Page 29 - FRUTAS DEL TRÓPICO

29
RepRoductive physiology of mango

Passioura, 1988). This backwards xylem flow towards root tips prevents upward xylem mo-
vement of shoot initiating hormones (cytokinins) that are synthesized in root tips (Davenport,

1990; Mok, 1994; Skene, 1975). Cytokinins instead accumulate in the tips of the roots. Active

water uptake by these roots when the first rains arrive move the accumulated cytokinins to

stem buds in the canopy, thus providing the stimulus to initiate an undesired flush of vegetative

growth in insufficiently mature stems when the first rains of the rainy season arrive (Oslund and

Davenport, 1987). In some areas, the first rains of the rainy season stimulate flowering in tho-

se stems that have reached sufficient time in rest due to lack of flushes during the dry season.

Drip irrigation provides a constant source of water to the canopy, but it has the same di-

sadvantage of watering only those roots that are located near emitters as does in-row furrow
irrigation. Experience has shown that if a grower needs to synchronize prune the orchard du-

ring the dry season and water availability becomes limited, then the post-prune flush will not

occur until arrival of the first rains (personal observations). If in-row furrow or drip irrigation

is available and a post-pruning flush occurs immediately after the prune, then a second flush

may occur upon arrival of the first rains, especially if leaf nitrogen levels are greater than 1.4%.

Microjet irrigation has the advantage of providing continuous water availability, but since water

is distributed in an area up to 6 meters in diameter to most of the roots, the entire root sys-
tem remains well hydrated throughout the dry period. This discourages the flush that normally

occurs after the first rain ending the dry season. Leaf nitrogen levels must be in the range speci-

fied above in order to discourage vegetative flushes that tend to occur during the rainy season,

especially if that period is between the synchronizing prune event and the nitrate spray dates.

Universidad Autónoma de Chiapas