BACKGROUND INFORMATION:

THE CONCEPT OF QUALITY AND INTEREST IN ITS USE.

Introducing the concept of quality (measured in a very objective manner) in the sector of plant production will most certainly grant the sector much greater transparency, enabling one to better define which companies produce better plants, starting from the aspect of rendering better services to farmers. As a result, these farmers will be able to choose the plants that best suit their needs, according to the price that they are willing to pay. Choosing the plants that will be transplanted is a crucial decision, as farmers establish many conditions with regards to the crops they are cultivating, not to mention to the final result of their efforts. Hence, seeing as they know precisely what kind of product they want to produce, they should make themselves fully aware about the products that the market has to offer them (Welles, 1989).

Some aspects regarding a plant’s quality are simply beyond one’s control in terms of being translated into parameters. However, one must bear in mind factors such as the plants’ healthiness and the homogeneity in the crops; differences in sizes and ages among plants are likely to lead to differences during plant production in terms of premature plants as well as in differences in quantity and quality (Hoyos, 1990).

Some parameters are easier to measure than others. Hence, it may cost less to define them and they may be put to use more widely. However, it is obvious that the validity of their results must be checked, for the results may be linked to the capacity of response in the field. Many other factors must also be taken into account, such as the time required to measure the parameters, whether they represent immediate readings or if time is required to measure them, as occurs regarding many criteria laid down that aim to determine the phyto-sanitary conditions of the plants.  In such cases, it is necessary to accompany the growth of the plants and to carry out these measurements directly in the field. Due to this time consuming process, when one finally reaches a result, it may be too late (Hoyos, 1995).

CHARACTERISTICS OF PLANTS AND POST-TRANSPLANT STRESS

The first question that should occur to a farmer is: “Will the plant be able to overcome the crisis that results from its transplant?” There are several measures that can be put into practice to help the plant respond successfully to the transplant and to later develop firm roots, thus achieving growth in its new medium. The way one can assess whether a plant is more or less likely to successfully overcome post-transplant stress is closely linked to its content of dry matter D.M. (%). This seems to be the best parameter to assess a plant’s sensitivity, the larger its amount of dry matter, the higher its resistance to stress.

Figure 1 – Relationship between the plants’ content of dry matter (D.M.) at the moment of transplanting and the percentage of firm rooting among tomato plants subject to low temperatures in the field after their transplanting

Measuring the percentage of a plant’s D.M. is a relatively simple task that does not require any complex equipment; just a greenhouse where the temperature can be kept between 70 and 75 °C. The plant under analysis should be maintained in the greenhouse until it has lost all the water that it initially contained and measurements of its dry weight bring constant figures. The temperature range suitable for this dehydrating process varies according to the species that is being studied (Leskovar, D.I. and Cantliffe, D.I., 1991).

The question is: “How can one improve the quality of a plant?” When plants are asexually disseminated one might say that applying liquid fertilizers would not increase the percentage of rooting. Nevertheless, the quality of a plant can be substantially improved through these applications, for they help the plant gain more resistance to stress during transplanting (Hartman, H., 1990).