Vol. 71 No: 1

Title:
Control of Bud Morphogenesis in Mango (Mangifera Indica L.) by Girdling, Defoliation and Temperature Modification

Authors:
R. NUNEZ-ELISEA, T.L. DAVENPORT and M.L. CALDEIRA

pp: 25-40

Abstract:
Dormant buds of mango are nondifferentiated, consisting of an arrested apical meristem and a set of preformed nodes. Cool temperatures around 15°C promote inflorescence (panicle) morphogenesis. Inflorescence differentiation involves a putative floral stimulus generated in mature leaves and translocated in the phloem. In field-grown ‘Keitt’ and ‘Tommy Atkins’ mango trees, branches bearing flowering shoots were girdled and defoliated (or defoliated and then girdled) using different lag periods to disrupt transport of the floral stimulus and prevent its production. The shoots were deblossomed on day 0 to activate growth and differentiation of axillary buds. Only vegetative shoots were produced when branches were girdled and defoliated at the same time. With the maximum lag period of 15 d, about 90% of deblossomed shoots produced axillary inflorescences. Girdled branches that were not defoliated produced inflorescences only. Thus, inflorescence morphogenesis required the presence of leaves during active bud growth. Increasing the lag period between defoliation and girdling also increased the production of inflorescences in relation to vegetative shoots. Defoliated branches that were not girdled often produced a unique type of vegetative-to-floral (V-F) transition shoot consisting of a leafy basal portion converting to distal inflorescence morphology. It is possible that such transitional buds initially produced leaves instead of inflorescence primordia because of the absence of nearby leaves to supply the floral stimulus during early bud differentiation, and that differentiation was completed in the presence of floral stimulus that arrived later from distant leaves. In separate experiments, container-grown ‘Tommy Atkins’ mango trees with apical buds in three differentiation stages (0 =nondifferentiated; 1 = early differentiation of leaf or inflorescence primordia; 2 = advanced differentiation of leaf or inflorescence primordia) were transferred from warm (30°C day/25°C night) to cool (18°C day/10°C night) temperature regimes (or the reverse sequence) to examine bud morphogenic responses. About 50% of stage 1 vegetative buds of trees transferred from warm to cool temperatures produced V-F transition growth. Nearly all stage 1 inflorescence buds of trees transferred from cool to warm temperatures produced a flush of vegetative growth instead of an inflorescence, while nearly 10% of buds produced a flush of floral-to-vegetative (F-V) transition growth in which the proximal portion contained axillary floral clusters typical of a purely generative inflorescence, and the distal portion contained only leaves. Of the stage 2 inflorescence buds transferred from cool to warm conditions, 73% produced inflorescences and about 10% produced a F-V transition. This result suggests that incipient inflorescence primordia that were initiated in cool temperatures (stage 1 inflorescence buds) ceased differentiation upon transfer to warm temperatures near 30°C, with bud differentiation progressing vegetatively. In comparison, the more differentiated inflorescence primordia of stage 2 inflorescence buds were not affected by the shift from cool to warm temperature regime. The occurrence of unique transitional phenotypes in mango indicates that the developmental fate of the preformed basal nodes is determined separately from that of the apical meristem. Activity of the floral stimulus appears to be promoted by cool temperatures, and inhibited by warm ones. Activation of either or both bud regions in warm temperatures near 30°C promoted leaf initiation, whereas activation of either or both regions in cool temperatures about 15°C promoted inflorescence morphogenesis.

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