Screening for iron‐efficient species in the genusmalus

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Abstract
Solution, sand, and soil cultures were used to evaluate plant growth responses of four Malus species, screened from preliminary tests involving 40 species and ecotypes at varying iron (Fe) or bicarbonate (HCO3) concentrations in order to identify Fe‐efficient species. Sand and solution cultures were used for examining a range of added Fe concentrations and soil cultures were used to examine the effect of added HCO3 levels on Fe‐chlorosis development. Results indicated that in solution and sand culture, symptoms of Fe deficiency for Malus xiaojinensis (Cheng et Jiang) were observed only at 0 μM Fe concentration, for M. micromalus (Makino) at 10 μM Fe, and for M. transitoria (Batal.) and M. baccata (L.) at 20 μM Fe. Results from soil culture indicated that only M. baccata exhibited Fe‐deficiency symptoms at 1,000 μg HCO3. The highest rate of photosynthesis was observed in M. xiaojinensis regardless of Fe or HCO3 concentration or culture medium. As Fe decreased or HCO3 increased in the media, the photosynthesis rate of M. baccata and M. transitoria decreased significantly. Transpiration rate of the four species tested showed the same trend as their photosynthesis rates at different Fe or HCO3 concentrations. The results indicate that of the four species investigated, only M. xiaojinensis appears to be Fe‐efficient. Additionally, during the course of these studies it was observed that M. xiaojinensis was resistant to mildew [(Podosphaera leucotricha) (EU. et Everk.) Salm.].