THE INFLUENCE OF DAYS AFTER PLANTING ON ROOT YIELD AND QUALITY OF ORANGE- AND PURPLE-FLESHED SWEETPOTATO (Ipomoea batatas (L.) Lam) CULTIVARS ASSESSED IN THE NORTHERN REGION, GHANA

Abstract

Time to harvest sweetpotato is very important in determining root quality. The focus of this investigation was to assess the appropriate time to harvest orange-fleshed sweetpotato (denoted OFSP1, OFSP2, & OFSP3) and purple-fleshed sweetpotato (PFSP) cultivars. OFSP1, a released variety in Ghana, was compared with OFSP2, OFSP3 and PFSP for storage root quality parameters. OFSP2 and PFSP are new cultivars introduced to Ghana by Tuskegee University, while OFSP3, is a landrace. The study was carried out at the Savanna Agricultural Research Institute (SARI), Nyankpala, Ghana in August, 2013. The design was 4x4 factorial in a randomized complete block design. Four harvesting times, denoted by days after planting (DAP): 65, 95, 125 and 155, were assessed to establish the root quality parameters. Standard agronomic practices for sweetpotato cultivation were employed in this study. Storage root quality indices including storage root yield was quantified gravimetrically, while, β-carotene, dry matter, and starch were determined using near infrared reflectance spectroscopy. The highest root yield of 28.20 tha−1 was obtained at 125 DAP as compared to 65, 95 and 155 DAP, in the range of 5.77 to 19.34 tha−1. Considering all the sweetpotato cultivars, OFSP1, on the average, had significantly (p < 0.05) the highest storage root yield (19.50 tha−1) β-carotene (31.50 mg 100 g−1), and sucrose (15.42 mg 100 g−1). The PFSP recorded the highest dry matter (38.67 g 100 g−1) and starch (67.59 g 100 g−1), but was devoid of β-carotene. Roots harvested at 155 DAP had the highest β-carotene, about 18.50 mg 100 g−1 but only marginally different from the16.00 mg 100 g−1of β-carotene in roots harvested at125 DAP. Roots harvested at 65 DAP had the least β-carotene concentration, 12.60 mg 100 g−1. The four cultivars investigated in this study could be harvested at 125 DAP. The OFSP2, and PFSP cultivars could be considered as food crops in Ghana, especially in Northern Ghana.