Barriers to Interspecific Hybridization Between Cucurbita pepo L. and Cucurbita moschata Duch.

Fertilization barriers often hinder the introgression of desired traits of interest in interspecific hybridization. In present study, the fertilization barriers in interspecific crosses of Cucurbita moschata (Punjab Nawab and Punjab Sardar) and Cucurbita pepo (PMK-1) were investigated. The results revealed that pollen grains were viable and stigmas were receptive at the time of pollination in all the genotypes. The maximum pollen germination (%) was observed in Punjab Nawab, while maximum pollen size, pollen tube length and style length were recorded in Punjab Sardar. Additionally, fluorescence microscopic images showed that the shorter pollen tubes of PMK-1 did not grow enough in the longer style of Punjab Sardar, hence the interspecific cross of Punjab Sardar x PMK-1 was incompatible. While in the reciprocal cross (PMK-1 x Punjab Sardar), formation of callose plugs in the pollen tubes of Punjab Sardar and its slow growth might had contributed to the failure of fertilization. However, in the interspecific cross of Punjab Nawab x PMK-1 and vice-versa, the pollen grains successfully germinated on stigma and pollen tubes reached the style but embryo was not able to attain a particular shape, therefore, the cross was partially incompatible. The fruit setting (%), fruit diameter, fruit weight, seed number, seed weight and seed germination (%) was lesser in interspecific crosses as compared to self-pollinated genotypes. Furthermore, cluster analysis revealed that partially compatible and incompatible crosses are present in different clusters and partially compatible cross showed strong positive correlation with fruit characters. Collectively, pre-and post-fertilization barriers hampered the interspecific hybridization between C. pepo and C. moschata genotypes. These findings would help the breeders to overcome such barriers and introgress the hull-less seed trait of C. pepo and disease resistant trait of C. moschata.