|Castle, William - UNIV OF FL, IFAS, CREC|
Submitted to: Fruits
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 10, 1998
Publication Date: N/A
Interpretive Summary: Iron is an essential nutrient needed for proper plant growth and in human nutrition. In many soil types, iron is unavailable in high enough concentrations to support proper plant growth. In such soils, plants have inadequate levels of iron, and thus suffer from iron-deficiency. Iron- deficiency is a common problem in many of the agricultural areas worldwide, and is especially common in citrus cultivation. The only known effective way to overcome iron-deficiency in citrus cultivation is to select varieties that appear to be more efficient in obtaining sufficient levels of iron from these soils. These varieties are known to be more tolerant to iron-deficiency stress. In this report, a large number of citrus varieties are screened for their tolerances to iron- deficiency stress. These findings allow us to rank these varieties as highly tolerant, moderately tolerant, poorly tolerant, and non-tolerant. It was discovered that many of the highly tolerant varieties are related to lemons and citrons. This finding will greatly facilitate future breeding programs designed towards producing new, highly tolerant citrus varieties, which in turn, will greatly increase citrus cultivation efficiency and fruit quality. This will also decrease the levels of the applications of metal ion nutrients, and thus contribute to better sustained agricultural practices.
Technical Abstract: Plants of 26 Citrus and closely related genotypes were assayed for their ability to reduce Fe(III) as a measure of their tolerance to Fe- deficiency stress. Three-month-old seedlings were grown for 2 to 3 months in nutrient solution without Fe. White root tips were periodically harvested and tested for their Fe reduction capacity. Genotypes with the largest Fe reduction responses were Volkamer lemon (Citrus volkameriana Ten. & Pasq.), `Eureka' lemon [C. limon (L.) Burm. f.], `Etrog' citron (C. medica L.), sour orange (C. aurantium L.), and Rangpur lime (C. limonia Osbeck). Seedlings of five mandarins showed low [Nasnaran (C. amblycarpa (Hassak.) Ochse); Changsha (C. reticulata)] to intermediate [Cleopatra (C. reticulata); Shekwasha (C. depressa Hayata); Sun Chu Sha (C. reticulata)] Fe reduction responses. Low to intermediate responses were also obtained from seedlings of Morton and C-35 citranges [C. sinensis (L.) Osb. x Poncirus trifoliata (L.) Raf.], Gou Tou (putative hybrid), Smooth flat seville (putative hybrid), and Kinkoji (C. obovoidea Hort ex Tak.). The poorest responses were from Swingle citrumelo (C. paradisi Macf. x P. trifoliata), and a number of papeda selections. These results complement previous rankings of low-Fe stress tolerance, and suggest that the high tolerance among certain Citrus genotypes may originate with C. medica.