Application Of Biotecnology And Mutation Techniques For Anthracnose Resistance And Compactness In Dioscore Sp.

Argüello, JF, Orozco R, García J, Peraza, W.

Laboratorio de Cultivo de Tejidos

Escuela de Ciencias Agrarias

Universidad Nacional
Costa Rica-2003

Abstract
High quality yam corms (Dioscorea alata), clone 5969, were collected so they would germinate a greenhouse to obtain nodal segments that were tested in vitro. The medium for regeneration, was used Murashige and Skood medium,modified with Benzilaminopurine (BAP) and activated charcoal. LD-50 was determined to be between 10 and 20 Gy, and one hundred explants were irradiated with a dose of 15 Gy. These explants were multiplied up to M1V6. Then, three different acclimatization tests were carried out. Throughout these tests, attention was focused on survival, number of leaves, initial and final height. Meanwhile, leavesinfected with anthracnose (Colletotrichum gloesporioides) were collected. The fungus was isolated, and acervulum and mycelium were produced to obtain conidia. Later, single spore cultures underwent a molecular analysis. The acclimated and irradiated plants were inoculated with 0.5 million / milliliter of conidia with Colletotrichum gloesporioides. These plants were placed within a humidchamber for 48 hours while survival and the percentage of plants that were damaged were observed for two months.



1. INTRODUCTION
Yam (Dioscorea alata) and yampi (Dioscorea trifida) belong to Monocotiledonean class, order Lililaes, family Dioscoreaceae. This genus originated from South East Asian jungles, the forest area in Western Africa and the Amazon Bassin. Dioscoreas areclimbing plants having an underground stem, out of which grow aerial stems, roots and tubers that represent a rich source of carbohydrates [1].


Due to its high quality tuber, D. alata is the most important species and the one preferred by farmers from Pococí, Talamanca, and Siquirres, in the Province of Limón (Caribbean Coast of Costa Rica) [2].

Producing yam at a commercial levelis of great importance for the economy of developing countries in the tropical areas of Africa, Asia and the Caribbean [3]. Costa Rica reached 14 million kilograms of fresh yam tuber exports; they were mainly sent to Puerto Rico and The United States. This represented an FOB value of $ 8.890.225,5 [1] Our country has been the mayor yam supplier to the US market [3].


Yam has beenmainly used as food for human consumption because it is a good source of carbohydrates and medical compounds of the steroid type[12] . As food, we can find it as puree, or flakes [7]. As a medicine and pharmaceutical product, many wild species contain substances named sapogenins, that have the same chemical structure as corticosteroids (cortisone, sexual hormones, contraceptives) [4].The most problematic situation in yam culture is its reproduction. Being the fastest and most economical method of reproduction, cloning is the most widespread method. Cloning is carried out by sowing full tubers or crosswise cut tubers that sprout after a period of latency [4-5]..


Anthracnose, caused by Collectrotrichum gloesporiodes, is the most common disease. It producesblack or dark brown spots in a nerve sense on the plant sheath and foliage [6]. However, there are reports of fungi from the genus Cercospora and Gloesporium sp. that also damage the plant [4-7-8].


The inoculates comes from within the seed. Thus, a healthy seed, chemically treated, as well as resistant varieties must be used in order to get a more effective control [7].The use of an aerial support represents another obstacle for production since it makes it more expensive The absence of an aerial support may cause a 30% to 50% decrease in poductivity [7-9-10-11].

The use of in vitro culture, as a propagation technique has increased in the last years. This has brought forth positive effects to solve the problem of contaminated seed because it...