Genetic Variability of Sugarcane Clones as Affected by Major Endemic Diseases in Ferké, Northern Ivory Coast

Background: Sugarcane is a major commercial crop grown in tropical and subtropical areas of the
world, including West and Central Africa. Across this region, smut, leaf scald and pokkah boeng are
considered as endemic diseases, the first two being economically important.
Aims: The overall objective of study was to contribute to sugarcane yield improvement in Ivory Coast.
The specific objective was to evaluate the diversity of susceptible sugarcane genotypes mainly in first
ratoon crop to three major endemic diseases under natural infection, namely leaf scald, smut and
pokkah boeng.
Methodology: The study was carried out over 2 seasons (2016-18) as plant and first ratoon cane at
Ferké 1 experimental station under full covering sprinkler irrigation in northern Ivory Coast.
Treatments were composed of 863 sugarcane genotypes split into 39 families planted at single row
density. Planting was done per genotype in rows of 3 m long depending on families, without
replication and compared to the check variety SP70/1006. That check was replicated every five rows
to ease comparison with the clones. Phytosanitary observations regarding the three endemic
diseases made at the age of five months were subjected to a series of multivariate analyses.
Results: The study showed that most relevant diseases determining the diversity of susceptible
sugarcane genotypes were, in descending order, pokkah boeng, smut and leaf scald. Increase in
clone infestations on first ratoon cane compared with plant cane was observed regarding the three
endemic diseases but more importantly for smut by 51%. The dendrogram deduced from cluster
analysis showed that infected genotypes were split into six groups with same families belonging often
to different clusters so that no family investigated specifically susceptible or resistant to any disease
was determined. In other words, each family investigated was composed of disease-free as well as
susceptible genotypes in proportions varying from one family to another. Conclusions: All families investigated were relevant to maintain the diversity required for the
breeding process under way. Examples of recommended families were the following: disease-free
(F02, F03, F04, F05, F06); resistant (F01, F06, F07, F08, F09); moderately resistant (F10, F11, F12,
F13, F14). It came out from the study that most relevant diseases determining the diversity of
susceptible sugarcane genotypes were, in descending order, pokkah boeng, smut and leaf scald.
Increase in clone infestations on first ratoon cane compared with plant cane was observed regarding
the three endemic diseases but more importantly for smut by 51%. Each family investigated was
composed of disease-free as well as susceptible genotypes in a certain proportion which varied from
one family to another. Cluster 5 was the most prolific of infected genotypes with 286 clones (33%)
split into 36 families (92%) whereas clusters 2, 3 and 4 were the least prolific ones, with 42, 52 and 56
infected genotypes split into 14, 23 and 21 families, respectively. Clusters 1 and 2 were much more
associated with genotypes susceptible to smut and pokkah boeng but also with genotypes moderately
susceptible to pokkah boeng. Clusters 3 and 4 were associated with genotypes susceptible or highly
susceptible to leaf scald. In contrast, clusters 0, 5 and 6 were related to disease-free, resistant or moderately resistant genotypes and which crosses or families would, therefore, be recommended for
Ferké agro-ecology. Examples of such families were the following: disease-free (F02, F03, F04, F05,
F06); resistant (F01, F06, F07, F08, F09); moderately resistant (F10, F11, F12, F13, F14).