Author
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Ferwerda Licha, Margarita |
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Submitted to: Journal of Agriculture of the University of Puerto Rico
Publication Type: Research Notes Publication Acceptance Date: 2/4/2002 Publication Date: N/A Citation: N/A Interpretive Summary: Cephaleuros virescens Kunze is an alga that has been reported in the tropics in several plant hosts. It may cause significant economic damage in crops such as tea, rubber, and cacao, in the warmer, moist regions of the world. This research indicates that longan (Dimocarpus longan) is a new host in Puerto Rico for C. virescens. Although the incidence and severity appears to be small on current plantings this might become a serious problem as this crop becomes better known and its cultivation increases on the island. Identification of the pathogen was accomplished as well as its relevance in terms of the climate and growth conditions of the area. This will benefit and have a direct impact on commercial growers of this crop by allowing them to properly identify the problem at an early stage and to apply control methods if it becomes necessary. Technical Abstract: The longan (Dimocarpus longan Lour.; Sapindanaceae) is a tree cultivated in Southeast Asia. At present, USDA-ARS-TARS has established experimental plots of commercial clones of longan, one being at the University of Puerto Rico Experiment Station in the town of Adjuntas. The station is located in the central-mountain region, latitude 18 degrees 11' N and about 550 m in elevation and mean minimum and maximum temperatures of 14.8 degrees Centigrade, and 27.7 degrees Centigrade, respectively, with a mean annual rainfall of 1,767 mm. During a trip to this region in May 2001, leaves of longan trees grown intercropped with bananas were observed with algal leaf spots. Symptoms consisted of round, bright, orange colored tufts, slightly raised with a velvet-like appearance present on the upper leaf surface. The orange tuft is the thallus of the alga; the orange coloration being due to discoid-shaped chloroplasts that contain B-carotene. The symptoms were more prevalent on older leaves, in the lower foliage of the trees. By examination of structures under the microscope the thallus develops subcuticularly in the leaf, is erect and branches arise from it with apical cells that enlarge and produce terminal sporangia of about 31 x 23 micrometers. Sporangia were observed to produce biflagellate zoospores. Sexual reproduction occurs by formation of bottle-shaped gametangia in the thallus, which release biflagellate gametes in the presence of water. The dissemination of gametes is by wind and water. The causal organism was identified as the green alga Cephaleuros virescens Kunze of the family Trentepholiaceae and the division Clorophyta. This problem affects plants in tropical and subtropical regions of the world. This is the first report of C. virescens causing leaf spots of longan trees in Puerto Rico. |
