The effect of post-harvest ammonium sulphate application, planting time and sucker size on plant growth and yield of queen pineapple, ananas comosus

Abstract

Queen pineapple plant mortality as well as poor growth and development are some of the major problems facing the Hluhluwe pineapple producers. Approximately 20% of the plants do not produce fruit, due to mortality or poor growth. Queen pineapple plantings are currently established from suckers taken from harvested plants. The speed and development of suckers on the mother plant is not rapid enough to be used as planting material at fruit harvest. Therefore, suckers are left to grow on the mother plant for 6 to 8 months after harvesting the plant crop for the suckers to attain a suitable size for planting. The aim of the study was to determine, under field conditions, the effects and interactions of post-harvest ammonium sulphate fertilizer application and the duration of sucker growth on the production and quality of suckers as well as on the growth and development of subsequent plantings. Post-harvest (NH4)2SO4 application had a significant influence on the percentage increase in sucker fresh mass and length when interacting with the duration of sucker growth on the mother plant. Growing suckers on the mother plant for up to 8 months, after the application of post-harvest (NH4)2SO4, produced more plantable suckers than growing them for 6 or 10 months. Four sucker sizes were produced namely, size 2, 3, 4 and 5. Grading suckers by length produced more plantable material than grading by fresh mass. Plant gain in fresh mass and stem diameter, was positively correlated with sucker size and post-harvest (NH4)2SO4 application. At 2 months after planting, 6 symptoms that could lead to plant mortality were identified namely, wilted plants, plants toppling over, plants planted doo deep, plants growing slowly, plants with funnel rot and plant that dying back. The total percentage of these plant mortality symptoms was 19.6% in the March planting, 26% in the May planting and 33.1% in the August planting. Wilted plants and plants planted too deeply formed a greater proportion of the plants affected by the mortality symptoms in all the plantings. Some of the plants affected by the mortality symptoms recovered and grew into healthy plants, whereas some grew slowly and some died. Sucker size and post-harvest (NH4)2SO4 application had no significant effect on levels of mealybug, Dymicoccus brevipes and red mite, Dolichotetranychus floridanus infestation. Post-harvest (NH4)2SO4 application influenced the percentage of P and K in leaves in the May and August planting. Sucker size had an influence on N percentage in the March planting only. Plants established from smaller sucker sizes had a significantly higher N percentage than plants established from bigger sucker sizes. Sucker size had an influence on flowering failure. Plants established from a smaller sucker size had a higher percentage of flowering failure than the plants established from a bigger sucker size. The March planting had a higher percentage of plants that failed to produce flowers after flower induction than the May and August planting. The total percentage of plants that failed to flower in the March planting was 15.92% (7.39% due to plant mortality symptoms and 8.53% due to unknown causes), in the May planting it was 6.02% (4.69% due to plant mortality symptoms and 1.33% due to unknown causes) and in the August planting it was 7.56% (5.39% due to plant mortality symptoms and 2.17% due to unknown causes). Plant mortality symptoms were the main cause of flowering failure in the May and August plantings. Postharvest (NH4)2SO4 application had a significant effect on wilted plants in the March planting and on natural flowering in the August planting. Flowering failure resulted in fruit yield loss. Fruit yield was more influenced by the sucker size than by post-harvest (NH4)2SO4 application. There was a positive correlation between sucker size and fruit yield. Fruit size was used to determine the influence of post-harvest (NH4)2SO4 application and sucker size on the external and internal quality of the fruit. Post-harvest (NH4)2SO4 application had a significant influence on fruit length, inter-fruitlet cracks, winter speckle occurrence and total soluble solids. Sucker size was found to have an influence on the number of fruitlet spirals, fruit length, crown fresh mass, fruitlet cracks, winter speckle occurrence and total soluble solids. Black spot, nectary duct and internal browning infestation were influenced by the number of days the fruit were kept in storage after harvesting. Post-harvest (NH4)2SO4 application and sucker size had no significant influence on black spot, nectary duct and internal browning infestation. Eight months after fruit harvest in the March and May planting, evaluation was done to determine the effect of post-harvest (NH4)2SO4 application, sucker size and mortality symptoms on sucker yield. Plants established from bigger suckers produced longer and heavier suckers as well as a higher number of plantable suckers than plants established from smaller suckers. Healthy plants produced longer and heavier suckers as well as a higher number of plantable suckers than plants that were affected by the mortality symptoms. Plants treated with post-harvest (NH4)2SO4 produced quality planting material in terms of fresh mass and length. Leaving the suckers to grow for 8 months after fruit harvest produces more plantable material. Planting the planting material obtained from plants treated with post-harvest (NH4)2SO4 increased fruit yield and profit.