Seed Dormancy Status Research Articles

Maturation temperature and rainfall influence seed dormancy characteristics of annual ryegrass (Lolium rigidum)

The role of temperature and rainfall during seed development in modulating subsequent seed dormancy status was studied for Lolium rigidum Gaud. (annual ryegrass). Climatic parameters relating to geographic origin were compared with annual ryegrass seed dormancy characteristics for seeds collected from 12 sites across the southern Western Australian cropping region. Seed germination was tested soon after collection and periodically during subsequent after-ripening. Temperature in the year of seed development and long-term rainfall patterns showed correlations with aspects of seed dormancy, particularly the proportion of seeds remaining dormant following 5 months of after-ripening. Consequently, for one population the temperature (warm/cool) and water supply (adequate/reduced) during seed development were manipulated to investigate the role of maternal environment in the quantity and dormancy characteristics of seeds produced. Seeds from plants grown at warm temperatures were fewer in number, weighed less, and were less dormant than those from plants grown at cool temperature. Seeds that developed under both cool temperature and reduced moisture conditions lost dormancy faster than seeds from well-watered plants. Seed maturation environment, particularly temperature, can have a significant effect on annual ryegrass seed numbers and seed dormancy characteristics.

Degradation of endosperm mRNAs during dry afterripening of cereal grains

AbstractThe endosperm of dormant wild oat (Avena fatuaL.) grains contains a number of mRNAs, including low levels of transcripts encoding avenin (AV10), puroindoline-like (AV1) and serine proteinase inhibitor-like (Z1) proteins. During dry afterripening, a period of warm dry storage that relieves dormancy, the abundance of these intact transcripts gradually declined to undetectable levels in pooled grain samples. In contrast, the three mRNAs did not decline in grains stored for the same period at −20°C, and levels of mRNA decay products derived from these transcripts did not change during afterripening. Disappearance of the three intact mRNAs was not a general phenomenon, since abundance of more than 5000 other seed mRNAs did not change during this period. Additional experiments were conducted to test the idea that the presence of these transcripts was positively correlated with seed dormancy status. First, the rate of intactZ1mRNA decline was similar to the rate of dormancy relief during 9 months of afterripening. Second, cultivated oat (A. sativa) grains (which are not dormant at maturity) contained much lower levels of these mRNAs than did highly dormant wild oat grains. Third, levels of full-lengthAV1andZ1mRNAs remained constant in dormant grains during 6 d of imbibition. However, Northern analyses of individual grains from a partially afterripened seed lot showed that amounts of intactAV1orZ1mRNAs were highly variable in germinating and dormant grains and were not correlated with dormancy status. Even though loss of these transcripts occurred under the same environmental conditions that promote afterripening, a causal relationship between the two processes seems unlikely. The apparently specific mechanism(s) by which these mRNAs are degraded in endosperm tissue may represent a novel post-transcriptional process for regulating levels of certain transcripts in dry grains.

Temporal changes in velvetleaf (Abutilon theophrasti) seed dormancy

Primary physical dormancy caused by seed coat impermeability to water is a major reason for the persistence of velvetleaf in soil seedbanks. Understanding temporal trends in seed dormancy status will help predict potential emergence in the spring. Experiments were begun in 1992 and 1993 to determine the effects of velvetleaf seed maturation time, storage environment, and storage duration on changes in seed dormancy and germination over 20 mo. Seeds buried 1 and 10 cm deep exhibited a 30 to 70% decline in physical dormancy from maturity until winter, little change in dormancy from winter through the following summer, and a further decline the next autumn. The loss of physical dormancy was more rapid for early than for late maturing seeds and more rapid in 1992 than in 1993. Physical dormancy of seeds held at 4 C declined steadily, at a rate of approximately 0.8% per day, over the course of the study. Germination of seeds buried 1 cm averaged 23 to 37% in the first spring after harvest, which was equivalent to 68 to 100% of seeds that had lost physical dormancy over autumn and winter. The percentage of seeds with enforced dormancy reflected the loss of physical dormancy during autumn and the loss of seeds to germination during spring and summer. Additional information on how autumn temperature and moisture conditions influence the pattern of dormancy decline could aid in explaining the variation in velvetleaf infestations over time.