NEUTRAL SUGARS IN SHOT-HOLE BORER (XYLEBORUS FORNICATUS) INFESTATION OF TEA (CAMELLIA SINENSIS)
NK BANDARANAYAKE, T BOMBUWELA, S KARUNARATNE, NS KUMAR and KMS WIMALSIRI
Department of Chemistry, University of Peradeniya, Peradeniya, Sri Lanka
Background and objectives
Camellia sinensis var. assamica (tea) is attacked by adult female shot-hole borer (SHB) beetles (Xyleborus fornicatus) which bore galleries in stems and have a symbiotic relationship with the Ambrosia fungus (Monacrosporium ambrosium) . SHB beetles cause extensive damage in the mid-country tea plantations of Sri Lanka. We have been studying the biochemical relationship between the beetle, the symbiotic fungus and the tea bush in an effort to develop a method to control the shot-hole borer beetle. Tea clone TRI 2023 is known to be the least susceptible and clone ml 2025 the most susceptible to SHB attack. In this paper we report the neutral sugar composition of stems from two clones and the effect, in vitro, of some of these sugars on the growth and development of the Ambrosia fungus and the SHB beetle grown in laboratory culture media.
Results and conclusions
Glucose was the major monosaccharide found in tea stems with substantial amounts of mannose and inositol. The glucose:inositol ratio was observed to be 5:1 in clone TRI 2023 and was 3:1 in clone TRI 2025. Sporulation in liquid media and spore germination of the Ambrosia fungus on glass surface was reduced when the carbon source, glucose, was replaced with mixtures of glucose and inositol in the ratios 5:1 and 3:1, the effect being greatest when the ratio was 5:1. The effect of these sugars on the growth and development of the beetle was studied by making observations on the number of days taken for the boring of galleries, appearance of fungus, laying of eggs, hatching of larvae and emergence of adult females from laboratory culture media. It was found that decreasing the proportion of inositol in the culture medium slowed down the appearance of the different developmental stages and significantly reduced the total number of emerging females. Tea plants produce nutrients required by the beetle and its symbiotic fungus. Our results suggest that the relative proportions of glucose and inositol found in the susceptible clone TRI 2025 are more favourable to the development of both the fungus and the beetle. It is possible that sugars found in tea stems play a significant role in determining host plant selection and host plant suitability, and may account for the greater susceptibility of clone TRI 2025 to attack by the shot-hole borer.
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