Evaluation of Onion Plant Introduction Accessions for Leaf Characteristics

Onion leaf color, leaf waxiness (bloom), and leaf axil pattern (or degree of openness) has been associated onion thrips feeding preference. Plants, that possess a closed (tight) leaf axil pattern, blue to dark green leaf color, and waxy leaves, are preferred by onion thrips while plants, that possess an open leaf axil pattern, light green leaf color, and glossy (non waxy) leaves, are not. Onion thrips is a major onion insect pest, that causes drastic yield losses and is difficult to control. Cultivars, that possess leaf characteristics not preferred for feeding by onion thrips, would be beneficial for increased yield and reduced chemical control methods. Seventy-five onion plant introduction accessions from the U.S. germplasm collection were selected because they possessed a low amount of leaf bloom (degree of wax deposition) in a previous evaluation or they had been originally collected from a country that is thought to include the center of domestication for onion (i.e. Central Asia). Accessions were evaluated for leaf color (on a scale of 1 to 4 where 1 = light green color and 4 = blue), leaf waxiness (on a scale of 1 to 4, where 1 = glossy and 4 = waxy), and leaf axil pattern (on a scale of 1 to 4, where 1 = very open and 4 = tight) when grown in Las Cruces, NM. Seventeen accessions were rated as having light to dark green leaf color, three were rated as having semi-glossy to glossy leaves, and one possessed an open leaf axil pattern. PI 239633 and PI 289689 possessed glossy foliage that was dark green in color. PI 258956, PI 546188, and PI 546192 possessed semi-glossy foliage that was dark green in color. This germplasm could be used to develop cultivars that have semi-glossy to glossy foliage that is lighter in color and possibly less attractive to thrips for feeding.