Exposing Seeds of Sarcococca confusa to Increased Concentrations and Durations of Ethyl Methanesulfonate Reduced Seed Germination, Twinning, and Plant Size

摘要

Sweetbox (Sarcococca confusa) is an evergreen shrub valued for attractive foliage, winter fragrance, black fruit, as well as shade and drought tolerance. The high degree of apomixis in Sarcococca limits the effectiveness of conventional breeding practices. However, mutation breeding may be a valuable tool to induce variation in seedling crops. As such, a study was conducted to expose seeds of S. confusa to ethyl methanesulfonate (EMS) at varying concentrations and exposure durations, and to evaluate the effects on seed germination, growth, and relative frequency of polyembryony. In 2010, seeds of S. confusa were treated with 0%, 0.2%, 0.4%, 0.8%, and 1.2% EMS for 24 and 48 hours. Seeds were sown and the relative germination and occurrence of polyembryony were recorded. Seedlings were later evaluated for size and phenotypic variation in the subsequent growing seasons. Percent germination was found to decrease with increasing EMS rates in the 24- and 48-hour treatments. The occurrence of polyembryony also decreased with increasing EMS rates in the 24-hour treatment but was observed to be greatest at 0.2% EMS. No significant differences in plant size index (SI) were found after four growing seasons. When mature, seeds were collected from any plants that bore fruit in each treatment and were then sown. The percentage of plants that bore fruit in each treatment decreased with increasing EMS rates, although the germination rate of these seeds did not differ. A chlorophyll mutant and several dwarf forms were identified in this population as well. They have been propagated asexually for future evaluation as new cultivars. This study demonstrates the utility of chemical mutagenesis to induce phenotypic variation in S. confusa while reducing the rate of polyembryony.