Colonizing ability in the Echinochloa crus-galli complex (barnyard grass). II. Seed biology

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Abstract
Comparisons of some seed parameters of two taxa of barnyard grass (Echinochloa crus-galli complex) were made in an effort to understand differences in habitat preference and colonizing ability. The taxa were E. crus-galli var. crus-galli, a cosmopolitan weed of wet, disturbed ground and E. crus-galli var. oryzicola, a crop mimic restricted to rice fields. In California, where all seed collections originated, the two taxa are ecologically differentiated within the rice-field ecosystem. Echinochloa crus-galli var. crus-galli is a weed of paddy banks and shallow water around the periphery of rice fields whereas E. crus-galli var. oryzicola is found primarily within permanently flooded rice fields. A survey of seed weight in 10 populations of each of the two taxa demonstrated that seeds of E. crus-galli var. oryzicola were on the average two to three times heavier than those of E. crus-galli var. crus-galli. Differences in weight were reflected in the buoyancy characteristics of fresh seeds of the two taxa. Approximately 50% of E. crus-galli var. crus-galli seeds remained afloat after 4–5 days in water whereas during the same period over 95% of the seeds of E. crus-galli var. oryzicola had sunk. Germination tests on 9- and 18-month-old seeds of 18 populations of E. crus-galli var. crus-galli and 11 populations of E. crus-galli var. oryzicola revealed significant differences between the taxa in the number of germinating seeds. The decay of dormancy in E. crus-galli var. oryzicola was more rapid than in E. crus-galli var. crus-galli following dry storage and burial in soil. The difference results in the greater germination synchrony of the crop mimic in comparison to the widespread weed. Emergence of seedlings from saturated and flooded soils was compared in the two taxa. In all treatments E. crus-galli var. oryzicola exhibited significantly greater levels of seedling emergence. The differences may explain changes in abundance of the two taxa in California rice fields, following the introduction of permanent flooding as a weed control practice, as well as their current microdistribution within the rice-field ecosystem.