Thesis Abstract of AGS Students

Off-Season Mango Production Systems in the Mekong Delta, Vietnam

Tran Van Hau (1997)

The floral induction by chemicals and methods of application were the major constraints for the off-season mango growers in the Mekong Delta. This study was carried out in order to evaluate the effect of chemical treatments in off-season mango production and to assess the economic aspects. A formal field survey was performed in Caolanh district, Dongthap province, Vietnam from March to April 1996 and field experiment was carried out at farmer’s field in the area from May 1996 to May 1997. The experiment was 4 x 3 factorial with 3 replications in completely randomized design, consisting of one tree in each experiment unit. The first factor was 3 different ages of mango 6, 7, and 8 year-old from seedings and the second factor was 4 treatments of floral induction chemicals i.e. paclobutrazol at 5 g a.i. per tree by collar drenches on the 15th of June, 1996, KNO3 and DHCT at 1.5 % applied twice as a foliar spraying on the 22 nd and 28th of August, 1996, and control without any floral induction chemical.

The results of field survey showed that off-season flowering of mango began in August and ended in December, but the most flowers concentrated in November. Majority of mango growers sprayed 12.5-30 g/l of potassium nitrate to induce off-season flowering, but the results was not consistent. In field experiment, all floral induction chemicals were able to induce flower of mango cv. “Cathoaloc” in September, while the control flowered in November. The off-season flowering prolonged till the end of December. Paclobutrazol was the most effective chemicals when compared with both DHCT and KNO3. It induced flowering at 85 days after treatment and exhibited 4 sets of flowering with about 340 inflorescences/tree compared to less than 3 sets and around 100 inflorescences/tree by other chemicals and control. The flowering between September and October, when the rainfall was heavily intensified in the Mekong Delta, were always seriously damaged by anthracnose disease. The flowering of control treatment appeared 1-2 month earlier than normal season because of flooding during September to November.

Number of hermaphrodite flowers per inflorescence, inflorescence length were not affected by floral induction, but age of the tree. Fruit retention decreased rapidly 10 days after fruit set and retained even less than 1 % at 70 days after fruit set. Tree induced by paclobutrazol retained at a higher number of fruits than other treatments, while age of the tree showed no difference. The off-season harvesting prolonged from the end of November, 1996 to March, 1997. Trees induced by paclobutrazol were harvested in early of December, 85 days after flowering, and were done 4 times. The highest yield (35.3 kg/tree) during off-season production was obtained by paclobutrazol only on age 8, but there was no difference among the chemical treatments on age 7 and age 6. This result was leading to the maximum net income later. Although paclobutrazol did not affect the flowering and yield during normal season and the whole growing year, net income of trees obtained by paclobutrazol on age 8 of both off-and on-season was about 2.7 times over control and other chemicals due to high price during off-season. Income of trees induced by DHCT and KNO3 on age 6 was impossible compensate the input cost for chemical application and disease control.

Trees induced by DHCT and KNO3 flowered within 39 and 29 days after spraying, respectively. The poor effect of KNO3 and DHCT might be due to incorrect application time.

The 8 year-old mango showed a better response to off-season floral induction by chemicals than the 6 year-old mango. It provided high number of flowering, fruit number, and yield per tree during off-and on-season leading to high net income. The good response of age 8 to off-season floral induction might be explained by larger size of tree canopy, more number of shoots per tree and mostly, the tree maturity, while age 6 seemed to be affected by their younger age.

To avoid the unfavorable conditions of heavy rain and flooding as well as anthracnose disease, it was suggested to delay the floral induction time for one to one and a half months. Pathogen attacked the basal bark of mango tree during the flooding which was caused by “phytophthora fungi” should receive further study, especially its control measure.

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