Onions are one of the most important vegetable crops worldwide. However, their production faces many challenges. Genetic improvement is one mechanism to address those challenges. In this review, we discuss recent research pertaining to the diseases Fusarium basal rot and Iris yellow spot, the insect pest onion thrips, onion pungency, and dormancy. Recent research for screening onion bulbs for Fusarium basal rot resistance has resulted in improved screening techniques and germplasm exhibiting less disease when inoculated with the disease-causing pathogen. Improved screening methods have resulted in germplasm exhibiting fewer and less severe Iris yellow spot symptoms when onion thrips and conducive environmental conditions are present. Onion germplasm with less and differing compositions of epicuticular wax on their leaves have shown a nonpreference for thrips feeding and have the potential for developing thrips tolerant cultivars. Conventional breeding efforts and genetic manipulation of the genes producing alliinase and lachrymatory factor synthase has resulted in low pungency, tearless onions. In long-day onions, an annual generation time has been achieved by artificially breaking bulb dormancy early while ensuring proper vernalization has been completed. Genetic improvement of these and many other onion traits will continue and result in better production in the future.

Onion is a biennial plant that produces a bulb. The larger the onion bulb, the more valuable it becomes. Therefore, it is important to study bulb weight and plant size components affecting it. For this study, four New Mexico State Univ. breeding lines and two commercial cultivars, ‘Rumba’ and ‘Stockton Early Yellow’, were selected. These breeding lines and cultivars were evaluated for plant height, leaf number and sheath diameter, at five different dates two weeks apart throughout the growing season, and for bulb weight upon harvest. The experiment was designed as a randomized complete block design with three blocks each containing four replications. Plant size components were all positively correlated with each other and with bulb weight with correlation coefficients above 0.50. NMSU breeding lines also exhibited greater average bulb weights than commercial cultivars. Sheath diameter proved to be the best predictor of bulb size, showing strong positive correlations with bulb weight at around 12 weeks after transplanting, and positive correlations are observed as early as 6–8 weeks after transplanting.

Iris yellow spot (IYS) disease in onion (Allium cepa L.) is caused by onion thrips (Thrips tabaci L.) vectored Iris yellow spot virus (IYSV). The absence of cultivars that are resistant/tolerant to thrips and/or IYS is a challenge for onion bulb and seed production worldwide. To measure selection progress for reduced/delayed IYS symptom expression in onion breeding lines after two selection cycles, selections were performed in 2011 on previously evaluated lines that exhibited a reduced symptom expression after one selection cycle. Selected plants from each line were massed in a cage and the resulted progenies were evaluated in 2013 and 2014 along with their original populations and a susceptible check—’Rumba’. In some comparisons, the selection progress for delayed/reduced IYS symptom expression was observed for some breeding lines. Plants of most selected breeding lines exhibited less disease expression than plants of ‘Rumba’. For some selections, a low disease severity was observed even with a relatively high number of thrips per plant. These results suggest that further improvement might be achievable with additional cycles of selection.

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.

We used enterprise budgets, ordinary least squares regression, and data from the USDA Agricultural Marketing Service to estimate potential changes in costs and returns from use of a partially onion thrips (Thrips tabaci L. Thysanoptera) resistant-cultivar and action-based spray thresholds in onion (Allium cepa L.) producing regions of Idaho and Eastern Oregon. Results suggested the need for management strategies that could reduce the number of insecticide applications used to protect the crop from damage by onion thrips and Iris yellow spot while ensuring a high yield of onions grade in the largest size categories. Analysis indicated an effective cultivar could increase profits $641.10 to $1,013.63 per hectare compared with current marketable yields and management practices.