TEAR-STAIN OF CITRUS FRUITS. 7 



In the fall of 1919 a more extensive test was conducted. Fifteen 

 lots of fruit were involved. Five of these lots were selected by the 

 writer, and the remaining ten lots were selected in various parts of 

 Florida by persons specially chosen for their competence to select 

 typical rust-mite injury and typical wither-tip tear-stain. Each 

 of these lots was sorted into several groups of one to four fruits 

 each according to the variety of fruit, the particular type of effect, 

 and the intensity of it. For a comparative study, cultures were 

 made from fruits in the same lot that were free from blemishes or 

 from unblemished areas on the russeted or tear-stained fruits. One 

 hundred bits of tissue, approximately 1 square millimeter in surface 

 area, were cultured from each test area of each fruit, using 10 Petri 

 dishes, each with 10 bits of tissue. The results when reduced to a 

 percentage basis, as in Table III, also represent the average numbers 

 of occurrence per fruit. Corn-meal agar was used as a culture 

 medium and the plates were held six days at room temperature. 

 Counts were made of the common saprophytic type of Cladosporium 

 as well as of Colletotrichum colonies. Bacteria and fungi other 

 than these were reckoned as miscellaneous. Two parallel series 

 were made, one for undisinfected tissue and one from similar areas 

 on the same fruits washed with a disinfectant. Bichlorid of mercury 

 solution (1 to 1,000) was used for 1 minute with subsequent rinsing 

 on all disinfected lots except K, L, and M; on these three lots undi- 

 luted fresh hydrogen peroxid was used without rinsing. Table III 

 gives the results, with fractions omitted for the higher percentages. 



Table III shows that Colletotrichum gloeosporioides is practically 

 universally distributed on citrus-fruit surfaces and that it escapes to 

 a considerable degree the surface disinfection process ordinarily prac- 

 ticed in culture work. It is present about equally on the average in 

 tear-stained and russeted areas. The amount varies in different lots 

 of fruits, but seems to be more abundant where the visible effects 

 are most pronounced. A saprophytic type of Cladosporium is isolated 

 with the same constancy as Colletotrichum gloeosporioides, but with 

 less frequency. These extensive culture tests show, therefore, that 

 it would be about as reasonable to ascribe the blemishes to one of 

 these organisms as to the other, if constancy of isolation from lesions 

 is to be the deciding consideration. However, neither fungus reaches 

 a frequency of occurrence high enough to justify holding it to be 

 the causative organism on this evidence alone. 



Certain fruits having the melanose type of tear-streak were 

 selected, and cultures were made from these in the manner already 

 described, comparative tests being made from unblemished areas, 

 from melanose tear-streak, and from diffused melanose areas; and 

 cultures from the surface blemish known as "shark skin" were also 

 made. The results are given in Table IV. 



