Evaluation of Leaf iron efficiency in different combination of orange scions on Iron Chlorosis resistance rootstocks in a calcareous soil.

Iron deficiency that usually appears as chlorosis in young leaves, is considered to be one of the most important nutritional disorder in citrus trees, particulary in calcareous soils, that seriously reduces yield and fruits quality. This experiment was carried out at Jahrom agricultural research station during 2000-2004.The independent effects of rootstock, scion and different rootstock - scion combination of citrus varieties on iron absorption and iron chl!rosis paradox was investigated. The experiment was calTied out as split plot factorial in randomized complet block design. The experimental factors included macrophylla (Citrus macrophylla Wester), volkamer lemon (Citrus volkameriana), sour orange (citrus aurantium), sourlime (Citrus aurantifolia Swing) as rootstocks; Valencia orange, Washington novel orange, Jahrom local orange, red pulp orange ( Moro) as scions and sequestrene 138 Fe with three levels O(control), 5 and 10 gr per tree. The rootstocks were also separately studied. The macrophylla and sour orange rootstocks had the best positive and significant effects in increasing the scions leaf chlorophyll index at 1 % statistical level. Macrophylla also had the highest iron absorption. The interaction between rootstocks and sequestrene 138 Fe showed that the application of sequestrene 138 Fe levels on macrophylla rootstock did not have significant difference on leaf chlorophyll index at 1 % statistical level, therefore macrophylla had high potential in increasing scions leaf chlorophyll index without any use of sequestrene 138 Fe as fertilizer. Sour orange had low iron absorption than other rootstocks, but significantly increased scions leaf chlorophyll index. In contrast, Sourlime with high potential for iron absorption had little effect on scions leaf chlorophyll index. This not only clearly showed the effect of rootstock on scions leaf iron chlorosis paradox, but also indicated that the effectiveness of rootstocks in resisting iron chlorosis is related to mechanisms other than the extent of iron absorption by the roots. Macrophylla 'II significantly increased iron, zinc, manganese and copper absorption in comparision with other rootstocks at 1 % statistical level, moreover, it absorbed the highest rates of phosphorus and potassium and a favorable rate of nitrogen.Moreover among the rootstocks that used in this experiment the lowest amount of boron absorption belong to macrophylla and the highest amount to volkameriana rootstocks. This high useful potential of macrophylla put it in the group of effective rootstocks for Jahrom region. The results of experiment also demonstrated the sigI?ificant difference between graft varieties on resistance against iron chlorosis, i.e., the novel and local orange that are resistant to iron chlorosis had high chlorophyll index irrespective of the rootstock, varieties. In contrast, the scions like red pulp and Valencia orange had lower chlorophyll index and more affected by the rootstock varieties than others. For example the macrophylla rootstock increased the red pulp orange (Moro) leaf chlorophyll index about 18 percent. Based on the experimental results, macrophylla, sour orange and volkamer lemon rootstocks had the highest level of iron chlorosis resistance respectivelly, and trom the view of experimental scions, the highes level of chlorophyll content belong to Washington novel orange, Jahrom local orange and Valencia orange respectivelly. Keywords: Citrus, Iron deficiency, Iron chlorosis paradox, chlorophyll index, leaf growth, Rootstock, Scion, Chlorosis.