Germination ecology of heteromorphic seeds of bur clover (Medicago denticulata willd.)

Abstract

Bur clover (Medicago denticulata Willd.) is a winter annual weed commonly found in wheat fields of Punjab, India. We observed it produces heteromorphic seeds varying in seed coat colour -cream and brownish-black. The information on germination ecology of M. denticulata seeds varying in seed coat colour is lacking. So, the present study was undertaken under laboratory conditions to study the effect of seed coat colour on germination characteristics of M. denticulata seeds in relation to various environmental variables. Germination of both cream and brownish-black seeds was independent of light. Cream seeds germinated in the wide temperature range of 15/5 to 30/20°C; while, brownish-black seeds germinated in a narrow temperature range of 15/5 to 25/15°C. Cream seeds were able to withstand greater salinity stress as some seeds (10%) were able to germinate under NaCl concentration of 200 mM; whereas germination of brownish-black seeds was completely inhibited at 200 mM NaCl. The NaCl concentration required for 50% inhibition of maximum germination for cream and brownish-black seeds was 100 and 70.6 mM NaCl, respectively. The osmotic potential required for 50% inhibition of the maximum germination of cream and brownish-black seeds was -0.37 and -0.32 MPa, respectively. These results indicated a greater ability of cream seeds to tolerate either salinity or osmotic stress. Both seeds germinated under acidic and alkaline pH with >40% germination in pH range 3-10. The highest emergence of cream and brownish-black seeds was recorded when seeds placed on the soil surface.