Bananas (Musa spp. AAA group) are an important food and a source of in
come for farmers in tropical countries, Black sigatoka (Mycosphaerella
fijiensis Morelet), a fungal leaf spot disease, is the major producti
on constraint worldwide, The replacement of most of the susceptible ba
nana landraces requires the proper assessment of host plant response t
o black sigatoka and the determination of yield potential (per unit ar
ea and time) the new selections. Although optimum plot sizes have been
reported earlier for banana trials, the number of plants per plot was
determined primarily by using a subjective visual assessment, based o
n the point of maximum curvature. This paper presents an objective met
hod to determine optimum plot size using segmented models. Data on hos
t response to black sigatoka, and growth and yield characteristics rec
orded in the plant crop and first ratoon on competing plants of the wi
dely grown banana cv. Valery, provided the sample to illustrate the pr
oposed method, With few exceptions, feasible solutions were obtained a
fter <10 iterations, The approximate solutions suggested that nine to
33 plants per plot could be optimal for banana trials. The optimum num
ber of plants per plot depended on the characteristic of interest and
the production cycle, About 13 +/- 1 plants may suffice to assess the
host response to black sigatoka, whereas 16 +/- 3 plants per plot are
needed to evaluate growth characteristics and yield potential of culti
vars. The optimum number of plants needed to assess the performance of
genotypes had Lower coefficients of variation in the plant crop than
in the ratoon crop. Hence, the recommended optimum plot size consisted
, on average, of 13 +/- 3 plants per plot for the plant crop, and 15 /- 2 plants per plot for the ratoon crop, The suggested procedure to d
etermine optimum plot sizes may prove useful for other crops.