THE INHERITANCE OF PARTHENOCARPY AND ASSOCIATED TRAITS IN PEPINO

Pazrthenocarpy in pepino (Solanum muricatum Aiton) can overcome poor f ruit set caused by pollination deficiencies. In two families involving a parthenocarpic parent (P-p), a nonparthenocarpic parent (P-np), and the generations P(p)x, P(np)x, F-1, BCp, BCnp, and F-2, we studied th ree traits that are often confused: parthenocarpy, efficiency of parth enocarpy over seeded fruit set, and the degree of facultative partheno carpy. Plants were trained to two stems (A and B). On stem A we emascu lated six flowers per truss; three were pollinated and the other three were left unpollinated. We considered that a plant was parthenocarpic if it set one or more seedless fruit similar in size and shape to tho se seeded, and nonparthenocarpic if it only set seeded fruit. The effi ciency of parthenocarpy over seeded fruit set was measured with a part henocarpic fruit set index (PFSI), defined as twice the ratio of seedl ess to total fruit on stem A. In stem B all flowers were left to self- pollinate naturally. We quantified the degree of facultative parthenoc arpy as the percentage of seedless fruit of the total. Parthenocarpy i s controlled by one dominant gene for which we propose the symbol P. P arthenocarpic fruit set in the homozygote PP was as efficient as the s eeded one (PFSI approximate to 1); in the heterozygote Pp it was less efficient (PFSI approximate to 0.6). The dose of gene P explained the differences found between generations for the PFSI and made it possibl e to predict the PFSI of a given generation from the proportions of PP and Pp genotypes. Although for the Pp hybrids parthenocarpic fruit se t was less efficient than the seeded one, their ability to set seedles s fruit in conditions of deficient pollination, together with their hi gh degree of heterosis, makes them agronomically useful. The degree of facultative parthenocarpy seemed to be a complex trait with low herit ability. In environments unfavorable for pollination, parthenocarpic g enotypes set seedless fruit, thus ensuring crop production and yield s tability. Using the degree of facultative parthenocarpy to classify pl ants for parthenocarpy is not recommended. Developing parthenocarpic c ultivars can help spread this crop and stabilize yields.