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Accueil du site → Master → Afrique du Sud → < 1995 → Some ecophysiological aspects of cashew (Anacardium occidentale L) with emphasis on possible flower manipulation in Maputaland

University of KwaZulu-Natal (1994)

Some ecophysiological aspects of cashew (Anacardium occidentale L) with emphasis on possible flower manipulation in Maputaland

Roe, Denis John

Titre : Some ecophysiological aspects of cashew (Anacardium occidentale L) with emphasis on possible flower manipulation in Maputaland

Auteur : Roe, Denis John

Université de soutenance : University of KwaZulu-Natal

Grade : M.Sc.Agric. 1994

Résumé
There has been interest in developing a cashew industry in Maputaland, the far north-eastern corner of Natal/KwaZulu. Flowering and fruit development coincide with a rainy period, with accompanying serious flower diseases (Oidium anacardii and Colletotrichum gloeosporioides). Glasshouse studies were carried out at Pietermaritzburg, concurrently with field trials in Maputaland, in an attempt to manipulate flowering and growth of cashew trees. Two glasshouse trial were carried out. A factorial design with treatments 0, 3, 6 and 9 weeks of low temperatures (24°C day/9°C nights)(factor A) and 0, 3, 6 and 9 weeks of water deficit (Factor B) was used, with both factors in all combinations. During the second season the durations were increased to 0, 4, 8 and 12 weeks for both factors. No flowering occurred in this trial. Tree growth was not affected significantly by drought and/or cold duration. Temperature appeared to be the dominant factor at low temperatures, stomatal conductance and transpiration being suppressed by cold regardless of soil water potential. At more optimum temperatures for growth, stomatal conductance was dependent on soil water potential (r² = 0.756). Starch levels in the roots, dry matter production in the leaves, roots and stems, as well as leaf area were decreased significantly (P≤0.01) with increasing low temperature duration. Another glasshouse trial to test the effects of foliar urea at concentrations of 0, 1, 2, 4 and 8 g urea 100 l⁻¹, applied once, twice or thrice at fortnightly intervals was undertaken. The treatments were applied in late autumn/early winter of 1990 and 1991. Tree growth and flowering were monitored, and starch and leaf NH₃/NH₄⁺ analyses carried out. The highest urea concentration (8%) resulted in leaf scorch and abscission, extremely low stem diameter growth rates, and was too high for glasshouse trees. The starch contents of the 8% urea treatment were depleted significantly (P≤0.01) more than the other concentrations. The other urea treatments resulted in vigorous growth and high dry matter production. There were no significant effects of the number of sprays on cashew growth. Only seven trees flowered, and therefore no definite conclusions could be drawn regarding urea effects on flowering. Most hermaphrodite flowers (max. 76.8% hermaphrodite) opened soon after first anthesis of a panicle, and all terminal flowers of panicle branches were hermaphrodite. Flowers generally opened basipetally in a panicle, starting with hermaphrodite flowers and with progressively more male flowers. Urea sprays resulted in NH₃/NH₄⁺ build-up in the leaves, concentrations in flowering trees ranging from 100 to 700 μg g⁻¹ DM for approximately a month.

Mots clés : Cashew nut.— Horticultural science

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Page publiée le 29 décembre 2014, mise à jour le 31 mars 2020