750 



SCIENCE 



[N. S. Vol. XXXI. No. 802 



The Central American Banana Blight: Dr. E. E. 

 B. MclvENNEY, Department of Agriculture 

 (Laboratory of Plant Pathology). 

 In 1904 the writer made a trip through a num- 

 ber of farms in Costa Rica and in the Province 

 of Bocas del Toro, Panama, for the purpose of 

 investigating a serious banana disease reported 

 by the planters during the two previous years. 

 Since that time the disease has been more or less 

 continuously studied by him. 



"The disease" or "the blight," as it is com- 

 monly called by the planters, spreads rapidly. 

 While in 1904 whole valley districts were free 

 from the disease, there is now scarcely a single 

 farm in the regions above mentioned that is not 

 suffering from its ravages. The blight occurs in 

 the Panama Canal Zone; also, by report, on the 

 Atlantic side of Nicaragua, Honduras and Guate- 

 mala. 



The disease has been known for many years, 

 but only within the last decade has it alarmed 

 the planters. As early as 1890 a few isolated 

 spots were known to be affected, and from these 

 the spread of the disease can be traced. 



In Panama at least 15,000 to 20,000 acres of 

 banana plantations have been abandoned and 

 many thousand more -are seriously affected, while 

 in Costa Rica the damage has been even greater, 

 so that it is safe to estimate at least $2,000,000 

 capital loss in these two regions in the last five 

 years. 



Young and old plantations are attacked with 

 equal intensity. Plants are also attacked on 

 various soils— sand, clay, etc. The disease seldom 

 becomes evident until the shoots have reached a 

 height of four to six feet at the collar (point 

 where the leaves diverge). Commonly the first 

 external sign is a rapid yellowing and subsequent 

 browning and wilting of one or more leaves. 

 Sometimes there is a striking curvature and yel- 

 lowing of the terminal part of the leaf-blade 

 while the remainder is still green. Eventually 

 all the leaves die and fall back against the trunk, 

 leaving a crop of suckers which in turn are killed 

 and give place to still weaker shoots. The fruit 

 of diseased shoots rarely matures and even when 

 mature is worthless with blotched, somewhat 

 shriveled surface and dry, pithy interior. Shoots 

 which develop after one or two suckers have died 

 rarely reach the flowering stage. When they do, 

 however, weak, distorted, worthless bunches are 

 produced. 



On cutting the pseudo-stem across and longi- 



tudinally many of the bundles are found to be of 

 of a yellow, reddish or reddish-purple color, the 

 color deepening toward the rootstock. In the last 

 stages the color of the bundles may be almost 

 black. While in recently affected plants the ves- 

 sels of the upper part of the stalk and the leaves 

 may be normal, those of the rootstock are always 

 colored. In most cases the thin partitions sepa- 

 rating the air chambers are wrinkled and col- 

 lapsed. The juice of diseased plants contains 

 much less tannin than that of normal plants. A 

 nauseating odor is often given off when leaf-stalks 

 which have been diseased for some time are cut 

 open, though there may be no sign of rotting in 

 the trunk. 



It has been proved that the disease is not due 

 to local conditions such as too wet or too dry 

 soil, etc., yet some of these conditions may predis- 

 pose the plants to the disease. 



There is a seasonal periodicity in the activity 

 of the blight corresponding to the periodicity of 

 gro^vth in the banana plants. It is during the 

 stage of most rapid growth that the plants most 

 easily succumb, particularly from April to July. 

 In periods of less active growth many plants seem 

 to recover, but only to die during the next season 

 of rapid growth. 



Neither drainage nor improved methods of cul- 

 tivation and pruning have cheeked the disease. 

 Indeed, increased fertilization seems to make it 

 more virulent. There is no evidence that insects 

 are in any way responsible for the trouble. 



Microscopic examination of the stained vas- 

 cular bundles above mentioned shows that the 

 coloring is due to a rather insoluble gummy sub- 

 stance (not a true gum) that more or less com- 

 pletely plugs the vessels and cells of the xylem. 

 In this bacteria and, in some cases, fungus hyphse, 

 were found imbedded. 



Bacterial organisms isolated in Central America 

 from diseased material have been cultivated by 

 the writer and inoculated into healthy plants on 

 the plantations and in greenhouses of the Depart- 

 ment of Agriculture in Washington. The results 

 of this phase of the investigation will be given 

 later. It may be stated, however, that the blight 

 is in all probability a vegetable parasite which 

 makes its entrance into the plant through the 

 rhizome or roots. 



No good method of control of the disease has 

 yet been found. The progress of the disease in its 

 early stages may be delayed by digging out and 

 burning diseased plants, replacing them with 

 healthy suckers. 



