slide 69: EARLY BLIGHT OF POTATO AND TOMATO: Infestation of this fungus (Alternaria solam) is severe in comparatively high temperature (20-25°C), dry weather and under intermittent rain condition.
BLACK ROT OF COLE CROPS : This bacterial disease caused by Xanthomonas campestris is particularly destructive in warm and humid climate but is not pronounced in low temperature condition.
FUSARIUM WILTS OF VEGETABLE CROPS: These diseases are incited by different f. sp. of the fungus Fusarium oxysporum.
Optimum temperature range for the incidence of the disease is 18-24°C.
Growth of the fungus is inhibited at 35°C. Slide 70: WHITE FLY : Population of this insect vector (Bemisia tebecti of virus) increases with the rise in temperature.
For this reason, incidence of leaf curl virus in tomato, yellow vein mosaic virus in okra, etc., is low when they are grown in comparatively low temperature condition.
APHID : Population of this virus vector (Myzus persicae) increases with the rise in temperature at the onset of spring.