Effects of morphactin and paclobutrazol flowering treatments on shoot and root phenology in mango cv. Kensington Pride

Mango cv. Kensington Pride, is the major horticultural tree crop in the tropical region of northern Australia. The warm, humid climate encourages vegetative growth and growers need to implement flowering treatments to maximise opportunities for high fruit yields. Two chemical-based flowering treatments have recently been introduced to the north Australian mango region. The first, paclobutrazol (P), inhibits the synthesis of gibberellins and is applied as a soil drench. The second, known as mango flowering treatment (M), uses the plant growth regulator morphactin which is applied by tying a length of twine that has been soaked in a solution of the chemical into a cincture cut around the circumference of the tree trunk. This experiment evaluated the effects of P and M on shoot phenology and the relationship between vegetative and floral growth of trees grown on nine commercial orchards in the Darwin-Katherine region of northern Australia over three consecutive seasons. In a supplementary experiment the effects of M on root growth were studied. In the year following application of P and M trees generally flowered more profusely, with the maximum intensity of flowering being up to twice that of control (C) trees at some sites. The effectiveness of M was not as consistent in the second year and by the third year this treatment had no effect on flowering. The P treatment consistently improved flowering but the attainment of maximum intensity of flowering in the Darwin region was delayed in the third year when there were fewer cool days in the pre-flowering period compared with the first 2 years. Vegetative growth was reduced by M and P at many sites, with canopy surface area of trees in these treatments being 20-30% lower than in C. Root growth of M trees was restricted to levels that were generally 33-50% of the growth achieved in C, although by the end of the year following treatment root growth in M and C was similar. Growers need to implement flowering treatments to maximise the potential for flowering of mango cv. Kensington Pride in the Australian tropics. The P treatment usually enhances flowering but may require a sustained period of cool weather in the pre-flowering period for maximum effect. The M treatment usually enhances flowering in the season following treatment but loses its effect in subsequent seasons. Root growth is reduced in M during the season following treatment which may be associated with the effects on vegetative growth and flowering and also affect the ability of trees to take up water and nutrients. (C) 2004 Elsevier B.V. All rights reserved.