8 MISC. PUBLICATION 498, U. S. DEPT. OF AGRICULTURE 



States, the West Indies, and other citrus-growing regions of the world 

 (pis. 5, A, and 6, J.). Diplodia rot is occasionally found in California 

 lemons, as is also a less destructive rot caused by Phomopsis calif ornica 

 Fawc. However, both of these are so rare on California fruit as to be 

 of decidedly minor importance, both in the grove and on the market. 

 Typical stem-end rot, whether caused by Phomopsis or Diplodia, 

 is characterized by a softening of the rind and underlying pulp, which 

 begins almost invariably at the stem end (pi. 5, A), although it some- 

 times begins at injuries on the side ; at ordinary temperatures it may 

 extend an inch a day so that only 4 or 5 days are required to rot the 

 fruit completely. Neither form of the rot shows much discoloration 

 in the early stages. In late stages the affected rind turns tan color to 

 brown and sometimes even black. Both forms progress rapidly down 

 the spongy, circular axis, usually reaching the blossom end sooner by 

 this route than through the surface rind; they sometimes show a 

 marked development in the rind along the lines that mark the divisions 

 between the segments of the pulp. Affected fruits do not shrivel or 

 lose their shape unless subjected to pressure, and they ordinarily show 

 no fungus growth on the surface. The taste is flat and somewhat bitter, 

 and affected tissues have an unpleasant, rancid odor. Immature 

 citrus fruit is very resistant to stem-end rot, whereas dead-ripe fruit 

 is very susceptible. 



CAUSAL FACTORS I 



The two commoner stem-end rot fungi flourish and form spores in or 

 on dead citrus bark. Phomopsis usually develops most abundantly in 

 recently killed bark of very small twigs and fruit stems; Diplodia 

 occurs most frequently on larger twigs and limbs. During periods of 

 rainy weather the spore crops are produced and disseminated. The 

 first infection produced on the fruit involves some portion of the stem 

 button at some time during the growing season; soon after the fruit 

 is clipped from the tree there is active growth of the fungus from the 

 button into the rind and flesh. 



Phomopsis and diplodia rots may occur in the same lot of fruit, but 

 Phomopsis is more frequent in Florida fruit and Diplodia in fruit from 

 Puerto Rico and Cuba. During the cooler months in Florida when no 

 gassing is used, Phomopsis occurs more frequently than Diplodia. 

 In summer Diplodia predominates even on ungassed fruit. When both 

 rots occur, an important factor in determining which will predominate 

 is temperature; the optimum temperature for growth of Diplodia is 

 about 86° F. and for Phomopsis about 73°. 



Under certain conditions stem-end rot may attack fruits on the tree, 

 causing them to drop. Usually, however, it does not develop to a 

 serious extent in the grove but may become severe by the time the fruit 

 reaches the retailer or the consumer. It is impossible to distinguish and 

 cull out fruits that may later develop stem-end rot, since at ordinary 

 temperatures the crest of the rot. in fruit packed as being perfectly 

 sound, is not reached until 10 to 20 days after packing. 



CONTROL MEASURES 



Practical prevention of excessive loss from stem-end rot depends on 

 several factors. One of the most important of these is prompt market- 

 ing and consumption of the fruit with as continuous cooling to 50° 

 F. or slightly lower as may be practicable. Temperatures of 40° to 



