Pollen germination and in vivo fertilization in response to high‐temperature during flowering in hybrid and inbred rice

Abstract

High-temperature during flowering in rice causes spikelet sterility and is a major threat to rice productivity in tropical and subtropical regions, where hybrid rice development is increasingly contributing to sustain food security. However, the sensitivity of hybrids to increasing temperature and physiological responses in terms of dynamic fertilization processes is unknown. To address these questions, several promising hybrids and inbreds were exposed to control temperature and high day-time temperature (HDT) in Experiment 1, and hybrids having contrasting heat tolerance were selected for Experiment 2 for further physiological investigation under HDT and high-night-time-temperature treatments. The day-time temperature played a dominant role in determining spikelet fertility compared with the night-time temperature. HDT significantly induced spikelet sterility in tested hybrids, and hybrids had higher heat susceptibility than the high-yielding inbred varieties. Poor pollen germination was strongly associated with sterility under high-temperature. Our novel observations capturing the series of dynamic fertilization processes demonstrated that pollen tubes not reaching the viable embryo sac was the major cause for spikelet sterility under heat exposure. Our findings highlight the urgent need to improve heat tolerance in hybrids and incorporating early-morning flowering as a promising trait for mitigating HDT stress impact at flowering.

Deterioration of ovary plays a key role in heat stress‐induced spikelet sterility in sorghum

“…Within the reproductive stage, flowering is known to be highly vulnerable due to a series of heat stress‐sensitive processes including anther dehiscence, pollination, pollen germination, and fertilization occurring in a short time span (rice, 1–4 hr [Cho, ; Shi et al, ]; and sorghum, about 30 min for pollen germination and growth, between 2 and 12 hr for fertilization [Stephens & Quinby, ; Bandyopadhyay, Frederickson, McLaren, Odvody, & Ryley, ]). Extensive investigations involving multiple crops have led to the conclusion that heat stress coinciding with the flower opening (anthesis) is the primary reason leading to lower fertilization and seed set.…”

“…Extensive investigations involving multiple crops have led to the conclusion that heat stress coinciding with the flower opening (anthesis) is the primary reason leading to lower fertilization and seed set. However, the negative impact is shown to be significantly reduced with similar stressful temperatures occurring even an hour after anthesis in rice (Shi et al, ; Yoshida, ). Both field and growth chamber studies have indicated that sorghum, similar to other crops, is sensitive to heat stress during anthesis, via a reduction in pollen viability, thereby lowering seed set and grain yield (Djanaguiraman, Prasad, Murugan, Perumal, & Reddy, ; Nguyen et al, ; Prasad, Djanaguiraman, Perumal, & Ciampitti, ; Singh et al, ).…”

“…Within the reproductive stage, flowering is known to be highly vulnerable due to a series of heat stress-sensitive processes including anther dehiscence, pollination, pollen germination, and fertilization occurring in a short time span (rice, 1-4 hr [Cho, 1956;Shi et al, 2018]; and sorghum, about 30 min for pollen germination and growth, between 2 and 12 hr for fertilization [Stephens & Quinby, 1934;Bandyopadhyay, Frederickson, McLaren, Odvody, & Ryley, 1998]).…”

A point mutation in LTT1 enhances cold tolerance at the booting stage in rice

“…Anthers were sampled at different developmental stages as defined previously (Zhang, Luo, & Zhu, 2011). The embryo sac was observed according to Shi et al (2018), and trypan blue staining was performed according to Chen et al (2016). Pollen viability was analysed by 1% I 2 /KI staining.…”

Reproductive success of soybean (Glycine max L. Merril) cultivars and exotic lines under high daytime temperature

“…peanut ( Arachis hypogeae L.), and cotton ( Gossypium hirsutum L.) showed that the cardinal temperatures for pollen germination vary among and within species (Coast, Murdoch, Ellis, Hay, & Jagadish, ; Djanaguiraman et al, ; Djanaguiraman, Prasad, Murugan, Perumal, & Reddy, ; Kakani et al, ; Kakani, Prasad, Craufurd, & Wheeler, ) and that differences in pollen cardinal temperatures among genotypes are related to combined high daytime and nighttime temperatures tolerance or susceptibility (Coast et al, ; Craufurd, Prasad, & Kakani, ; Djanaguiraman et al, ; Djanaguiraman, Perumal, Jagadish, et al, ). Under combined high daytime and nighttime temperature, a significant, positive relationship between pollen viability or in vitro pollen germination percentage and seed‐set percentage was observed in rice (Shi et al, ); sorghum (Nguyen et al, ; Singh et al, ); and peanut (Prasad, Craufurd, & Summerfield, ). However, the effects of HDT on soybean pollen viability and its reproductive success, namely, pod‐set percent, was not documented under field conditions.…”