Effect of Various Water Application Strategies on Root Development of Opuntia ficus-indica and O. robusta Under Greenhouse Growth Conditions
Keywords:Cactus pear, cladode mass, root/cladode ratio, root length, root mass, root thickness, wateruse efficiency.
This study aimed at determining the influence of different water applications on the root/cladode ratio and water-use efficiency (cladode or root dry-mass production per unit of water used) of one-year-old Opuntia ficus-indica (L.) Miller (cultivar Morado – green cladode) and O. robusta Wendl. (cultivar Monterey – blue cladode) plants. The one-year-old cactus-pear cladodes were planted in pots (210-mm diameter and 550-mm-deep soil) and grown in the greenhouse at day/night temperatures of 25-30oC/15-18oC. The water treatments applied were 0-25%, 25-50%, 50-75% and 75-100% depletion of total plant-available water. Root mass and root length decreased significantly with water stress over the three months for both Opuntia species. The finer root system of O. robusta showed a lower root mass than O. ficus-indica. Although the influence of water stress on root die-back was clearly observed, it was less striking in O. robusta than in O. ficus-indica. The dry-mass-based root/cladode ratio decreased significantly with water stress for all three months for both species. The roots comprised only 11% and 12% (average of all months and water treatments) of the total plant biomass for O. ficus-indica and O. robusta, respectively. The water-use efficiency expressed in terms of cladode mass decreased with water stress for O. ficusindica and increased with water stress for O. robusta. A water application of only 13.63 mm and 11.64 mm was enough to fill up the cladodes for O. ficus-indica and O. robusta, respectively, at the lowest water treatment. It seems that O. robusta is less sensitive to water stress conditions than O. ficusindica. The quick reaction to water makes the cactus pear plant adaptable to very low rainfall conditions.