Studies on the Germination and Emergence of Castor Seedlings

Abstract

Castor (Ricinus communis) is an oilseed usually cultivated in tropical and semi-arid conditions. The slow and uneven germination of castor seed is causing poor crop establishment and reduced seed yield. This series of studies investigated several factors influencing the time for castor seed germination and seedling emergence. Studies were made on the effect of seed coat permeability to water and the influences of temperature, morphology, and the hormone gibberellin. The best temperature for castor seed germination was near 31 °C, and the seed coat was permeable to water. The mechanical resistance of the seed coat was a mechanism controlling the germination of the castor seed. The time for germination was strongly associated with the seed coat relative weight, but it had little influence from other morphological characteristics. After the castor plants were subjected to three cycles of selection for fast germination, the seed weight was reduced, the caruncle became larger, and the seed coat became thinner. Gibberellin applied to the seed promoted a faster and higher germination rate. Pre-germination of the castor seed was not effective for promoting faster seedling emergence. Attempts to improve castor seed germination should integrate the many factors that influence this physiological process.