Importance of a sufficiently high temperature to prevent male flower shortage in zucchini (Cucurbita pepo L.)

S. Craeye, A. Decombel, J. De Win, P. Bleyaert
Insufficient pollination, resulting from low pollen availability, leads to dark and pointy, non-marketable fruits. It is a major cause of economic losses during spring zucchini production in Flanders, where hormonal sprays are not authorized. As the differentiation of flower primordia into male flowers is being favored by summer conditions, low daily temperatures are one of the key limiting factors regarding pollen production. This research aimed to determine an optimal heating strategy for early season production. During spring 2016 and 2018, field trials were conducted to determine the minimal temperature required to prevent a shortage of male flowers. In 2016, a flat temperature regime (DIF=0°C) was compared to a positive DIF of 6°C at two research stations; in one location the daily temperature (DT) was set at 13°C, in the other at 17°C. An average daily temperature (ADT) below 14°C during the first month after planting resulted in plants with a flower sex ratio male:female (FSR) below 1:9 for nearly two months. This ratio is considered to be the minimal threshold for zucchini setting. At 17°C, FSR stayed above this threshold and less pointy fruits were harvested. Installing a positive DIF had no effect on FSR and is preferred over a DIF=0°C heating regime because of its lower energy consumption. In 2018, ADT was decreased from 17 to 15°C after one month cultivation, leading to a slight drop in sex ratio and a relative short period lacking male flowers. The highest fruit quality was seen at the highest ADTs tested. Prevention of male flower insufficiency requires at least an ADT above 15°C.
Craeye, S., Decombel, A., De Win, J. and Bleyaert, P. (2020). Importance of a sufficiently high temperature to prevent male flower shortage in zucchini (Cucurbita pepo L.). Acta Hortic. 1294, 77-84
DOI: 10.17660/ActaHortic.2020.1294.10
Cucurbita pepo L., male flowers, heating strategy

Acta Horticulturae