A comparative study of the free carbohydrates in healthy and Phytophthora cinnamomi-infected avocado root tips

Root tips of three root-rot tolerant avocado cultivars, Duke 7, G6 and Martin Grande, and a susceptible Edranol cultivar, were inoculated with Phytophthora cinnamomi zoospores. Percentages of sugars and starch present in healthy and infected root tips were determined. There were some differences among cultivars in percentages fructose, glucose and sucrose in control roots but no significant difference in percentage total sugars. Infected roots of Duke 7 contained a higher percentage sucrose and G6 a higher percentage fructose and both cultivars contained higher percentages glucose and total sugars than both Martin Grande and Edranol. Infected roots of Martin Grande had lower percentages of fructose, glucose and total sugars, and those of Edranol lower percentages of glucose, sucrose and total sugars than control roots. None of the cultivars showed a significant difference in percentage starch between infected and healthy root tips. This preliminary study shows that further studies are required to determine the role free carbohydrates play in resistance mechanisms.