- The effects of manganese nutrition on growth, mineral composition,
carbohydrate and nitrogen metabolism, IAA oxidase and phenols
of 'Northwest' strawberry plants are reported. Growth and mineral
composition response were investigated in sand culture and Hoagland's
solution 2 modified to contain 0.0, 0.5, 2.5, 12.5, 25.0, 62.5 and
125.0 ppm substrate manganese. The remaining aspects of the study
were conducted using the Hoaglands solution in a hydroponics system
with manganese levels of 0.0, 0.5, 2.5, 12.5 and 25.0 ppm in the
In sand culture, symptoms of manganese toxicity occurred first
in old leaves after three weeks of 125.0 ppm Mn treatment; after five
weeks at 62.5 ppm; and after 13 weeks at 25.0 ppm substrate Mn. Toxicity
symptoms appeared as necrotic spots along the margins of leaves;
these spots enlarged greatly within a few days and ultimately killed all
the leaves. All the plants treated with 62.5 and 125.0 ppm Mn died
within 7 and 11 weeks, respectively.
Young leaves of runners from the plants treated with 0.0 ppm Mn
developed interveinal chlorosis and cupping after 12 weeks. Later,
these leaves developed chlorotic spots which expanded to chlorotic
Plant weight and total leaf area of the plants harvested after 20
weeks was greatest with 2.5 ppm Mn treatment, and decreased both at
lower or higher substrate manganese. The most leaves and runners
were produced at 25.0 ppm treatment; whereas area per leaf was highest
at 0.5 ppm Mn.
Manganese present in tissue was directly correlated to substrate
manganese levels and was also related to the plant part. Accumulation
of manganese occurred in all tissues at high substrate Mn levels,
indicating that the tolerance of strawberry plants to high Mn is not
because of low uptake but due to their ability to endure large amounts
of accumulated Mn. In Mn deficient plants, the differences in the concentration
of Mn in the various tissues were small, suggesting the
possibility of redistribution of the element under conditions of deficiency.
Highest levels of tissue iron were found in 0.0 ppm Mn treatment
followed in order by 2.5, 0.5, 12.5 and 25.0 ppm substrate Mn.
A strong inverse relationship was noted between the tissue iron/
manganese ratio and the substrate Mn. The deficiency and excess of
Mn resulted in a decrease in the concentration of Mg and P in the
leaves. Highest levels of these elements were observed with 2.5 ppm
The most vigorous plants were produced at 2.5 ppm Mn treatment
when old and young leaves contained 955.7 and 617.4 ppm Mn,
respectively. Typical toxicity symptoms were shown by plants when
Mn in young leaves reached about 4,000 and in old leaves 9,000 ppm.
In the hydroponic system, manganese deficiency and toxicity
resulted in a decrease in sugar as well as starch content in the leaves,
except in old leaves at 25.0 ppm Mn treatment which contained the
highest levels of starch.
Total and insoluble N increased whereas nitrate N decreased with
the increase in substrate Mn. Lowest levels of soluble and soluble
reduced N were found at 2.5 and 0.5 ppm Mn treatment, respectively.
Both the excess and deficiency of Mn resulted in the accumulation of
amino acids. The highest concentrations of nitrate and lowest concentrations
of insoluble N observed in Mn deficient plants indicate that the
Mn is not involved in nitrate N absorption but may be concerned in
High IAA oxidase activity was found in enzyme extracts of young
and old leaves of deficient and toxic plants. Total and bound phenols,
in general, were directly related to substrate manganese. Low levels
of free phenols were found in conditions of excess and deficiency of Mn.
The increase in the level of IAA oxidase activity at high level of
tissue Mn was accompanied by simultaneous decrease in the concentration
of o-dihydroxyphenols. These results indicate the possible
involvement of phenols in the inhibition of IAA oxidase in the leaves of
strawberry plants and manganese seems to affect the levels of the