EVALUATION OF SWEETPOTATO (Ipomoea batatas (L.) Lam.) GENOTYPES FOR VINE MULTIPLICATION IN SANDPONICS SYSTEM USING OPTIMIZED NUTRIENT MEDIA

Abstract

Sweetpotato (Ipomoea batatas (L.) Lam.) is one of the most affordable and nutrient rich food crops in sub-Saharan Africa (SSA). However, the production of the crop is constrained by several biotic and abiotic stresses. Sweetpotato breeding has continuously developed cultivars to overcome some of these constraints. Unfortunately, insufficient planting materials limit the adoption and utilization of these improved cultivars. Availability of sufficient pre-basic seed as the starting material for bulking sweetpotato planting material, usually from research institutes is crucial. One of the critical deterrence for pre-basic sweetpotato seed multiplication is the high cost of sterilizing soil substrate. This study aimed at using sand substrate with fertigation also called ‘sandponics’ to produce pre-basic sweetpotato seed for selected genotypes instead of the conventional soil substrate method. Two experiments were conducted at Kenya Plant Health Inspectorate Service – Plant Quarantine and Biosecurity Station, Muguga Kenya between March 2018 to March 2019: to optimize the nutrient media for sweetpotato seed multiplication in the sandponics and to assess the cost-effectiveness of the sandponics system. Nutrient omission pot experiments were conducted to optimize the nutrient media for sweetpotato seed multiplication in the sandponics in the screenhouse and vine growth using cultivar Kabode. Five levels of each nutrient were replicated four times and the effect of N, P, Ca, S and B on sweetpotato vegetative growth parameters were measured 45 days after planting. Results showed that application of 200, 60, 200, 120 and 0.3 ppm of N, P, Ca, S and B respectively recorded the highest vegetative growth for sweetpotato. To assess the cost-effectiveness of the sandponics system, seed multiplication of virus indexed 3-node cuttings of genotypes Irene, Kabode, Ejumula and Gweri in the sandponics and conventional soil substrate method were compared. Vines were harvested at 42-day intervals in a crop calendar year of nine months. A significant (p<.0001) increase of 21.8% in vine multiplication rate was observed in the sandponics system compared to the conventional soil substrate method. The cost of producing one sweetpotato node in sandponics system was significantly (p<.0001) lower by 0.9 KSH (US$ 0.009) compared to conventional soil substrate method. Ejumula was the most cost-effective genotype to produce in sandponics system with a significant (p<.0001) reduction in the cost of producing one node by 1.2 KSH (US$ 0.012) compared to the conventional soil substrate method of production. Sandponics system has shown high potential for increasing the availability of pre-basic seed in the sweetpotato seed systems in SSA.