Abstract
Ratoon sugarcane plantlets in southern China have suffered a serious chlorosis problem in recent years. To reveal the causes of chlorosis, plant nutrition in chlorotic sugarcane plantlets and the role of manganese (Mn) in this condition were investigated. The study results showed that the pH of soils growing chlorotic plantlets ranged from 3.74 to 4.84. The symptoms of chlorosis were similar to those of iron (Fe) deficiency while the chlorotic and non-chlorotic plantlets contained similar amount of Fe. Chlorotic plantlets had 6.4-times more Mn in their leaf tissues compared to the control plants. There was a significantly positive correlation between Mn concentration in the leaves and the exchangeable Mn concentration in the soils. Moreover, leaf Mn concentration was related to both seasonal changes in leaf chlorophyll concentration and to the occurrence of chlorosis. Basal stalks of mature sugarcanes contained up to 564.36 mg·kg-1 DW Mn. Excess Mn in the parent stalks resulted in a depress of chlorophyll concentration in the leaves of sugarcanes as indicated by lower chlorophyll concentration in the leaves of plantlets emerged from basal stalks. Ratoon sugarcane plantlets were susceptible to chlorosis due to high Mn accumulation in their leaves (456.90–1626.95 mg·kg-1 DW), while in planted canes chlorosis did not occur because of low Mn accumulation (94.64–313.41mg·kg-1 DW). On the other hand, active Fe content in chlorotic plantlets (3.39 mg kg-1 FW) was only equivalent to 28.2% of the concentration found in the control. These results indicate that chlorosis in ratoon sugarcane plantlets results from excessive Mn accumulated in parent stalks of planted cane sugarcanes grown on excessive Mn acidic soils, while active Fe deficiency in plantlets may play a secondary role in the chlorosis.
Highlights
Manganese (Mn) is an essential element for plant growth but in excess, especially in acidic soils, it can become phytotoxic
Chlorosis of ratoon sugarcane plantlets grown in acidic soils was resulted from excessive Mn
We demonstrated that the chlorosis of sugarcane plantlets grown on acidic soils in southern China was caused by excessive Mn accumulation in the plants
Summary
Manganese (Mn) is an essential element for plant growth but in excess, especially in acidic soils, it can become phytotoxic. The bioavailability of Mn increases as soil pH decreases below 5.5 [1, 2]. The symptoms of Mn toxicity vary widely among plant species; necrotic brown spotting on leaves, petioles and stem is a common symptom [9,10,11]. Another common symptom, ‘crinkle-leaf’, which occurs in the youngest leaf, stem and petiole tissues, is associated with chlorosis and browning of these tissues [10, 12]
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