26 BULLETIN 1474, U. S. DEPARTMENT OF AGRICULTURE 
On 18 hybrid forms, mentioned in Table 1, 636 inoculations gave 
90 per cent infection that averaged severe in degree. In general, the 
degree of infection was worse on the kumquat hybrids and on the 
f austrimedin than on any other. The 213 water blank checks failed 
to develop melanose. 
One hundred and ninety-two inoculations were made on leaves of 
six miscellaneous citrus forms — namely, the Nagami, Marumi, and 
Meiwa kumquats, the Corsican and Etrog citrons, and the calamon- 
din. The kumquats were found to be extremely susceptible, and the 
others were moderately so. The 78 water blank checks remained 
free of melanose. 
Three hundred and fifteen inoculations were made on the eight 
noncitrus rutaceous genera mentioned in Table 1. Of these, Toddalia 
lanceolata, Chalcas exotica, and Citropsis schweinfurthii failed to 
show signs of infection, and none of the remaining five gave indica- 
tion of being more susceptible than the orange. The 165 water 
blank checks failed to develop melanose. 
Leaves of the orange and the grapefruit are extremely susceptible 
when about one-fourth inch (6 millimeters) in width. As they ex- 
pand they become progressively resistant and acquire practical im- 
munity about the time they toughen, which usually takes place con- 
siderably before the leaf takes on a deep-green color. Ordinarily 
leaves are susceptible to infection for two weeks or less in periods 
of good growing weather, but for a considerably longer time if the 
weather is unf aA^orable to growth. Likewise the width of a leaf at a 
given age varies greatly, owing to conditions of weather and of tree 
vigor. Because of this variation the width of leaf does not indicate 
with definiteness the condition of susceptibility. 
INOCULATIONS ON FRUITS 
Table 4 gives the results of inoculations with spores of Phomopsis 
citri on the fruit of various citrus types. 
Table 4 shows that the orange is susceptible to infection until it 
reaches a diameter of approximately iy 2 inches (38 millimeters), and 
it also shows that the degree of infection is much more severe on 
small fruits than on larger ones. All commercial varieties tested 
were about equally susceptible. The water blank checks show that 
melanose did not develop on those fruits, indicating that moisture 
alone is not responsible for melanose lesions. 
The grapefruit is susceptible to infection from blossoming time 
until it reaches a diameter of approximately 2y 2 inches (63 milli- 
meters). As is the case with the orange, there is sufficient evidence 
to conclude that the grapefruit is very susceptible when very small 
and becomes progressively resistant with increasing size. Again all 
commercial varieties tested were about equally susceptible. Gen- 
eral observations and the results of spraying tests in commercial 
plantings confirm these findings. The checks on the young named 
varieties failed to develop melanose markings. 
The kumquat, lemon, lime, sour orange, bergamot orange, cala- 
mondin, citrangequat, faustrime, limequat, and tangor were all very 
susceptible to melanose infection, whereas melanose did not develop 
on the checks. 
