Photosynthetic Evaluation of Sweetpotato Germplasm

Abstract

Field experiments were conducted from 1980-1983 to evaluate sweetpotato [Ipomoea batatas (L.) Lam.] germplasm for photosynthetic efficiency, harvest index [HI; (storage root dry matter/total plant dry matter) × 100], and yield. Most genotypes maintained leaf area index (LAI) above five until final harvest, 164 days after planting (DAP). The higher LAI (> 8) for PI 318859, PI 344134, and PI 308205 compared to the other genotypes was maintained at the expense of the storage root development. Single leaf net photosynthesis (Pn) of the genotypes ranged from 0.61 to 1.09 mg CO2/m2 per sec during 1980. Canopy photosynthesis on a ground area (CPn-Ga) basis ranged from 0.95 to 1.56 and 1.04 to 1.30 mg CO2/m2 per sec during July and August 1983, respectively. Canopy photosynthesis expressed on leaf dry-weight (CPn-Dwt) basis was higher for PI 344122 than the other genotypes, except PI 344138, indicating its superior photosynthetic efficiency. Photosynthetic efficiency and stomatal conductance were not related to yield. Stomatal conductance and CPn-Ga were significantly correlated. Harvest index differed significantly at each sampling and ranged from 14.0% to 75.5% at final harvest. Fresh storage root yield for 1983 and 4-year mean yield ranged from 8.6 to 60.1 and 14.1 to 42.2 t·ha-1 respectively. At final harvest, HI correlated significantly with fresh-(r = 0.91) and dry-matter storage root yield (r = 0.95). Despite significant photosynthetic variations among the genotypes, sweetpotato yield was influenced more by HI and storage root sink strength than by photosynthetic efficiency.