Reduced Translocation of Carbon and Nitrogen from Leaves with Symptoms of Pear Curl1

With normal pear leaves, soluble carbohydrates (sorbitol, sucrose, glucose, fructose) and starch were higher in green than in abscising, yellow senescent ones. Considerable accumulation of these components occurred in curl leaves which were about to abscise. Greatly reduced transport of photosynthetically fixed 14 C from the leaves occurred in curl-affected trees. Normal leaves photosynthesized and exported C even when abscission was imminent as long as chlorophyll was present. Curl-affected leaves abscised earlier while considerable photosynthetic potential remained. As normal leaves approached senescence their N content decreased dramatically. Curl-affected leaves abscised when N levels were still high. Curl deprives the tree of potentially utilizable carbohydrate and N resources through inhibition of translocation and premature abscission. These effects of curl may explain reduced vigor and productivity as well as difficulties in establishing young trees. It is postulated that curl and decline are not solely graft union problems.