Preface India has diverse climates and soil for cultivation of horticulture crops providing ample opportunities for the development of fruit industry but the greatest challenge in present is to produce sufficient fruit to feed the ever-increasing human population. This demands infusion of technology for an efficient utilization of resources for deriving higher output per unit of input with excellent quality of the produce within short span of time.In the present era of open economy; it has become increasingly necessary that our produce is competitive, both in the domestic as well as in international markets. This would be possible only through deployment of high-tech application and precision farming methods. Fruits are very important for human beings and also play an important role in religious practices, mythology and art. They are not only delicious but also have many nutrients which are necessary for human health. India is the second largest producer of fruits in the world. Fruit production requires a lot of science and some basic fundamental knowledge to grow them successfully. This book compiles many fundamental issues of fruit production like layout and planting, many cultural practices, growth and bearing habits of fruit crops, unfruitfulness etc. Understanding of all these topics will help the students for proper knowledge of fundamentals of fruit production. We hope that this book would also be helpful for growers, nurserymen, farmers, teachers, scientist, extension officer and all those who wish to become familiar with the topic in relation to their professional interest. We have tried to keep the language as simple and straightforward as possible and consistent with accurate representation of the content. Every effort has been made to present the ideas in very easy and understandable language and the interests of each reader. Finally, we would like to thank one and all who have contributed directly or indirectly in bringing out this book.

Growing fruits can be fun, delightful experience and a challenging hobby. There are several good reasons to grow fruits. Fruits add beautiful colour and variety to your garden. Large amounts of fruit can be grown in a relatively small area.Store-bought fruits are often picked, shipped, and sold before they are fully ripened and generally stock selections that look prettiest but are not necessarily the best tasting. In addition, fresh garden fruits are a good source of vitamins; minerals, carbohydrates, fibre (Table 1) and will provide your family with flavorful, delicious and nutritious food. As an added bonus, the fruits you grow will taste much better than the fruits you find in the grocery store. Establishment of an orchard are a long term investment and require critical planning, selection of proper location and site, planting system and planting distance, varieties and the nursery plants to ensure maximum production. Even if you have limited space, you can still enjoy growing fresh fruits in your garden by growing fruit plants in containers. You can grow any fruit tree in a container for a few years and then transplant it. You can also choose a dwarf variety, which is well suited to living in a container. If you carefully choose the kind and varieties of a fruit before you plant, you can harvest dessert-quality fruit from early summer through the fall. Many fruit plants are aesthetically pleasing and are good for “edible landscaping.” Some fruits, such as apple, citrus, blueberries and figs, make outstanding ornamental plants. Some people find a natural setting with plants placed throughout the landscape most aesthetically pleasing. But this makes maintenance more challenging.

The damage due to frost in fruit crops has been a problem for farmers since starting from their cultivation. Damage caused by frost is a worldwide problem because if all aspects of crop production are well managed, one night of freezing temperatures can lead to complete crop loss. According to Bagdonaset al. (1978) frost periods in temperate regions are shorter in duration and occur more frequently whereas in subtropical climates it is occurs with slow moving cold air masses. In tropical regions, there is usually no or very less freezing damage except at higher elevations. In subtropical fruits crops, damages occurs mainly during the winter, whereas in deciduous fruit and nut trees, it occur mainly in spring, but sometimes it occurs in autumn as well. The region prone to frost should adjust the date of planting of crop, microclimate, variety and other preventive measure. According to Attaway (1997) in South Carolina, northern Florida and Georgia, orange fruit were commonly grown before 1835, but losses due to frost damage, farmers did not prefer to grow oranges in that regions. The history of frost damage is more sporadic in nature leading to some major losses from time to time. In December 1990 and 1998 Californiacitrus industry suffered two major damaging events of frost which ranged from little damage in some regions to severe damage in the other region. The economic losses to fruit crops were high in the frost occurring in 1990 compare to frost in 1998.

