Importance of anther dehiscence for low-temperature tolerance in rice at the young microspore and flowering stages

Abstract

Low temperature, particularly during the reproductive stage in rice (Oryza sativa L.), leads to reduced fertility and yield and is a major constraint faced in temperate rice ecology. The floral trait anther dehiscence length has not been quantified in relation to low-temperature tolerance in rice. Two controlled-temperature glasshouse experiments evaluated 120 genotypes from BC1F6 recombinant inbred lines when exposed to low air temperature at the booting (young microspore) and flowering stages. Genotypic differences existed for spikelet sterility (SS) after low-temperature exposure at booting and flowering stages, and a significant positive correlation (R2=0.22**) was found between SS of individual genotypes at booting and flowering stages. Number of dehisced anthers had the highest correlation with SS, and accounted for 58% and 44% of variation in SS with exposure to low temperature at booting and flowering, respectively. Anther dehiscence length and number of dehisced anthers were highly correlated (r=0.90**). After low-temperature exposure at booting, pollen number in the anther as well as the pollen’s capacity to germinate effectively further differentiated low-temperature-tolerant and -susceptible genotypes. Positive relationships (r=0.56** and 0.46*) between SS in the glasshouse and in field experiments in 2015 and 2016 seasons, respectively, provided validation of the phenotypic glasshouse screening methods utilised for low-temperature tolerance in relation to target production environments. This repeatable phenotyping system in combination with improved understanding of underlying floral traits will lead to increased efficiency in breeding for low-temperature tolerance in rice.

The genetic analysis of physiological traits in rice (Oryza sativa L.) contributing to aerobic adaption

“…Conversely in flooded conditions, spikelet sterility was significantly associated with all floral traits. The number of dehisced anthers accounted for 84% of the variation in spikelet sterility under flooded conditions, which is comparable to the findings ofSusanti et al (2019), and also was almost double that explained in the aerobic conditions. In both flooded and aerobic conditions, cold tolerant genotypes had a larger number of dehisced anthers and consequently number of pollen on stigma, contributing to reduced spikelet sterility.…”

“…The phenotypic relationship between spikelet fertility and the number of dehisced anthers previously identified by Susanti et al (2019) was also identified in both the flooded and aerobic experiment. In flooded conditions, the number of dehisced anthers explained 71% of the phenotypic variation for spikelet fertility; whereas the explained phenotypic variance was considerably less in aerobic conditions at 42%.…”

“…In 12 genotypes in the cold treatment, six unopened spikelets on the main stem panicle were collected from the third, fourth and fifth position on the first (terminal) and second panicle branch at 1-2 days after heading and preserved in 70% ethanol at 4°C. A minimum of three anthers were then processed as per Susanti et al (Susanti et al 2019) to determine the number of filled pollen (fertile) and total pollen number per anther. A further four spikelets from each of the 12 genotypes were sampled shortly after floret opening (palea and lemma separate) but before anther extrusion (Mitchell et al 2016).…”

“…Cold tolerance at the EMS has been extensively studied under flooded conditions and is relatively well understood (i.e. Saito et al 1995;Farrell et al 2006b;Ye et al 2009;Mitchell et al 2016;Susanti et al 2019). However, little work has been completed on the expression of cold-induced sterility at EMS under aerobic conditions and whether current flooded screening methods are suitable for identification of genotypes suitable for aerobic production.…”

“…Apo and Tachiminori are considered to have adaption to an aerobic environment mostly through an extensive root system(Mitchell et al 2012), while Takanari has an enhanced photosynthetic capacity. The remaining 5 lines were selected from the Kyeema//Kyeema/Norin PL8 (KKN) breeding population, with 3 considered cold tolerant at EMS (KKN 10-230, 9-229 and 11-221) and two (14-224 and 14-226) susceptible(Ha et al 2018;Susanti et al 2019).…”