Disorders producing symptoms mainly on the older leaves

Deficiencies

One of the most extraordinary features of the nutrition of kiwifruit is their high requirement for chlorine (chlorine is always present in plant tissues as the chloride ion). A deficiency of chlorine severely reduces the growth of kiwifruit (Photo 6a). Furthermore, solution culture studies at Ruakura have shown that kiwifruit will not respond to potassium in the absence of chlorine.

Symptoms of chlorine deficiency develop first on the oldest leaves. Discrete patches of pale green chlorotic tissue appear between the main veins near the tip of the leaf (Photo 6b). The chlorosis usually develops at the leaf margin and spreads between the veins towards the midrib. In some cases the chlorotic patches at the margin of the leaf coalesce to form a continuous bond of chlorotic tissue. There may also be a downward cupping of the older leaves. As the deficiency becomes more pronounced the young leaves remain pale green with a noticeable reduction in leaf area (Photo 6c). At no stage does the affected leaf tissue become necrotic (Photos 6b and 6c).

Chlorine deficiency also results in a marked reduction in root growth as well as the development of abnormal swellings of the tissue 2-3 cm from the root apex (Photo 6d). Such swellings could be mistaken for nematode cysts.

Chloride concentrations in leaves from healthy kiwifruit vines sampled in the field at midseason usually range from 0.8 to 2.0 per cent dry matter. Results from solution culture experiments indicate that the requirements for chlorine depend in part upon the potassium status of the plant. Thus, where potassium was not limiting growth, the critical concentration of chloride in the youngest fully expanded leaves was 0.2 per cent dry matter. However, for moderately potassium deficient plants with potassium concentrations in their leaves of less than 1.0 per cent dry matter, a higher concentration of chloride (0.6 per cent dry matter) was required in the leaf for growth. For many sensitive plants such as avocado, citrus, and most stonefruit, concentrations of chloride as high as those required in the leaves for healthy growth of kiwifruit would be sufficient to seriously reduce their growth³⁵.

Chlorine deficiency is not expected to be a problem where potassium chloride is used regularly or in coastal orchards where large quantities of chloride are deposited in seaspray (Table 8). However, this disorder is more likely to be a problem in vines grown inland on light sandy soils in high rainfall areas since chloride is very readily leached out of soils²³. Chloride deficiency in kiwifruit can be corrected by applying potassium chloride (50 per cent w/w C1). Sodium chloride (common salt) should not be used as a source of chloride as kiwifruit are very sensitive to excess sodium (see section on salinity for the effects of excess sodium and chloride on kiwifruit).

Table 8: Quantities of sodium chloride in airborne sea spray deposited on parts of New Zealand by rain and wind.

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6a	6b	6c	6d