Biological World

  Reason behind the selection of pea plant by Mendel 1)       In the pea varieties available commercially, several characters had two contrasting forms, which were easily distinguishable from each other. This permitted an easy classification of F 2 and F 3 progeny from various crosses into clear-cut classes on the basis of contrasting from of the different characters. 2)       Flower stricter of pea ensured self-pollination; this was experimentally verified by Mendel. 3)       Pea flowers are relatively large, which facilitates emasculation and pollination. 4)       Every year one generation of pea can be grown. 5)       Pea seeds are large and present no problem in generation. Pea plants relatively easy to grow and each plant occupies only a small space.   In addition to pea, Mendel worked on Rajma ( Phaseolus vulgaris L.) as well. The res...

  Systemic Acquired Resistance        Resistance may be regarded as the ability of a plant to overcome completely or in some degree, the effect of a pathogen or other damaging factor. Systemic acquired resistance is one of the promising means of plant disease control. In this process pathogenic micro organisms or chemical compounds are applied in the plants. As a result of this process in the treated plant, appear and consequently the defense of the whole plant against subsequent infections by pathogens of same or different types is inactivated. Systemic acquired resistance spread systemically and develops in distal, untreated parts of the plant. Introduction of SAR:-        Systemic acquired resistance become a subject of great importance and enquiry. It is a broad physiological immunity that develops from infection with a pathogen. In addition to this, certain natural and synthetic chemical compounds trigger simila...

                                          Host pathogen interaction        In pathogenesis, relation between pathogen and host factors is an important phenomenon. This relationship determines the intensity of the disease. In addition with this the influences of environmental factors are also effective. For the process of establishment of disease the following steps are required.   Host + Pathogen + Environment → Host-Pathogen complex →Pathogenic interactions        When a pathogen spread to and affects may individuals with in a population over a relatively large area and within a short time, the phenomenon is called epidemic. An epidemic is simply defined as the increase of disease in defined as the increase of disease in a population. For epidemism the necessary factors must be exists in their optimum form. The o...

   Late Blight of Potato Late blight of potato is one of the important diseases found in all potato growing areas of the world. It is a native of north Andis in South America. This disease becomes well established in Ireland, Europe and England. In India the late blight was introduced in the Nilgiri hills but now a days it is frequently available in all potato growing region of India. Causal organism :- Phytophthora infestans is the causal organism of late blight of potato, Solanum tuberosum . It is also pathogenic to other plants of family Solanaceae including tomato. Symptoms   They appear 1 st as water soaked or hydrotic areas along the margin and tips of lower leaflets. The spots enlarge rapidly become necrotic, turned brown and then blackish or blighted. The infected leaves ultimately become limb and rot away producing a characteristic odour. If dry weather intervenes spreading of the lesions is temporarily checked. But the favourable condition helps th...

                                                Chemotherapy and Fungicides Chemotherapy refers to the chemical treatment which is applied to eradicate the pathogens from tissues of the diseases plant and thus curing it. Chemical treatment act as a chemical defence mechanism either by destroying the pathogen or by inducing temporary resistance.   Tropical and systemic fungisides :-        The chemical which are use to kill pathogenic fungus are called fungisides. Fungisides maybe of 2 types- (a) Tropical fungisides and (b) Systemic fungisides.          The 3 tropical fungisides are- i) Bordeaux mixture, ii) Ferric dimethyl-dithiocarbmate, iii) Tetrachloro-ρ-benzoquinone.               The 3 systemic fungisides are- i) B...

  Agencies for plant pathogens spreading.           Distribution of a pathogen is very essential for the spreading of pathogen and establishment of disease epidemics. The spread of plant pathogen depends on some agencies. Such agencies are as follows-   Air :- A lot of pathogens are spreaded by air. This type of spread was discovered by Gaumenn. All fungal pathogens which produce spores or cinidi\a on the surface are disseminated by the wind such as downy mildews, powdery mildews, rust, smuts, and leaf spot causing pathogens.        Spread of plant pathogen by air may take place in 2 general ways- (i) by wind distribution of diseased plant parts and (ii) by wind dispersal of spores and vegetative cells. For effective spreading high spore production is also essential because a large number of spores are wasted during this process.   Water :- Water is also act as an agent for dissemination...