High temperatures and parthenocarpic fruit set: Misunderstandings about the pepino breeding system

Abstract

SummaryThe sensitivity of pepino (Solanum muricatum Aiton) to high temperatures, together with the variability in the expression of parthenocarpy among cultivars, have led to confusion about its breeding system. We have studied, under greenhouse conditions, the effect of two temperature regimes (T25 and T35) on parthenocarpic fruit set in three pepino clones; a strong parthenocarpic clone, a non-parthenocarpic clone, and the hybrid between them. The T25 regime (25°C maximum, 10–14°C minimum) was shown to be close to the optimum regime for pepino fruit set. High temperatures of T35 (maximum of 35°C) completely hampered fruit set of the non-parthenocarpic clone, but did not affect fruit set of either the parthenocarpic clone or the hybrid. High temperatures reduced pollen fertility and pollen release from the anthers in all clones, but had no significant adverse effects on pollen germination or pollen tube growth in the style. The percentage of seedless fruit varied greatly with the temperature regime, and is therefore not a good index of parthenocarpic fruit set ability. This ability can be exploited to expand the areas suitable for pepino cultivation and the possible growing cycles. The re-interpretation of published data, together with our own experimental results confirm that Solanum muricatum is a predominantly self-pollinating species.