SEED GERMINATION

Seed Germination

Seed Germination

1. Introduction

Problem Statement

Three laboratory experiments were carried out to answer certain important questions related to the use of 'photo control' as a weed-control strategy. The first experiment documented that seeds of Rumex obtusifolius L. and Silene noctiflora L. germinated more slowly in total darkness than after a short exposure to light, whereas there were no significant differences for Cerastium fontanum Baumg. This suggests that seedling emergence in total darkness would not only result in fewer seedlings, but would also be slower; hence the crop might be given a competitive advantage. The second experiment demonstrated that germination of C. fontanum and S. noctiflora showed a linear response to the logarithm of photon fluence, with levels .1 mmol m-2 being stimulatory.

This suggests that a nearcomplete elimination of light during dark harrowing would give the best result. R. obtusifolius, however, had a sigmoid dose-response curve with a lower threshold for germination at 500 mmol m-2. Hence, this species had a clear threshold under which unnecessary germination was prevented. The third experiment tested for interaction between light and nitrate in their stimulatory effect on germination percentages. For Descurainia sophia (L.) Webb ex Prantl, R. obtusifolius and Thlaspi arvense L., but not for C. fontanum, such interactions were significant. This stresses the fact that light response will vary substantially depending on the seed's environment.

Relevance of testable Question

How dark it has to be during soil disturbance to attain maximum reduction in weed emergence, i.e. when should the work be done in relation to sunset, and can tractor headlights be used?

Literature Review

The emergence of weed seedlings can be reduced if soil-disturbing activities are conducted in darkness. In addition, it has been observed that seedling emergence in field experiments with dark harrowing can be delayed in the dark treatment (. Such a delay would enhance the effect of dark harrowing by reducing the weed biomass even further because the crop would be given a competitive advantage. Threshold values would also be useful when developing covered implements for use during the day. Light is one of the main cues initiating germination in weeds but its effect can interact with other factors in the seed's environment. Nitrate is one of the main agents that can weaken the dormancy level of a seed batch and stimulate germination. Here, three experiments are reported, each with three or four weed species. The first tested whether germination rate in darkness differed from that after short exposure to light. The second experiment aimed at establishing the minimum amount of light, i.e. photon fluence, needed to induce germination. The third experiment was designed to reveal any interaction between short-term light exposure and nitrate in their stimulatory effect on germination.

Experimental Design

Seeds of Descurainia sophia (L.) Webb ex Prantl, Silene noctiflora L. and Thlaspi arvense L. were collected in August 1994 and seeds of Rumex obtusifolius L. and Cerastium fontanum Baumg. In August 1995, in southern Sweden. Seeds were collected from natural populations on arable land or on waste ...