In nature, plantspecies flowers produce fruits and seeds and the primary objective is to reproduce them. Plant species those are unable to produce viable seeds, reproduce themselves by other means. With a common of these processes they vary in various aspects of flowering and fruiting. The variations may be due to their different growing habits, requirement of different environments, differences in their basic nature etc. Here we are going to discuss different types of bearing habits do exists in fruit crops. Growth Habit Growth is quantitative irreversible increase in the existing size of say plant or a shoot or simply a leaf etc. Fruit crops can be classified on the basis of their growth habits in two major classes. One is evergreen and second is deciduous. Evergreens include those plants which bear their leaves throughout the year. Examples are mango, litchi, guava and orange. Whereas, deciduous trees shed their leaves during a part of year (when weather is adverse i.e. during winter). Mostly temperate fruits belong to this category. The presence or absence of leaves makes very big difference in their physiology, their bearing season and pattern etc. These two categories also make a basic group to study them separately with respect to many aspects viz. source and sink relationships, pruning etc.

Growth is the fundamental property of all living organisms. It is an irreversible permanent increase in size, volume or mass of a cell or organ or whole organism accompanied by an increase in dry weight. Where, development is sum total of growth and differentiation. It is governed by both environmental and internal factors. The development of a plant is highly complex phenomena (Table 1).

In the words of Leonardo the vinci, “water is the driver of life”. It is said to be the liquid of life or elixir of life. Water availability is essential to consider as commercial orchards must have reliability of supply and cannot produce optimum yields without irrigation. Water management is one of the largest and most important inputs into an orchard. The single environmental component which determines the type of fruit plants to be selected for a specific ecological situation is the moisture status of the region. Different fruit plants preferring diverse moisture status have wide peculiarity in their anatomical and morphological structures as well as various modifications in their water absorbing organs. They are also seen to have varied capabilities to acquire and utilize water efficiently. In the plant system, the rate of dry matter production has a definite relation with the rate of transpirational loss of water and this transpiration ration is calculated on the basis of unit of water required to produce unit of drymatter. However, while calculating the water requirement of fruit plants, a number of factors, in addition to water use efficiency, are taken in to consideration. Naturally water requirement of a particular fruit plants varies with the agro-ecological condition of different places. Moreover the same cannot be equal in an established orchard and a newly planted one. In established orchard, the trees are grown in community where improved water use efficiency lower down the water requirement of the trees.

Water is one of the most important and critical input for agricultural production system. The demand for food grains is increasing day by day due to increasing population. The irrigated agriculture provides the crop water productivity of about 2.5 tonnes per hectare and the overall irrigation efficiency is only about 30%, which is below the world average level. In the above scenario it is necessary to have the irrigation system in which both the crop water productivity and irrigation efficiency increases considerably. Micro irrigation has become the most viable and efficient technology in such a situation. It provides several advantages in the context of crop agronomy, water and energy conservation. Micro irrigation has the potential to achieve the crop water productivity to a desired level of 4 tonnes per hectare and simultaneously maintain the irrigation efficiency above 80%. The total coverage of micro irrigation in the tenth plan is only about 2 million hectare. The task force on micro irrigation (2004) has indicated a potential of 69 million hectare for our country. So there is a tremendous potential available and the coverage of micro irrigation has to be increased to cover more crop and more new areas.

Introduction Fruits play a vital role in improving human health which are called as protective foods rich in vitamins, minerals, fats, oils, proteins and improves in economy of producers, exporters and industrialists. Fruit crops can be classified into two broad categories i.e. ever green and deciduous trees. Evergreen fruit trees grow under tropical and subtropical climate and they are not dependent on chilling requirement for floral bud differentiation and flowering. Ex: Mango, Citrus, Guava, Sapota, Papaya etc., Deciduous fruit trees require dormancy during winter season and chilling units for floral initiation and have specialized modifications to protect sensitive growing tissue from unfavourable conditions. Ex: Apple, Pear, Peach, Plum, Apricot, Cherry, Grapevine, Walnut, Almonds etc.,

