Abstract
<jats:p>Seedlessness, a key market trait in citrus, is governed by interdependent processes whose expression is strongly influenced by genotype and environment. In this study, we integrated complementary experiments conducted on six lemon cultivars to (i) quantify pollen viability and in vitro germination across temperatures; (ii) characterize pollen tube kinetics in vivo; (iii) evaluate fruit set, seed traits and fruit size, under field conditions; (iv) identify the S-genotypes. Pollen viability was generally high, but in vitro germination was temperature-sensitive, and these results were sustained under field conditions. In vivo, germination on the stigma increased over time, and pollen tubes generally reached the base of the style within 9 days, progressing faster after cross- vs. self-pollination. In field experiments, most cultivars were moderately self-compatible, ‘Fino 49’ was the most self-compatible and ‘Verna 51’ the least; parthenocarpy was consistently low except in ‘Lisbon’. Cross-pollination improved the fruit set in several combinations but did not systematically increase fruit size. The number of seeds per fruit in cross-pollination was similar to that in the self-pollination experiments, however, a substantial proportion of aborted seeds was observed, especially after self-pollination. Together, these results indicate that lemon cultivars are varyingly self-compatible and broadly cross-compatible, with parthenocarpy insufficient on its own to ensure stable seedless production. Breeding and orchard design should therefore consider parental compatibility, temperature windows at bloom, and the limited parthenocarpic capacity of many cultivars.</jats:p>