Flooding, soil temperature, iron nutrition, physiology, and growth of Annona species

A study was conducted to evaluate the effects of soil temperature, flooding, and Fe-deficiency on physiology and growth of two Annona species with potential as flood-tolerant rootstocks, pond apple ( Annona glabra L.) and soursop (A. muricata L.) in comparison with commercially grown 'Gefner' atemoya ( A. squamosa L. x A. cherimola Mill) on sugar apple (A. squamosa L.) rootstock. Plants were exposed to soil temperatures of 5, 10, 20, 25 or 35°C in a glasshouse. Soil temperatures at 5 and 10°C decreased net CO2 assimilation (A) and growth of all species. The highest A, leaf chlorophyll index, and growth occurred at 20--25°C for pond apple, and 25--35°C for soursop and 'Gefner' atemoya on sugar apple rootstock. The effect of floodwater temperatures on physiology and growth of pond apple and soursop was also studied using above soil temperatures. Both species developed hypertrophied stem lenticels and adventitious roots when flooded at 20, 25, and 35°C. Plants died at 5 and 10°C. Flooding increased root electrolyte leakage and reduced leaf chlorophyll index, A, and growth of soursop. Pond apple was more flood-tolerant than soursop showing the highest growth at 20--25°C soil temperatures.; Pond apple plants grown in calcareous soil were fertilized with 5 different rates of chelated or non-chelated Fe, under flooded or non-flooded conditions. Flooding decreased leaf concentrations of N, P, K, Ca, Mg, Zn, and Cu, and increased Fe and Mn. Plants in chelated-nonflooded treatments had the highest leaf chlorophyll index and growth at 2.5--5 g Fe/plant. In general flooded plants in chelated or nonchelated treatments had similar leaf chlorophyll index and growth.; In two different experiments pond apple and soursop were screened for Fe deficiency tolerance in hydroponic solution containing 0 or 90 muM Fe, or 2, 22.5 or 45 muM Fe. Root ferric chelate reductase (FCR) activity was not induced by either the 0 or 2 muM Fe concentration in both species. Soursop exhibited higher leaf FCR activity than pond apple. Leaf chlorophyll index and growth were severely reduced in pond apple at 2 muM Fe.; The results indicated that pond apple is more flood-tolerant but less tolerant to Fe-deficiency than soursop. Soursop may be a good flood-tolerant rootstock only for areas subjected to short-term flooding. Soursop and sugar apple require higher soil temperatures (25--35°C) than pond apple (20--25°C) for optimum growth.