Fruit is a structure which arises from an ovary or fusion of several ovaries after fertilization and may or may not carry associated floral parts. Fruit formation is an evolutionary mechanism designed to support and dispersal of seed by various agencies.With few exceptions e.g. banana, it is necessary for the flowers to be fertilized to set fruit. Fruit set succeeds the process which involves fusion of male and female gametes inside the ovary and is called fertilization. Fruit setting has long been remained a major problem as is evident from the old Greek literature and wall paintings where male panicles of date palm were being rubbed against the female flowers to get good fruit set.Lack of pollination with compatible source leads to the flowers drop except the flowers which set parthenocarpically. Further if fertilization is affected even then the flower drop and this decision depends upon the internal hormonal levels of the plant and prevailing climatic conditions.On the basis of pollination requirement fruit plants can be autogamous, allogamous or geitonogamous. In case of fruit plants like grape, peach where pollen produced by the same flower affect the fertilization are called autogamous and fruits like apple, kiwi, pistachio necessarily require pollen produced on some other plant or cultivar which are compatible can affect fertilization are called allogamous. Another condition exists where pollen grains from the same plant affect fertilization in flower at different part of the plant e.g. Walnut, pecan nut and is called geitonogamy. Similarly on the basis of compatibility between pollen and stigma, plants can be self unfruitfull, partially self fruitfull and self fruitfull.Self fruitfulness indicates that fruit species or cultivars produce abundant viable pollen grains whose shedding coincides with the receptivity of stigma, pollination is effective and there are no pre and post fertilization barriers. However, partial self fruitfulness and self un-fruitfulness exhibits number of causes. In case of fully self fruitfull types, a solid block of a single cultivar can be raised without making any provision for cross pollination, however it has been reported that provision of cross pollination in autoganmous crops increases the fruit-set. In case of self unfruitful and partially self unfruitful types, provision of cross pollination is necessary to get the fruits. Proper selection of the cultivars is therefore important from the point of fruit yield for which besides overlapping of blossoming season over long periods, the time of maturity, productiveness, market values etc. are of importance. Pollenizer must be a heavy pollen producer to ensure better chances of cross fertilization. Although pollenizers are desirable, their number must be restricted so that these do not become uneconomical because the pollenizer trees occupy space, consume nutrition and take away attention of the fruit grower without any return in yield, which would have otherwise been diverted to the trees capable of bearing fruits. Numerous environmental, edaphic, plant characters affect the fruit set and are discussed as under:

Fruit drop is a premature shedding of fruitsbefore harvesting for commercial purpose. There are so many reasons for fruit drop like internal (Hormonal balance, morphological and genetical) and external (biotic and abiotic) factors. Fruit drop is very much serious in some fruits like apple, peach, currant, mango, citrus etc. Fruit drop may occur at various stages of fruit growth,starting right from fruit setting till its harvesting. It may be natural, environmental or pest related.Losses due to fruit drop at various stages have long been a serious threat to the fruit growers. After determining the actual cause of fruit drop, adoption of a suitable control measure can bring relief to the growers. Among different drops, pre-harvest drop is of great economic importance which can cause serious crop loss to farmer.

After doing all hard work during fruit production the last operation is harvesting on field. Though it is last operation, it should be done very carefully to get the quality harvest. Harvesting of fruits mainly depends upon the nature of fruit. Here nature refers to the classes of fruits divided on the basis of their respiratory pattern and ethylene production. On the basis of the respiratory pattern the fruits can be divided in to two categories, first one is climacteric and the second one is non climacteric. Climacteric fruits: The meaning of word „climacteric is a critical period or event. Here, climacteric refers to the event of respiratory rise before the ripening phase. Those fruits which show such patterns are known as climacteric fruits (Taiz and Zeiger, 2002) Examples: Mango, guava, apple, banana, sapota, papaya, peach, pear, plum, fig, Annona. Non climacteric fruits: Non climacteric fruits do not exhibit the respiration and ethylene production rise (Taiz and Zeiger, 2002). Examples: Citrus, grapes, pineapple, pomegranate, litchi, ber, jamun, cashew, cherry, strawberry.

1. Mango Varieties released from I.A.R.I., New Delhi Malliaka: (Neelum x Dashehari) This variety was released in 1971. Tree moderate, semi-vigorous to vigorous, moderate spreading, bearing moderately and regular. Fruit large, ovate-oblong; beak slight, sinus absent, peel thick, apricot yellow; flesh firm, fibreless. Fruit quality superb with excellent sugar acid blend., TSS (24-20° Brix), good keeping quality (15 days). It is suitable for table and canning purposes. Maturity during 3rd – 4th week of July.

