An Economic Assessment of Banana Genetic Improvement and ...

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58 CHAPTER 5
Table 5.12 Results of hypothesis tests comparing distributions of
expected yield loss due to three constraints, by elevation, across use
groups, Uganda
Kolmogorov-Smirnov test (p-value)
Use group
Black Sigatoka Weevils Fusarium wilt
Cooking cultivars 0.000 0.000 0.764
Beer cultivars 0.000 0.931 0.000
Sweet cultivars 0.000 0.324 0.412
Multiuse cultivars 0.359 0.775 0.099
Roasting cultivars 0.049 0.010 0.928
do not confirm the same relationship for
Uganda, it should be borne in mind that the
number of farmers growing hybrids, and
thus the number of observations compared,
are few. A t-test comparing the expected
yield losses for endemic and hybrid bananas,
for the farmers in Tanzania who
grow both, indicates that they are on average
less susceptible at a 10 percent significance
level. These data, though sparse, provide
some evidence that farmers perceive
benefits from the introduction of hybrids in
Tanzania. The evidence is less clear in
Uganda, perhaps as a consequence of the
smaller volume of hybrids disseminated,
differences in disease pressures, and farmers’
knowledge of the diseases.
In Uganda, expected yield loss distributions
were compared for the three biotic
constraints of interest (black Sigatoka,
Fusarium wilt, and weevils) by elevation
across use types. The p-values of test results
comparing the distributions are shown in
Table 5.12. 4 Data support the hypothesis
that the underlying statistical distributions
of expected yield losses from black Sigatoka
differ by elevation for cooking, beer, sweet,
and roasting cultivars. The geographical
focus of the disease is the low-elevation
areas, with limited incidence in the highlands.
This pattern is less evident for Fusarium
wilt and weevils, with no statistically
significant differences being evident between
expected yield loss distributions for
most banana use groups. The importance of
altitude in the incidence and severity of biotic
pressures that farmers perceive supports
biophysical studies conducted previously
and the sample stratification scheme
(Gold, Kiggundu, and Abera 1998; Gold et
al. 2004), although the data indicate that
leaf spots and weevils are less important
considerably above 1,200 m.a.s.l., the dividing
line used in this study.