Diversity of Flower Opening Time and Duration in Rice (Oryza sativa ssp. indica) Landraces of South and Southeast Asia in Different Cultivation Seasons

Different cultivars of rice(Oryza sativa)open at different times of the day,and the overlap of anthesis time in rice between the neighbouring cultivars is of crucial importance to the degree of cross pollination in rice.Nevertheless,none of the past experiments with cross pollination between different rice cultivars ever reported the respective flower opening time(FOT)and flower exposure duration(FED)of the parent cultivars,until recently.The authors present here the first record of FOT and FED of 1114 indica rice landraces of South and Southeast Asia,growing during sum-mer and winter seasons in three consecutive years.The authors also present an analysis of the influences of the grow-ing season on the anthesis behaviour,and present the first records of the FOT and FED variability on sunny and cloudy days of a large number of landraces.The data show that rice florets tend to open later in the morning(that is,take longer time to anthesis after sunrise)on sunny days than on cloudy days,and also significantly later during long day seasons(spring and summer)than during short day season(winter);and that FED is inversely related to both FOT and the length of duration from sunrise to first flower opening.The wide ranges of FOT(8:50 a.m.to 12:40 p.m.)and FED(15 to 194 minutes)also suggest the ample time window for receiving pollen from neighbouring cultivars with differ-ent FOT,enhancing the chances of cross pollination between hundreds of rice landraces with FOT and FED overlaps.

Molecular understanding of postharvest flower opening and senescence

Flowers are key organs in many ornamental plants,and various phases of flower development impact their economic value.The final stage of petal development is associated with flower senescence,which is an irreversible process involving programmed cell death,and premature senescence of cut flowers often results in major losses in quality during postharvest handling.Flower opening and senescence are two sequential processes.As flowers open,the stamens are exposed to attract pollinators.Once pollination occurs,flower senescence is initiated.Both the opening and senescence processes are regulated by a range of endogenous phytohormones and environmental factors.Ethylene acts as a central regulator for the ethylene-sensitive flowers.Other phytohormones,including auxin,gibberellin,cytokinin,jasmonic acid and abscisic acid,are also involved in the control of petal expansion and senescence.Water status also directly influences postharvest flower opening,while pollination is a key event in initiating the onset flower senescence.Here,we review the current understanding of flower opening and senescence,and propose future research directions,such as the study of interactions between hormonal and environmental signals,the application of new technology,and interdisciplinary research.

Heat Resistance of Rice Landrace D43 at Anthesis

Rice is extremely sensitive to high temperature, especially at the fowering stage. Identifying new germplasm and breeding heat-resistant rice varieties are therefore essential. After multi-year evaluations, a heat-resistant rice landrace D43 was identifed in our previous research. In this study, the relationship between heat resistance and flower opening time （FOT） was analyzed both in the field and in phytotron. The results showed that high temperature could accelerate fower opening of a range of rice varieties. The D43 showed early morning fowering （EMF） habit in different conditions, and the FOT of which was mainly concentrated in the period of 8：30~10：00 AM under high temperature. The spikelet fertility of D43 was relatively low after exposure to invariably high temperature during fower opening. However, the EMF habit of D43 was conducive to avoiding mid-day high temperature, and therefore increased the spikelet fertility under rising high temperature conditions in the feld and in phytotron. In addition, morphological traits including the anther dehiscence rate, the total number and germinated number of pollens on the stigma were signifcantly correlated with the spikelet fertility, and therefore they could be used to evaluate rice heat resistance at anthesis.