Abstract
Onion is one of the most valuable vegetable crops in the US. Onion thrips were identified as one of the main threats to the US onion industry. An integrated approach, including host plant tolerance, is required. For this study, four New Mexico State University breeding lines, along with two thrips-attractive cultivars, were evaluated for their attractiveness to thrips. In addition, this study observed thrips population dynamics throughout the growing season and the relationship between onion plant size and thrips attractiveness. The experiment was designed as a randomized complete block design with three blocks, each containing four replications. Thrips-infested bulbs were used to ensure the presence of thrips and thrips-attractive plants were used to ensure equal thrips distribution throughout the field. Ten plants were randomly selected from each plot and thrips and leaf numbers were counted multiple times through the growing season. Plants of NMSU breeding lines were observed to have fewer thrips, be more tolerant to thrips pressure and produce more leaves and larger bulbs than thrips-attractive entries. Early in the growing season, leaf number was not a determining factor in thrips population dynamics. The larger bulb weights of the breeding lines allowed them to maintain their market value. A delay in thrips population buildup in plants of the breeding lines may result in the critical threshold for spraying for thrips being reached later in these lines. This would potentially allow for fewer pesticide applications by growers, increasing growers’ profits and ensuring a more environmentally friendly approach to plant production.
Highlights
Onion is one of the most valuable vegetable crops in the US with an annual farm-gate value of more than USD 1 billion [1]
If hot and dry climatic conditions that are favorable to thrips persist, Iris yellow spot (IYS) disease can destroy entire onion fields [8]
Research has found that onions with waxy leaves suffer more thrips damage compared to onions with semi-glossy and glossy leaves, since their leaves accumulate only intermediate or sparse amounts of epicuticular waxes and have lighter green colors that result in slower thrips population growth and reduced egg hatching [8,14,16,17,18,19]
Summary
Onion is one of the most valuable vegetable crops in the US with an annual farm-gate value of more than USD 1 billion [1]. Research has found that onions with waxy leaves suffer more thrips damage compared to onions with semi-glossy and glossy leaves, since their leaves accumulate only intermediate or sparse amounts of epicuticular waxes and have lighter green colors that result in slower thrips population growth and reduced egg hatching [8,14,16,17,18,19]. Progress for reducing thrips numbers per plant was observed in several breeding lines, including NMSU 12-236, NMSU 12-243, NMSU 12-335, NMSU 12-337 and NMSU 12-796, when compared to their respective original population and Rumba, showing the possibility of further progress through additional indirect selection cycles [32]. We hypothesized that NMSU breeding lines have fewer thrips and suffer less thrips damage mainly because of different foliar characteristics, such as leaf color and wax amounts, which are caused by genetic differences. We hypothesized that plants that have fewer thrips will produce larger-sized bulbs than plants that have more thrips, since it has been demonstrated that a positive correlation exists between plant height and bulb yield, while a negative correlation exists between thrips population size and yield [40]
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