Depending on the plant being field tested, cross pollination is blocked by bagging the flowers, growing crops in cages that keep insects from carrying pollen out, removing the plants' reproductive structures, and isolating the plants from other crops.
(cages; keep; insects; from carrying pollen out) (the plant; being tested; field tested, cross pollination is blocked by bagging the flowers,) (insects; from carrying out; pollen) (cross pollination; is blocked; by bagging the flowers)
cages the plant insects cross pollination
keep being tested from carrying out is blocked
insects from carrying pollen out
field tested, cross pollination is blocked by bagging the flowers,
pollen
by bagging the flowers