Temperatures during flower bud development affect pollen germination, self‐incompatibility reaction and early fruit development of clementine (Citrus clementina Hort. ex Tan.)

Abstract

One of the key environmental factors affecting plant reproductive systems is temperature. Characterising such effects is especially relevant for some commercially important genera such as Citrus. In this genus, failure of fertilisation results in parthenocarpic fruit development and seedlessness, which is a much-prized character. Here, we characterise the effects of temperature on flower and ovary development, and on pollen-pistil interactions in 'Comune' clementine (Citrus clementina Hort. ex Tan.). We examine flower bud development, in vitro pollen germination and pollen-pistil interaction at different temperatures (15, 20, 25 or 30 °C). These temperatures span the range from 'cold' to 'hot' weather during the flowering season in many citrus-growing regions. Temperature had a strong effect on flower and ovary development, pollen germination, and pollen tube growth kinetics. In particular, parthenocarpic fruit development (indicated by juice vesicle growth) was initiated early if flowers were exposed to warmer temperatures during anthesis. Exposure to different temperatures during flower bud development also alters expression of the self-incompatibility reaction. This affects the point in the pistil at which pollen tube growth is arrested and confirms the role of sub- and supra-optimal temperatures in determining the numbers of pollen tubes reaching the ovary.

Temperature stress interferes with male reproductive system development in clementine (Citrus clementina Hort. ex. Tan.)

“…Temperature stress induces different alterations to plant reproductive system physiology and phenology, including changes in flowering initiation (De Storme & Geelen, ). In citrus, temperature stress has been demonstrated to be effective in affecting pollen germination, self‐incompatibility reactions and early fruit development (Distefano et al, ). In the current study, focused on clementine, one of the most important citrus species, we monitored the effect of three temperatures in the pollen development process.…”

“…In the current study, focused on clementine, one of the most important citrus species, we monitored the effect of three temperatures in the pollen development process. We observed that low temperature (15°C) resulted in slower growth of the flower buds starting at the young microspore stage (Stage C in Figure ), which is in accordance with our previous results (Distefano et al, ). The flower exposure to higher temperatures resulted in earlier anthesis and flower maturation without any evidence of flower functionality alterations.…”

“…These results agree with previous studies in which the pollen germination rate under different in vitro incubation temperatures increased from 15 to 25°C, which is the optimum temperature for pollen germination of citrus in vitro , and sharply decreased when the temperature reached 30°C (Distefano et al, , ).…”

“…Additionally, exposure to different temperatures during flower bud development alters the expression of the self‐incompatibility reaction affecting pollen tube growth along the pistil. However, little is known about the effects of temperature stresses during male gametophyte development in citrus (Distefano, Gentile, Hedhly, & La Malfa, ; Yang & Nakagawa, ).…”

“…Three different temperature regimes (15, 25, 30°C) were tested. These regimes simulate the thermal range, from cold to hot, recorded in the Mediterranean area during the citrus flowering season (Distefano et al, ). Histological analyses were performed on the anthers of the flower buds from the appearance of the first petal until anthesis.…”