The propagation of plants has been one of the fundamental occupations of mankind since civilization begins. Most of the selected plant would have lost or could have attained undesirable forms if they were not propagated under strict environment conditions. Growth, in all nature, result from the division of cells to form more similar cells. Thus bacteria reproduce by simple division, in higher plants and animals, a new individual is genetically formed only when cell division fallows the fusion of two cells. This is known as sexual reproduction. There are thus two methods of producing new plants, sexual and asexual or vegetative reproduction. I. Sexual Propagation Raising of plants by means of seeds is called sexual propagation. There are many plants raised for our garden from seeds. The plants produced through seeds are called seedlings. In sexual method, the sex organs of flower are involved in process like pollination and fertilization, resulting the formation of seeds. eg rootstocks plants of many fruit crops are grown through seed propagation.

Rootstocks play an important role in the propagation of plants. It may modify form or stature, adapt a variety of a soil, fit in an incompatible climate, impart or resist disease to the scion, increase production, hasten maturity of crop, change the colour of the fruit, effect the flavour of the fruit, shorten life of the tree, increase the size of the fruit, develop vigour, effect salt tolerance and influence storage capacity.

What is Nursery? Nursery is a place, where seedlings, samplings, trees and other plant material are grown and maintained until they are planted in permanent place. Setting up of a horticultural nursery is a long term venture and needs proper planning for good return. Establishment of Nursery To be a viable venture, the nursery should be established in such an area where cultivation of fruit crops is on sizeable area and there is need for a nursery, having demand for saplings. In such area/region, following considerations need to be observed for selecting an appropriate location.

The packing methods practiced by nurserymen for transport of nursery plants to distant places in India are neither uniform nor efficient. In different parts of the country, various practices are followed which are claimed to have been evolved by long experience of the local nurserymen. They vary according to nature of the plant, the season and the cheapest packing material available at the time of packing. In many parts of the country, citrus nurserymen uproot plants, tie them in large bundles (with or without soil), keeping the plant tops exposed to air and roots tightly packed or tied in the gunny cloth. The pomegranate and guava plants prepared by air layering are packed as such if they are not already potted in small pots. Many nurserymen pack the rooted or newly lifted plants in a ball of sticky clay. The ball of earth is then covered with grass and tied as firmly as possible, thus securing the roots against drying. A number of plants, thus prepared, are filled closely in light locally knit bamboo baskets. The baskets are covered thinly with coconut leaves as protection against injury during railway shipment. Mango grafts in pots are packed in light baskets with some cushion of grass to reduce the impact while loading and unloading the parcels on their long journey by rail and road. Some nursery men use large baskets, woven out of coconut leaves with limp walls or sides. Plants such as coconut, chikoo, guava, mango are packed tightly in these baskets and shipped by truck or rail. This packing is done irrespective of plant containers such as pot or a ball of earth, with or without grass covering. The plants packed in all such fashions are usually damaged and some of them do not survive, unless care is taken during or after transplanting them in the permanent places. For better success, it should be seen that the roots of grown up plants do not get irreparable injury while removing from the bed or the pot. During transport, loss of water by transpiration should be kept at minimum, while the plants are awaiting dispatch or delivery at the railway platform, precaution should be taken against pilferage or damage by animals.

Plant Growth Regulator (PGR) are diverse group of organic compound other than nutrients, produced artificially or by plants which in low concentrations promote, inhibit or modify the physiological process in plant. Among the PGRs produced by plants are auxins (indole-3-acetic acid and its derivatives), gibberellins, cytokinins, abscisic acid and ethylene. Application of certain plant growth regulators promotes the process of seed germination, and development of roots in cuttings and layers. Various growth regulators have been used with striking success. Of these auxins such as indole3-acetic acid (IAA), indolebutyric acid (IBA) and naphthalene acetic acid (NAA) have the greatest effect on root formation in cuttings and layers. These chemicals speed up the healing of the wound, induce more roots and their development. They are now used universally in the propagation of many fruit plants. The growth regulators are effective in minute concentration and are usually applied in dilute solutions and dust formulations or rarely in grease bases such as lanolin. Plant growth regulators are generally calculated in the form of parts per million (ppm) or microgram per gram (mg/g).

There are several planting plans or systems which can be adopted for planting an orchard. The main principle for the layout of orchard is: It should accommodate maximum number of plant per unit area. Provide adequate space for the development of the tree. Ensure convenience in orchard operations. The various lay out systems used are the following

Training and pruning are an important activity in fruit crops to have better frame work and optimum fruiting area. Training refers to giving a desired shape to the plants by tying or staking or supporting over a structure and or selective pruning for a good strong frame work. Pruning refers to cutting of certain portion of plants for maintenance of fruitfulness and quality besides vigour of the trees or vines. Pruning affects the functions of the plants and assists in better fruiting and in getting more quality fruits. It is one of the most crucial operations and require some scientific knowledge regarding bearing behavior of the plants.

