PRESIDENTIAL ADDRESS — SECTION C. 85 



vated, and has been reported as troublesome in the Rustenburg 

 District and in Swaziland. 



Bean Blight. Bacterium phaseoU Sm. (20). 



The bacterial blight of beans occurs quite commonly, and 

 judging by a sample of local seed which was infected to the 

 extent of 75 per cent., must at times be severe. Such seed 

 germinates fairly well, but the hypocotyls of the young plants 

 are attacked, and they soon succumb. It is probable that this 

 disease was introduced into South Africa with infected seed. 



Black Rot of Cruciferous Plants. Bacterium campcstre 

 (Pam.) Sm. (16). 



The black rot of cruciferous plants is another disease which 

 has evidently been introduced with contaminated seed ; it occurs 

 commonly throughout the country, and in some of the warmer 

 districts makes it impossible to grow cabbages during the summer. 

 The blackening of the veins of the leaves and the fibro-vascular 

 bundles of the stem are the characteristic symptoms. 



Potato Scab. Actinomyces chromogcnns Gasp. 



The well-known potato scab, causing corky patches and pits 

 on the surface of the potato tubers, is caused by the organism 

 described by Thaxter as Oospora scabies, but recently (35) shown 

 to be identical with Actinomyces c'hroinogenus Gasp. 



Black Leg or Soft Rot of Potatoes. Bacillus atrosepticus 



van Hall. 



Very little is as yet known of the distribution of the disease 

 known as black leg or stalk rot of potatoes, caused by Bacillus 

 atrosepticus van Hall. It occurs in Natal, but whether it can be 

 regarded as a serious trouble there, I have had no opportunity (if 

 judging. 



Bacterial Wilt of Potato and Tomato. Bacterium sola- 



naceanim Sm 



The bacterial wilt of potato, known locally as " vrot-pootje," 

 and the wilt of tomato, caused by the same organism, are very 

 common in Natal and in the Western Province of the Cape ; 

 Bocteriuni solanaceartim occasionally causes considerable loss 

 in the Transvaal, especially during wet seasons. On the Natal 

 coast it has been found causing a wilt of tobacco, but nothing 

 IS known of the occurrence of this parasite on other hosts in 

 this country. 



A nun^ber of other diseases of bacterial origin are known 

 to occur, but the identity of the causal organism has not been 

 established. These include the shot hole of apricots, crown 

 rot of lucerne, leaf spot diseases of cauliflower,^ pepper trees, 

 Johnson grass, and other plants. 



