Plant growth Regulators introduction Flashcards

Question

What is the relationship between a PGR and Plant pest and Disease?

Answer 1

The relationship between plant growth regulators (PGRs) and pests/diseases in plants can be complex and multifaceted: 1. **Indirect Effects**: PGRs can indirectly influence the susceptibility of plants to pests and diseases by altering their growth and development. For example, PGRs that promote vigorous growth may make plants more attractive to certain pests or susceptible to certain diseases. Conversely, PGRs that regulate plant defense mechanisms or enhance stress tolerance may help plants resist pest infestations or disease infections. 2. **Direct Effects**: Some PGRs have direct antimicrobial or insecticidal properties that can affect pests and diseases. For instance, certain synthetic PGRs may have pesticidal properties that directly target pests or inhibit the growth of pathogenic microorganisms, thereby reducing disease incidence. 3. **Modulation of Defense Mechanisms**: PGRs can modulate plant defense responses against pests and diseases. They may enhance the production of defense compounds such as phytoalexins, lignins, and secondary metabolites, which can deter pests or inhibit pathogen growth. Additionally, PGRs can regulate the expression of genes involved in plant defense pathways, thereby enhancing the plant's ability to withstand pest attacks or disease infections. 4. **Integrated Pest and Disease Management**: PGRs are often used as part of integrated pest and disease management (IPM/IDM) strategies, where they are combined with other control measures such as cultural practices, biological control agents, and chemical pesticides. PGRs may be employed to enhance plant resistance, mitigate stress, or promote recovery from pest or disease damage, thereby reducing the reliance on conventional pesticide applications. 5. **Risk of Imbalance**: However, improper or excessive use of PGRs can sometimes lead to unintended consequences, such as increased susceptibility to certain pests or diseases, phytotoxicity, or disruption of ecological balance. Therefore, it's essential to use PGRs judiciously and in accordance with recommended guidelines to minimize potential risks to plant health and ecosystem integrity. In summary, the relationship between PGRs and pests/diseases involves a combination of direct and indirect effects, modulation of plant defense mechanisms, and considerations within the broader context of integrated pest and disease management strategies.

Answer 2

Growth mainly refers to the quantitative increase in plant body such as increase in length of the stem and root, the number of leaves, the fresh weight and dry weight etc. On the other hand, germination of seed, formation of flowers, fruits and seeds, emergence of lateral buds, falling of leaves and fruits are qualitative changes, referred to as development.

Answer 3

Plant growth regulators or plant regulators are the organic compounds other than nutrients which modify or regulate physiological processes in an appreciable measure in the plants when used in small concentrations. They are readily absorbed and these chemicals move rapidly through the tissues when applied to different parts of the plant. Plant hormones or phytohormones are also regulators but produced by the plants in low concentrations and these hormones move from the site of production to the site of action. The term plant growth regulators’ is relatively new in use. In earlier literature these were mentioned as Hormones. Hormone is a Greek word derived from “hormao” which means to stimulate. Now the term phytohormone is used in place of plant hormone. Growth and development of the plant body are controlled by two sets of internal factors, namely, nutritional and hormonal. Nutritional factors supply the plant necessary mineral ions and organic substances such as proteins, carbohydrates and others. These constitute the raw materials required for growth. However, utilization of these substances for proper development of the plant is controlled by certain chemical messengers, called plant growth substances or plant growth regulators, which in minute amounts increase or decrease or modifies the physiological processes in plants.

Answer 4

Therefore, the difference between the plant regulator and plant hormone is in that the former one is synthetic and the latter one is natural from the plant source. “All plant hormones are plant growth regulators, but not all plant growth regulators are plant hormones,”

Answer 5

* Propagation ( rooting in stem cuttings, Layering, grafting and budding) * Flowering control * control of sex orieantation of the plants * Fruit set * Fruit Drop * Fruit Quality and size * Ripening of Fruits * Parthenocarpy

Answer 6

Certain kind of plants may not successfully root under normal condition and with the aid of plant regulators; they can be easily made to induce rooting. The most commonly employed growth regulators for rooting are auxins like IBA, IAA, and NAA. Among these chemicals IBA is most ideally used since, it is the most effective one. Concentrations ranging from100-500ppm are used for long dip method of treatment of cuttings for 12-24 hours and high concentrations of 10,000 to 20,000 for quick dip method for a few seconds. The concentrations differ according to the type of cutting i.e. herbaceous, Semi-hard wood and hard wood cuttings. Applications in the form of dust as talcum preparation or in the form of a paste in lanolin are also used.

Answer 7

Another usage of plant regulators in plant propagation is in aiding rooting of air layering. Layering is the practice of inducing rooting on shoots/stems while it is still attached to the parent plant. This is practiced in fruit trees like guava, pomegranate etc. The main principle of layering is that a part of the aerial portion of the intact plant is girdled. This results in severing of phloem. Consequently, hormones and food substances coming from the leaves accumulate above the girdled portion. When the ring of bark is removed from the stem, the growth regulators like IBA or IAA in powder or in Lanolin paste is applied at the distal end of the bark-removed portion to promote root formation

Answer 8

Grafting of plants is a widely used horticultural practice of multiplying the desired genotypes in mango, citrus and others. For this, a portion of the plant is inserted in to another plant of the same species or sometimes compatible plants of different species or genera. There are mainly two types of grafting: bud grafting and scion grafting. Whatever may be the method employed, the principle remains the same. When the cambium of a stock plant comes into physical contact with the cambium of a scion both from new xylem and phloem simultaneously together. Consequently, these become united and grow as one plant. Since, auxins have the property of promoting cell division of cambium these are often employed. Before grafting, either stock or scion or both are dipped in auxin solution. This promotes an early union and consequently, a better success of grafted plants.