Water is an important input in crop production. It acts as solvent, reactant and used for transpiration and maintaining cell turgidity. Hence, knowledge of soil moisture is essential for making irrigation scheduling. For determining soil moisture status, the commonly used methods and instruments are discussed along with their advantages and disadvantages. The soil moisture can be measured by determining either the soil water content or the soil water potential. The measurement of soil water content is an estimation of the mass or volume of water in the soil, while the soil water potential is an expression of the soil water energy status. The relation between content and potential is not universal and depends on the characteristics of the local soil, such as soil density and soil texture. We can measure soil moisture content both by direct and indirect methods. In direct method, we remove the water from the soil sample by evaporation and the amount removed is determined. This method is popularly known as gravimetric method. We measure property of soil that is affected by soil water content under the indirect methods. Indirect methods employ tensiometric, nuclear (neutron and gamma radiations), electromagnetic (radar and time domain reflectometers), hygrometric (electrical resistance, capacitance, Infrared absorption) techniques besides remote sensing for making soil water models. In the following paragraphs both the methods of soil water measurement has been discussed.

Alternate bearing (AB) or biennial bearing (BB) is a major challenge to growers and traders of fruit crops. It is typically initiated by an abnormally heavy crop in trees (on year), followed by a light or no subsequent crop (off year).When on and off year sequence does not follow a systematic pattern it is called periodicity of cropping or irregular bearing. Alternate bearing is assigned due to genetic factor while irregular bearing may be due to lack of good orchard management practices. Alternation becomes entrained and difficult to change unless severe climatic events intervene, or drastic management interventions are made. A heavy “on” crop results in reduced vegetative shoot and root flushing, and less carbohydrate (energy reserves) build-up. Phenomenon of alternation is more prominent in the perennial fruit crops particularly in Anacardiacae (mango and pistachio), Carylaceae (Hazelnut), Oleaceae (olives), Rosaceae (apple, pear, plums, apricot etc), Rutaceae (orange, Tangor, Satsuma etc) and also tamarind, jamun etc. fruit crops. Within a tree species some cultivars are regular while others are alternate bearer e.g. in mango Amrapali is regular while Langra is strongly alternate bearer.

Maturity indices and their adoption at harvesting and in post harvest management of fruits provide a information against quality loss, microbial decay and deterioration of external appeal. Fruit harvesting at proper stage of maturity has direct effect on quality and market value of produce. Stage of harvesting also influence the after harvest enzymatic activities of the horticultural produce, which determines the levels of different pigments, sugars, acids and vitamins in fruits, flowers and vegetables. Maturity can be described as the attainment of a particular size, stage after which ripening takes place. However, horticultural maturity is defined as the stage of development when a plant or plant part possess the prerequisites for utilization by consumers for a particular purpose. Cucumbers, lettuce and peppers are harvested at various stages (Horticultural maturity) prior to reaching physiological maturity, or completion of growth phase. There are many methods to determine produce maturity. The most common is the size of the individual commodity.Some other commonly used crude methods are colour change, Softening of the tissues (fig,sapota) ease of detachment from the stalk (Sapota, annona), shrivelling of fruit stalk (water melon), time elapsed from the date of flowering to picking maturity, sound by tapping jack and water melon when ripe produce hollow and dull sound on tapping but produce metallic sound if unripe etc. Another physical characteristic is the firmness and it is determined with a pressure tester. Firmness is often correlated with chemical changes that occur during ripening. Chemical characteristics include TSS, acidity, sugar, vitamins and pigments. There are certain test which accurately gives the maturity measurements such as use of colour charts (judge colour), penetrometers (firmness), brix: acid ratio etc. Other recent methods viz. thermal conductivity X-rays and NIR have also come in practice to judge the maturity of fruits and vegetables. Some commonly use maturity indices are given below in some of the important fruits.

Losses resulting from pre harvest and harvest drop of fruits have long been a serious problem to the fruit growers. As the fruits of some species and varieties approach the picking maturity, they tend to loosen from the stalk and considerable quantities may drop prior to and during the picking operation. Such fruits are badly damaged and if salvaged have a very low value compared with those picked from the tree. In certain fruit crops, the problem of fruit drop is very serious. Whereas in some, the fruit drop starts right from the time of fruit set and is severe at a number of stages of fruit development. In some fruit crop serious drop occurs before harvest.

