Germination capacity of Japanese knotweed (Reynoutria japonica Houtt.)

Ar present weed infestation of some localities of the Czech Republic by the species of the genus Reynoutria became a great problem. Generally it came down that both the knotweed species (Japanese knotweed, Sakhalin knotweed, R. x bohemica) are propagated vegetatively by rhizomes, eventually by stem cuts. Generative propagation of this species is considered as irrelevant. O ur study has been concentrated on the study of the possibilities of ripenin g and germination of seeds of Japanese knotweed (Reynoutria japonica Houtt. ). Seed samples for the study of germination of Japanese knotweed were take n from six sites in the districts Bmo-City, Brno-Country, Blansko and Znojm o. Temperature and precipitation conditions in different sites are presente d in Tab. I. Soil conditions at the site of seed collection were in all loc alities characterized by weighed samples with share of earth, clay, gravel and sand. All seed sampling localities were situated on sunny sites. In tot al nine seed samples were taken in five dares, in the period from 12 Septem ber 1997 to 26 October 1997 (Tab. I). Germination capacity was studied in t wo periods (in November 1997 and February 1998). In the date of finishing o f autumn test within nine studied samples the germination capacity ranged f rom 0 to 45%. Seeds taken in the second decade of September have not been y et sufficiently developed, or were dormant and showed a zero or very low ge rmination capacity. Samples taken in the first and third decades of October had also a relatively low germination capacity (4.75 and 6.75%). A conside rable percentage of Japanese knotweed seeds was characterized in autumn tes t in different samples as not germinating seeds (55.0 to 94.5%). It was typ ical for all non-germinating seeds that in the time of test finishing that they seemed to be healthy and vigorous. It could be supposed that these see ds are in the stage of dormancy which should be followed by the phase of ge rmination. In replication of the germination capacity test in February 1998 higher values of germination capacity have already been found in greater p art of seed samples after six days than in autumn period. This tendency con tinued also after further days of germination. Germination was similar, lik e in autumn evaluation, finished after 20 days from the beginning of the te st (Tab. IV). In the sample which did not germinate in autumn period at all , 10.75% germination capacity was found in February date. In samples 6, 8 a nd 9 the differences between November and February germination capacity amo unted to 28.75, 45.25, and 50.25%. These values show that in the time of au tumn test the seeds of Japanese knotweed were in dormancy and only after it s finishing intensive germination was found in February. Germination capaci ty of numerous samples (above all in February 1998) was so high that seeds were able to provide generative propagation of Japanese knotweed. With resp ect to very low average monthly temperature differences among different sit es the effect of temperature in the time of flowering and seed ripening is not considered as the basic one. The confirmed possibility of seed propagat ion should explain the occurrence of Japanese knotweed also in the regions without water flows, in higher altitudes and in the sites where vegetative propagation could not take place by the action of a man.