Answer 9

The plant growth regulators are used for the regulation of flowering in certain crops. In pineapple flowering is irregular and harvesting becomes a problem and hence to regulate flower production, plant regulators are used. The treatment generally consists of pouring a required quantity of (50ml), the solution containing 0.25 to 0.5 mg of the chemical of NAA in the central core of plants. In recent studies, Cycocel and Alar at 5000ppm and Ethrel at 100-200ppm have been shown to induce flowering in mango during an off year. In Jasminum grandiflorum, the flowering period is extended by the application of Cycocel at 500ppm. Flowering can also be induced in certain vegetables such as radish, beet root and carrot with the application of GA.

Answer 10

Various growth regulators like IAA, IBA, IPA, NAA, 2, 4-D, and GA have been found to improve fruit set in many crops. Among these chemicals 2, 4-D and NAA (Planofix) have been found in general to be most effective in increasing the fruit set. The optimum concentrations for this purpose are 10-20 ppm of auxins and 10-100ppm of GA in different crops. Spraying the flower cluster thoroughly 4-6 days after full bloom with 100 ppm GA increased the fruit set in grape. It has been found that in chillies spraying of Planofix @ 1ml in 4.5 liters of water at 60th and 90th day after planting is beneficial for good fruit setting.

Answer 11

Losses resulting from pre-harvest drop of fruits have long been a serious problem. When the growth regulators have been put in to use in apples and pears, pre-harvest fruit drop can be checked by the application of 2,4-D effectively. Pre harvest fruit drop in citrus is controlled with 2,4-D at a concentration of 20ppm2,4-D, 10- 15ppm of NAA and 2,4,5-T at 15 to 30ppm at pea stage and marble stage and 2,4D at 20ppm and 2,4,5-T at 10-15ppm in mandarins. At 10ppm and NAA at 20ppm have effectively prevented fruit drop in mango. Application of planofix containing NAA at‖ pea stage and marble‖ size of the fruits completely controlled early fruit drop in Guava.

Answer 12

Partenocarpic fruit set could be induced in a number of vegetables like cucurbits, bhendi, brinjal, chillies and tomato and fruits like guava, straw berry, citrus, watermelon etc.IAA,IBA,NAA,NAD,2,4-D,IPA and GA are effective in different plants. Application of GA at 100 ppm induced complete seedless in grapes.

Answer 13

The plant growth regulators can be employed to hasten or delay fruit ripening. Plant growth regulators like 2, 4, 5-T at concentrations of 25 to 100ppm has been found to hasten the ripening in some varieties of plums and peaches. In banana ethrel treatment at 2500ppm induces ripening in 24 hours. Application of 2, 4-D at 16ppm delays ripening in Washington navel oranges. In tomatoes all fruits on a plant won‘t mature and ripen at a time .This is a serious disadvantage for mechanical harvesting .Ethephon applied 1-2 weeks before harvest promotes de-greening and ripening of tomatoes. Application of smoke is commercially employed to hasten and ripen bananas, the active ingredient responsible being ethylene.

Answer 14

Increase in berry size in grape varieties was reported when GA was applied at 40ppm at bud and flower stages. Higher concentrations resulted in the increase in the length of berries.

Answer 15

Plant regulators can be employed to modify the sex expression in crops. In cucurbitaceous vegetables the production of male flowers will be always more in number than the female flowers and this sex ratio can be narrowed down by the application of ethrel at 100 to 250ppm, if sprayed four times at weekly intervals commencing from 10 to 15 days after sowing. This growth regulator not only increases the number of female flowers to male flowers, but also produces female flowers at earlier nodes. Application of GA, the sex ratio is shifted towards maleness in several cucurbits. Certain plant regulators are employed to induce male sterility in crop plants, so that such male sterile plants can be used as a female plant in the hybridization work. Complete male sterility in okra can be obtained by spraying with 0.4% of MH. A single spray one week before floral bud initiation offers male sterility for 10 days and a subsequent spray at floral initiation extends the effect to 22 days.

Answer 16

Solution form: To prepare an alcoholic solution of any plant growth regulator, dissolve 1 gm. of growth regulator in 50 ml of ethyle alcohol or methyl alcohol or methylated spirit and then dilute this with an equal volume of water to make 100ml of solution containing 10,000 ppm of growth regulator. This acts as stock solution for further dilutions with distilled or de-ionized water. Stored in well-stoppered bottles in a refrigerator, the solutions retain their activity indefinitely. Dust form: To prepare a dust containing 10,000ppm of growth regulator dissolve 1gm of the regulator in 40 ml of methylated spirit of 95% alcohol and stir this into 100g of pharmaceutical talc to form a smooth paste. This should be done in a dark room away from strong light. Stir the paste while it is drying until it becomes a fine dry powder. This prepared dust remains active for six months or more if stored in a closed opaque container in a refrigerator. From this stock, before using, dilute the growth regulator by mixing the stock with talc powder. Lanolin pastes: These are particularly convenient for use in air layering but now regarded as an obsolete treatment for cuttings and are made by stirring the growth regulators into the molten lanolin and then allowing it to cool. To make a paste containing 5,00ppm of growth regulator melt 200gm of lanolin and thoroughly stir into this molten lanolin 1gm of required growth regulator. This prepared paste will keep indefinitely if stored in a well stoppered opaque glass vessel in a refrigerator.