Qualitative and Quantitative Measures of Onion Bulb Firmness

Abstract

Current onion varieties that are grown in New Mexico were developed for hand harvesting and not for mechanical harvesting. In order for onion production in New Mexico to remain a viable commodity, firmer onion varieties need to be developed for mechanical harvesting. In this study, bulb firmness of onions was examined in short and intermediate-day onion entries comparing a qualitative `finger pressure' method with a digital FFF-series durometer. After harvesting and curing of the onion bulbs, dry outer scales were removed before durometer measurements were taken at two perpendicular points on the vertical center axis of the bulb. Following the durometer measurements, bulb firmness was rated by `finger pressure' applied to multiple points on the vertical center axis. For intermediate and late-maturing entries, durometer measurements and firmness rating were positively correlated in a strong fashion (r = 0.77 to 0.87). Early maturing entries, NMSU 02-25 and NMSU 02-03 both had high durometer averages and firmness ratings. `NuMex Crimson' and `NuMex Crispy' had the highest durometer averages and firmness ratings among intermediate maturing entries while `NuMex Solano' and NMSU 01-06 had the highest among late maturing entries. From our results, the durometer can be useful in providing a quantifiable measure of bulb firmness.