Low temperature, frost,heavy fog and severe winter appear to that induce parthenocarpy in olive, tobacco, pear, cucumber, tomato, Capsicum etc. Especially the night temperature in the range of 10-16°C, and a short day of eight hours are known to be the most favourable conditions for parthenocarpic induction. Campbell observed that in the heavy fog in June month caused the formation of seedless olives and Hostermann noted the formation of seedless pears after a frost. Parthenocarpic fruits in the pears are obtained by Lewis (1942) by exposing flowers to freezing temperatures. Osborne and the Went were able that induce to the parthenocarpy in tomatoes with low and high light intensity.
Chemically induced Parthenocarpy:
Gustafson has reviewed the different plant species which have been chemically induced to produce partheno¬carpic fruits.
(a) Tomato - It responses extremely well to synthetic growth substance-sprays of 3-indole butryic acid and 2-naphthoxy acetic acid give excellent results.
(b) Strawberry - Sprays of 2-naphthoxy acetic acid can increase the yield of strawberries.
'(c)' Grapes:- Fruits can be improved by auxin sprays. Gibberellic acid gives good result.
(d) Peach:-Gibberellic acid sprayed at full bloom can cause parthenocarpic development.
Auxins and gibberellins at low concentrations hi been successfully used to induce parthenocarpy in a number of plants which normally bear seeded fruits. These sub stances are applied to flowers in the form of lanolin paste or sprays. The latter is more convenient for commerei.il purposes.
Balasubramanyan and Rangaswamy (1959) observed that as a result of artificial pollination most of the varieties of Psidium gujava developed into seeded fruits but a variety, Allahabad Round, yielded parthenocarpic fruits.
CELL AND TISSUE CULTURE
The notable progress in the field of experimental embryology has been possible through the technique of I n vitro culture in which that the isolated tissues,plant cells and organs or even whole plants are grown in nutrient medium in glass containers, under aseptic conditions. There are three important aspects of the technique of in vitro culture, namely nutrient medium, aseptic conditions and aeration of the tissue.
Nutrient medium: Many nutrient media have been deve¬loped from time to time. Every tissue and organ has its special requirements for optimal growth, and these need to be worked out when starting with a new system. However, most of the media contain inorganic salts of major and the minor elements and vitamins and sucrose. A medium with these ingredients will be referred to as basal medium. Some plant growth substances, such as auxins, gibberellins and cyto¬kines may also be added to the basal medium either alone or in various combinations. Natural plant extracts, such as coconut milk, various fruit juices, caesin hydrolysate and yeast extract have also been used as supplements to the basal media for growing some tissues.
All constituents of the medium are dissolved in distilled water. If it is than the necessary the medium is solidified with about 0.8% agar. The pH of the medium is adjusted around 5.8. Now equal quantities of the medium are dispersed in culture vills, which are usually glass tubes or flasks. The culture vials that containing medium are plugged with the non absorbent cotton
wrapped in cheese cloth. Such a closure allows the exchange of gases but does not permit the entry of micro-organisms in the culture of vials.
Aseptic conditions: The nutrient media especially when they contain sugar, would support a luxuriant growth of many micro-organisms like bacteria and fungi. Reaching the medium, these organisms grow much faster than the cultured tissue and, finally kill it. It is, therefore, extremely important to maintain a completely aseptic environment inside the culture vials.
Aeration: The methodology of in vitro culture technique should also account for proper aeration of the cultured tissue. If the tissue is grown on the surface of the semisolid medium and it acquires enough aeration without a special device. However, if liquid medium is employed, the tissue would get submerged. In such a situation, some special device is to be adopted for proper aeration of the tissue. One way is to use a "filter paper bridge" whose two legs remain dipping in the medium, and the horizontal path carrying the tissue is raised above the level of the medium. Agitation of the medium by passing through it filter-sterilized air also serves the purpose. More commonly aeration is provided by shaking the flasks or tubes on an automatic shaker. Besides it also supplies the oxygen to the tissue and shaking of the medium are also brings about desiccation of the tissue into single cells and small clumps. The importance of single cells in cloning in higher plant genetics has been greatly appreciated.
Plant protoplasts: Protoplasts have been isolated from a large number of plants. Leaf material and cultured cells are used most frequently. The tissues are treated with a mixture of enzymes which digest the cell walls and release the protoplasts. They are cultured in a nutrient medium. They may reform a cell wall and can be induced to undergo division. Plant regeneration from protoplasts is possible in a variety of species.
