Floral morphology in rice grown under cold temperatures at booting and flowering and its effect on spikelet sterility

Abstract

Booting and flowering in rice (Oryza sativa L.) are considered to be the two most sensitive stages to cold temperature stress. The controlled temperature glasshouse experiment compared a population of 120 genotypes from F6 Kyeema//Kyeema/NorinPL8 (KKN) when exposed to cold air temperature at the booting and flowering stages. The study aimed to examine the relationship between percentage of spikelet sterility (SS) and floral characteristics, namely the number of dehisced anthers (NoDA), anther dehiscence length (ADL), the number of pollen grains on stigma (PoS) and the anther length (AL) when subjected to cold temperature at the two development stages. Two sets of genotypes were sown 18 days apart and grown at 28/21°C day/night controlled temperature glasshouse, and were moved to the cold room (21/15oC day/night) at heading (set-1) and at early booting stage (set-2). A highly significant genotypic difference existed in percentage SS in both flowering (ranged from 49-100%) and early booting (4-99%) with flowering stage having higher average SS (88 vs 57%). A significant positive association existed between SS of flowering and booting (r=0.39**) with five genotypes performing consistently well. Highly significant negative correlations existed in both flowering and booting stage between SS and all the floral traits measured. Furthermore, multiple regression analysis indicated that 37% of the variation in SS was explained by the number of dehisced anther, anther dehiscence length and anther length when exposed to cold at flowering stage, while at booting stage the number of dehisced anther and anther length alone explained 58% of the variation in SS. The importance of the number of dehisced anther in explaining variation in SS has been highlighted and plays a significant role in cold tolerance