Portal de Periódicos da CAPES

Helminthosporium Spot of Citronella and Lemon Grass in Guatemala

1942; Missouri Botanical Garden; Volume: 29; Issue: 2 Linguagem: Inglês

10.2307/2394334

2162-4372

Carroll W. Dodge,

Botany, Ecology, and Taxonomy Studies

During August, 1941, a severe epiphytotic developed on citronella (Cymbopogon Nardus (L.) Rendle subspec. genuinus) and lemon grass (Cymbopogon citratus (DC.) Stapf) at Los Cerritos, a very large plantation near the upper edge of the coastal plain below Escuintla in Guatemala. The weather had beensomewhat abnormal, with earlier light rains and higher humidities at the end of the preceding dry season, although the rainfall for the whole subsequent rainy season was not conspicuously high. Owing to the increased demand for essential oils, the plantation had been irrigated throughout the dry season instead of cutting off the water for the last two or three months as in previous years. This kept the trash and marcescent leaves at the bases of the plants moist for the production of a larger number of spores while the higher humidities probably aided in securing more abundant germination and infection. By the end of August all but the very young leaves had died back about half their length, and the distilling plant was closed for about six weeks for the first time since the plantation came into production about ten years before. An examination of a large number of plants showed that the principal damage resulted from a leaf spot, although an occasional plant of citronella showed a rot associated with Fusarium sp. at the bases of the stems a short distance above the soil. The leaf spot begins as a small yellowish area between the veins. It develops more rapidly between the veins than across the smaller ones, resulting in an elliptic to nearly linear area of necrosis with a reddish margin, quite similar in appearance to the Helminthosporium leaf spot of sugar cane. The central portion soon becomes brown and dry, but does not drop out. As the spots increase in number, evidently the water supply is reduced and the distal portion of the leaf slowly