Relationship between environmental temperature and rainfall on beta carotene content and yield in selected sweet potato (Ipomoea batatas (L.) Lam.) varieties

Abstract

Sweetpotato (Ipomea batatas (L.) Lam) is becoming one of the most important tuber crops in Zambia and ranks second in importance from cassava. Orange fleshed varieties are being introduced to reduce vitamin A deficiency. However, the expression of β-carotene content, dry matter content and tuber yield among these varieties under different environmental conditions is not known. This study was conducted to establish the relationship between environmental temperature and rainfall on β-carotene content and yield of four orange fleshed sweetpotato varieties namely; Orange Chingovwa, Olympia, Kokota and Zambezi. The study was conducted in the Eastern province of Zambia at three sites with different climatic conditions. Sites were categorised into high temperature site (HTS) (38.5 oC), moderate temperature site 1 (MTS1) (32.2 oC) and moderate temperature site 2 (MTS2) (31.2 oC). Average rainfall for the 3 sites was 341 mm, 647 mm and 520 mm, respectively during the 2013/2014 growing season. Results showed that environment significantly influenced β-carotene content. HTS showed lower β-carotene contents than the 2 MTS. HTS showed 7.23mg/100g whereas MTS recorded MTS1 (15.56mg/100g) and MTS2 (15.46mg/100g). Among varieties, Zambezi and Orange Chingovwa were best performers for β-carotene content across all sites at 21.21mg/100g followed and (18.85mg/100g), respectively. Kokota was least performing genotype (3.28mg/100g) followed by Olympia (7.65mg/100g). β-carotene differed within genotypes and across production environments. Results indicated that β-carotene increased with warm temperatures and declined with hot temperatures. HTS showed lower yields (0.97 t/ha) than the two moderate temperature sites. The two moderate temperature sites had similar root yield results of 11.96 and 9.41 t/ha. Genotype Olympia consistently produced highest root yield across sites 12.2 t/ha followed by Kokota (7.6 t/ha) while Zambezi and Orange Chingovwa had 3.6 and 6.4 t/ha. Vine Yield (VY) was highly significantly different for sites at p < 0.001. HTS showed highest VY (23.6 t/ha) while the two MTS had lowest VY of (8.7 and 12.9 t/ha). Leaf area (LA) was significantly different for sites, varieties and their interactions. Significant interactions were recorded under different environments for Orange Chingovwa and Olympia. Genotype Kokota and Zambezi had consistently high mean LA across all sites. HTS exhibited high leaf development, high LA, high VY with low tuber development, low β- carotene, and low root yield as compared to the other two MTS. However further research to further quantify these relations particularly under controlled temperature regimes are necessary and sweetpotato breeders should be breeding genotypes ideal for specific environments for enhanced yield and β-carotene content in sweetpotato roots.