Upland rice breeding for early flowering and high temperature tolerance

Abstract

In Brazil, the upland rice system contributes to the national production of this cereal. Strategies to improve the performance of upland rice and its insertion in the Brazilian grain production system have guided research in breeding programs. Among these, there is a reduction in rice life cycle, increase in grain yield and tolerance to abiotic stresses. One strategy is to combine conventional breeding with the new techniques of modern biotechnology. The search for possible candidate genes and their manipulation aiming at high temperature tolerance has been essential in breeding programs. The ERECTA family genes (ERfs) encode receptor-like kinase proteins that are involved in morphological and physiological development of plants, as well as in the response to different environmental stimuli. In the rice genome there are three ERfs genes, OsER1, OsER2 and OsERL, which have potential in development of heat-tolerant genotypes using genetic engineering techniques. The work identified the expression pattern of OsERfs in rice genotypes in the reproductive stage from R2 to R6 stage. T0 transgenic plants carrying a truncated ER protein (ΔKinase), functioning as an ER suppressor, were obtained to study its influence on the expression pattern of OsERfs. Subsequently, progenies T1 from genotypes with the highest ΔKinase expression were submitted to high temperature stress for 14 days during the reproductive stage. Greater expressions of OsERfs were observed at the beginning of the reproductive stage, R2 to R4. A genetic compensation effect was observed, with a positive transcriptional regulation of OsERfs in the presence of ΔKinase. However, transgenic plants did not show heat tolerance during the reproductive stage, resulting in high sterility and reduced grain yield. An alternative in addition to the heat stress tolerant cultivars are early flowering cultivars which reduce the time of exposure of the crop to periods of extreme temperatures and allow its insertion in succession systems with other crops. In order to reduce the cycle in rice genotypes, an alternative is hybridization. However, the success of this technique depends on the efficiency in the selection of parents or segregating populations from crosses. Thus, some procedures to predict the genetic potential of segregating populations were applied to select a population with early flowering and grain yield. Populations were obtained from a biparental crossing between an early flowering cultivar, BRSMG Caçula, and two high grain yield lines, BRSMG Caravera and CMG1590. The selection was based on estimates of genetic and phenotypic parameters, mean and variance components, and probability of F∞ lines that surpass a pre-established standard. Furthermore, progenies in advanced generations of inbreeding were evaluated for each population. The different methods used were satisfactory in the selection of early flowering and productive populations. The association of two or more procedures can help the breeder to select populations with good performance and genetic variability. The BRSMG Caçula x Caravera population was superior for selection of early flowering and high grain yield genotypes.