STUDIES ONCLASSIFICATION OF CITRUS ROOTSTOCKS ON THEBASIS OF THEIR DWARFING CHARACTERISTICS Effects of P, K and Ca deficiency on the root morphology and nutrient absorption of Poncirus trifoliata seedlings Effects of iron stress on growth, physiological character and iron distribution of the three citrus rootstocks PHYSIOLOGICAL AND BIOCHEMICAL STUDIES ON PRE-SELECTED INDICES FOR DWARFISM IN CITRUS ROOTSTOCKS