DISEASES OF VARIOUS CROPS 1547 



Idaho Rural Infected with blackrot . . 



Pearl do 



Netted Gem Infected with jelly-end rot 



Idaho Rural Disease free, disinfected . 



Pearl do 



Netted Gem do 



enormous proportions ; in fact anything up to 80 per cent of the tubers may 

 be attacked. On the other hand, in a fertile and well irrigated soil, previ- 

 ously planted with grain or leguminous crops, the conditions are unfavoura- 

 ble to the forms of rot mentioned above, and the percentage of infected tu- 

 bers is always very low. 



Control of blackrot : i) precede potatoes by a crop of lucerne or of 

 other plants which can improve the soil ; 2) maintain the lowest possible 

 temperature in all storage places. 



11^1 ~ Phytophthora sp., as the Cause of Black Thread Disease of Hevea bra- 



Si/tens/s in Burma. — Dastur,I. F., in Deparhmnt of A iriculturc, Burma, Bulletin 14, 

 pp. 1-4, I plate, Rangoon, 1916. 



In Hevea brasiliensis black vertical grooves appear on those parts of the 

 trunk that have been laid bare by tapping ; these sink into the wood through 

 the cam.bium. The infected parts crack and the latex oozes out and some 

 times accumulates between the wood and the new cortical tissue that is being 

 formed. The latter withers and comes off leaving a deep wound or canker 

 in the uncovered woody tissue. 



In this way the cambium can be absolutely destroyed. The destruction 

 and alterations in the cambium put a stop to the ordinary renewal of the 

 cortex, bitt there is an abundant proliferation of callous tissue, and the sur- 

 face of the trunk which has become gnarled and irregular is not suitable 

 for new incisions. In sections of the diseased tissue the cells are swollen 

 without protoplasmic contenc, and filled with a yellow-brown gummy 

 substance. 



The constant presence of intercellular, non septate hj^phae at once sug- 

 gests the existence of a species of Phytophlhora, especially, when in addition 

 to the disease of the trunk, a characteristic alteration is observed in the 

 fritits, accompanied by an exudation of latex undoubtedly caused by a 

 Phytophthora. ^ 



Cultures obtained from diseased fruits and inoculated into the stems 

 of Hevea give rise to pathological symptoms identical with those described. 



Drought and light are important factors in checking the develop- 

 ment of the fungus, which requires moisture. The disease appears soon 



