PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Non-living agents (contd)
GENETIC ABNORMALITIES.
A mutation is an abrupt appearance of a new characteristic as the result of an accidental change in a
gene or chromosome. Some mutations may be beneficial, eg Washington Leng navel oranges which
have no seed originated from such a mutation.
Fig. 240. A chimera is a tissue segment with a different , genetic , makeup from adjacent , cells. In Greek mythology
species or varieties commonly produce chimeras. Left: Normal yellow tulip on left, one with a 50% red chimera on
right. Right: An apple showing a mutant section of more deeply colored skin. PhotoCIT, Canberra (P.W.Unger).
Fig. 241. Linear fasciation in a rose cane.
clusters of leaves at the end of the fasciated area.
Fasciation is common in many plants, eg daphne,
euonymus, cucumber. PhotoCIT, Canberra (P.W.Unger).
Fig. 242. A variegated lemon leaf
(genetic makeup).
Fig. 243. ‘Burr knots’ on Prunus spp. are tissue
which can produce adventitious shoots if necessary, eg
if the top of the tree was lopped off. They have a similar
function to the lignotubers of eucalypts. PhotoCIT, Canberra
(P.W.Unger).
Fig. 244. Mutant orange with a
very thick rind. Rind thickness can
also vary with the variety, eg the rind
of Meyer lemons is much thinner
than that of Eureka or Lisbon. Photo
NSW Dept. of Industry and Investment.
Non-parasitic pests and diseases 397