evaluation of dieback and early yellowing of sycamore trees (platanus sp.) in mashhad by using gge biplot analysis

dieback of trees is a serious problem in many different regions of the world and city authorities are concern about conserving and maintaining the green spaces in the big cites. this study was conducted to evaluate the early dieback and yellowing of sycamore trees (platanus sp.) by using a completely randomized block design (split split plot) in 15 replications (sites) in 2009. the main plot was plant sampling times (spring, summer and autumn), sub plot was the plant condition (green and yellow) and sub-sub plot was the place of sampling on the tree (down, middle and upper). after sampling, preparation and chemical analysis, total nitrogen, phosphorus, potassium, iron, manganese, zinc and sodium were measured by standard methods and the data was interpreted by using site regression model (gge biplot analysis). the results showed that nitrogen deficiency was occurred with more intensity in the down layer in summer time compare to the spring time. the results also showed that iron deficiency occurred in the yellow tree groups and zinc deficiency also occurred simultaneously. however zinc deficiency was not proven in the spring time but it occurred in summer time. iron deficiency was started in the spring time and then more deficiency observed in summer time. with regarding to the obtained results it dose not seem that nutritional deficiency is the main reason of dieback of sycamore trees in mashhad. these symptoms also might be caused by drought stress and water deficiency, low temperature in winter or early spring. fungi attack and other diseases can cause similar symptoms.