Kiwifruit Nutrition diagnosis of nutritional disorders
The following section is devoted to a number of important leaf symptoms caused by factors other than mineral nutrition which have not been covered in detail elsewhere36.
20. Drought stress
Kiwifruit require a well distributed rainfall and high humidity36. A recent estimate of the amount of water transpired by mature kiwifruit vines suggests that between 50 and 100 litres of water is used per vine over a 24 hour period22.
Insufficient moisture, particularly during phases of rapid growth, results in wilting and the sudden appearance of light-brown patches of necrotic tissue on the leaves (Photos 20a, 20b and 20c). These patches may enlarge, eventually covering an extensive area of the leaf (Photo 20b). As the affected tissue dries, the margins of the leaf may roll up (Photos 20b and 20c).
An important point of difference from nutritional disorders such as chloride toxicity which produce similar symptoms, is that the necrotic patches on the leaves of plants affected by water stress often do not appear in symmetrical patterns (Photo 20c). Once the humidity increases again after rain, the damaged tissues readily become infected with a number of fungi including Alternaria alternata, Colletotrichum sp, Glomerella sp Phoma sp, and Phomopsis sp36. Severe drought stress can cause premature defoliation of the vine.
In late autumn, fruit may be stained by brown pigments washed out of damaged leaves.
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| 20a | 20b | 20c |
Bacterial leaf spot is caused by Pseudomonas viridflava, the bacterium which is also responsible for bacterial blossom rot. Symptoms of P. viridiflava infection appear on the leaves from late spring onwards causing dark angular spots surrounded by yellow halos (Photos 21a and 21b). As the season progresses, these spots may coalesce forming large irregular patches of necrotic tissue on the leaf (Photo 21c). In late autumn, fruit may be stained by brown pigments washed out of heavily infected leaves. Leaf spot is considered to have no discernible effect on the vigour of the vine55.
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| 21a | 21b | 21c |
Kiwifruit grown at a constant air temperature of 10 deg C have substantially reduced shoot growth29 and develop a general chlorosis of the leaves (Photo 22a). Such symptoms are often seen on vines shortly after bud break and could be mistaken for nitrogen or sulphur deficiency.
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| 22a | ||
