Factors Affecting the Seed Production of Teesdalia Nudicaulis: I. Germination Date

Abstract

This paper is part of an autecological study of the crucifer Teesdalia nudicaulis in the Breckland region of England. Teesdalia is a winter annual it normally germinates in Sept. or Oct. The mean seed production per plant in permanent field plots in 1958-60 was: 1958, 40.3; 1959, 3.6; 1960, 5.0. Certain developmental changes were noted in all years: (a) flowering was in two bursts; (b) the number of fruits formed per 100 flowers and the number of seeds per fruit declined as the flowering season proceeded. In 1959-60 and 1961-2 comparison was made between populations of different germination dates. Delaying germination from early to late Oct. caused a marked reduction in (a) the size of the plant at the end of winter and (b) the rate of flower production; it also caused a somewhat later start to flowering. Fruits per 100 flowers and seeds per fruit were not affected by germination date. It is concluded that a delay of germination of 3 weeks in mid-Sept. to mid-Oct. would in most years reduce seed production by the order of 40%. The results indicate the importance to the plant of the relatively short period in the autumn between the time when the soil becomes sufficiently moist to allow germination and the time when temperatures become so low that only very slow growth can occur.