RHIZOPUS EOT OF STRAWBERRIES IN TRANSIT. 13 



and allowed to dry in the shade of the packing house or even in 

 the sun. 



SOURCES OF INFECTION BY RHIZOPUS NIGRICANS. 



INFECTION IN THE FIELD. 



Infection with Rhizopus apparently could occur either in the field 

 before picking or in the packing shed. Microscopic examination of 

 diseased fruits (13), as well as observations and inoculation experi- 

 ments in the laboratory, the field, and the packing house, indicates 

 that Ehizopus rarely, if ever, enters berries through the uninjured 

 epidermis. The proportion of injured or wounded berries in a field 

 usually is low. Some fruits, of course, are injured by insects or 

 birds, but rapidly growing strawberries have a strong power of 

 preventing infection by the quick covering of wounds with an im- 

 pervious protective layer. 



This was well illustrated in an inoculation experiment made in 

 the field on February 23, 1916. One hundred sound berries of 

 various ages from one to seven days before maturity were wounded 

 with a sterile needle while still on the vines. One hundred similar 

 berries were wounded in the same way, and a small quantity of 

 dirt from underneath the plants was forced into each wound. One 

 hundred wounded berries in another series were inoculated with 

 mycelium from a pure culture of Rhizopus. These berries were 

 picked when mature and their condition compared with that of 

 100 uninjured berries. No rot was apparent among the fruits 

 merely wounded. All but two of the berries into which dirt had 

 been introduced matured without showing any signs of infection; 

 a callus layer underneath the wound was evident in each case. 

 Two exceptions showed at the end of five days soft spots on one 

 side of the wounds. All of the berries inoculated with Rhizopus 

 mycelium developed into typical leaks in from two to four days, 

 most of them before the maturity of the berry. Leaky berries 

 are rarely, though occasionally, found in the field. 



Similar experiments were performed with ripe berries at the 

 time of picking and the berries shipped in iced containers to Wash- 

 ington. In this series some of the fruits were wounded also with 

 pine needles from the mulch. Records taken after shipment showed 

 the following percentages of fruit still sound: Unwounded, 72 per 

 cent; wounded with sterile needle, 61 per cent; wounded with pine 

 needles, 62 per cent ; dirt introduced into wounds, 42 per cent. Those 

 inoculated with Rhizopus mycelium had become a mass of rotten 

 berries before reaching destination. Wounding the fruit with pine 

 needles gave practically the same result as the use of a sterile needle. 

 The introduction of soil into the wounds apparently induced con- 



