Changes of seed quality and germination of some black cumin ecotypes (Nigella sativa L.) during development and maturity

There are some reports on seed development in medicinal plants, but no information has been reported in seed development of Nigella sativa. The purpose of this study was to investigate seed quality traits including time to maturity and physiological maturity, germination and dormancy changes in 14 different ecotypes of black cumin.

A randomized complete block design was conducted at the Aburaihan Campus of University of Tehran in 3 replications and 7 harvest times during two years of 2018 and 2019. Treatments were 14 native black cumin ecotypes (across Iran), germination temperature and post-flowering time during seed development on the mother plants. The studied traits included seed weight and moisture content and seed germination percentage during seed development. For germination test, a factorial experiment was conducted based on completely randomized design in three replicates which treatments consisted of different incubation temperatures and 14 ecotypes of N. sativa.

The results showed that the moisture content during development on the mother plants had a decreasing trend. In the first sampling, the highest percentage of moisture was observed in Arak ecotype and had a decreasing trend until harvest. At full maturity, seed moisture content in all ecotypes were less than 18%. Ecotypes of Zabol1, Bajestan, Sarayan, and Ashkedaz required the lowest time after flowering to reach their maximum seed weight, thus there was recommended for regions with short growing season. The Khaf ecotype with 2.3 mg seed weight had the highest weight and the Hamadan ecotype with 0.072 mg/day had the highest seed filling rate. In the ecotypes of Tafresh, Zabol2, Eghlid, Semirom, Arak, Hamadan, Razan, and Gerdmiran germination started 20 days after flowering and had an increasing trend until physiological maturity. In ecotypes such as Isfahan, Eshkezar, Zabol1, Sarayan, and Khaf germination started from 20 days after flowering and up to 30 days after flowering there was an increase in germination percentage, but after this time the percentage of germination decreased and reached zero until the full maturity, which in fact primary dormancy induced to the seeds.

Therefore, if the planting of seeds is done immediately after harvest, ecotypes of Tafresh, Zabol2, Eghlid, Semirom, Arak, Hamadan, Razan, Gerdmiran are suitable. Incubation temperature also showed that the highest germination percentage for all ecotypes was observed at 10 °C and decreased with increasing temperature and reached zero at 30 °C. Ecotypes of Hamadan, Semirom, Zabol1, Tafresh, and Gerdmiran had the highest germination percentage at 10 °C among the studied ecotypes. Therefore, dormancy in black cumin is probably Type 1 of nondeep physiological dormancy.