Date of Award

1-1-2001

Thesis Type

Masters

Document Type

Thesis

Divisions

Faculty of Science

Department

Institute of Biological Sciences

Institution

Universiti Malaya

Abstract

Field evaluation of banana plants for disease tolerance in soil infested with Fusarium oxysporum f. sp. cubense is commonly used. The process is slow as disease expression usually takes 4-5 months, while inoculum concentration, edaphic conditions, temperature and other variables that may affect disease expression are difficult to control. An alternative method of screening plantlets at the nursery stage was developed. The technique consisted of a double tray set up; a perforated inner tray containing sterilized river sand or a sand-clay mixture (4 sand : I clay) on which hardened tissue-cultured plantlets were grown, and a larger outer containment tray for collecting surplus Hoagland nutrient solution and pathogen wash-out. The inner tray lits snugly into the outer tray, which is deeper and larger. The method was tested using plantlets of various sizes derived from meristem culture against a range of pathogen inoculum concentrations of F. oxysporum f. sp. cubense race 4 under different time duration. Banana clones tested include 'lntan' (Pisang Berangan, AAA), 'Gold Finger' (AAAB}, 'Novaria' (Cavendish, AAA) and 'Mutiara' (an improved Pisang Rastali, AAB). Two-months old plantlets (10-15 cm height) were found to be capable of showing wilting and rhizome discoloration similar to those of older banana plants inoculated in the field (hot spot) in small experimental trays. Plantlets with heights of less than 10-cm did not produce consistent symptoms. Plantlets with vigorous root systems were gently removed from the growth tray and their root immersed in microconidial of 10², 10⁴, and 10⁶ spores/ml of the pathogen for a period of 2 hrs, 2½ hrs, 3 hrs, and 3½ hrs. Root immersion of 2-hr duration in the pathogen suspension was found to be effective. All susceptible plants produced foliage and rhizome symptoms at inoculum concentrations higher than 10⁴ spores/ml. Both 'Gold Finger' and "Mutiara' showed high tolerance to F: oxysporum f. sp. cubense while 'Intan' and 'Novaria' were susceptible. All susceptible plants (i.e. 'Intan' and 'Novaria') showed both foliage and rhizome symptoms within a period of 10-28 days. More than 94% of tolerant plants as well as all the uninoculated control plants did not show any symptoms. The Double Tray Technique, besides being a rapid method for early screening against Fusarium wilt tolerance in banana at the nursery stage, affords effective containment. By eliminating cross contamination, this technique allows potential investigations on concurrent virulence testing of multiple F. oxysporum f. sp. cubense isolates against a range of test cultivars. It is easily adapted for growth-chamber studies on the effects of various environmental factors and treatments on disease expression. The technique was also applied on mass screening of somaclonal variants of 'lntan' and 'Novaria' as well as the Cavendish cultivar of GCTCV-215, which was reported to be tolerant to the Taiwanese race 4 of F. oxysporum f. sp. cubense (Hwang, 1991). Few plantlets of 'Novaria' and 'lntan' showed tolerance in double tray while the GCTCV-215 became susceptible to the Malaysian race 4 of F. oxysporum f. sp. cubense.

Initial

snms

Additional Information

Dissertation (M.A) -- Faculty of Science, Universiti Malaya, 2001.

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