Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

E. Charles Brummer


Establishment of alfalfa stands planted in the early spring requires rapid germination and vigorous seedling growth at cool temperatures. The extent of variation among ten alfalfa cultivars, 'Marathon' red clover, and 'Norcen' birdsfoot trefoil for germination time and radicle growth rate at 5, 10, and 15 C was evaluated, variation for germination time at 5 and 10 C among seven alfalfa cultivars was compared with variation among seed lots within these cultivars, and same of these cultivars were evaluated for field emergence. The initial radicle growth rate of cultivars increased with temperature, and the germination time of cultivars and of seed lots within cultivars decreased. When seed lots within cultivars were evaluated, differences among cultivars for germination time were observed only at 5 C. Both germination time and initial radicle growth were correlated with field emergence 8 d after planting at one of two locations tested. Laboratory selection for and against early germination and vigorous seedling growth was conducted. Populations were planted in the field at two locations in the early spring 1998 and evaluated for seedling emergence, seedling growth, and other agronomic traits. Two cycles of laboratory selection for early germination decreased germination time by 28.9%, with a mean realized heritability of 0.49 averaged over all populations. Response to selection was greatest in the first cycle, suggesting that further decreases in germination time may be limited. Two cycles of selection for high seedling vigor increased laboratory seedling height by 14.9%, with a mean realized heritability of 0.18. On average, seedling height in the field 27 d after planting increased by 20.7% after two cycles of selection for seedling vigor. Two cycles of laboratory selection for early germination increased seedling height 27 d after planting by 9.0%, but the response among cultivars was highly variable. Laboratory selection for seedling vigor under suboptimal temperatures is useful for improving seedling vigor of some alfalfa populations in the field under early spring conditions.



Digital Repository @ Iowa State University,

Copyright Owner

Kathy Lynn Esvelt Klos



Proquest ID


File Format


File Size

76 pages