Survival, germinability and fungal colonization of dimorphic achenes of the annual weedGalinsoga parvifloraburied in the soil

Abstract

Summary Galinsoga parviflora (Asteraceae) is a widespread annual weed that produces capitula containing both disc achenes with pappus and ray achenes without pappus. The latter are dispersed within a winged structure formed by capitulum bracts. We buried both achene types in an agricultural soil to be exhumed regularly to investigate whether they differed in survival, germinability and fungal colonization in the soil seedbank. Ray achenes remained viable longer than disc achenes, with different loss rates for the achene types. In both cases, loss rate was very high for the first 10 months, and then loss rates for the achene types tended to level off and even converge by the end of the observation period. The percentage of remaining viable disc achenes was always c. 10–15% lower than that of the ray achenes, except on the first and last sampling dates. Germination percentages for viable ray and disc achenes before burial and after exhumation were not statistically different during most of the observation period, except for that between 100 and 200 days of burial (mid‐autumn–winter). There, germination of disc achenes reached 26.4% after 126 days of burial, whereas germination of ray achenes was close to zero. In addition, after 779 days, the germinability of ray achenes was 21.3%, whereas it was 0% for disc achenes. Surface‐disinfected viable disc and ray achenes had low infection rates (0–15%) for both fungi and bacteria during the observation period. The fungal and bacterial infection peaks for both achene types were asynchronous. In general, the expected difference (lower infection rate for ray achenes) was not observed for fungal or bacterial infection.

Effect of burial on the germination of Opuntia tomentosa's (Cactaceae, Opuntioideae) seeds

“…In the soil, fluctuations in temperature and moisture, and the action of microorganisms, may affect the integrity of the hard seed covers, although few papers have adequately documented this fact (Baskin and Baskin, 2000). The effect of microorganisms on seed covers, which has implications for seed viability and germination, has been variously reported as deleterious (Kremer and Schulte, 1989;Greenfield, 2000), beneficial (Pfeiffer, 1934;Gogue and Emino, 1979;Morpeth and Hall, 2000), and harmless (Espinosa-García et al, 2003;Schafer and Kotanen, 2003).…”

Influence of achene heteromorphism on life-cycle traits in the annual weed gallant soldier (Galinsoga parviflora Cav.)

“…This strategy is deployed by plants germinating from peripheral achenes to increase the pool of peripheral achenes, which are much less involved in species reproduction. Espinosa-García et al (2003) found that in the soil seed bank the peripheral achenes of G. parviflora remained viable for a longer period of time and lost their viability slower than the central achenes. This seems to be an important feature of the peripheral achenes of G. parviflora, because these peripheral diaspores thus can create a longer-lived seed bank than the central achenes.…”

“…Peripheral achenes are without a pappus (or less frequently with an only vestigial one), and contain more protein and carbohydrates than central achenes. Central achenes have a pappus formed by a crown of scales (Espinosa-García et al, 2003;Rai and Tripathi, 1987). According to Rai and Tripathi (1987), peripheral achenes germinate faster and better than central ones.…”

Morphological variability and resource allocation in the annual teosinte (Zea mays ssp. mexicana (Schrader) Iltis) of the Toluca Valley, Mexico

“…(Venable et al 1987), Bidens odorata Cav., B. pilosa L. (Corkidi et al 1991;Pitty 1997) and Galinsoga parviflora Cav. (Espinosa-García et al 2003). It is usually an adaptation to varying germination conditions.…”