market diseases of fruits and vegetables 11 



nia lemons, particularly on those that have been in storage for some 

 time before shipping or that are held for several weeks at the receiv- 

 ing point before being put on the retail market. Fruits that are 

 overripe or have been weakened by orchard freezing, drought, or 

 internal decline are very susceptible. Under present conditions alter- 

 naria rot is second in impurtance only to the rots caused by blue and 

 green molds. 



The decay begins almost invariably at the stem end. the fungus 

 gaining entrance through the button (pi. 8. A). For the most part, 

 it affects the central core and the stem end, but it may also occur 

 purely as a stem-end rot with no faster development in the core than 

 elsewhere. In the commoner type of decay the button first browns, 

 and then a slowly developing discoloration proceeds along the central 

 axis (pi. 8. B and C) and to some extent in the inner tissues of the 

 rind, without at first visibly affecting the exterior. Once established 

 in the fruit the fungus develops rapidly, breaking down the rag until 

 this becomes a slimy leaden-brown mass, and then continues to grow 

 outward through the rind. When it reaches the surface, dark-colored 

 diseased areas one-eighth to one-fourth inch or more in diameter be- 

 come apparent. These increase rapidly in size and become a deeper 

 leaden brown as they enlarge, until the entire rind is broken down 

 into a slimy, dull-brown mass similar to the decayed rag. 



Weak fruit shows a greater susceptibility to alternaria rot than 

 fruit that is physiologically strong. A good indication of the latter 

 condition is the fresh green appearance of the buttons. Prolonged 

 exposure to high temperatures used for ethylene treatment or curing 

 favors the development of the disease. At a temperature of 55° F. 

 or lower the progress of the causal organism is slow. Fruit that is 

 left on the trees until it has full lemon color is more susceptible than 

 that which is picked in the green or "silver" stage. 



(See 12, 14,42, 43, 49.) 



ANTHRACNOSE 



(See Grapefruit, Anthracnose. p. 3. and pi. 1, A.) 



BLACK pit 



(Phytomona* sijringae (Van Hall) Bergey et al.) 



Black pit of lemons is caused by the bacterium Phytomonas 

 syiingae. It occasionally occurs on oranges as well as on lemons and 

 is found in most of the citrus-growing regions of the world, yet it is 

 of relatively minor importance in the United States. It is seen only 

 rarely on the market. 



On lemons black pit produces sunken spots or pits that usually 

 range from one-fourth to one-half inch in diameter (pi. 8, E). The 

 collapsed area is first light brown, then dark brown, and finally black. 

 Under California conditions the disease is most likely to be trouble- 

 some after heavy winter winds with rain. No special control meas- 

 ures have been developed. 



(See !&, ±3, 45, 106.) 



blue mold and green mold rots 



(See Oranges. Blue Mold and Green Mold Rots, p. 19. and pi. 

 6, B and C.) 



