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Abstract
In-vitro Evaluation of Exotic Hevea Genotypes
for Resistance to Corynespora cassiicola
Hevea leaf fall disease caused by Corynespora
cassiicola (Berk & Curt) Wei, is one of the major disease constraints to
the production of natural rubber (Hevea brasiliensis) in South
Cameroon. Attempts to control this disease by traditionally recommended
practices such as artificial defoliation or aerial spray of fungicides have
not yielded satisfactory results in Cameroon. Production of disease resistant
planting material may provide a more efficient disease control strategy.
As part of a screening process of a large pool of Hevea genetic
resources for disease resistance, we evaluated in-vitro, 28 genotypes collected
from Ama onia. These genotypes were tested for resistance to two isolates
of C. cassiicola (NKO1 and NK02), obtained from different clones showing
different levels of susceptibility to the disease in the same field in South
Cameroon. The two isolates had similar growth characteristics on culture
media. However, isolate NKOI grew faster than NK02 on Potato Dextrose Agar
and was also more virulent on the test material. The two isolates may belong
to different races. To verify this, further characterisation of the isolates
is recommended. Significant differences were observed in the response of
the tested Hevea genotypes to each of the isolates. Genotypes AC/.S/12/22,
X0/07/48, and AC/BII9/22 had the highest resistance to both isolates. These
could constitute good source material in breeding for disease resistance.
Due to their high susceptibility to both isolates, genotypes AC/S/12/02,
MT/1/25, MT/C/04/22, MT/C104/27 and RO/C108/33 may have to be avoided in
any such breeding programme.

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