Plant Growth Regulators in Citriculture: World Current Uses

Plant growth regulators (PGRs), both naturally occurring and synthetic, are used extensively in citriculture not only to help growers solve production problems, but also to increase the market value of the crop and to improve grower returns. Yield increases are obtained via an improvement in fruit set, particularly for shybearing cultivars, and/or fruit size, especially for the “small-fruit” group of mandarins. Increased fruit number per tree is achieved indirectly through an increase in flower number as a result of better flower initiation or by a direct effect on fruit set. Improved fruit size is brought about directly by stimulating the growth of fruit tissues or indirectly by reducing fruit number by partial inhibition of flower initiation or by subsequent fruit removal. PGRs are also used to hasten maturity, to delay harvest, and to maintain fruit quality postharvest, resulting in greater profits to the grower. This article provides an overview of current uses of PGRs in citriculture. The reported information is based on an international survey and a review of recent technical and scientific literature published on the subject. Procedures and techniques used to enhance the efficacy of PGRs, including surfactants and compatibility considerations, are presented and discussed. The detailed information presented in the text is summarized in tables designed to provide a convenient reference for researchers and growers alike. Included in the tables are the names of the individuals who were the source of the information. A comprehensive list of these individuals and their addresses follows the tables. Whereas the results of the survey indicate extensive uses of PGRs in citriculture, the authors admit that the survey is incomplete and extend their apologies to researchers in countries not represented in the review and for inadvertent omissions.     

Reduction in population growth under different contraceptive policies

A number of equations for the various population control policies are worked out for a desired reduction in the rate of growth. At the ages of 25 and 30 respectively, 61 and 97% of contraceptive users are necessary to reduce the present rate of growth of 0.026 to 0.010. While at the age of 25 about 69 and 76% contraceptive users are required for the same reduction in the rate of growth, assuming that 25 and 50% would discontinue the use of contraceptives at the age of 35. The birth and death rates in the study area (Varanasi Rural) have remained almost constant for several years, justifying the assumption of a stable population. This study emphasises the need for the use of contraceptive devices at two or more age levels.