Effect of irrigation water bicarbonate on leaf chlorosis, photosynthetic pigments and iron uptake of kiwifruit seedlings.

In kiwifruiy vineyards, the high concentration of bicarbonate ions in irrigation water or soil is one of the main limiting factors on growth and production. The high levels of bicarbonate in irrigation water caused soil alkalinity and reduced the root accessibility to nutrients such as irons. Iron deficiency in kiwifruit vineyards caused leaves chlorosis and therafter, fruits. Fruits with iron deficiency have an unacceptable taste and low shelf life. Iron deficiency is usually more severe in June and July with increasing irrigation frequency. Growing suitable rootstocks that have a high tolerance to soil alkalinity is a good strategy to overcome this problem. Therefore, in this study, the response of seedlings in different populations of kiwifruit from three different species to irrigation water bicarbonate was investigated.

In this study, the effect of different concentrations of bicarbonate ions in irrigation water (0, 170, 350, and 550 mg L-1) on leaf chlorosis and iron uptake of seedlings of six kiwifruit seed populations (Green 11, Bruno, Red 2, Red 6, Red 22 and Baby kiwi) from three different species (Actinidia deliciosa, A. chinensis and A. arguta) was investigated as a factorial experiment in a completely randomized design with three replications in research greenhouse of faculty of agricultural sciences, University of guilan. Each replication was one potted seedling. The plants were irrigated with different bicarbonate level for 6 weeks with three days intaervals. Traits such as leaf fall percentage, stem diameter, chlorosis percentage, necrosis percentage, chlorophyll a, b, total chlorophyll, carotenoids and iron content of leaves were measured.

The results showed that increasing bicarbonate concentration in irrigation water caused leaf abscission. The highest leaf abscission percentage was observed in Baby kiwi from A. arguta with 16.6% and the lowest one in Bruno (1.19%) from A. deliciosa species as compared to their control, when exposed to high bicarbonate stress. Genotype type, different levels of bicarbonate and their interaction did not show a significant effect on the percentage of stem diameter changes. The Red2 from A. chinensis species seedlings showed the highest leaf chlorosis (38.46%) and the lowest leaf chlorosis was found in Green 11 seedlings from A. deliciosa with 6.95%. With increasing the amount of bicarbonate in irrigation water, the percentage of leaf necrosis also increased. Total leaf chlorophyll and carotenoid content significantly declined in all genotypes with increasing bicarbonate ion content in irrigation water. With increasing bicarbonate ion concentration in irrigation water, leaf iron content significantly decreased. The lowest iron declining percentage compared to the control when seedlings exposed to 170, 350, and 550 (mg L-1) of bicarbonate of irrigation water was found in Bruno from A. deliciosa species with 3.28, 4.29, and 4.72%, respectively. Moreover, the results showed that there is a significant correlation between leaf iron content and chlorophylls content, chlorosis percentage and necrosis percentage.

Overall, because of low leaf abscission and higher iron absorption in Bruno seedlings when exposed to high bicarbonate concentration in irrigation water or soil cab be recommend as a souperior rootstock.