The relationships between fruit yield and yield components in several cucumber ( Cucumis sativus L.) populations were investigated as well as how those relationships changed with selection for improved fruit yield. In addition, the correlations between fruit yield and yield components were partitioned into partial regression coefficients (path coefficients and indirect effects). Eight genetically distinct pickling and slicing cucumber populations, differing in fruit yield and quality, were previously subjected to modified half-sib family recurrent selection. Eight families from three selection cycles (early, intermediate, late) of each population were evaluated for yield components and fruit number per plant in four replications in each of two testing methods, seasons, and years. Since no statistical test for comparing the magnitudes of two correlations was available, a correlation ( r ) of 0.7 to 1.0 or –0.7 to –1.0 ( r ² ≥ 0.49) was considered strong, while a correlation of –0.69 to 0.69 was considered weak. The number of branches per plant had a direct positive effect on, and was correlated ( r = 0.7) with the number of total fruit per plant over all populations, cycles, seasons, years, plant densities, and replications. The number of nodes per branch, the percentage of pistillate nodes, and the percentage of fruit set were less correlated ( r < |0.7|) with total fruit number per plant (fruit yield) than the number of branches per plant. Weak correlations between yield components and fruit yield often resulted from weak correlations among yield components. The correlations among fruit number traits were generally strong and positive ( r ≥ 0.7). Recurrent selection for improved fruit number per plant maintained weak path coefficients and correlations between yield components and total fruit number per plant. Selection also maintained weak correlations among yield components. However, the correlations and path coefficients of branch number per plant on the total fruit number became more positive ( r = 0.67, 0.75, and 0.82 for early, intermediate, and late cycles, respectively) with selection. Future breeding should focus on selecting for the number of branches per plant to improve total fruit number per plant.

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.

Iris yellow spot is an economically important disease of onion that reduces bulb size and yield and is difficult to control. The disease is spread by Thrips tabaci (onion thrips) and disease symptoms are exacerbated by hot, dry climatic conditions that also favor rapid thrips multiplication and make control programs less effective. Currently, no onion cultivar is resistant to the disease and/or thrips. Certain onion foliar characteristics have shown nonpreferential feeding activity by thrips and may be the first step in developing Iris yellow spot (IYS)-tolerant onion cultivars. Seventy-five onion PI accessions from the U.S. germplasm collection were evaluated for leaf color, waxiness (bloom), and axil pattern; thrips number per plant; and IYS disease severity under conditions that favored thrips and disease buildup. Plants of PI 289689 were less attractive to thrips and had a lower number of thrips per plant than plants of most other accessions. These plants were rated as having light green to green-colored foliage and a relatively low amount of epicuticular leaf wax. Plants of PIs 239633 and 546192 generally exhibited less severe IYS disease symptoms than those of other accessions. Individual plants, that exhibited less leaf area exhibiting IYS disease symptoms, were selected at bulb maturity from 22 different accessions with PI 546140 producing the largest number of selected bulbs. Physiological plant development, environmental conditions, and tolerance to plant stress may influence the degree of disease symptom expression. Further work that examines the role of plant maturity and host plant tolerance to stress with respect to disease expression is needed.

Fusarium basal rot (FBR), caused by a soil-borne fungus, Fusarium oxysporum f. sp. cepae (FOC), is a major disease hindering onion production worldwide. This study was conducted to evaluate the initial and the most advanced selected populations of seven open-pollinated short-day onion cultivars for FBR susceptibility, along with two check cultivars using the conidial inoculation of mature bulbs for two consecutive years. The artificial inoculation of mature bulbs was carried out by applying a virulent FOC isolate ‘CSC 515’ at a final concentration of 3.0 × 10⁴ spores mL⁻¹ to the transversely cut basal plates of onion bulbs. The basal plates of 20 arbitrarily chosen bulbs per plot were recut after 20 days of incubation and then were rated for FBR severity using a rating scale of 1 (no disease) to 9 (≥70% of the basal plate is infected). The bulbs with a rating of 1 were saved and then bulked to form the seeds for the next generation. The selected populations exhibited a variable response for FBR severity when evaluated over two years, with an improvement in the most advanced selections observed for a majority of the cultivars. For example, the advanced selections of ‘NuMex Sweetpak’ exceeded the partially resistant check ‘Serrana’ in their levels of resistance when both were evaluated in the second year. A conidial inoculation can be effective in the development of FBR-resistant cultivars. In addition, this inoculation method can accelerate breeding efforts by determining the genetic mechanism(s) responsible for FBR resistance, locating quantitative trait loci, and facilitating marker-assisted selection.

Allium species are known for their culinary, medicinal, and ornamental purposes. Fusarium basal rot is one of the most damaging soilborne fungal diseases of Allium species and poses a significant threat to yield, quality, and storage life worldwide. Various species of Fusarium have been identified as causal agents for Fusarium basal rot, depending on the Allium species involved. Diverse disease management practices have been implemented to mitigate the impact of Fusarium basal rot. This review article provides a comprehensive overview of the recent progress in detecting different species of Fusarium involved in Fusarium basal rot and strategies to control them in affected Allium species involving chemical, biological, and cultural methods. It covers the latest advancements in host plant resistance research from traditional breeding to modern molecular techniques and studying secondary metabolites involved in defense mechanisms against Fusarium basal rot.

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.