Determination of Specific Gravity The palatability of the citrus fruit is associated with its internal quality. Measuring specific gravity provide clues to internal quality of the fruit. The ratio of the weight of the fruit to its submerged weight indicates specific gravity. Specific gravity also indicates relationship between fruit weight and volume. Steps: To determining specific gravity Record the weight of fruit in air on top loading balance.

Management system adopted for fruit trees are quite different, especially with regard to nutrient than that adopted for field crops. The shift in management system could be commenced 3-4 years after planting depending on the tree size. Nutrients are required for flowering and fruiting while at the same time trees are allowed to grow and maintain sufficient vigour for producing high yields in following years. To maintain productivity of trees in long run and maintain the sustainability of tree production capacity, application of nutrient should be based on actual requirement and availability of nutrient in the soil. Application of plant nutrients economically at correct time with right amounts in a way that nutrients could be taken up by plants efficiently with minimum losses. The purpose of assessment of nutrient requirement of fruit trees is to keep mineral nutrient levels in the tree with in the desired range to have the growth and development effects and fruiting of trees as desired. The most important thing in nutrient management for bearing trees is to analyze the importance of timing of nutrient application in relation to tree phenology or growth cycle.

Diseases are often the most important constraint to the production of different fruit crops. They directly or indirectly reduce yields by debilitating the plant, and depleting the fruit quality. They range from aesthetic problems that lower the marketability of the harvested product to lethal problems that devastate the overall production. Virtually all fruit crops are affected by one or more serious diseases. Diseases determine how and where a crop is produced, what postharvest treatments are utilized, in what markets the crops are sold, and whether production is sustainable and profitable. Hence, as a fruit crop student one should know have the knowledge of different diseases occurring on major fruit crops, their symptoms and management strategies;

The decline of productivity and health of the tress may be due to faulty management i.e. unsuitable site and climate, cultivation of intercrops, inadequate nutrition, improper planting, undesirable planting materials, incidence of insect pest and disease and other biotic and a biotic stresses. The decline of trees are characterized by sparse appearance, yellowing and different type foliage symptoms, undergrowth and sickly appearance, dried-up top growth with small and less number of fruits. The branches of trees start to die from the top to downwards, ultimately resulted poor quality fruits. Such type of decline may be seen in whole orchards, on in a single tree or patches. Senile orchards with poor productivity are now a common problem in temperate, tropical and subtropical fruits. Since most of the fruit trees has long juvenile period, hence going for replanting, rejuvenation may be better option to convert sick tree into productive ones.

Various types of winter damage can occur to fruit trees. Temperature-related injuries include sunscald, tip dieback, bud death and heartwood damage. Even after planting frost tolerant varieties and rootstocks, it is important to manage frost occurring in regions where it is suspected to happen, it is necessary to prevent injury. When temperatures dip below the freezing point, water molecules move out of plant cells through the cell membrane due to ice formation in the intercellular spaces. Other cell constituents like sugars become more concentrated within the cell and with gradual reduction in water leads to dehydration and necrosis. At relatively short and moderate freezing temperatures little damage occurs to plants, but when temperatures fluctuate drastically or descend below -4oC, ice crystals form and intracellular freezing occurs leading to cell death. Tip dieback, bud death, and heartwood damage usually occur in situations where temperatures drop dramatically before the plant has hardened off adequately.

Rapid urbanization and industrialization has led to continuous deterioration of air quality, which is a major environmental problems in many urban areas in both developed and developing countries. Air pollution is characterized by high concentration of suspended particulate matter, oxides of sulphur and nitrogen resulting primarily from increased use of vehicles. Air pollution effects are not limited to the short term nor to the plant damaged or killed. Rather, air pollution has long term effects that affect plants including fruit trees. Horticultural crops are injured when exposed to higher of abnormal levels of various air pollutants. The injury symptoms range from visible marks on foliage, reduced growth and yield to premature death of the plant. The development and severity of injury depends not only on the concentration of the particular pollutant, but also on a number of other supporting factors. These include the duration of exposure to the pollutant, the plant species and development stage as well as conducive environmental factors.