Castor (Ricinus communis L.) is cultivated around the world because of the commercial importance of its oil.
Castor is extensively grown in Western India and in a few places around the world. Brazil and China complement castor seed production. In the recent years, the two countries have experienced a shift in the crop pattern coupled with a steady increase in its domestic consumption.
Castor is grown under tropical conditions. It loves heat and humidity and does best in regions where both are ample. India, gifted with an ideal climatic condition, has recorded a produce of close to 1200,000 tones of castor seed. This accounts for 75.6% of the world production. Gujarat produces 86% of the total castor seeds in India followed by Andhra Pradesh and Rajasthan. Mehsana and Banaskantha are the largest castor producing districts in Gujarat.
In India, Castor is planted during July or August and harvested around December or January. The seed pods are dried, de-podded and brought to the market yards from December to January for trading. The Indian variety of castor has an oil content of 48% and 46% can be extracted.
Although commonly referred to as a "bean," castor is not a legume. The plant has also been called the "castor oil plant." The Egyptians used castor oil, one of the oldest commercial products, in lamps more than 4,000 years ago, and seeds have been found in their ancient tombs (Weiss 1971). Castor is considered by most authorities to be native to tropical Africa, and may have originated in Abyssinia (Weiss 1971).
Although grown as annual plants, they act as perennials in the tropics and subtropics and the plants reach heights of 9 to 12 metres. The dwarf-internode cultivars 'Hale' and 'Lynn', and hybrids using them as the pollen parent, vary in height from 0.9 to 1.5 m, compared to 1.8 to 3.7 m for the normal-internode types formerly grown (Brigham 1970a,b). Soil conditions, availability of moisture, and levels of nutrients can cause considerable variation in height of plants. Plants have a tap root, plus prominent lateral roots below the soil surface.
The large leaves are palmately lobed, (hence the name Palma Christi used for castor) and are borne more or less alternately on the stems, except for the two opposite leaves at the node just above the two cotyledonary leaves. The petioles are usually several times as long as the long axis of the leaves. The main stem is terminated by the first or primary raceme, which often is the largest on the plant. The primary raceme of early dwarf-internode cultivars usually occurs after the 6th to 10th node. On later cultivars, the primary raceme may occur after the 8th to 16th node. In introductions from other countries, dwarf-internode types flowering after 40 or more nodes are known.
After the first raceme appears, branches originate at the nodes below it. The number of branches depends on plant spacing and in some cases the cultivar. Under field conditions, two or three branches occur at almost the same time, but generally in the following order: the first branch at the node immediately beneath the primary raceme, the second at the second node, and the third at the third node below the primary raceme. The first racemes formed on the branches are commonly called the "second set" of racemes. Subsequent branches arise from the nodes just beneath the racemes of the second set. This sequence of development continues as long as the plant remains alive and growing actively. Thus, the development of racemes along any one axis is sequential, making it possible for a plant to have racemes in all stages of development from bud stage to complete maturity.
Typically, the racemes usually bear pistillate flowers on the upper 30 to 50% and staminate flowers on the lower 70 to 50% of the raceme. Number of staminate and pistillate flowers can vary greatly, depending upon raceme size. The flowers are without petals. After the pollen is shed, the staminate flowers dry up and usually drop. The pollen, which is discharged forcibly from the anthers, is carried to stigmas mainly by wind (Brigham 1967). After fertilization, the pistillate flowers develop into spiny capsules, though spineless types are known. At maturity, the hull (pericarp) of the capsule may split along the outside seam (dorsal suture) of each of the three capsule segments (carpels). If splitting is violent, as in wild types, the seed will be ejected and scattered on the ground around the plant. This type of splitting (dehiscence) is not present in cultivars grown for mechanized production. Seeds of present cultivars are held within the capsule for several weeks after frost with no appreciable loss.
Seeds of current cultivars weigh from 3.0 to 3.5 g. Seed color ranges from light to dark brown, with various mottling patterns. The seed coat makes up about 25% of the weight of the seed. Oil content averages 48% on a dry weight basis.
Chromosome number of castor is 2n = 20. Autotetraploids have been produced using colchicine, and haploids have been reported, but in nature, castor is found mainly in the diploid form. There is little or no loss of vigor when castor plants are inbred (Moshkin 1980).