Comparison of some physiological and biochemical characteristics between iron-efficient and iron-inefficient species in the genus Malus

During the past 10 years, our laboratory has collected more than 40 species and ecotypes of the genus Malus, our aim being to find some iron-efficient genotypes. The results have shown that M. xiaojinensis Cheng et Jiang is iron-efficient while M. baccata (L.) Borkh. iron-inefficient. The results presented in this paper is a follow-up of experiments using solution culture to compare some physiological and biochemical characteristics between these two species, showing their different response to iron deficiency. It was found that under adequate iron supply, no significant difference was apparent between the two species in the content of total iron, acid extract iron, and ferrous-iron in the leaves at the upper part of the seedlings. Under conditions of iron stress, however, the content of total iron in the upper leaves of M. baccata significantly decreased, whereas that of M. xiaojinensis significantly increased. In both cases, the content of acid-extract iron in the upper leaves significantly decreased, 49.1% in M. xiaojinensis and 79.5% in M. baccata. Ferrous-iron also decreased significantly in M. xiaojinensis but only slightly in M. baccata. Low iron resulted in a significant decrease of the potassium/calcium ratio in the leaves of both species, but the decrease was less for M. xiaojinensis than M. baccata. Analysis of peroxidase in the upper leaves and ATP content in the roots indicated that under iron stress, peroxidase activity in both species decreased, ATP content in the root of M. xiaojinensis markedly increased, but that in the roots of M. baccata markedly decreased. In light of these results, it is proposed that in solution culture, the content of acid-extract iron in the leaves of the upper part of the seedling and the ATP content of the roots may be used as a reliable criteria in the screening for iron-efficient genotypes in the genus Malus.