UC Riverside

Distant Citrus relatives often possess genetically-based traits that can be useful for the improvement of standard Citrus cultivars, such as natural resistance to pathogens. Thus, sexual compatibility data between Citrus and its relatives has potential value to Citrus improvement programs as it can be used to predict the introgressability of these genes. This study reviews the current knowledge of cross compatibilities among Citrus and related genera and identifies gaps in the data. Although many gaps are identified, compatibility data within the Hard-Shelled Citroid subtribe, Balsamocitrinae, is largely lacking. To address this deficiency, a selection of diverse germplasm from the Aurantioideae subfamily was cross pollinated onto Aegle marmelos, the most economically important species in the Balsamocitrinae. Pollinations from the Clauseneae and the Triphasiinae were unsuccessful. Pollinations from the Citrinae subtribe resulted in fruit set in Aegle marmelos, but all of the nearly 1800 seeds produced from these unions were inviable. When male parents from the Balsamocitrinae were utilized, fruit set and germination rates were high. Additionally, geitonogamy in Aegle marmelos caused flower abortion indicating self-incompatibility. The author concludes that Aegle marmelos is obligately outcrossing with the requirement for pollen to be received from other closely related taxa in the Balsamocitrinae. These findings provide an important update in what is known regarding cross compatibilities within the Aurantioideae.