The Responses of African Vegetable Amaranth (Amaranthus spp.) Varieties to Drought Stress

Amaranth (Amaranthus spp.) is a drought resistant crop widely grown and consumed for its nutritious leaves in East Africa.  Among the many issues facing smallholder farmers in this region is a lack of high quality germplasm and increasing climate variability that makes rain during the growing season unpredictable.  Identifying germplasm that exhibits drought resistant characteristics will increase the resilience of agricultural systems in this region of the world.  The goal of this research was to characterize differences in drought response between four varieties of vegetable amaranth grown in this area: AC45, AM38, ExZan, and ExZim, including their response at different stages of vegetative development.  All varieties were exposed to both short term and long term stress while plant responses were evaluated.  Under short term drought stress (up to 8 days without water) one variety, ExZim, showed the least effects of water stress in terms of biomass reduction.  However, all varieties exhibited a high capacity to recover from water stress in terms of stomatal conductance and relative water content, which showed that plants were able to acclimate to stressed conditions.  Under long term drought stress, each variety was exposed to moderate water stress of 0.15 m3/m3 volumetric soil water content for an extended period of up to 6 weeks.  ExZan was the only variety with significant reductions in both dry weight and leaf area, though it was also the variety with the greatest biomass under well-watered conditions.  Drought response was assessed across vegetative development stages by maintaining soil moisture of 30% of water holding capacity during one of the following growth stages: 10-15 nodes, 15-20 nodes, or 20-25 nodes.  Contrary to previous literature reports, drought during later stages of development (20-25 node growth period) had the greatest negative impact on biomass production.  These results suggest that amaranths can acclimate to drought stress and survive but growers should minimize water stress to plants at later growth stages to optimize harvestable leaves.  In selecting amaranth varieties, growers should bear in mind that while some varieties yield better in well-watered conditions (ExZan in our experiments) others may be more resilient under drought stress (ExZim in our experiments). These considerations can help growers budget scarce water resources and preserve yield even in times of water stress.  Planting more drought resistant crops such as amaranth will help improve the sustainability of agroecosystems and their resilience to climate change.