HARVESTING COMPOUNDS THE EFFECT OF WATER DEFICIT ON THE GROWTH AND YIELD OF WATER LEAF [TALINUM TRIANGULARE (JACQ.) WILLD.

Waterleaf is an important leafy vegetable in many parts of West and Central Africa, which can survive long periods of water deficit owing to its succulence and induced crassulacean acid metabolism. However, it is not known whether harvesting during the offseason i.e. under water-limited conditions can alter the resilience of the plant to adverse environmental conditions. To investigate this, a pot experiment was set up in the screen house in which, uniform-sized cuttings of waterleaf were planted in 10-L pots filled with field soil and irrigated as needed until the plants were established. Ten days from planting, irrigation was withheld in two groups of plants, while one group (control plants) continued to receive water regularly as needed. In the water deficit groups, one group (T1) received water every two weeks coinciding with a period of harvest, while the other group received no water till the end. The shoot fresh and dry mass, height, leaf area, chlorophyll concentration, and leaf mass area ratio of the plants were recorded before and after harvesting. The results showed that at the first harvest, the fresh mass decreased by 33 % and 2.1 folds under T1 and T2 treatments, respectively, while at the second harvest, the decrease was 2.4 and 4.6 folds under T1 and T2 respectively. The dry mass remained unaltered in T1, but dropped by 34 % in T2 at the first harvest, while at the second harvest, the reduction was more pronounced (39 % and 3.1 fold for T1 and T2, respectively). In addition, the leaf area did not change with an increase in leaf thickness for T1, but decreased with a drop in leaf thickness for T2; meanwhile Chl a, Chl b and Chl a+b increased in T1, but remained unaltered in T2. Taken together these results indicate that harvesting reduces the ability of waterleaf to adapt to water deficit, leading to a marked reduction in shoot production especially under severe stress (T2) due probably to downregulation of photosynthesis following source (leaf area) size reduction. Therefore minimal irrigation of water leaves after every harvest in the offseason could improve production.