- Genetic differences, extent of hybrid vigor, nature of gene
action, heritability estimates, and associations among characteristics,
and between progenies and their respective mid-parents were determined
for seed and plant characteristics in white clover (Trifolium
Ten seed and seedling vigor characteristics, including seed
weight, ATP content in seed, seed respiration, and seedling vigor
index were studied for a diallel cross consisting of 28 single crosses,
five test-crosses, four checks, and eight open-pollinated seed and
Twenty-three plant characteristics on stolon, petiole, leaf,
and forage were examined on the eight clones diallel cross, five test-crosses,
three checks, the eight parental clones of single crosses,
and six parent clones of the test-crosses. These 14 parent clones
for this study were assembled on the basis of diverse
morphology and origin.
Most seed and seedling vigor characteristics, except RQ
values, and most plant characteristics, except internode length,
LAR and diurnal ratio in SLW, expressed significant differences
among and within most groups of progenies and parental clones.
All seed and seedling vigor characteristics, except RQ
values, responded primarily to the nonadditive type of gene action.
This suggests that the plant breeder should design his breeding program
to develop varieties where hybrid vigor can be used to advantage.
Among the criteria used in this study to measure seed and
seedling vigor, ATP content per seed was closely associated with
seedling vigor index and with certain plant characteristics, including
forage yield per plant. The associations of seed weight with other
seed and seedling vigor characteristics were negative or poor.
Most plant characteristics showed apparent hybrid vigor when
progenies were compared with their respective mid-parents. With
few exceptions, most plant characteristics, stolon, petiole, leaf and
forage yield per plant, responded primarily to the nonadditive gene
system. This indicated that the plant breeder may use the hybrid
approach to white clover variety development. The exceptions were
leaf ratio and SLW which responded primarily to additive gene
action, and area and dry weight per leaf appeared to respond
equally to additive and nonadditive gene action. Genetic differences
were more readily identified for stolon number and length when
measurements were taken after 70 days of growth.
Yield components, such as number, length, and diameter of
stolon, petiole length, number of leaves per plant, and dry weight
per leaf were closely related to each other. The leaf components
of yield, dry weight per leaf and number of leaves per plant, had the
highest direct and indirect effects on forage yields per plant among
the yield components.
This study showed nonadditive gene action primarily responsible
for most seed and plant characteristics. Considering the ease of vegetative
propagation in this species along with the self-incompatibility,
mechanisms, it is suggested that parent geneotypes may be developed
by some recurrent selection procedure, then crossed on a two clone
synthetic basis to form experimental lines for testing purposes.