Diversity, distribution and effects on cassava cultivars of Cassava Brown Streak Viruses in Malawi

Cassava brown streak disease (CBSD) has emerged as a major threat to
cassava (
Manihot esculenta
) in eastern and southern Africa. CBSD was
first reported in Malawi in the 1950s, but little data on the distribution
and epidemiology of the disease are available. A diagnostic survey was
therefore conducted in Malawi to determine the distribution, incidence
and diversity of viruses causing the disease, and to characterize its effects
on local cassava cultivars. Diagnostic tests confirmed the presence of cas-
sava brown streak viruses (CBSVs) in 90% of leaf samples from symp-
tomatic plants. Average CBSD foliar severity was 2.5, although this
varied significantly between districts. Both
Cassava brown streak virus
(CBSV) and
Ugandan cassava brown streak virus
(UCBSV) (genus
Ipomovi-
rus
, family
Potyviridae
) were detected from sampled plants. UCBSV was
widespread, whereas CBSV was detected only in the two most northerly
districts. The average abundance of the whitefly vector (
Bemisia tabaci
)
was 0.4 per plant, a low value that was partly attributable to the fact that
the survey was conducted during the cool part of the year known to be
unfavourable for
B. tabaci
whiteflies. Spearman’s correlation analyses
showed a positive correlation between CBSD foliar incidence and CBSD
severity and between CBSD severity and CBSD stem incidence. Of the
31 cassava varieties encountered, 20
–
20 was most severely affected,
whilst
Mtutumusi
was completely unaffected. Although data from this
study do not indicate a significant CBSD deterioration in Malawi,
strengthened management efforts are required to reduce the current
impact of the disease.Cassava brown streak disease (CBSD) has emerged as a major threat to
cassava (
Manihot esculenta
) in eastern and southern Africa. CBSD was
first reported in Malawi in the 1950s, but little data on the distribution
and epidemiology of the disease are available. A diagnostic survey was
therefore conducted in Malawi to determine the distribution, incidence
and diversity of viruses causing the disease, and to characterize its effects
on local cassava cultivars. Diagnostic tests confirmed the presence of cas-
sava brown streak viruses (CBSVs) in 90% of leaf samples from symp-
tomatic plants. Average CBSD foliar severity was 2.5, although this
varied significantly between districts. Both
Cassava brown streak virus
(CBSV) and
Ugandan cassava brown streak virus
(UCBSV) (genus
Ipomovi-
rus
, family
Potyviridae
) were detected from sampled plants. UCBSV was
widespread, whereas CBSV was detected only in the two most northerly
districts. The average abundance of the whitefly vector (
Bemisia tabaci
)
was 0.4 per plant, a low value that was partly attributable to the fact that
the survey was conducted during the cool part of the year known to be
unfavourable for
B. tabaci
whiteflies. Spearman’s correlation analyses
showed a positive correlation between CBSD foliar incidence and CBSD
severity and between CBSD severity and CBSD stem incidence. Of the
31 cassava varieties encountered, 20
–
20 was most severely affected,
whilst
Mtutumusi
was completely unaffected. Although data from this
study do not indicate a significant CBSD deterioration in Malawi,
strengthened management efforts are required to reduce the current
impact of the disease.Cassava brown streak disease (CBSD) has emerged as a major threat to
cassava (
Manihot esculenta
) in eastern and southern Africa. CBSD was
first reported in Malawi in the 1950s, but little data on the distribution
and epidemiology of the disease are available. A diagnostic survey was
therefore conducted in Malawi to determine the distribution, incidence
and diversity of viruses causing the disease, and to characterize its effects
on local cassava cultivars. Diagnostic tests confirmed the presence of cas-
sava brown streak viruses (CBSVs) in 90% of leaf samples from symp-
tomatic plants. Average CBSD foliar severity was 2.5, although this
varied significantly between districts. Both
Cassava brown streak virus
(CBSV) and
Ugandan cassava brown streak virus
(UCBSV) (genus
Ipomovi-
rus
, family
Potyviridae
) were detected from sampled plants. UCBSV was
widespread, whereas CBSV was detected only in the two most northerly
districts. The average abundance of the whitefly vector (
Bemisia tabaci
)
was 0.4 per plant, a low value that was partly attributable to the fact that
the survey was conducted during the cool part of the year known to be
unfavourable for
B. tabaci
whiteflies. Spearman’s correlation analyses
showed a positive correlation between CBSD foliar incidence and CBSD
severity and between CBSD severity and CBSD stem incidence. Of the
31 cassava varieties encountered, 20
–
20 was most severely affected,
whilst
Mtutumusi
was completely unaffected. Although data from this
study do not indicate a significant CBSD deterioration in Malawi,
strengthened management efforts are required to reduce the current
impact of the disease.