Gametophytic self-incompatibility causes seedlessness in 'Kagzi Kalan' lemon (Citrus limon)

The present study aimed to study the flower and pollen structure, pollen viability, in vitro pollen germination of Kagzi Kalan' lemon (Citrus limon (L.) Osbeck), and in vivo pollen tube growth in self- and cross pollination to understand the mechanism of seedlessness. The results revealed that Kagzi Kalan had tetra-colporate spherical shaped pollen of uniform size. The results of Acetocarmine and FDA test and in vitro germination indicated normal pollen viability and germinability in Kagzi Kalan. In vivo pollen tube growth showed > 50% pollen germination on stigma in all treatments though a greater number of pollen tubes at the mid style, base of the style, and near the ovule was found in cross pollination. Contrary to this, despite optimum pollen germination (53.51-70.37%) in self-pollination treatments, none of the pollen tubes reached the base of the style due to abnormal growth of pollen tubes, viz. curvatures, inhibition of pollen tube growth, and callose deposition. The inhibition of pollen tubes at the mid style under self-pollination treatments, and production of seeded fruits under cross pollination treatments, indicate the presence of self-incompatibility and the site of inhibition of pollen tubes. Thus, gametophytic self-incompatibility (SI) caused seedlessness in Kagzi Kalan by blocking fertilization in the ovary.