xui. A, 5 Reinking: Philippine Economic-Plant Diseases 



221 



definite spots, usually somewhat elongated, from 5 millimeters 

 to 2.5 centimeters in length (Plate XI, fig. 2). Spots may have 

 a grayish center surrounded by a black ring, or they may be 

 entirely blackened with a darker border. In the center of the 

 grayish portion are minute black specks, the perithecia. Spots 

 may coalesce and, if the leaf be badly infected, a general brown- 

 ing may occur. 



Causal organism. — The .perithecia are produced under the 

 epidermis, are brown with definite wall markings, and have 

 ostiola. Within are produced the asci, containing typically 

 eight, hyaline, two-celled spores similar to those produced by 

 Mycosphaerella on papaya. 



Control. — All fallen leaves should be collected and burned. 



MUSA TEXTILIS NEE. ABACA 



BACTERIAL HEART ROT 



Symptoms. — The disease is characterized by the rotting of 

 the central group of rolled young leaves. Rot starts usually 

 at the tip and advances downward until the entire young central 

 portion of the plant is attacked. The diseased portion is at 

 first yellowed, then turns black, and rots. A slight odor may 

 accompany the rot. Frequently the central group of diseased 

 leaves near the tip is pushed upward in a folded mass. In early 

 stages the disease is confined to the young central heart and 

 does not penetrate into the surrounding older sheaths. In 

 advanced stages the entire central portion becomes diseased and 

 the plant dies (Plate XI, fig. 

 7). The disease is most severe 

 in thick plantings where there 

 is a high humidity and a lack of 

 aeration. It may also be severe 

 in excessively damp locations. 

 From these seats of infection 

 the disease may spread to sur- 

 rounding plants. A large 

 amount of destruction is done in 

 infected areas. 



Causal organism. — M i c r o- 

 scopic examination shows only 

 the presence of bacteria. They 

 advance through the plant tissue 



by mass action (fig. 22). Isolations from diseased stems have 

 produced pure cultures of bacteria. The bacteria, when inocu- 

 lated into healthy plants, produce the typical disease. The study 



Fio. 22. Section through diseased abaca 

 leaf, in heart of plant, showing 

 mass of bacteria in tissue ( X 

 330). 



