Phytophthora Rot of Tomato 303 



tions, it seemed likely that the bulk of the infection took place wlien the 

 fruits were green. 



On the eggplant, the fungus produces a dark-brown spot on the 

 fruit with a conspicuous light-colored border. (Fig. 2, A). When the 

 fruit is cut open, the fungus is found to extend well into the flesh as 

 evidenced by the dark-brown discoloration of the tissues. (Fig. 2, B). 

 The fungus appears to advance most rapidly in the vascular bundles 

 since these show as dark strands running out from the badly discolored 

 area. (Fig. 2, B). Aifected fruits drop from the stem prematurely 

 and in no case was a fruit observed to remain on the stem after more 

 than one-half the fi'uit had become involved. This premature dropping 

 of the fruit from the stems is attributed to the invasion of the fibro- 

 vascular tissues at the stem-end and a stimulation of the abscission 

 process. 



The symptoms on pepper are not as pronounced as on either tomato 

 or eggplant. The first symptom is a small dark-green water-soaked 

 spot. The lesion enlarges rapidly and before the rot involves one-half 

 of the fruit, it drops from the plant. The somewhat wilted pedicels 

 remain attached to the fruits and when cut longitudinally, show dis- 

 colored vascular bundles. When these pedicels were incubated in a damp 

 chamber, a fungus similar to the one isolated from the fruits grew out 

 of them. The fungus penetrates the pedicels of the pepper fruits but 

 apparently not the branches of the plant. In the eggplant, the fungus 

 apparently does not invade the pedicel at all. In the case of peppers 

 only the green fruits are susceptible. 



The Fungus. — The fungus was readily isolated from infected tomato, 

 eggplant and pepper fruits by planting small blocks of infected tissue, 

 cut out aseptically, in poured plates of potato agar. In practically 

 every case, a white, rather dense, spreading and somewhat tufted fungus 

 developed from the tissue plantings. The organism grows well on 

 potato agar, which has been used almost entirely in the laboratory cul- 

 tural work. 



The mycelium is at first continuous, but later becomes sparingly 

 septate and branched. Peculiar distortions or tuberous outgrowths are 

 very common on the mycelium in old cultures. Conidia are produced in 

 cultures on potato agar in four to six days, but not abundantly. In 

 Petri dish cultures on sterilized sugar beet and radish leaves in water, 

 an abundance of conidia are produced in three days. Conidia are usually 

 borne terminally, but often are intercalary, and are oval to oblong and 

 papillate at the apex. The great majority of the conidia are uniformly 

 oval in shape, especially in liquid cultures. The measurements of the 

 conidia from the liquid cultures were 47.6x54.9 (45.9-50x53.2-55.8) jx, 

 while from agar cultures they were 31x41 (29.5-33.5x33-92.5) (x. The 

 conidia germinate either by swarm-spores or by one to three or more 

 germ tubes. 



Chlamydospores were produced rather abundantly, especially in 

 old cultures. They were globose and measured 24.7 (27.5-27.9)^. Oos- 

 pores were found in old cultures. These were thick-walled and globose 

 and measured 21 (17.5-26)(j,. 



